United States
Environmental Protection
U M * Agency
2013 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
Southeast Michigan Council of Governments
Detroit, Ml
OURS TO PROTECT
Green Infrastructure Targeting in
Southeast Michigan
An Outcome-based Strategic Planning Framework to Identify
and Evaluate Green Infrastructure Opportunities
SEPTEMBER 2016
EPA 832-R-16-011
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About the Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped
areas, soil and plants absorb and filter the water. When rain falls on our roofs, streets, and parking lots,
however, the water cannot soak into the ground. In most urban areas, stormwater is drained through
engineered collection systems and discharged into nearby water bodies. The stormwater carries trash,
bacteria, heavy metals, and other pollutants from the urban landscape, polluting the receiving waters.
Higher flows also can cause erosion and flooding in urban streams, damaging habitat, property, and
infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier
urban environments. At the scale of a city or county, green infrastructure refers to the patchwork of
natural areas that provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a
neighborhood or site, green infrastructure refers to stormwater management systems that mimic nature
by soaking up and storing water. Green infrastructure can be a cost-effective approach for improving
water quality and helping communities stretch their infrastructure investments further by providing
multiple environmental, economic, and community benefits. This multibenefit approach creates
sustainable and resilient water infrastructure that supports and revitalizes urban communities.
The U.S. Environmental Protection Agency (EPA) encourages communities to use green infrastructure to
help manage stormwater runoff, reduce sewer overflows, and improve water quality. EPA recognizes
the value of working collaboratively with communities to support broader adoption of green
infrastructure approaches. Technical assistance is a key component to accelerating the implementation
of green infrastructure across the nation and aligns with EPA's commitment to provide community-
focused outreach and support in the President's Priority Agenda Enhancing the Climate Resilience of
America's Natural Resources. Creating more resilient systems will become increasingly important in the
face of climate change. As more intense weather events or dwindling water supplies stress the
performance of the nation's water infrastructure, green infrastructure offers an approach to increase
resiliency and adaptability.
For more information, visit http://www.eDa.gov/areeninfrastructure.
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Acknowledgements
Principal CPA Staff
Bob Newport, USEPA Region 5
Jamie Piziali, USEPA
Christopher Kloss, USEPA
Key Southeast Michigan Area Stakeholders
Mark Jones, Southeast Michigan Council of Governments
Kelly Karll, Southeast Michigan Council of Governments
Amy Mangus, Southeast Michigan Council of Governments
Gerard Santoro, Macomb County Department of Public Works
Lynne Seymour, Macomb County Department of Public Works
Noel Mullett, Wayne County Department of Public Services
Jennifer Lawson, City of Ann Arbor
Ric Lawson, Huron River Watershed Council
Anne Vaara, Clinton River Watershed Council
Michelle Selzer, Michigan Department of Environmental Quality
Peter Vincent, Michigan Department of Environmental Quality
Dave Dortman, Michigan Department of Transportation
Mike O'Malley, Michigan Department of Transportation
Harold Zweng, Michigan Department of Transportation
Consultant Team
Bruce Cleland, Tetra Tech
Dan Christian, Tetra Tech
Martina Frey, Tetra Tech
John Kosco, Tetra Tech
This report was developed under EPA Contract No. EP-C-11-009 as part of the 2014 EPA Green
Infrastructure Technical Assistance Program.
Cover photo credits (clockwise from upper left):
Miller Avenue Rain Garden (Ann Arbor), Plumbrook (Sterling Heights), Easy Street Pervious Pavers (Ann
Arbor), Tonquish Creek (Plymouth Township)
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Contents
Acronyms and Abbreviations ix
Executive Summary x
1 Overview 1
1.1 Project Objective 1
1.2 Background 2
1.2.1 Watershed Planning in Southeast Michigan 2
1.2.2 Green Infrastructure Vision for Southeast Michigan 5
1.3 Outcome-based Strategic Planning 7
2 Technical Approach 8
2.1 Hydrologic Analysis 8
2.2 Pilot Subwatersheds 13
2.3 Target Development 16
2.3.1 Previous Work in Southeast Michigan 16
2.3.2 Relationship to Macroinvertebrates 18
2.3.3 Impervious Cover Analysis 21
2.3.4 Stormwater Volume Reduction Targets 24
3 Green Infrastructure Opportunities 27
3.1 Native Plant Grow Zones 27
3.2 Tree Canopy 28
3.3 Constructed Management Practices 29
4 Pilot Subwatershed Assessment Results 33
4.1 Malletts Creek Subwatershed 35
4.1.1 Land Use and Land Cover 35
4.1.2 Existing Conditions Related to Flashiness 40
4.1.3 Stormwater Runoff Reduction Targets 40
4.1.4 Areas of Opportunity and Priorities 42
4.1.5 Recommendations 46
4.1.6 Pilot Watershed Summary 52
4.2 Plumbrook Drain Subwatershed 54
4.2.1 Land Use and Land Cover 54
4.2.2 Existing Conditions Related to Flashiness 59
4.2.3 Stormwater Runoff Reduction Targets 59
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4.2.4 Areas of Opportunity and Priorities 61
4.2.5 Recommendations 65
4.2.6 Pilot Watershed Summary 71
4.3 Tonquish Creek Subwatershed 73
4.3.1 Land Use and Land Cover 73
4.3.2 Existing Conditions Related to Flashiness 78
4.3.3 Stormwater Runoff Reduction Targets 79
4.3.4 Areas of Opportunity and Priorities 80
4.3.5 Recommendations 83
4.3.6 Pilot Watershed Summary 89
5 Conclusions 91
6 References 92
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Figures
Figure 1. Southeast Michigan watersheds and subwatersheds 4
Figure 2. Green infrastructure vision in southeast Michigan 6
Figure 3. Outcome-based strategic planning framework 7
Figure 4. USGS stream gage sites examined 10
Figure 5. Comparative analysis of flow-duration curves for several southeast Michigan sites 12
Figure 6. Relationship between R-B Index and 2-year peak flow 12
Figure 7. Multiscale analysis framework 13
Figure 8. Final pilot subwatersheds selected 15
Figure 9. Example Rouge basin draft target water yield 17
Figure 10. Relationship between key indicators in establishing stormwater volume targets 18
Figure 11. Comparison of R-B Index and P51 bioassessment scores 19
Figure 12. Comparison of R-B Index and percent caddisflies scores 20
Figure 13. Comparison of R-B Index and dominant taxa scores 20
Figure 14. Comparison of R-B Index to several southeast Michigan volunteer monitoring sites 21
Figure 15. Relative effect of impervious cover on 1-day flow-duration interval 22
Figure 16. Relative effect of impervious cover on R-B Index 24
Figure 17. Non-exceedance rainfall-runoff—Detroit Metro airport 25
Figure 18. Relative response of R-B Index to reduction of annual average stormwater runoff volume.... 26
Figure 19. Relative effect of increased infiltration benefit on stream flashiness 28
Figure 20. Relative effect of impervious cover and tree canopy on stream flashiness 29
Figure 21. Pilot subwatershed impervious surface composition 30
Figure 22. Constructed practice options by impervious surface type 30
Figure 23. Bioswale screening analysis using different relative infiltration assumptions 31
Figure 24. Bioswale volume reduction estimates at different infiltration rates 32
Figure 25. Porous pavement volume reduction estimates at different infiltration rates 32
Figure 26. Location of Malletts Creek pilot subwatershed within Huron River watershed 36
Figure 27. Aerial imagery of catchment boundaries—Malletts Creek subwatershed 37
Figure 28. Land use—Malletts Creek subwatershed 38
Figure 29. Daily average streamflow patterns in Malletts Creek (4/1-6/30/2010) 40
Figure 30. Malletts Creek subwatershed effective impervious cover and R-B flashiness screening
analysis 41
Figure 31. Green Infrastructure Vision—Malletts Creek subwatershed 43
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Figure 32. Land cover—Malletts Creek subwatershed 44
Figure 33. Impervious surface composition—Malletts Creek subwatershed 46
Figure 34. Public parcels—Malletts Creek subwatershed 48
Figure 35. School properties—Malletts Creek subwatershed 49
Figure 36. Road ROWs—Malletts Creek subwatershed 51
Figure 37. Priority parking lots in Green Infrastructure Vision—Malletts Creek subwatershed 53
Figure 38. Location of Plumbrook Drain pilot subwatershed within Clinton River watershed 55
Figure 39. Aerial imagery of catchment boundaries—Plumbrook Drain subwatershed 56
Figure 40. Land use—Plumbrook Drain subwatershed 57
Figure 41. Daily average streamflow patterns Plumbrook Drain (4/1-6/30/2010) 59
Figure 42. Plumbrook Drain subwatershed effective impervious cover and R-B flashiness screening
analysis 60
Figure 43. Green Infrastructure Vision—Plumbrook Drain subwatershed 63
Figure 44. Land cover—Plumbrook Drain subwatershed 64
Figure 45. Impervious surface composition—Plumbrook Drain subwatershed 65
Figure 46. Public parcels—Plumbrook Drain subwatershed 67
Figure 47. School properties—Plumbrook Drain subwatershed 68
Figure 48. Road ROWs—Plumbrook Drain subwatershed 70
Figure 49. Priority parking lots in Green Infrastructure Vision—Plumbrook Drain subwatershed 72
Figure 50. Location of Tonquish Creek pilot subwatershed within River Rouge watershed 74
Figure 51. Aerial imagery of catchment boundaries—Tonquish Creek subwatershed 75
Figure 52. Land use—Tonquish Creek subwatershed 76
Figure 53. Estimated daily average Tonquish Creek streamflow patterns (10/1-12/31/2003) 78
Figure 54. Tonquish Creek subwatershed effective impervious cover and R-B flashiness screening
analysis 79
Figure 55. Green Infrastructure Vision—Tonquish Creek subwatershed 81
Figure 56. Land cover—Tonquish Creek subwatershed 82
Figure 57. Impervious surface composition—Tonquish Creek subwatershed 83
Figure 58. Public parcels—Tonquish Creek subwatershed 85
Figure 59. School properties—Tonquish Creek subwatershed 86
Figure 60. Road ROWs—Tonquish Creek subwatershed 88
Figure 61. Priority parking lots in Green Infrastructure Vision—Tonquish Creek subwatershed 90
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Tables
Table 1. Land use types in southeast Michigan watersheds with potential for implementing green
infrastructure 5
Table 2. Description of hydrology-based indicators 8
Table 3. Hydrology-based indicator summary by watershed size 11
Table 4. Hydrologic statistics for potential pilot watersheds 14
Table 5. River Rouge ecological targets for fish protection based on duration curve framework 17
Table 6. Modeled relative effect of impervious cover on key hydrologic indicators 23
Table 7. Green infrastructure opportunities within the pilot subwatersheds 34
Table 8. Malletts Creek subwatershed land use 39
Table 9. Malletts Creek subwatershed land cover by land use category 39
Table 10. Malletts Creek subwatershed impervious cover estimates by surface type 45
Table 11. Malletts Creek subwatershed publicly owned property by jurisdiction 47
Table 12. Malletts Creek subwatershed road ROW land cover 50
Table 13. Plumbrook Drain subwatershed land use 58
Table 14. Plumbrook Drain subwatershed land cover by land use category 58
Table 15. Plumbrook Drain subwatershed impervious cover estimates by surface type 62
Table 16. Plumbrook Drain subwatershed publicly owned property by jurisdiction 66
Table 17. Plumbrook Drain subwatershed road ROW land cover 69
Table 18. Tonquish Creek subwatershed land use 77
Table 19. Tonquish Creek subwatershed land cover by land use category 77
Table 20. Tonquish Creek subwatershed impervious cover estimates by surface type 80
Table 21. Tonquish Creek subwatershed publicly owned property by jurisdiction 84
Table 22. Tonquish Creek subwatershed road ROW land cover 87
viii
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Acronyms and Abbreviations
BMP
best management practice
EPA
U.S. Environmental Protection Agency
GIS
geographic information system
HSG
hydrologic soil group
HSPF
Hydrologic Simulation Program FORTRAN
HUC
hydrologic unit code
LSPC
Loading Simulation Program C++
MDEQ
Michigan Department of Environmental Quality
MDOT
Michigan Department of Transportation
MS4
municipal separate storm sewer system
NPDES
National Pollutant Discharge Elimination System
R-B Index
Richards-Baker Flashiness Index
ROW
right-of-way
SEMCOG
Southeast Michigan Council of Governments
SUSTAIN
System for Urban Stormwater Treatment and Analysis INtegration
SWAG
Subwatershed Advisory Group
SWMM
Storm Water Management Model
TMDL
total maximum daily load
USGS
U.S. Geological Survey
WQS
water quality standards
ix
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Executive Summary
Recognizing the value of the Lake Huron—Lake Erie corridor to the region (economically,
environmentally, and socially), southeast Michigan faces some unique challenges regarding stormwater
management. The region is home to approximately 5 million people, over half of Michigan's entire
population. The region also houses all or part of 16 major watersheds that drain directly to Lake Huron
and Lake Erie. The connecting corridor between the two Great Lakes includes Lake St. Clair, the St. Clair
River, and the Detroit River, which share an international border with Canada. Having a concentrated
urban population located directly on two of the state's Great Lakes highlights the significant need to
properly manage stormwater to protect water quality.
Within the 16 watersheds, priorities include addressing urban runoff and nonpoint source pollution such
as the effects of excessive stormwater runoff volume and pollutant loading. In 2014, the Southeast
Michigan Council of Governments (SEMCOG) published the Green Infrastructure Vision for Southeast
Michigan (SEMCOG 2014). An important focus underlying development of this document was
strategically implementing green infrastructure practices that will achieve multiple desired outcomes.
Stakeholder visioning and public polling in the region confirmed that a priority outcome for green
infrastructure implementation is improved water quality. As green infrastructure is implemented, both
runoff volume and pollutant loading will be reduced. In the long term, biological communities within the
watersheds will improve.
SEMCOG recognized that a priority need in moving forward with the green infrastructure vision was a
framework to estimate the amount of green infrastructure necessary to demonstrate substantial
improvements in local water resources. With that need as a driving force, a project was initiated to
determine the role green infrastructure can play in working towards meeting water quality standards in
southeast Michigan and in protecting western Lake Erie. The project used a regionalized, outcome-
based strategic planning approach for green infrastructure targeting based on local ambient monitoring,
land use, and impervious cover information. Key activities conducted include:
• Hvdroloaic analysis using flow data from 40 U.S. Geological Survey gages in southeast Michigan
to bracket the range of local conditions and identify key metrics to guide the green
infrastructure targeting process.
• Selection of pilot subwatersheds based on land use/land cover characteristics representative of
green infrastructure planning challenges and opportunities in southeast Michigan to support
development and testing of the green infrastructure targeting process.
• Establishment of green infrastructure targets based on local monitoring data that focus on
stormwater runoff volume reduction using stream flashiness to connect aquatic biology and
stream channel concerns with total maximum daily loads and stormwater management activities.
• Opportunity assessment highlighting priority catchments within each pilot subwatershed based
on impervious cover density/composition and using desktop screening analyses to estimate the
relative benefit of different implementation strategies.
• Incorporation of the results into the green infrastructure vision by evaluating and identifying
options to achieve stream flashiness and stormwater volume reduction targets and developing
plans to implement them across the region. Key strategies in the Green Infrastructure Vision for
Southeast Michigan include native plant grow zones, increasing tree canopy, and the use of
constructed practices (e.g., bioretention, pervious pavement, and bioswales) (SEMCOG 2014).
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The process for developing the framework detailed in this report involved setting targets for green
infrastructure that hopefully can be implemented in other southeast Michigan watersheds. As a
separate project, the framework will be extended to other Detroit area subwatersheds in support of
efforts to develop a broader strategy for implementing water quality programs and aligning Michigan
Department of Transportation infrastructure goals with watershed management plans. In addition, this
framework will serve as a baseline from which to evaluate progress for urban watershed restoration in
the region.
xi
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! Overview
The Southeast Michigan Council of Governments (SEMCOG) published the Green Infrastructure Vision for
Southeast Michigan in 2014 (SEMCOG 2014). Green infrastructure encompasses both natural features such
as wetlands and woodlands, as well as constructed features such as rain gardens and bioswales. A crucial
component of a successful green infrastructure program involves strategically implementing its features to
achieve multiple desired outcomes. Stakeholder visioning and public polling in the southeastern Michigan
region confirmed that a priority outcome for green infrastructure implementation is improved water
quality. Recognizing the value of the Lake Huron—Lake Erie corridor to the region (economically,
environmentally, and socially), SEMCOG focused this project on estimating the amount of green
infrastructure necessary to be implemented to demonstrate improvements in local water resources.
When it comes to stormwater management, southeast Michigan faces a unique set of circumstances
compared with other regions in the nation. Nestled in the lower corner of Michigan's Lower Peninsula,
the region is home to approximately 5 million people, which constitutes over half of the state's entire
population. The region also houses all or part of 16 major watersheds that drain directly to Lake Huron
and Lake Erie. The connecting corridor between the two Great Lakes includes Lake St. Clair, the St. Clair
River, and the Detroit River, which share an international border with Canada. Additionally, five Areas of
Concern1 are located within the southeast Michigan region. Location of the large, concentrated urban
population directly on two of the state's Great Lakes highlights the significant need to properly manage
stormwater to protect water quality.
Within the 16 watersheds, addressing urban runoff and nonpoint source pollution, including the effects
of excessive stormwater runoff volume and pollutant loading, is a priority. Many existing watershed
plans in the region identify implementing green infrastructure as one method for addressing those
effects. The watersheds plans also contain approved total maximum daily loads (TMDLs) for biota, total
suspended solids, dissolved oxygen, phosphorus, and E. coli. As green infrastructure is implemented
incrementally, runoff volume and pollutant loading are reduced. In the long term, biological
communities within these watersheds will improve.
'oject Objective
The overall objective of this project was to determine the role green infrastructure can play in achieving
water quality standards (WQS) in southeast Michigan and protecting western Lake Erie. In three pilot
subwatersheds, hydrologic stormwater runoff reduction targets were identified to protect aquatic
biology and help address concerns with TMDLs and stormwater management activities. The targets
were used to examine alternative green infrastructure implementation techniques that could achieve
WQS and protect biological communities. The project involved four tasks:
• Task 1: Establish baseline flow-duration curves for selected subdrainage areas.
• Task 2: Establish stormwater runoff volume targets.
• Task 3: Assess green infrastructure opportunities.
• Task 4: Incorporate results into the green infrastructure vision.
1 A 1978 agreement between the United States and Canada identified 43 Areas of Concern (AOCs) on the Great Lakes, including 14
in Michigan. AOCs are locations where beneficial uses are impaired, such as the loss offish and wildlife habitat. (SEMCOG 2014)
1
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SEMCOG intends to transfer the outcome-based strategic planning process established for the pilot
subwatersheds to other SEMCOG area subwatersheds. Michigan will use the information from this
project as a tool to evaluate progress for urban watershed restoration statewide.
1.2 Background
Successfully managing stormwater runoff is a significant component of the water system infrastructure
challenges facing southeast Michigan. The demographic and economic changes that have taken place in
the region over the last decade, combined with aging distribution, treatment, and other systems and the
decline in revenue to maintain them, have led to an infrastructure crisis. Roads are deteriorating at an
alarming rate, and the vast majority of water and sewer systems are more than 50 years old—well past
their useful life.
Investment in infrastructure must be strategic and based on the region's economic reality. The
southeast region of Michigan wants to install high-quality, functional infrastructure that is also fiscally
sustainable and supports the region's economy and quality of life. Strategic investment includes having
a defined target for stormwater management and green infrastructure implementation. The target will
facilitate focused investments in high-priority areas to realize demonstrated improvements in local
stream water quality.
Watershed planning efforts in southeast Michigan can help set the stage for implementing green
infrastructure. Aligning watershed planning with other infrastructure planning efforts will lead to more
strategic implementation opportunities for defined targets.
Numerous watersheds and subwatersheds blanket the region and primarily drain to the Lake Huron-
Lake Erie Corridor (Figure 1). The water quality of the rivers and lakes within the watersheds as well as
of the Huron—Erie Corridor is directly connected to activities on the land.
Watershed management plans developed over the last decade—which consider all uses, pollutant
sources, and impacts within a drainage area—serve as guides for communities, counties, and watershed
groups to protect and improve water quality and related natural resources. More than 150 watershed
management plans exist at the local level across the state, many funded through Michigan Department
of Environmental Quality (MDEQ) nonpoint source grant opportunities (see
httpi/'Zwww.michiaan.gov/dea/0,4561,7-135-3313 3682 3714-.00.html).
The three largest watersheds in southeast Michigan that are located almost entirely within the region
are the Clinton, Huron, and Rouge watersheds (Figure 1). Within those watersheds are subwatersheds
with active stakeholder groups working towards enhancing the quality of local water resources.
Elements of the subwatershed management plans in the Clinton, Huron, and Rouge watersheds include
goals, objectives, and actions to address water quality and water quantity challenges in addition to
identifying protection and restoration opportunities. The basis of those planning efforts is the
underlying theme for defining runoff reduction targets.
Both land use and land cover play significant roles in directly impacting the quality of rivers and streams
in local watersheds. Historic landscapes in southeast Michigan serve multiple purposes that provide
various functions and values benefiting water resources. Wetlands, woodlands, grasslands, prairies, and
riparian corridors all play integral parts in the overall water cycle. Those landscapes also filter and
2
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reduce stormwater runoff entering local streams. As development has progressed across the region, the
expanse of urban area and associated impervious cover has increased, while the area of the historic
landscapes has decreased.
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Historical Watersheds and Subwatersheds
Southeast Michigan
~ Looking Glass Watershed
¦ Maumee Watershed
~ Pine Watershed
¦ Raisin watershed
~ Red Cedar Watershed
~ Rouge watershed
n Shiawassee watershed
~ Stony Creek Watershed
Drains directly to:
~ Lake Erie
~ Lale Huron
¦ Lale St Clair
~ St Ctar River
SEMCOG
Southeast Michigan Council of Governments
535 Griswold Street Suite 300, Detroit Michigan 48226-3602
Phone (313)961-4266. Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2009
I I Anchor Bay Watershed
Q Belie watershed
Q Black watershed
~ aintonWatershed
~ Ecorse Creek Watershed
O Flirt Watershed
~ Grand watershed
D Huron watershed
Figure 1. Southeast Michigan watersheds and subwatersheds.
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I
In southeast Michigan, green infrastructure consists of two broad categories: the natural, undisturbed
environment—wetlands, woodlands, trees, prairies, lakes, rivers, and streams—and constructed, or
built, environment—rain gardens, bioswales, community gardens, and agricultural lands.
SEMCOG (2014) recently completed the Green Infrastructure Vision for Southeast Michigan, which, for
the first time:
• Benchmarks green infrastructure in southeast Michigan,
• Envisions where communities want to go, and
• Contains regional policies on how to get there.
Reducing the volume of stormwater runoff is a common priority in southeast Michigan watersheds.
Within both the natural and built categories of green infrastructure, the connection to water quality is
significant. Wetlands, woodlands, and prairies naturally capture, filter, and infiltrate rainwater, while
constructed techniques aim to replicate natural systems. These systems work together to improve water
quality in local lakes, streams, and rivers in southeast Michigan and, by extension, in the Great Lakes.
Results from stakeholder visioning sessions and public surveys supported the connection between green
infrastructure and the region's water by identifying "protecting water quality" as the top-rated green
infrastructure benefit.
Watersheds in southeast Michigan contain more than 10 percent impervious cover, which presents
many opportunities to implement green infrastructure in the region. More than 25,000 acres of open
space designated for institutional land uses could also be evaluated for the potential for managed turf
areas to be converted to native plant grow zones and trees. Table 1 summarizes by land use type the
areas of opportunity that should be considered for constructing green infrastructure. The following
section provides detailed information on opportunities in the region by watershed and subwatershed.
Figure 2 depicts long-term green infrastructure implementation opportunities across the region.
Table 1. Land use types in southeast Michigan watersheds with potential for implementing green
infrastructure
Institutional Land Use
(publicly owned acres)
Roadways
(publicly owned acres)
Privately
Owned
Parking
Lots
(acres)
Riparian Corridor
(acres)
Impervious
Surfaces:
Buildings
Impervious
Surfaces:
Parking Lots
Open
Space
(turf &
trees)
Impervious
Surfaces:
Pavement
Open
Space
(turf &
trees)
Tree
Canopy
Existing
Open
Space
4,354
9,553
25,598
39,935
17,393
51,192
11,167
3,815
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SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400. Detroit. Michigan 48226-1904
Phone (313) 961-4266. Fax (313) 961-4869
www semcog.org Copyright: SEMCOG. 2014
A
1 819.028
0
State Plane NAD83 HARN
December 2014
Southeast Michigan
Green Infrastructure Vision
Increase Tree Canopy
Potential Green Streets
| Conservation & Recreation Lands
Potential Conservation & Recreation Lands
Existing Green Infrastructure
Figure 2. Green infrastructure vision in southeast Michigan.
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1.3 Outcome-based Strategic Planning
The outcome-based strategic planning framework used by SEMCOG aligns watershed needs with
available green infrastructure opportunities to enable project implementation to result in measurable
improvements in mitigating the adverse effects of stormwater (Figure 3). Task 1 (Establish baseline flow-
duration curves for selected subdrainage areas) and task 2 (Establish stormwater runoff volume targets)
involve an assessment of receiving water conditions, which determines green infrastructure project
needs. The first part of task 3 (Assess green infrastructure opportunities) involves an analysis of the
drainage system (e.g., land use/land cover, natural channels, storm sewer network) to identify green
infrastructure opportunities. The second part of task 3 uses a screening analysis of proposed projects in
"areas of opportunity" to conduct a feasibility/effectiveness assessment of stormwater runoff reduction
targets.
Outcome-Based Strategic Planning Framework
Tasks 1 & 2
Receiving
Water
Project
Needs
Task 3
Figure 3. Outcome-based strategic planning framework.
7
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2 Technical Approach
Baseline flow-duration curves were established for selected subdrainage areas. Subwatersheds across
the seven-county region were identified by hydrologic unit code (i.e., a 12-digit hydrologic unit code, or
HUC). Those with U.S. Geological Survey (USGS) gage data with a sufficient number of flow records to
conduct a hydrologic analysis and develop meaningful duration curves were selected. Based on the
results of this analysis, five subwatersheds were considered for pilot testing. Working with SEMCOG and
the Southeast Michigan Partners for Clean Water, final selection was narrowed to three project pilot
subwatersheds.
Methods to connect hydrologic and water quality concerns to green infrastructure were examined.
Hydrologic targets were developed to guide green infrastructure planning in the region. Development of
the targets was important because hydrology affects stream stability, habitat, aquatic biology, and the
delivery of pollutant loads.
2.1 Hydrologic Analysis
Several indicators can be used to evaluate historic streamflow patterns in southeast Michigan, including
key points on the flow-duration curve such as the flow or volume associated with the 1-day recurrence
interval (i.e., 1 day divided by 365 days, or the 0.274 percentile). This is a common indicator used to
calculate TMDLs based on the hydrology of a water body. This limit represents a daily maximum value
and reflects conditions in which the most erosion and sediment transport occur, resulting in the highest
pollutant concentrations and loading rates.
The Richards-Baker Flashiness Index (R-B Index) is an indicator of how frequently and rapidly short-term
changes in stream flow occur. Increased flashiness often reflects unstable watersheds and degraded
habitat that adversely affects aquatic life. Stable flow regimes support the establishment of healthy
macroinvertebrate populations (thus influencing bioassessment scores). Flashy flows—caused by
increased peak flow rates and volumes from urban runoff—disrupt aquatic community structure and
increase the delivery and transport of pollutant loads that exacerbate downstream water quality
problems. The R-B Index typically increases as watershed impervious cover becomes greater. Table 2
presents a brief summary of these indicators.
Table 2. Description of hydrology-based indicators
Metric
Name
Description
2-year
Peak
2-year Peak Flow
Instantaneous maximum peak flow associated with a 2-year recurrence interval
Annual
Average
Annual Average
Runoff Volume
Annual average runoff volume expressed as either cubic feet per second per square
mile or as inches of runoff
FDC 1-day
Flow-Duration Curve
Average daily maximum flow associated with 1-day recurrence interval from flow-
duration curve
TQmean
Annual Average Flow
Exceedance
Percentage of time that daily average flows exceed the annual average flow
R-B Index
Richards-Baker
Flashiness Index
Indicator of frequency and rapidity of short-term changes in streamflow
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Forty USGS gage sites with a sufficient number of flow records to develop meaningful duration curves
were identified within the seven-county SEMCOG area (Figure 4). Data were downloaded from the USGS
National Water Information System to conduct the hydrologic analysis for this project using Microsoft
Excel spreadsheets for each gaged location.
A study by the University of Michigan established hydrologic targets for southeast Michigan and
determined that watershed size, characteristic land use, and underlying geologic features produce a
significant hydrologic response (Wiley et al. 1998). A report by the MDEQ examines gaged streams and
rivers across Michigan, and provides an opportunity to incorporate flashiness into the stormwater
assessment process (Fongers et al. 2007). That study also included a summary of R-B Index quartile
rankings based on the size of the drainage area for Michigan watersheds.
Fongers et al. (2007) determined that smaller watersheds tend to naturally have flashier flows.
Flashiness tends to decrease as drainage area increases as a result of the varied timing of tributary
flows. Such varied timing helps attenuate main channel peak flows. Factors such as soil, land use, and
the influence of ground water become more varied as watershed size increases.
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Southeast Michigan Counties and Watersheds
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Car>z**
-------
Recognizing the effect of watershed size, Table 3 summarizes results of the hydrologic analysis by
drainage area class (the same size classes used by Fongers et al. [2007]). Values for each parameter
reflect the range (i.e., minimum to maximum). The effect of watershed size is most noticeable for the 2-
year peak, the 1-day flow-duration curve recurrence interval (FDCi-day), and the R-B Index. A comparative
analysis of flow-duration curves for several gages is shown in Figure 5; the graph also summarizes the
distribution using a box-and-whisker format of duration curve statistics at the midpoint of each zone
(high, moist, mid-range, dry, low) for all 40 gages examined across the seven-county SEMCOG region.
One exception to the general pattern for each indicator is the maximum R-B Index value for group B
(1.01). This maximum occurred at the Red Run near Warren gage, which appears to be an outlier for this
size class. The land use for this particular site is highly impervious.
Relationships between different parameters can be examined to determine if one or more indicators is
particularly well suited for target development that would address multiple concerns. An example
relationship using the R-B Index and 2-year peak is shown in Figure 6, using data from the 40 gages
included in the hydrologic assessment. In this case, an R-B Index target also could address peak flow
concerns. This information is helpful because the period of record needed to calculate R-B Index values
is significantly less than the amount of data required to determine the 2-year peak flow rate.
Table 3. Hydrology-based indicator summary by watershed size
Size
Class
Drainage
Area
(mi2)
Flow (inches)
Metric Comparison
2-year
Peak
Annual
Average
FDC l-day
FDC s%
TQmean
R-B Flashiness
A
<30
0.14-2.43
5.8-14.9
0.14-0.94
0.06-0.13
16-37%
0.13-0.86
B
30-100
0.07-1.83
8.6-20.0
0.09-0.65
0.06-0.14
19-44%
0.07-1.01
C
> 100
0.08-0.46
8.1-12.6
0.11-0.49
0.06-0.11
20-42%
0.06-0.45
Note: mi2 = square miles.
11
-------
T3
N
100
0.08-0.46
0.11-0.49
8.1-12.6
0.06 - 0.45
High
Flows
Mid-range
Flows
Moist
Conditions
I
Dry
Conditions
I
-Median
¦ Red Run
- Malletts
-Huron
20 30 40 50 60 70
Flow Duration Interval (°/c)
100
USGS Flow Data
Figure 5. Comparative analysis of flow-duration curves for several southeast Michigan sites.
2.5
(U
c
w 1.5
CO
CD
a- 1
i—
03
a>
>s
CS| 0.5
Hydrologic Assessment Sites
2-year Peak Flow vs. R-B Flashiness Index
~
~
R2 = 0.9206
~
~ /
* 75th percentile
* ~ Median
0 2 0.4 0.6 0.8
R-B Flashiness Index
12
Figure 6. Relationship between R-B Index and 2-year peak flow.
12
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2.2 Pilot Subwatersheds
The project's use of pilot subwatersheds establishes a process for identifying, prioritizing, and
implementing green infrastructure projects; a process that is transferable across the SEMCOG area. The
approach uses multiscale analysis, specifically by scaling down to progressively smaller geographic areas
based on priority concerns and implementation opportunities (Figure 7). Scale of analysis is an
extremely important aspect of stormwater management. Any size land area can be selected for
assessment and strategic planning.
At the broadest scale (e.g., region or county), analyses of stormwater problems provide the context for
policy formulation, regulations, codes, and ordinances. At the finest scale (e.g., specific streets or
parcels), technical analyses provide the basis for project implementation and can be used to evaluate
site-specific impacts. Midscale analyses (e.g., at the subwatershed or catchment level) provide the
context for management through a description and understanding of typical stormwater problems as
well as examining the capabilities that exist to address those problems.
The multiscale analysis evaluates geographic information system (GIS) data to identify high-priority
catchments for best management practice (BMP) implementation. High-priority catchments are critical
areas that have a disproportionate effect on hydrology and water quality. This approach is consistent
with a focus advocated by EPA and a number of states—one that recognizes that BMPs placed in critical
locations can help treat small areas that produce disproportionate amounts of excess stormwater runoff
and pollution. The multiscale analysis framework provides a solid foundation for identifying priority
catchments and assessing green infrastructure opportunities.
TonquishCreek
Subwatershed
HUC-12
Multiscale Analysis Framework
Morgan
Creek
Catchment
Rouge Watershed
HUC-8
Figure 7. Multiscale analysis framework.
13
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The following five watersheds, representing a range of land use and land cover conditions within the
region, were identified for consideration as project pilots:
• Malletts Creek (Huron watershed; Washtenaw County)
• Plumbrook Drain (Clinton watershed; Macomb County and Oakland County)
• Tonquish Creek (Rouge watershed; Wayne County)
• Gloede Drain (Clinton watershed; Macomb County)
• Bell Branch (Rouge watershed; Wayne County and Oakland County)
Flow data were available in three of the watersheds (Table 4): Malletts Creek (2009-14 at site
04174514, 1999-present at site 04174518), Plumbrook (1968-present), and Gloede Drain (1959-64).
Table 4. Hydrologic statistics for potential pilot watersheds
Location
Area
(mi2)
Gage ID
Flow (inches)
Metric Comparison
2-year
Peak
Annual
Average
FDC l-day
TQmean
R-B
Flashiness
Malletts Creek at Ann Arbor
(below Mary Beth Doyle Park)
8.48
04174514
n.a.
14.6
0.820
23.7%
0.700
Malletts Creek at Ann Arbor
(above mouth)
10.9
04174518
2.447
12.9
0.567
21.7%
0.724
Plumbrook Drain
16.5
04163400
0.868
12.3
0.554
23.8%
0.560
Gloede Drain
16.0
04165200
0.662
6.3
0.302
24.6%
0.475
Note: mi2 = square miles.
Discussions between SEMCOG staff and Southeast Michigan Green Infrastructure Partners led to
selecting Malletts Creek, Plumbrook Drain, and Tonquish Creek as the project pilot subwatersheds
(Figure 8). Each pilot subwatershed has land use/land cover characteristics representative of green
infrastructure planning challenges and opportunities for southeast Michigan. Although Tonquish Creek
does not have gaged discharge data, it is indicative of other subwatershed situations where green
infrastructure planning is needed in spite of the absence of flow information.
14
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Watersheds
Southeast Michigan
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Belle Watershed
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Clinton Watershed
Lake Erie
Lake Huron
Lake St. Clair
St. Clair River
Ecorse Creek Watershed
Flint Watershed
Grand Watershed
Huron Watershed
Looking Glass Watershed
Maumee Watershed
Pine Watershed
| Raisin Watershed
Red Cedar Watershed
Rouge Watershed
Shiawassee Watershed
Stony Creek Watershed
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www semcog org Copyright SEMCOG, 2014
1 775,395
0
State Plane NAD83 HARN
December 2014
Figure 8. Final pilot subwatersheds selected.
15
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2.3 Target Development
The concept of using hydrologic indicators associated with biological resources in southeast Michigan
was initially precipitated by University of Michigan work in developing Ecological Targets for
Rehabilitation of the Rouge River (Wiley et al. 1998). Recently, MDEQ examined the use of hydrologic
indicators connected to bioassessment scores as part of a stormwater TMDL project. That aspect of the
project involves reviewing both approaches and considers other options to establish runoff targets for
the pilot subwatersheds.
2.3.1 Previous Work in Southeast Michigan
The Ecological Targets for Rehabilitation of the Rouge River study (Wiley et al. 1998) provides an
example framework for identifying approaches, indicators, and targets that reflect desired biological
conditions as determined through Michigan's bioassessment protocol, the Procedure 51 Biological
Community Assessment Protocol (P51) (MDEQ 1997). That effort focused on fisheries management and
identified desirable discharge regimes using a duration curve framework. Ecologically based, target flow-
duration curves were developed by summarizing pooled discharge from subsets of Michigan River
Inventory (MRI) sites where selected target fishes were known to be abundant.
Discharge data in the MRI database included both gage data, where available, and synthetic exceedance
discharges modeled from landscape variables for ungaged sites. Figure 9 provides an example target
duration curve from the report. The flow-based targets were developed to protect fish communities and
are expressed at intervals on the duration curve that range from the 5th percentile to the 95th
percentile. In addition to annual average targets at each interval, the document defined upper and
lower bounds. Table 5 summarizes those targets for small streams. Recognizing that geology exerts a
major influence on local hydrology, targets were identified for very low base flow streams, low base flow
streams, and moderate base flow streams (Wiley et al. 1998).
The Wiley study describes the relationship between flow exceedance frequencies and fish communities.
The targets presented in Table 5 indicate that identifying a specific value is no simple task; physical
factors at each site must be considered (notably base geology). Information from this study
demonstrates a relationship between exceedance flows and fish communities. However, the highest
flow condition target identified corresponds to a duration curve interval at the 5th percentile (Wiley et
al. 1998).
Work in other states suggests that green infrastructure practices are most effective in addressing water
quality and drainage problems between the 1st and the 10th to 20th percentiles on the flow-duration
curve. For instance, Washington State uses 50 percent of the 2-year peak as the upper duration curve
interval specified in the MS4 permit as a performance standard (i.e., approximately the 1st percentile for
duration curves developed using daily average flow data). Other options for estimating runoff volume
reduction targets are explored below.
16
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TARGET YIELD AT EXCEEDENCE FREQUENCIES
GAGE MUS4- MAPLE RD.
0.25 -¦
S 0.20--
0.15 -¦
0.10 --
0.05 -
20
40 60
Exceedence(%)
80
100
H— Pred Mn
Upper Var
¦ ¦ - ¦ Lower Var
t—Observed
from ""Ecological Targets for Rehabilitation of the Rouge River"
(Wiley et al, 1998}
Figure 9. Example Rouge basin draft target water yield.
Table 5. River Rouge ecological targets for fish protection based on duration curve framework
Stream Type
Flow-Duration Curve Target
(inches per day)
Target
Description
High
Moist
(25th %)
Mid
(50'" %)
Dry
(75th %)
Low
(Sm %)
(10th %)
(90th %)
(95th %)
Small stream
(Very low base flow)
0.117
0.064
0.027
0.015
0.010
0.006
0.006
Upper Range
0.104
0.059
0.022
0.010
0.005
0.003
0.003
Average
0.092
0.054
0.017
0.004
0.000
0.000
0.000
Lower Range
Small stream
(Low base flow)
0.073
0.046
0.026
0.015
0.011
0.008
0.006
Upper Range
0.070
0.044
0.024
0.014
0.009
0.007
0.005
Average
0.066
0.042
0.022
0.013
0.008
0.006
0.005
Lower Range
Small stream
(Moderate base flow)
0.091
0.062
0.034
0.021
0.014
0.012
0.011
Upper Range
0.086
0.060
0.031
0.018
0.012
0.010
0,008
Average
0.081
0.057
0.027
0.014
0.009
0.007
0.005
Lower Range
17
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2.3.2 Relationship to Macroinvertebrates
Hydrology can be a major factor affecting aquatic communities, thus influencing bioassessment scores
(Figure 10). Stable flow regimes support the establishment of healthy macroinvertebrate populations.
Flashy flows (e.g., caused by urban runoff) disrupt aquatic community structure and increase the
transport of total suspended solids loads that cause downstream siltation problems. Flashiness is an
indicator of the frequency and rapidity of short-term changes in stream flow, particularly during runoff
events (Baker et al. 2004). Increased flashiness is typically associated with both unstable watersheds and
degraded habitat, which can adversely affect aquatic life.
are adversely affected by
due to increased
resulting from
due to
increased
from higher
associated with excess
Siltation
Degraded Habitat
Total Suspended
Solids
'Flashy" Flows
Streamflow Rates
and Velocities
STORMWATER Volume
Macroinvertebrates and Other Aquatic Life
Note: Boxes depict measured or calculated key indicators
Figure 10. Relationship between key indicators in establishing stormwater volume targets.
A list was assembled of sites with a watershed area of less than 30 square miles based on the Fongers
study (Fongers et al. 2007). The sites examined include a number of streams located in southeast
Michigan. As an initial screening analysis, stream flashiness for the sites was compared to P51
bioassessment scores reported by MDEQ. In addition, the R-B Index was examined relative to two P51
component metrics: percent caddisflies and percent dominant taxa.
The purpose of this screening analysis was to determine, through an examination of general patterns, if
there is (1) a relationship between stream flashiness and bioassessment metrics that will lead to
improvement in MDEQ's P51 scores; or (2) a threshold flashiness value above which MDEQ's
bioassessment metrics show consistently poor communities.
18
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The results of the analysis are shown in Figure 11 through Figure 13. Vertical lines drawn from the x-axis
represent the median R-B Index value for all sites in the Fongers study that are less than 30 square miles
(Fongers et al. 2007). Vertical lines also are drawn at the 25th and 75th percentiles. As indicated, some
general patterns start to appear at the 75th percentile (i.e., above an R-B Index value of 0.5).
One useful statistical measure is the coefficient of determination, or r2. For purposes of this analysis, r2
provides a measure of how useful the R-B Index might be in estimating the biological response for each
metric considered (e.g., P51 score, percent mayflies, percent caddisflies, percent dominant taxa). In
each case, the r2 value was less than 0.3, indicating that any relationship between the R-B Index and
biological response is not linear. The relationship between stream flashiness and biological response,
however, could be a step function.
A step function relationship implies that there is a threshold value above which a bioassessment metric
shows consistently poor communities. While that could be the case (particularly for R-B Index values
above 0.5), the sample population size is too small to identify a specific threshold value. In addition,
other site-specific stressors could be influencing the results of this preliminary screening analysis.
Bioassessment Sites near USGS Gages
Comparison of R-B Flashiness Index to P51 Scores
Above Average
if)
Below Average
o
0.4
1
Flashiness (R-B Index)
Sites with drainage areas less than 30 square miles
Figure 11. Comparison of R-B Index and P51 bioassessment scores.
19
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Bioassessment Sites near USGS Gages
Comparison of R-B Flashiness Index to Percent Caddisflies
60
(/)
-------
Local organizations in the SEMCOG area are engaged in volunteer monitoring efforts to foster
stewardship and encourage action. These organizations include the Clinton River Watershed Council, the
Friends of the Rouge, and the Huron River Watershed Council. Several locations monitored by the
groups coincide with streams where flow gaging data exists. Collectively, that information can be used
to further examine the relationship between macroinvertebrates and stream flashiness (Figure 14).
Patterns using the volunteer data are similar to those observed based on MDEQ bioassessment surveys;
the condition of the macroinvertebrate community decreases with increased stream flashiness.
Volunteer Monitoring Data Summary
Scores vs. Flashiness
60-
J
f\
Excellent
©
o
CO
ro
o
40
20
0.0
0.2
/
Target Flashiness
Range
H
<1
. . . .
-e # ><£
or a*
K
H—•-
Good
Fair
Poor
0.4 0.6
R-B Flashiness Index
0.8
1.0
Figure 14. Comparison of R-B Index to several southeast Michigan volunteer monitoring sites.
2.3.3 Impervious Cover Analysis
In benchmarking the amount of green infrastructure needed in southeast Michigan, SEMCOG evaluated
land cover information from 2010 aerial imagery and land use data. A portion of that analysis included a
compilation of total impervious cover, estimated to be over 16,800 acres across the three pilot
subwatersheds. One way to assess the benefits derived from green infrastructure is by looking at
potential volumes of stormwater produced. For example, annual average precipitation at the Detroit
Metropolitan Airport is just over 30 inches. Volume estimates used by the Detroit Water and Sewerage
Department in developing their Green Infrastructure Plan for the Upper Rouge Tunnel Area indicate that
this translates to about 680,000 gallons of stormwater annually per acre of impervious cover (Tetra Tech
2014).
Stormwater volume reduction targets for this project were identified based on the relationship between
aquatic biology and hydrology. An assessment of macroinvertebrate data and stream flashiness shows a
general range above which bioassessment scores reflect poor conditions for aquatic life. This range
occurs somewhere between an R-B Index value of 0.35 and 0.50, which is used as the target for
evaluating green infrastructure opportunities in the pilot subwatersheds.
21
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The R-B Index was calculated using daily average flow values (as opposed to stormwater volume). A
rainfall-runoff model, which generates daily average flow estimates, was used to examine green
infrastructure practices relative to the effect on R-B Index values.
Models are particularly useful tools in evaluating the effect that different land uses could have on any
particular receiving water. A basic watershed model allows consideration of unique features that affect
local hydrology; both natural factors (e.g., soils, topography, vegetation) and alterations such as
increased impervious cover. Principles behind the Loading Simulation Program C++ (LSPC) can be
coupled with precipitation information to examine the effect of land use on runoff. Rainfall-runoff
analysis in LSPC is based on algorithms from the Hydrologic Simulation Program FORTRAN (HSPF), a
model widely used to support watershed analysis.
One major advantage of the modeling approach is that it provides a platform for consistent comparisons
showing the relative effect of significant factors on key hydrologic indicators (e.g., increase in
impervious cover associated with land use changes, infiltration rates dependent on soil types). An
important focus of stormwater management is the effect of impervious cover on flow patterns. LSPC, for
example, enables an analysis of the relative effect of changing impervious cover on hydrology when all
other variables are held constant. For example, Figure 15 shows the relationship between the 1-day flow
(FDCi-day in Table 2) and impervious cover using the LSPC model information. As indicated, increased
impervious cover results in a higher 1-day flow.
Impervious Cover and Modeled Peak Flow
2.0
5
o
Ll_
E
3
E
10% Effective
Impervious Cover
>.
03
o
a>
c
O
0.0
0
20
40
80
100
Effective Impervious Cover (%)
LSPC Model Hydrology
Figure 15. Relative effect of impervious cover on 1-day flow-duration interval.
22
-------
One point worth noting is the increase in the slope of the line in Figure 15, which occurs at around 10-
percent impervious cover. A number of studies have shown that streams can show signs of degradation
and are considered stressed when the impervious cover exceeds 10-15 percent. A modeling analysis
allows for a closer examination of the effect that increased effective impervious cover exerts on other
flow-related parameters.
Table 6 summarizes modeled changes in several key hydrologic indicators as impervious cover increases.
For reference purposes only, values associated with an effective impervious cover level of 10 percent
are highlighted. Because of the effect of flashiness on aquatic organisms, the relationship between
impervious cover and the R-B Index is shown in Figure 16. As indicated in Table 6 and Figure 16, the
greatest increase in stream flashiness occurs at impervious cover levels between 10 and 15 percent.
Table 6. Modeled relative effect of impervious cover on key hydrologic indicators
Effective Impervious
Cover
(%)
Hydrologic Indicator3
FDC l-day
(in/day)
R-B
Index
Average Annual
Runoff Volume
(inches)
0
0.184
0.135
12.4
2.5
0.189
0.178
12.8
5
0.215
0.236
13.1
10
0.266
0.353
13.7
15
0.331
0.462
14.3
20
0.419
0.563
15.0
25
0.497
0.656
15.6
30
0.577
0.743
16.2
40
0.719
0.897
17.5
50
0.871
1.030
18.8
60
1.026
1.147
20.0
70
1.163
1.250
21.3
80
1.313
1.342
22.5
90
1.476
1.424
23.8
100
1.639
1.497
25.1
Note: a Hydrologic indicators are defined in Table 2.
23
-------
Relationship Between Impervious Cover and R-B Flashiness
1.6
1.4
10%
Effective
Impervious
Cover
1.2
R-B
Index
1.0
Flashiness percentiles
represent Michigan streams
less than 30 square miles
(Fongers, et.al.)
0.8
] 75'" percentile |—
0.4
Median
0.2
\ 25'" percentile |—
o.o
0
20
40
60
80
100
Effective Impervious Cover (%)
LSPC Model Hydrology
Figure 16. Relative effect of impervious cover on R-B Index.
2.3.4 Stormwater Volume Reduction Targets
The Low Impoct Development Manual for Michigan describes a methodology for estimating the level of
volume control needed to manage stormwater (SEMCOG 2008). The approach emphasizes BMPs
designed to mimic presettlement hydrology—as defined by ground water recharge, stream channel
stability, and flooding. It is an approach routinely used in other stormwater management guidance
documents. This project extended the target development process to also consider aquatic biology.
The R-B Index can be a good indicator of the relationship between hydrology and its effect on
macroinvertebrates (Figure 10 through Figure 14) In addition, the R-B Index is related to effective
impervious cover (Figure 16), the reduction of which is a major focus of green infrastructure
management areas. Unlike volume, however, stream flashiness is not particularly well suited for
evaluating specific stormwater runoff mitigation practices, which are typically implemented at smaller
scales (i.e., site or catchment level as opposed to the watershed scale).
MDEQ, has suggested the 90-percent non-exceedance method for managing runoff from multiple sites
or for watershedwide design (Fongers 2006). The 90-percent non-exceedance event is the storm in
which 90 percent of the runoff-producing precipitation events are equal to or less than a specified value.
The 90-percent method generally results in green infrastructure management strategies that will retain
approximately a 1-inch, 24-hour storm volume and maintain release rates at predevelopment levels. The
primary objective of the 90-percent method is channel protection, which in turn affects stream habitat
and aquatic biology.
The result of the 90-percent non-exceedance analysis using Detroit Metro Airport precipitation data is
0.98 inches of rainfall, as shown in Figure 17. A stormwater runoff reduction target can be derived using
the retention volume that corresponds to the 90-percent non-exceedance storm. Retention means that
24
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water from rainfall at or below that level is held on-site; it can leave only through infiltration or
evapotranspiration. From Figure 17, a green infrastructure practice sized to retain the 90-percent
rainfall event (0.98 inches) will reduce the annual average runoff volume by 85 percent.
Nort-Exceedance Rainfall-Runoff
90% Non-exceedance
Retention = 85%
90% Non-exceedance
Rainfall = 0.98 inches
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Percentile
Figure 17. Non-exceedance rainfall-runoff—Detroit Metro airport.
The LSPC model analysis provides information that connects annual average runoff volumes to R-B Index
values (see Table 6). Results from the analysis can be used to estimate R-B Index values that correspond
to different annual average runoff reductions. In Table 6, the annual average runoff volume associated
with no effective impervious cover (i.e., 12.4 inches) represents a baseline condition. The excess annual
average runoff above the baseline condition is the volume that can be attributed to increased levels of
impervious cover (i.e., the effective impervious area that needs to be managed for stormwater using
green infrastructure). The difference between the annual average runoff resulting from 100-percent
impervious cover (or 25.1 inches) and the baseline condition represents the total volume that could be
reduced through green infrastructure practices (i.e., 25.1 minus 12.4, or 12.7 inches excess runoff
volume).
25
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The relationship between reductions in annual average runoff volume and R-B Index values is shown in
Figure 18, which depicts how the relative infiltration benefit of pervious areas affects the R-B Index
values for different reduction volumes. For example, catchments with low infiltration rates in pervious
areas will require a higher level of volume reduction to achieve the same R-B Index value than those
catchments with higher infiltration rates in pervious areas. That result illustrates the benefit of using
multiple green infrastructure management strategies such as implementing grow zones or increased
tree canopy to complement structural practices.
Estimated Volume Reduction - Fiashiness Relationship
(Note: for illustrative purposes only)
Relative
Effective
Background
Infiltration
Benefit
Low
High
X
-------
3 Green Infrastructure Opportunities
For the purposes of this analysis, green infrastructure includes both natural areas and constructed
management practices (e.g., bioswales, rain gardens, pervious pavement, green roofs). The outcome-
based strategic planning framework recognizes the need to examine green infrastructure opportunities
concurrently with target development. This approach minimizes potential confusion that could result
from establishing reduction targets that have no clear connection to implementation options. For that
reason, desktop screening analyses are developed to estimate the relative benefit of different green
infrastructure strategies in the context of hydrologic targets (either R-B Index values or volume
reduction).
The following sections describe major implementation activities highlighted in the Green Infrastructure
Vision for Southeast Michigan that can significantly reduce stormwater runoff volume and improve
water quality (SEMCOG 2014). Included are native plant grow zones, tree canopy, and constructed
management practices. The desktop screening analyses illustrate the connection between each
implementation option and the hydrologic targets. Green infrastructure opportunities within each pilot
subwatershed are then examined.
3.1 Native Plant Grow Zones
Native vegetation has significant root systems that promote runoff infiltration and plant uptake. The
term grow zone was coined by Wayne County as they began converting large-scale park areas to native
planting areas to improve water quality and habitat and reduce the volume of stormwater runoff. Grow
zones work best in adjacent roadside areas where roadway runoff is directed via sheet flow. Large open
areas that have been traditionally managed as
turf can be easily converted to native plant
grow zones and can include large highway
medians and cloverleaf areas around on- and
off-ramps for highways. Grow zones also are
feasible in linear vegetated areas adjacent to
roadway impervious surfaces.
One way to illustrate the contribution of grow
zones toward achieving hydrologic targets is
through a screening analysis. A major benefit
of grow zones is the increased ability of
pervious areas to infiltrate precipitation. The
relative effect of improved infiltration can be
illustrated through continuous simulation of rainfall-runoff over an extended period of time. Figure 19
provides an example of the relative effect of increased infiltration on reducing R-B Index values. The
screening analysis was developed using LSPC and hourly precipitation data over a 34-year period from a
SEMCOG area climate station.
The range of target R-B Index values is included as a point of reference. As indicated, minor
improvements in soil conditions resulting from green infrastructure practices (e.g., grow zones) provide
the greatest relative benefit in pervious areas with lower relative infiltration benefit (e.g., hydrologic soil
groups C and D or compacted urban soils found in developed portions of the SEMCOG region).
27
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ScreeningAnalysis
Relative Pervious Area Infiltration and Flashiness
(Note: for illustrative purposes only)
Low Benefit
High Benefit
Relative Pervious Area Infiltration
Target Flashiness
Range
Figure 19. Relative effect of increased infiltration benefit on stream flashiness.
3.2 Tree Canopy
Tree canopy is another component of green
infrastructure that has the potential to provide
numerous benefits. In addition to improving
aesthetics, trees provide water
quality/hydrologic benefits by intercepting
precipitation, improving soil conditions with
increased infiltration, and reducing runoff
volume through evapotranspiration.
SEMCOG's Green Infrastructure Vision for
Southeast Michigan indicates that southeast
Michigan will strive to meet the standards
developed by American Forests, including a 40-percent tree canopy for the region. It focuses on urban
areas where tree canopy is below 20 percent and prioritizes specific land uses around industrial
property and central business districts and along roadways and parking lots (SEMCOG 2014).
A screening analysis similar to the one used for grow zones can be used to illustrate the contribution of
tree canopy towards achieving hydrologic targets. Figure 20 shows the benefits derived from increasing
tree canopy by comparing R-B Index estimates across a range of impervious cover assumptions using
LSPC In this example, the upper flashiness target is reached in areas with no tree canopy when
impervious cover is lower than when the remaining pervious area consists of a full tree canopy. For this
particular situation, a full tree canopy mitigates the adverse effect of the additional impervious cover—
an important consideration in areas in which options to reduce effective impervious cover are limited.
28
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Relationship Between Impervious Cover and R-B Index
(Note: for illustrative purposes only)
Range of effective
impervious cover
needed to achieve
upper flashiness
target
Target Flashiness
Range
Limited
Tree
Canopy
Full Tree
Canopy
0.0
20
40
60
80
100
Effective Impervious Cover (%)
Figure 20. Relative effect of impervious cover and tree canopy on stream flashiness.
3.3 Constructed Management Practices
The integrated network of green infrastructure includes constructed practices (e.g., bioswales,
permeable pavement, rain gardens). Constructed practices play an important role in developing green
infrastructure strategies by providing ecological, environmental, economic, and social benefits. These
techniques work primarily to improve water quality by reducing stormwater runoff entering surface
waters. Their characteristics and designs can increase economic value of adjacent properties due to
improved aesthetics and quality of life. The recommended amount of constructed green infrastructure is
linked to the percentage of impervious surfaces. Priority areas for constructed practices in southeast
Michigan include roadways, institutional properties, and both public and private parking lots.
A key part of SEMCOG's Green Infrastructure Vision is a focus on volume reduction through infiltration
(SEMCOG 2014). The presumption is that decreased stormwater flows also result in lower stream
flashiness and reduced pollutant loads. Roads and parking areas, for instance, are high-priority surfaces
for treatment because they are the most likely to be directly connected to storm sewer systems that
discharge to streams. They also represent a significant proportion of total impervious area in the pilot
subwatersheds, as shown in Figure 21. The graph depicts the total impervious area and the impervious
area for the primary land use categories (i.e., residential, commercial/industrial, road right-of-way
[ROW], and institutional). Information in this form conveys the amount of constructed green
infrastructure opportunity in each subwatershed. The percent impervious cover, also shown in Figure
21, reflects density.
29
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Pilot Subwatershed Composition Summary
Impervious Area by Land Use Type
B.000
Subwatershed
5.000
1 otal IC
> 4,000
2.000
~ Commercial
~ Institutional
Malletts
Plumbrook
Tonquish
Figure 21. Pilot subwatershed impervious surface composition.
An important part of evaluating constructed green infrastructure opportunities is assessing options.
Impervious area by land use category as shown in Figure 21 is one consideration. Figure 22 shows an
example schematic for determining where certain types of constructed practices could actually be
implemented. As indicated in Figure 22, bioretention and porous pavement are options for parking lots.
Bioswales are a viable option for some roads and residential streets. These linear practices are designed
to provide off-line retention for road runoff and surrounding areas. In addition to assessing individual
practices, another option to consider could be the use of treatment trains (e.g., flow from porous
pavement systems to bioretention).
Impervious Surface Type
Residential Impervious
Transportation
Impervious
Porous
Pavement
Porous
Pavement
Bioswale
Rain Garden
Roof
Roof
Street
Road
Parking
Driveway
Sidewalk
Trench/Bioretention
Commercial
Impervious
Figure 22. Constructed practice options by impervious surface type.
30
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Another aspect of the opportunity assessment involves estimating the level of implementation that
might be needed beyond the site scale (e.g., catchment or subwatershed level). Once areas of
opportunity and potential BMPs are identified, desktop analyses can be used to evaluate constructed
green infrastructure options. The screening analyses are designed to recognize and account for
uncertainty associated with physical constraints and key design parameters. Specifically, screening
analyses can be used to evaluate relative BMP performance given the array of sizing options (e.g.,
bioretention media depth, amount of area retrofitted, and so forth) and the range of design
assumptions (e.g., native soil infiltration rates). An example of a constructed bioretention practice sized
to retain the 90-percent non-exceedance storm under different relative infiltration assumptions is
shown in Figure 23.
Determining the maximum extent to which impervious surface types could be converted to constructed
practices is an important part of the opportunity assessment. That amount represents the percentage of
impervious area managed for stormwater using green infrastructure. Figure 24 and Figure 25 provide
examples for two constructed practices that show how volume reduction and the amount of area
managed using green infrastructure vary with key assumptions (e.g., relative effective infiltration
benefit). The curves shown in the examples were developed using the BMP assessment module of the
System for Urban Stormwater Treatment and Analysis INtegration, or SUSTAIN (Shoemaker 2009).
Bioretention Analysis
Estimated Volume Reduction under Different Design Assumptions
(Note: for illustrative purposes only)
Relative
Effective
Infiltration
Benefit
BMP surface size at 1" rain event:
(90-percent non-exceedance storm)
100 T
0.2 04 0.6 0.8 1 12 14
Depth of Rain Event Treated (inches)
1.6
Figure 23. Bioswale screening analysis using different relative infiltration assumptions.
31
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Bioswale Analysis
Estimated Volume Reduction under Different Scenarios
(Note: for illustrative purposes only)
100
Relative
Effective
Infiltration
Benefit
¦High
'Medium
'Low
Green Infrastructure Area:
Percentage of impervious
area managed for
stormwater
0 2 4 6 8 10 12 14 16
Green Infrastructure Area (%)
re 24. Bioswale volume reduction estimates at different infiltration rates.
Porous Pavement Analysis
Estimated Volume Reduction under Different Scenarios
(Note: for illustrative purposes only)
Relative
Effective
Infiltration
Benefit
Medium
Green Infrastructure Area:
Percentage of impervious
area managed for
stormwater
6 8 10 12 14
Green Infrastructure Area (%)
re 25. Porous pavement volume reduction estimates at different infiltration rates.
32
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4 Pilot Subwatershed Assessment Results
SEMCOG's Green Infrastructure Vision is intended to highlight solutions that address hydrology and
water quality challenges in surface waters across southeast Michigan (SEMCOG 2014). While solutions
include the entire network of green infrastructure, focusing on urban areas and the extent of impervious
cover is a priority. Consistent with the vision, the pilot subwatershed opportunity assessments focus on
major areas of impervious surfaces and publicly
owned properties. This approach emphasizes
the following land use types:
Institutional properties include publicly owned
property such as municipal facilities and
complexes, libraries, parks, schools, and
universities. The focus for those properties is to
evaluate opportunities for managing runoff from
paved surfaces and rooftops. In addition, large
open spaces dominated by turf present options
for increasing tree canopy or developing native
plant grow zones.
Roadways are generally represented by major arterials, including local, county, and state roads.
Southeast Michigan's transportation infrastructure (e.g., roads, bridges, nonmotorized pathways, transit
routes, and facilities) along with the people and vehicles that use it affect the physical landscape.
Transportation infrastructure can provide connectivity with natural areas and features for recreational
enjoyment and represents the land use type with the highest levels of impervious cover directly
impacting the region's water resources. Green infrastructure, both natural and constructed, can be
strategically used along roadway corridors to provide recreational, social, and aesthetic amenities to
surrounding communities in addition to providing local and regional environmental benefits.
Within the southeast Michigan region, there are over 23,400 miles of roadways with approximately
245 square miles of impervious cover, which comprises approximately 36 percent of ali impervious
cover in southeast Michigan. Roadway pavement, including residential streets, is nearly 40 percent of ali
impervious cover in the three pilot
subwatersheds. Major roads comprise
approximately 150 square miles in the region,
with approximately 86 square miles of
impervious cover and 64 square miles of open
space and tree canopy.
Green infrastructure can be constructed within
the ROW in existing open space or, where traffic
data support it, as part of a road diet to reduce
the number of travel lanes while adding other
features. Local residential streets, although not
emphasized in the vision, represent secondary
opportunity areas.
33
-------
Parking lots, both publicly and privately owned,
represent a major opportunity category for
green infrastructure implementation. Publicly
owned parking lots are included as part of the
impervious cover within the institutional
properties. Privately owned parking lots
represent the larger commercial areas in each
pilot subwatershed. Bioretention areas,
bioswales, and porous pavement are techniques
that can significantly reduce stormwater runoff
from paved surfaces. From a planning
perspective, inverted parking lot islands can
double as bioretention areas when coordinated
with engineering design.
In benchmarking the amount of green infrastructure and identifying opportunities in the region,
SEMCOG relied primarily on land cover information from 2010 aerial imagery and its own land use data.
The Green Infrastructure Vision used impervious surface land cover data to estimate the annual
stormwater runoff volume generated in the SEMCOG area (SEMCOG 2014). Information from SEMCOG's
land cover database also includes estimates of impervious surface types (e.g., building, road, parking).
Table 7 summarizes green infrastructure opportunities by land use category for each pilot
subwatershed.
Table 7. Green infrastructure opportunities within the pilot subwatersheds
Institutional
(publicly owned acres)
Roadways
(publicly owned
acres)
Other
(privately owned acres)
Total
Impervious
Area
(percent)
Subwatershed
Total
Area
(acres)
Impervious Surface:
Buildings
Impervious Surface:
Pavement
Open Space
Impervious Surface:
Pavement
Open Space
Privately Owned
Parking
Tree Canopy
Open Space
Malletts
Creek
6,725
51
120
259
650
282
588
1,457
1,287
35%
Plumbrook
Drain
21,625
100
294
639
2,050
1,234
1,642
4,104
5,219
36%
Toriquish
Creek
15,952
84
223
435
1,558
675
1,584
3,283
3,227
42%
34
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4.1 Malletts Creek Subwatershed
Malletts Creek drains approximately 11 square
miles of land in the Huron River watershed
(Figure 26). It is located in Washtenaw County
and includes the City of Ann Arbor and Ann
Arbor, Lodi, and Pittsfield townships. Portions of
the University of Michigan also are located
within this subwatershed. Malletts Creek is a
designated county drain encompassing
approximately 10 miles of open streams, many
of which have been enclosed. The Washtenaw
County Water Resources Commission has
jurisdiction over Malletts Creek.
Substantial restoration efforts have been
implemented across the subwatershed, including the Malletts Creek Library, the Mary Beth Doyle Park
wetland complex, the Malletts Creek streambank restoration, the Buhr Park Children's Wet Meadow,
and the Easy Street pavement rehabilitation. Challenges remain due to the urban nature of the stream,
with stormwater runoff from impervious surfaces leading to increased stream flashiness, degraded
water quality, and poor biological conditions.
To help address those concerns, Ann Arbor is currently refining their stormwater management model
(SWMM) to develop a shared understanding with the local community of stormwater behavior in the
city. A key aspect of the pilot subwatershed opportunity assessments was the use of a multiscale
analysis framework to identify high-priority areas for BMP implementation. Ann Arbor's SWMM model
units were examined as a starting point. For the Malletts Creek subwatershed, there are nearly 500
model units with an average size of nearly 14 acres per unit. Catchment delineations for the Malletts
Creek subwatershed also were developed by MDEQ's Hydrologic Studies Unit. The MDEQ catchments
provide a platform for clustering Ann Arbor's SWMM model units into a manageable number for
purposes of conducting opportunity assessment screening analyses. Catchment boundaries used for the
screening analyses are shown in Figure 27.
4.1J Land Use and Land Cover
Land use and land cover information inventoried by SEMCOG for each pilot subwatershed is an
important part of the overall analysis. The data can be used to develop subwatershed-scale runoff
estimates that reflect the mix of different land uses present across the Malletts Creek drainage. The
SEMCOG inventory provides impervious cover estimates based on an evaluation of parcel-scale data,
including building footprints, parking lot locations, and transportation corridors. The SEMCOG land use
information for the Malletts Creek subwatershed is shown in Figure 28 and summarized by catchment in
Table 8. This tabular summary highlights land use categories in each catchment that exceed the
subwatershed average—a useful indicator in targeting priority areas for green infrastructure planning.
Another way to view SEMCOG's land use data is by examining land cover patterns for each category
(Table 9). In addition to supporting development of subwatershed-scale runoff estimates, information
presented in this manner helps identify implementation options (e.g., what percentage of road ROW is
pavement that could be routed to grow zones or constructed bioretention, how much commercial land
use is parking area potentially available for green infrastructure practices, and so forth).
35
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jJWINGSTQN
WASH'
Malletts Subwatershed
Huron River Watershed
Malletts Creek Subwatershed
Huron Watershed
Southeast Michigan Council of Governments
1001 Woodward Avenue. Suite 1400. Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www semcogorg Copyright: SEMCOG, 2014
N
A
A
1:451.245
0 3
6
0 5
10
Kilometers
State Plane NAD83 HARN
December 2014
Figure 26. Location of Malletts Creek pilot subwatershed within Huron River watershed.
36
-------
tray '
~
Malletts Creek Subwatershed
SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
Malletts Subwatershed Catchments
A
1:40,574
o 1
State Plane NAD83 HARN
December 2014
-------
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Malletts Creek Subwatershed
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State Plane NAD83 HARN
December 2014
Land Use Categories
Agricultural
Single-family residential
Multiple-family residential
| Commercial
| Industrial
| Governmental / institutional
Park, recreation, and open space
Airport
I Transportation, communication, utilities
~ Water
SEMC€XS
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
-------
Table 8. Malletts Creek subwatershed land use
Land Use (percent)
Total
Impervious
Area
(percent)
Catchment Group /
Catchment ID
Area
(acres)
Single-family
Residential
Multifamily
Residential
Commercial
Institutional
Industrial
Road ROWS
Parks, Open
Other
A
10 - Cranbrook Mall
322
34%
8%
23%
2%
—
32%
1%
—
37%
11 - Briarwood/l-94 Corridor
1,153
15%
8%
35%
5%
15%
22%
0.2%
1%
47%
20 - Upper Malletts
873
55%
2%
10%
9%
—
19%
2%
3%
29%
B
22 - Cranbrook Park
107
54%
10%
8%
6%
—
8%
15%
—
39%
23 - State & Eisenhower
140
15%
13%
37%
15%
1%
16%
2%
1%
53%
C
30 - Upper South
205
—
—
15%
33%
41%
11%
—
0.1%
22%
31 - Middle South
172
12%
—
—
5%
69%
8%
—
6%
38%
D
40 - Junction Reach
110
40%
21%
5%
3%
—
28%
3%
—
33%
E
50 - Upper State - Packard
2,078
36%
5%
13%
14%
3%
18%
10%
0.1%
35%
60 - Doyle Park
223
32%
22%
1%
4%
—
14%
26%
—
31%
F
61 - Packard
121
46%
—
4%
11%
—
19%
19%
—
27%
62 - Scheffler Park
558
45%
5%
7%
13%
0.2%
17%
11%
0.2%
29%
70 - County Farm Park
371
40%
6%
5%
31%
—
16%
1%
—
28%
G
71 - Huron Parkway
250
62%
2%
12%
1%
—
14%
7%
—
27%
72 — Malletts Outlet
43
81%
—
2%
—
—
17%
0.1%
—
26%
Total
6,725
36%
6%
15%
11%
7%
18%
6%
1%
35%
Note: Yellow highlighted cells identify land use categories in each catchment that exceed the subwatershed average.
Table 9. Malletts Creek subwatershed land cover by land use category
Land Use Category
Area
(acres)
Impervious Surface Types (percent)
Pervious Area (percent)
Building
Pavement
(road surface, parking,
driveways, sidewalks)
Open
Tree Canopy
Single-family residential
2,385
12%
11%
28%
49%
Multifamily residential
405
18%
27%
28%
27%
Commercial
1,036
15%
41%
31%
13%
Institutional
763
7%
19%
34%
40%
Industrial
443
15%
30%
43%
12%
Road ROWs
1,236
0.1%
53%
23%
24%
Parks, Open Space
409
1%
7%
58%
34%
Other
48
1%
24%
49%
26%
Total
6,725
10%
26%
31%
33%
39
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4.1.2 Existing Conditions Related to Flashiness
Flooding arid water quality problems in Malletts
Creek have been well documented (WCDC 2000).
Existing flow conditions are best described as
unstable and flashy in response to storm events
(Wuycheck 2004). Flashy streams are characterized
by rapid rates of change, high pulses, and frequent
flow reversals as runoff quickly leaves the land in
response to storms. Figure 29 shows daily average
flows monitored over a 3-month period at two USGS
gage locations in Malletts Creek, illustrating the rapid
rise and fall in flow as Malletts Creek responds to
different rain events (shown across the top of
Figure 29).
Based on USGS data, R-B Index values in Malletts Creek currently exceed 0.7 (see Table 4). The focus of
the pilot subwatershed opportunity assessment was to examine green infrastructure implementation
opportunities that will work towards reducing stream flashiness in Malletts Creek to a target range
between 0.35 and 0.50 as measured by the R-B Index.
Malletts Creek
Daily Flow Patterns (4/1 - 6/30/2010)
¦ Precip
"Doyle Park
I
V
1
150
250 3
I ''
Figure 29. Daily average streamflow patterns in Malletts Creek (4/1-6/30/2010).
4.1.3 Stormwater Runoff Reduction Targets
The LSPC screening analysis offers a method to evaluate subwatershed-scale runoff patterns in the
context of current land use information. R-B Index estimates based on local meteorological information
and the SEMCOG land cover data were used to benchmark existing conditions for relative comparison
with different implementation strategies, including identifying the percentage of effective impervious
40
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cover that would need to be managed for stormwater using green infrastructure to meet the target R-B
Index range.
The results of the screening analysis are represented in Figure 30, The box in the upper left identifies the
estimated baseline effective impervious cover that corresponds to the current Malletts Creek R-B Index
value. It is important to note that the effective impervious cover is less than the total impervious area in
Table 8. The effective amount acknowledges that not all impervious surface runoff reaches the stream.
For example, a portion of storm runoff from residential roofs likely flows to yards, where it infiltrates
into the ground. Similarly, some storm runoff from roads without curb and gutter or well-defined ditch
systems could simply flow from pavement to pervious areas and infiltrate into the ground.
The screening analysis shown in Figure 30 used baseline assumptions to examine the change in R-B
Index values as effective impervious cover is varied across the Malletts Creek subwatershed. Under
those baseline scenario assumptions, effective impervious cover would need to be managed to
approximately 11 percent to meet the upper R-B Index target (i.e., 0.50) This represents an ambitious
goal from the current 24-percent estimated effective impervious cover, particularly in light of significant
changes to the existing subwatershed land cover that might be needed.
Developing stormwater volume reduction targets using LSPC estimated an annual 12.7 inches of excess
runoff from effective impervious surface areas. That translates into approximately 63 million cubic feet
annually of excess stormwater runoff volume to be reduced to achieve the upper R-B Index flashiness
goal (depending on background infiltration benefit assumptions). Another way to view this challenge,
however, is to focus on simply estimating the percentage of effective impervious cover that would need
to be managed for stormwater using green infrastructure.
Relationship Between Impervious Cover and R-B Flashiness
(Malletts Screening Analysis)
Estimated effective
impervious cover
corresponding to current
Malletts Creek flashiness
Baseline
Estimate
Current
Flashiness
Condition
x
CD
TD
03
C
CD
ck
TargetFlashiness
Range
o
20
40
60
80
100
Effective Impervious Cover (%)
Figure 30. Malletts Creek subwatershed effective impervious cover and R-B flashiness screening analysis.
41
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The current estimated effective impervious area
in the Malletts Creek subwatershed is 24
percent, or approximately 1,600 acres. The
screening analysis indicates that this effective
impervious area should be reduced to 11
percent, or to approximately 740 acres. The
difference of 860 acres represents an effective
impervious cover target that should be
prioritized for identifying areas that could be
managed using green infrastructure.
In summary, the baseline curve shown in Figure
30 provides an initial frame of reference from
which to examine green infrastructure
implementation strategies. Options include the use of grow zones at key locations, increasing tree
canopy across the subwatershed, and evaluating design alternatives for constructed BMPs intended to
reduce effective impervious cover.
4.1A Areas of Opportunity and Priorities
SEMCOG's Green Infrastructure Vision sets a direction for southeast Michigan based on stakeholder
input and identifies 10 primary regional policy recommendations on how to get there (SEMCOG 2014).
Regional policies that relate directly to improving water quality include:
• Encouraging policies to integrate constructed green infrastructure in publicly funded projects,
including institutional properties and major roadways. Focus implementation on roads, parking
lots, and large managed turf areas.
• Minimizing mowing within riparian corridors, and seeking opportunities to increase tree canopy
and native plant grow zones in open space areas.
Figure 31 shows the green infrastructure vision for the Malletts Creek subwatershed. The Current Green
Infrastructure network is shown as the background on Figure 31, representing the larger green
infrastructure network of tree canopy and open space based on the 2010 land cover analysis for
southeast Michigan. The region's public parks and conservation lands are classified as Conservation and
Recreation Lands. The Potential Conservation & Recreation Lands classification highlights areas that
could be added to the network. The Potential Green Streets classification identifies major roads that
have opportunities for improving infiltration through grow zones, enhancing tree canopy coverage, and
implementing constructed practices. In addition, the top 10 percent by area of institutional properties is
highlighted as an initial priority. Finally, the top 1 percent by area of private parking lots is identified.
The SEMCOG land cover data provide a starting point from which to describe opportunities (Figure 32).
An important aspect is identifying potential impervious surface types that could be managed for
stormwater using green infrastructure. Within the Malletts Creek pilot subwatershed, pavement (e.g.,
roads, parking lots, driveways, sidewalks, and so forth) represents nearly three-quarters of all
impervious surface types (Table 10).
42
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Malletts Creek Subwatershed
2
3 Mites
4
Kilometers
Green Infrastructure Vision
Potential Green Streets
Conservation & Recreation Lands
Potential Conservation & Recreation Lands
Current Green infrastructure
/ Increase Tree Canopy
Gl Opportunities: Institutional Land
• Gl Opportunities: Parking Lots
A
1:43,682
SEMCOG c
Southeast Michigan Council of Governments o 2
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869 State Plane NAD83 HARN
www.semcog.org Copyright: SEMCOG, 2014 December 2014
-------
Malletts Creek Subwatershed
Southeast Michigan Council of Governments
1001 VWaodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:43.099
o
State Plane NAD83 HARN
December 2014
2010 Land Cover
| Impervious Surfaces; Buildings/Structures
| Impervious Surfaces: Paved Oram to Sewer
Open Space - Grass/Scattered Trees Grass cover > 75%
| Trees Grass/turf understory Ground cover 50% - 75%
| Trees Grass/turf underslory. Ground cover > 75%
| Trees Impervious underslory
H Urban.Bare
W&ter Area
-------
Table 10. Malletts Creek subwatershed impervious cover estimates by surface type
Catchment Group /
Catchment ID
Area
(acres)
Total
Impervious
Area (acres)
Percent of Total Impervious Area
[percent)
Tree
Canopy
(percent)
Building
Road
Other
Pavement
A
10 - Cranbrook Mall
322
121
25%
37%
38%
19%
11 - Briarwood/l-94 Corridor
1,153
540
25%
21%
54%
15%
B
20 - Upper Malletts
873
251
31%
41%
28%
35%
22 - Cranbrook Park
107
42
34%
14%
52%
23%
23 - State & Eisenhower
140
75
22%
18%
60%
14%
C
30 - Upper South
205
45
25%
20%
55%
28%
31 - Middle South
172
65
27%
9%
64%
11%
D
40 - Junction Reach
110
37
25%
39%
36%
44%
E
50 - Upper State - Packard
2,078
731
28%
27%
45%
37%
F
60 - Doyle Park
223
69
26%
28%
46%
36%
61 - Packard
121
33
26%
41%
33%
53%
62 - Scheffler Park
558
164
29%
34%
37%
44%
G
70 - County Farm Park
371
103
26%
34%
40%
51%
71 - Huron Parkway
250
67
31%
25%
44%
59%
72 — Malletts Outlet
43
11
31%
36%
33%
41%
Total
6,725
2,351
27%
28%
45%
33%
The land use/land cover inventory data compiled by SEMCOG provide detailed information that can be
used to identify priority areas. Figure 33 summarizes the impervious surface composition for catchment
groups in the Malletts Creek subwatershed. The 15 catchments in Figure 27, Figure 28, and Table 8 are
clustered into groups A through G, shown in Figure 33. The number behind each letter on the x-axis
represents the first digit of those catchment identifiers, which have been clustered in that particular
group (e.g., catchments 10 and 11 in group A; catchments 20, 22, and 23 in group B; and so forth).
This chart conveys two types of information useful for targeting green infrastructure implementation
efforts: the quantity of impervious area and the density of impervious cover in each catchment group.
The quantity aspect identifies the groups that contain higher amounts of total impervious area. In the
Malletts Creek subwatershed, those are catchment groups A (Briarwood) and E (Upper State-Packard).
The value in the oval for each group represents the percent impervious cover (or the density aspect).
The combination of both aspects points to Briarwood as a high priority for targeting green
infrastructure, which does not mean that green infrastructure in other groups is less important. Instead,
it highlights the fact that managing impervious cover in the Briarwood catchment group must play a
major role in reducing stream flashiness in the Malletts Creek subwatershed.
45
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Malletts Creek - Catchment Group Summary
Impervious Area by Land Use Type
Groupie
Percentage
ED Residential
Commercial
/ Indus trial
¦ ROW
~ Institutional
A-1 B-2 C-3 D-4 E-5 F-6 G-7
Figure 33. Impervious surface composition—Malletts Creek subwatershed.
The impervious surface composition shown in Figure 33 provides other useful information for targeting
green infrastructure implementation. As indicated, Briarwood (A) is a high-priority group. The greatest
amount of impervious area in group A catchments is associated with commercial land use followed by
roads. The green infrastructure vision map identifies parking lot and green street opportunities (Figure
31). While the Upper State-Packard group (G) has high amounts of commercial land and road surfaces,
targeting residential areas in that catchment should play an important role for green infrastructure,
which is consistent with Ann Arbor projects in place (e.g., Easy Street, Miller Avenue). In addition, this
group has the greatest amount of impervious area on institutional properties with opportunities noted
in the vision (Figure 31).
4.1.5 Recommendations
Significant restoration efforts have already been implemented to address flooding and water quality
problems in the Malletts Creek subwatershed. In addition, other efforts are either underway or have
been suggested as potential opportunities, including:
• State Street—transportation corridor planning (catchments 11, 23, 50)
• Stone School Road—bioswales (catchment 11)
• Springwater subdivision—sand filter BMPs within ROW (catchment 61)
• Buhr Park—parking lot infiltration (catchment 62)
• Reimagine Washtenaw—integrated transportation opportunities (catchments 62, 71)
To complement these ongoing activities, several recommendations are offered based on an analysis of
existing conditions related to flashiness and priorities identified using land use/land cover information.
These recommendations follow key components of SEMCOG's Green Infrastructure Vision (SEMCOG
2014).
46
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Institutional Properties
Green infrastructure on institutional properties offers several benefits, including a public display of the
types of practices suitable for implementation in the local community. Based on SEMCOG's analysis of
parcel-level information, more than 1,000 acres of the Malletts Creek subwatershed are publicly owned
or institutional property, including parks and open space areas (Figure 34). Managing impervious
surfaces on publicly owned property is another priority opportunity identified in the vision. Table 11
details the land cover breakdown of those properties by jursidiction.
Figure 35 highlights the extent of school district property in the Malletts Creek subwatershed. School
districts can benefit from green infrastructure implementation through construction of schoolyard
habitats and native plant grow zones. In addition to the educational value, green infrastructure on
school properties can work to reduce long-term maintenance costs by improving drainage and replacing
high-maintenance turf with lower maintenance trees, shrubs, and ornamental grasses.
Of the different types of impervious surfaces on publicly owned properties, pavement represents the
largest proportion. The Low Impact Development Manual for Michigan provides detailed information on
suitable practices for those surface types (SEMCOG 2008). Recommended BMPs include bioretention,
infiltration trenches, pervious pavement, planter boxes, level spreaders, and vegetated swales. The
manual also describes the range of design options available to accommodate site-specific situations. The
Site Development Stormwater Tool, which has been applied in Michigan, can be used to guide more
parcel-specific screening analyses (similar to that shown in Figure 23) to reflect design configurations
appropriate for each location (Christian 2014).
The level of implementation curves shown in Figure 24 and Figure 25 are based on southeast Michigan
climate data. The curves provide a general estimate of environmental benefits that could be derived
from constructed green infrastructure on institutional properties across all catchments in the Malletts
Creek subwatershed. A significant percentage of the soils in the subwatershed are in hydrologic soil
group (HSG) D, which provide lower infiltration benefit. That local challenge can be addressed either
with enhanced design for constructed practices (e.g., soil amendments, increased BMP treatment
capture depth) or by improving the infiltration of pervious areas (e.g., grow zones, increased tree
canopy).
Table 11. Malletts Creek subwatershed publicly owned property by jurisdiction
Jurisdiction
Area
(acres)
Impervious Surface Types (acres)
Pervious Area (acres)
Building
Pavement
(parking, driving
surfaces, sidewalks)
Open
Tree
Canopy
City of Ann Arbor
293
7
22
119
145
Washtenaw County
201
3
20
56
123
Pittsfield Township
4
0
1
3
0
State of Michigan
12
0
2
5
5
Federal Property
3
1
1
1
0
University of Michigan
262
12
39
151
60
School Property
266
20
53
113
80
Total
1,041
42
138
448
413
47
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Malletts Creek Subwatershed
Public Parcels
I'1 COUNTY OF WASHTENAW
PITTSFIELD CHARTER TOWNSHIP
STATE OF MICHIGAN
UNITED STATES
UNIVERSITY OF MICHIGAN
CITY OF ANN ARBOR
SCHOOL PROPERTY
~ Malletts Subwatershed Catchments
-------
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SEMCOG
Southeast Michigan Council of Governments
1001 V\foodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
k
1:40,574
o 1
State Plane NAD83 HARN
December 2014
2
3 Miles
Malletts Creek Subwatershed
Malletts Subwatershed Catchments
School Property
-------
Roadways
The aerial imagery and land use displayed in Figure 27 and Figure 28 show the extent of the roadway
network in the Malletts Creek subwatershed. That information is summarized in Table 12 by general
jurisdictional ownership for the Malletts Creek subwatershed. As indicated, nearly 10 percent of the
entire 6,725-acre land area is comprised of roadway impervious surfaces. The SEMCOG parcel data
identify major roadways as potential opportunities for increasing green infrastructure in the Malletts
Creek subwatershed (Figure 36).
Roadway type affects the applicability of different green infrastructure practices within the ROW. Within
the Malletts Creek subwatershed, roadway types include interstates (e.g., 1-94), arterial and collector
roads (e.g., State Street, Ann Arbor-Saline Road, Eisenhower Parkway), local and residential streets, and
alleys. Roads—including those under the jurisdiction of the City of Ann Arbor, the Washtenaw County
Road Commission, and the Michigan Department of Transportation (MDOT)—represent 650 acres, or
more than one-quarter, of the total impervious surface area of 2,351 acres in the Malletts Creek
subwatershed.
Open spaces within the road ROW represent potential opportunities to increase green infrastructure,
depending on the array of site-specific factors. In addition to the Low Impact Development Manual for
Michigan, the Green Streets Guidebook: A Compilation of Road Projects Using Green Infrastructure also
provides information on suitable practices for use on road ROWs (SEMCOG 2008, 2013). Recommended
BMPs include bioretention, permeable pavement, bioswales, and native plant grow zones.
As with institutional properties, the benefits of green infrastructure across all catchments in the Malletts
Creek subwatershed (both constructed practices and the use of grow zones) can be estimated using the
level of implementation curves (see Figure 24 and Figure 25). The screening analysis guided by
spreadsheet methods (e.g., the Site Development Stormwater Tool) can be used to account for site-
specific design adjustments appropriate to each location (see Figure 23 for an example).
In addition to recognizing the significant percentage of HSG D soils in the Malletts Creek subwatershed,
continuing to address local roads should be an integral part of green infrastructure implementation
efforts in the subwatershed. Green infrastructure practices recommended for the roadways already
have been successfully implemented in the Ann Arbor area (e.g., Miller Avenue).
Table 12. Malletts Creek subwatershed road ROW land cover
Jurisdiction
Area
(acres)
Pavement
(acres)
Pervious Area
(acres)
Open
Tree Canopy
Local
871
479
163
229
Washtenaw County
137
77
49
11
MDOT
228
94
71
63
Total
1,236
650
283
303
50
-------
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Malletts Creek Subwatershed
| State TrunWme 100« ROW
| County Primary 6011 ROW
County Local 30(1 ROW
I I Malletts Subwatershed Catchments
-------
Parking Lots
Publicly and privately owned parking lots comprise a
significant percentage of ali impervious surfaces in the
Malletts Creek subwatershed. The SEMCOG parcel
data identify priority parking lots for increasing green
infrastructure in the subwatershed (Figure 37): one
institutional parking lot (in catchment 50) and three
privately owned parking lots (two in catchment 11 and
one in catchment 23). Recommended BMPs include
bioretention, infiltration trenches, pervious pavement,
and increasing tree canopy.
As noted in Figure 33, catchment 11 is located in group A (Briarwood) and is a high-priority area for
green infrastructure implementation to reduce stormwater volume in the Malletts Creek subwatershed.
It is recommended as a high-priority area based on both the amount and density of impervious cover.
Commercial land use dominates total impervious cover in the area and is one reason implementing
green infrastructure for the two priority parking lots could be an important component in reducing
stream flashiness in Malletts Creek. Incorporating stormwater volume reduction practices into the
priority parking lots would represent a major step towards addressing the 860-acre target of effective
impervious cover to be managed using green infrastructure in this pilot subwatershed.
Similar to the discussion of institutional properties earlier in this section, the benefits of green
infrastructure across all catchments in the Malletts Creek subwatershed can be estimated using the level
of implementation curves (Figure 24 and Figure 25) included in this report. The screening analysis (e.g.,
Figure 23) is based on spreadsheet methods (e.g., Site Development Stormwater Tool) and can be used
to account for site-specific design adjustments appropriate for each location.
4.1.6 Pilot Watershed Summary
The Malletts Creek subwatershed assessment illustrates the value of the outcome-based strategic
planning framework to determine the role green infrastructure can play in working towards WQ5
attainment by addressing documented stormwater problems. The pilot assessment describes overall
existing conditions related to flashiness in the subwatershed (Figure 29). The amount of impervious
cover that needs to be managed to achieve the stream flashiness goal is identified (Figure 30). Land
use/land cover detail is provided in the form of maps (Figure 28 and Figure 32) and tables (Table 8, Table
9, and Table 10). Priority catchments are defined using impervious cover composition and density
information (Figure 33). Recommendations are summarized based on areas emphasized in SEMCOG's
Green Infrastructure Vision for Southeast Michigan (SEMCOG 2014).
52
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Figure 37. Priority parking lots in Green Infrastructure Vision—Malletts Creek subwatershed.
53
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4.2 Plumbrook Drain Subwatershed
The Plumbrook Drain subwatershed is a
tributary to Red Run, which flows into the
Clinton River near Utica (Figure 38). It consists
of two HUC-12S (04090003-1218 and 04090003-
1219) for a combined drainage area of 23.8
square miles. SEMCOG communities located
within the Plumbrook Drain subwatershed
include the City of Sterling Heights and Shelby
Township in Macomb County, and the cities of
Rochester Hills and Troy in Oakland County.
Plumbrook Drain is a designated county drain in
both Oakland and Macomb counties. Planning
efforts in the Clinton River watershed are
widespread with a goal of reducing "runoff impacts through sustainable stormwater management"
(R2W SWAG 2006, p. xxi). Additionally, degradation of fish and wildlife populations and the habitats that
support them are identified as beneficial use impairments within the Clinton River Area of Concern.
More specifically, Plumbrook Drain was identified as one of the most impaired reaches for habitat and
wildlife populations.
Given this high priority for addressing both habitat and fish and wildlife populations, an analysis of green
infrastructure target setting and opportunities will help support strategic implementation. Green
infrastructure implementation will reduce stormwater runoff and ultimately stream flashiness to work
towards removing the habitat and wildlife population beneficial use impairments.
As a starting point, evaluating the extent of land use and land cover based on delineated catchments
enabled the study to identify and prioritize areas of opportunity. Working with MDEQ, catchments were
defined, as shown in Figure 39.
4.2.1 Land Use and Land Cover
Land use and land cover information inventoried by SEMCOG can be used to develop subwatershed-
scale runoff estimates that reflect the mix of different land uses present across the Plumbrook drainage.
The SEMCOG inventory provides impervious cover estimates based on an evaluation of parcel-scale
data, including building footprints, parking lot locations, and transportation corridors.
The SEMCOG land use information for the Plumbrook Drain subwatershed is shown in Figure 40 and
summarized by catchment in Table 13. The primary land use type in the Plumbrook Drain subwatershed
is single-family residential housing, covering approximately 47 percent of the entire drainage. This
subwatershed also is home to several large industrial facilities along the Van Dyke transportation
corridor, including Chrysler and Ford assembly plants.
The Table 13 summary highlights land use categories in each catchment that exceed the subwatershed
average, which is a useful indicator in targeting priority areas for green infrastructure planning. Another
way to view SEMCOG's land use data is by examining land cover patterns for each category (Table 14). In
addition to supporting development of subwatershed-scale runoff estimates, information presented in
this manner helps identify implementation options.
Plumbrook Drain
at Sterling Heights
Photo credit: B.CIeland
54
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Southeast Michigan Council oI Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Ptvww (313.) 961-4266, Fa* (313) 961-4869
www.semc'og.org Copyright SEMCOG, 2014
A
1:349.141
0
Stale Plane NAD&3 HARN
0«*rnbei2O14
Plumbrook Subwatershed
ClintonWatershed
Clinton River Watershed
Plumbrook Drain Subwatershed
Figure 38. Location of Plumbrook Drain pilot subwatershed within Clinton River watershed.
55
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Plumbrook Drain Subwatershed
~ Plumbrook Subwatershed Catchments
SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:93,323
0 1 2
Miles
0 2 4
Slate Plane NAD83 HARN
December 2014
-------
Plumbrook Drain Subwatershed
Land Use Categories
Agricultural
Single-family residential
| Multiple-family residential
| Commercial
| Industrial
| Governmental / institutional
|[ Park, recreation, and open space
Airport
| Transportation, communication, utilities
Water
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www semcog.org Copyright: SEMCOG, 2014
A
1:99,019
o
State Plane NAD83 HARN
December 2014
-------
Table 13. Plumbrook Drain subwatershed land use
Catchment Group /
Catchment ID
Area
(acres)
Land Use (percent)
Total
Impervious
Area
(percent)
Single-family
Residential
Multifamily
Residential
Commercial
Institutional
Industrial
Road ROW
Parks, Open
Other
A
01 - Chrissman Drain
3,050
39%
6%
10%
2%
20%
16%
0%
7%
35%
B
10/11 - Dequindre
2,494
43%
4%
4%
17%
1%
17%
13%
2%
29%
C
20/21/22 - Upper Gibson
3,318
51%
5%
14%
6%
—
19%
3%
2%
34%
23/24 - Square Lake
1,185
65%
5%
2%
7%
—
13%
0.3%
7%
27%
25/26 - Gibson Tributary
885
71%
—
2%
6%
—
14%
6%
0.1%
27%
D
30/31/32/33 - Middle Gibson
1,386
58%
—
2%
12%
—
15%
11%
2%
26%
34 - Lower Gibson
1,343
60%
1%
4%
7%
—
16%
10%
2%
36%
E
40 - Plum below Gage
970
72%
2%
1%
7%
1%
16%
—
1%
32%
F
50 - Plum/Van Dyke
586
2%
1%
15%
7%
41%
17%
15%
1%
49%
51 - Plum/Dodge Park
2,169
47%
1%
7%
4%
20%
17%
3%
1%
46%
52/53/54 - Lower Plum
1,173
46%
4%
3%
13%
—
21%
12%
—
32%
G
60 - Canterbury
3,066
32%
3%
11%
5%
27%
20%
1%
0.2%
51%
Total
21,625
47%
3%
7%
7%
10%
17%
5%
2%
36%
Note: Yellow highlighted cells identify land use categories in each catchment that exceed the subwatershed average.
Table 14. Plumbrook Drain subwatershed land cover by land use category
Land Use Category
Area
(acres)
Impervious Surface Types
Pervious Area
Building
Pavement
(road surface, parking,
driveways, sidewalks)
Open
Tree Canopy
Single-family residential
10,257
13%
14%
38%
35%
Multifamily residential
675
17%
34%
26%
23%
Commercial
1,620
13%
46%
26%
15%
Institutional
1,577
6%
23%
41%
31%
Industrial
2,157
23%
37%
32%
8%
Road ROWs
3,716
0.4%
55%
33%
11%
Parks, Open Space
1,125
1%
9%
62%
28%
Other
498
1%
74%
19%
6%
Total
21,625
11%
29%
36%
25%
58
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4.2.2 Existing Conditions Related to Flashiness
Flooding arid water quality problems in the
Plumbrook Drain subwatershed have been well
documented (R2W SWAG 2006). Existing flow
conditions are best described as unstable and flashy
in response to storm events. Figure 41 shows daily
average flows monitored over a 3-month period at
the USGS gage on Plumbrook Drain. It illustrates the
rapid rise and fall in flow as Plumbrook Drain
responds to different rain events (shown across the
top of Figure 41).
Based on USGS data, R-B Index values in Plumbrook
Drain at the gage location currently exceed 0.56 (see
Table 4). The focus of the pilot subwatershed opportunity assessment was to examine green
infrastructure implementation options that could reduce stream flashiness in Plumbrook Drain to a
target range of 0.35 to 0.50 as measured by the R-B Index.
Mil
Plumbrook
Daily Flow Patterns (4/1 - 6/30/2010)
-USGS Gage
250 3
4/1/10 4/15/10
Figure 41. Daily average streamflow patterns Plumbrook Drain (4/1-6/30/2010).
4.2.3 Stormwater Runoff Reduction Targets
The LSPC screening analysis offers a method to evaluate subwatershed-scale runoff patterns in the
context of current land use information. R-B Index estimates based on local meteorological information
and the SEMCOG land cover data were used to benchmark existing conditions for relative comparison
with different green infrastructure implementation strategies. This included identifying the impervious
cover that would need to be managed to meet the target R-B Index range. Figure 42 presents the
screening analysis results. The box in the upper left of the graph points to the estimated baseline
59
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effective impervious cover that corresponds to current Plumbrook Drain R-B Index values at the USGS
gage site.
The screening analysis shown in Figure 42 assumed baseline conditions when examining the change in
B Index values as effective impervious cover is varied across the Plumbrook Drain subwatershed. Again
effective impervious cover is less than the total impervious cover reported in Table 13, which
acknowledges the fact that not all impervious surface runoff reaches the stream. The baseline curve
assumes that no other green infrastructure opportunities are used. Under this scenario, effective
impervious cover would need to be reduced to approximately 11 percent using green infrastructure to
meet the upper R-B Index target (i.e., 0.50).
Relationship Between Impervious Cover and R-B Flashiness
(Plumbrook Screening Analysis)
Current
Flashiness
Condition at
USGS Gage
Estimated effective
impervious cover
corresponding to current
Plumbrook flashiness
at USGS gage
Baseline
Estim ate
x
-------
To account for the array of uncertainties (e.g., differences in land use/impervious surface types,
background infiltration rate assumptions), planners can estimate the amount of impervious area that
needs to be managed for stormwater using green infrastructure in priority catchments (as shown
below).
4.2.4 "c [riiy ¦ jih; a. ¦ 5 Fbiur'Hz.h
The Green Infrastructure Vision, which sets out a direction for southeast Michigan based on regional
policy recommendations and stakeholder input, was the basis for SEMCOG developing green
infrastructure vision maps (SEMCOG 2014). The vision for the Plumbrook Drain subwatershed is shown
in Figure 43. The map shows the following classifications: Potential Green Streets on state-owned
roadways, Conservation & Recreation Lands (current and potential), Current Green Infrastructure, Gl
Opportunities: Institutional Land, and Gl Opportunities: Parking Lots.
The SEMCOG land cover data provides a starting point from which to describe opportunities (Figure 44).
An important aspect is identifying potential impervious surface types that could be managed for
stormwater using green infrastructure. Within the Plumbrook Drain pilot subwatershed, pavement (e.g.,
roads, parking lots, driveways, and so forth) represents more than 70 percent of all impervious surface
types (Table 15).
In terms of priority areas, in the catchment along Van Dyke (catchment 50), industrial land use
comprises more than 40 percent of the area with at least 49 percent impervious cover. The extent of
impervious cover in this industrial setting presents numerous opportunities for strategic partnerships to
reduce runoff to the local stormwater infrastructure discharging to Plumbrook Drain. In addition,
SEMCOG's Green Infrastructure Vision further highlights the numerous large parking lots as potential
opportunities for green infrastructure implementation in addition to increasing tree canopy coverage
within the City of Sterling Heights (SEMCOG 2014).
The land use/land cover inventory data compiled by SEMCOG provides detailed information that can be
used to identify priority areas. Figure 45 summarizes the impervious surface composition for catchment
groups in the Plumbrook Drain subwatershed. The 22 catchments in Figure 39, Figure 40, and Table 13
have been clustered into A through G, shown in Figure 45. The number behind each letter on the x-axis
represents the first digit of those catchment identifiers, which have been clustered in that particular
group (e.g., catchments 10 and 11 into group B, catchments 20 through 26 into group C, and so forth).
61
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Table 15. Plumbrook Drain subwatershed impervious cover estimates by surface type
Catchment Group /
Catchment ID
Area
(acres)
Total
Impervious
Area (acres)
Percent of Total Impervious Area
[percent)
Tree
Canopy
(percent)
Building
Road
Other
Pavement
A
01 - Chrissman Drain
3,050
1,081
28%
24%
48%
27%
B
10/11 - Dequindre
2,494
734
23%
29%
48%
33%
C
20/21/22 - Upper Gibson
3,318
1,143
22%
30%
48%
30%
23/24 - Square Lake
1,185
316
26%
30%
44%
35%
25/26 - Gibson Tributary
885
240
23%
35%
42%
38%
D
30/31/32/33 - Middle Gibson
1,386
362
24%
35%
41%
38%
34 - Lower Gibson
1,343
477
32%
32%
46%
24%
E
40 - Plum below Gage
970
311
36%
27%
37%
19%
F
50 - Plum/Van Dyke
586
289
29%
15%
56%
11%
51 - Plum/Dodge Park
2,169
991
33%
22%
45%
14%
52/53/54 - Lower Plum
1,173
370
34%
31%
35%
19%
G
60 - Canterbury
3,066
1,560
35%
20%
45%
10%
Total
21,625
7,874
29%
26%
45%
25%
62
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Plumbrook Drain Subwatershed
Green Infrastructure Vision
Potential Green Streets
Conservation & Recreation Lands
Potential Conservation & Recreation Lands
Current Green Infrastructure
/ Increase Tree Canopy
• Gl Opportunities: Institutional Land
• Gl Opportunities: Parking Lots
A
1:91,570
SEMCOG °
Southeast Michigan Council of Governments 024
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904 ^Kilometers
Phone (313) 961-4266, Fax (313) 961 -4869 State Plane NAD83 HARN
www.semcog.org Copyright: SEMCOG, 2014 Decemfaer2014
-------
Plumbrook Drain Subwatershed
Land Cover
Impervious Surfaces: Buildings/Structures
Impervious Surfaces: Paved: Drain to Sewer
Open Space - Grass/Scattered Trees: Grass cover > 75%
Trees: Grass/turf understory: Ground cover 50% - 75%
Trees: Grass/turf understory: Ground cover > 75%
Trees: Impervious understory
Urban:Bare
Water Area
SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
2010
A
1:89.195
0 1 2
State Plane NAD83 HARN
December 2014
-------
Plumbrook Drain -- Catchment Group Summary
Impervious Area by Land Use Type
Group IC
Percentage
@ Res idential
~ Commercial
/Industrial
~ Institutional
A-0
B-1
C-2
D-3
E-4
F-5 G-6
/
SS
& 0^
&
/V
V
a%°
Jrf
~V
r
// i/
-V /
C?
Figure 45. Impervious surface composition—Plumbrook Drain subwatershed.
Figure 45 conveys two types of information useful for targeting green infrastructure implementation
efforts: the quantity of impervious area and the density of impervious cover in each catchment group.
The quantity aspect identifies groups that contain the higher amounts of total impervious area. In the
Plumbrook Drain subwatershed, those are catchment groups C (Upper Gibson), F (Lower Plumbrook),
and G (Canterbury). The value in the oval for each group represents the percent impervious cover (or
the density aspect). The combination of both aspects points to Lower Plumbrook and Canterbury as high
priorities for targeting green infrastructure, which does not mean that green infrastructure in other
groups is less important. Instead, it highlights the fact that managing impervious cover in these groups
must play a major role in reducing stream flashiness in the Plumbrook Drain watershed.
The impervious surface composition shown in Figure 45 provides other useful information for targeting
green infrastructure implementation. As indicated, Lower Plumbrook (F) and Canterbury (G) are high-
priority groups. The greatest amount of impervious area in those catchments is associated with
commercial/industrial land use. The Green Infrastructure Vision map (Figure 43) identifies parking lot
and green street opportunities. While groups F and G have high amounts of commercial/industrial
impervious surfaces, targeting residential areas in other catchments (e.g., Upper Gibson) should play an
important role for green infrastructure.
4.2.5 Recommendations
Substantial restoration efforts already have been implemented to address flooding and water quality
problems in the Plumbrook Drain subwatershed. To complement the ongoing activities, several
recommendations are offered based on an analysis of existing conditions related to flashiness and
priorities identified using land use/land cover information. These recommendations follow key
components of SEMCOG's Green Infrastructure Vision (SEMCOG 2014).
65
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Institutional Properties
Green infrastructure on institutional properties offers several benefits, including a public display of the
types of practices suitable for implementation in the local community. Based on SEMCOG's analysis of
parcel-level information, more than 1,550 acres of the Plumbrook Drain subwatershed are publicly
owned or institutional property (Figure 46). Table 16 details the land cover breakdown of those
properties by jursidiction.
Figure 47 highlights the extent of school district property in the Plumbrook Drain subwatershed. School
districts can benefit from green infrastructure implementation through construction of schoolyard
habitats and native plant grow zones. In addition to the educational value, green infrastructure on
school properties can work to reduce long-term maintenance costs by improving drainage and replacing
high-maintenance turf with lower-maintenance trees, shrubs, and ornamental grasses.
Pavement represents the highest percentage of impervious surface types on publicly owned properties.
Recommended BMPs for these surface types include bioretention, infiltration trenches, pervious
pavement, planter boxes, level spreaders, and vegetated swales. The Low Impact Development Manual
for Michigan also describes the range of design options available to accommodate site-specific
situations (SEMCOG 2008). The Site Development Stormwater Tool, which has been applied in Michigan,
can be used to guide more parcel-specific screening analyses (similar to that shown in Figure 23) to
reflect design configurations appropriate for each location (Christian 2014).
The level of implementation curves shown in Figure 24 and Figure 25 are based on southeast Michigan
climate data. The curves provide a general estimate of environmental benefits that could be derived
from constructed green infrastructure on institutional properties across all catchments in the Plumbrook
Drain subwatershed. While individual opportunities might have unique site constraints, local challenges
can be addressed either with enhanced design for constructed practices (e.g., soil amendments,
increased BMP treatment capture depth) or by improving the infiltration benefit of pervious areas (e.g.,
grow zones, increased tree canopy).
Table 16. Plumbrook Drain subwatershed publicly owned property by jurisdiction
Jurisdiction
Area
(acres)
Impervious Surface Types (acres)
Pervious Area (acres)
Building
Pavement
(parking, driving
surfaces, sidewalks)
Open
Tree
Canopy
City of Rochester Hills
267
2
38
106
121
City of Sterling Heights
456
3
50
212
191
City of Troy
449
2
38
302
107
Macomb County
111
1
9
82
19
Oakland County
43
1
7
30
5
State of Michigan
17
0
1
8
8
School Property
586
59
133
312
82
Total
1,929
68
276
1,052
533
66
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Sterling Heights
Plumbrook Drain Subwatershed
Public Parcels
| City of Rochester Hills
H City of Sterling Heights
Oty of Troy
] Macomb County
Bj Oakland County
SOW
School Properly
SEMCOG
Southeast Michigan Council of Governments
1001 VWoodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone <313) 961-4266, Fa* (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:93,323
D 1 2
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0 2 4
KjlQfTWtflf*
State Plane NAD83 HARM
December 2014
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Sterlluo Heights
~
Plumbrook Subwatershed Catchments
School Property
SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:93.323
0 1 2
Miles
State Plane NAD83 HARN
December 2014
Plumbrook Drain Subwatershed
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Roadways
The aerial imagery and land use displayed on Figure 39 and Figure 40 show the extent of the roadway
network in the Plumbrook Drain subwatershed. This information is summarized in Table 17 by general
jurisdictional ownership for the Plumbrook Drain subwatershed. As indicated, 10 percent of the entire
21,625-acre land area is comprised of roadway impervious surfaces. The SEMCOG parcel data identify
major roadways as potential opportunities for increasing green infrastructure in the subwatershed
(Figure 48).
Open spaces within the road ROWs represent potential opportunities to increase green infrastructure,
depending on an array of site-specific factors. In addition to the Low Impact Development Manual for
Michigan, the Green Streets Guidebook: A Compilation of Road Projects Using Green Infrastructure also
provides information on suitable practices for use on road ROWs (SEMCOG 2008, 2013). Recommended
BMPs include bioretention, permeable pavement, bioswales, and native plant grow zones.
Similar to the discussion of institutional properties, the benefits of green infrastructure (both
constructed practices and the use of grow zones) across all catchments in the Plumbrook Drain
subwatershed can be estimated using the level of implementation curves (Figure 24 and Figure 25). The
screening analysis (e.g., Figure 23) guided by spreadsheet methods (e.g., Site Development Stormwater
Tool) can be used to account for site-specific design adjustments appropriate for each location.
Table 17. Plumbrook Drain subwatershed road ROW land cover
Jurisdiction
Area
(acres)
Pavement
(acres)
Pervious Area
(acres)
Open
Tree Canopy
Local
2,536
1,404
820
315
County (Oakland/Macomb)
688
408
218
62
MDOT
492
238
210
41
Total
3,716
2,050
1,248
418
69
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Plumbrook Drain Subwatershed
| State Trunkline 100ft ROW
| County Primary 60ft ROW
j County Local 30ft ROW
A
1:93,323
o
Southeast Michigan Council of Governments
1001 Waodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266. Fax (313) 961-4669
www.semcog.org Copyright: SEMCOG, 2014
State Plane NA083 HARN
December 2014
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Parking Lots
Publicly and privately owned parking lots comprise a
significant portion of ali impervious surfaces in the
Plumbrook Drain subwatershed. The SEMCOG parcel
data identify 15 privately owned parking lots that are
high priorities for increasing green infrastructure in
the Plumbrook Drain subwatershed (Figure 49); most
of the privately owned parking lots are located in
catchment groups F and G. Recommended BMPs
include bioretention, infiltration trenches, pervious
pavement, and increasing tree canopy.
As noted in Figure 45, catchment groups F and G are high-priority areas for green infrastructure
implementation to reduce stormwater volume in the Plumbrook Drain subwatershed. Those
recommended high-priority areas are based on both the amount and density of impervious cover.
Commercial/industrial land use dominates total impervious cover in this area and is one reason that
green infrastructure implementation for the priority parking lots will be an important component in
reducing stream flashiness in Plumbrook Drain. Incorporating stormwater volume reduction practices
into the priority parking lots would represent a major step towards reducing the amount of effective
impervious cover that needs to be managed using green infrastructure in this pilot subwatershed.
Similar to the discussion of institutional properties earlier in this section, the benefits of green
infrastructure across all catchments in the Plumbrook Drain subwatershed can be estimated using the
level of implementation curves (Figure 24 and Figure 25) included in this report. The screening analysis
(e.g., Figure 23) guided by spreadsheet methods (e.g., Site Development Stormwater Tool) can be used
to account for site-specific design adjustments appropriate for each location.
4.2.6 Pilot Watershed Summary
The Plumbrook Drain subwatershed assessment illustrates the value of the outcome-based strategic
planning framework to determine the role green infrastructure can play in working towards WQ5
attainment by addressing documented stormwater problems. The pilot assessment describes overall
existing conditions related to flashiness in the subwatershed (Figure 41). The amount of impervious
cover that needs to be managed to achieve the stream flashiness goal is identified (Figure 42). Land
use/land cover detail is provided in the form of maps (Figure 40 and Figure 44) and tables (Table 13,
Table 14, and Table 15). Priority catchments are defined using impervious cover composition and
density information (Figure 45). Recommendations are summarized based on areas emphasized in
SEMCOG's Green Infrastructure Vision for Southeast Michigan (SEMCOG 2014).
71
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Plumbrook Drain Subwatershed
Priority Parking Lots Identified in Gl Vision
0 Private Parking Lots
AH Parking Lots
k
1:93,323
0 1 3
^ I MM
Southeast Michigan Council of Governments «
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869 State Plane MAD83 HARM
www.semcog.org Copyright: SEMCOG 2014 December 2014
-------
4.3 Tonquish Creek Subwatershed
The Tonquish Creek pilot subwatershed (HUC
04090004-0202), located in Wayne County, is a
tributary to the Middle Rouge River, draining an
area of approximately 25 square miles (Figure
50). Tonquish Creek and its tributaries flow
through the communities of Canton Township,
Plymouth Township, and the cities of Livonia,
Plymouth, and Westland, entering the Middle
Rouge below Nankin Lake.
Tonquish Creek is a headwater tributary of the
Rouge River watershed. The dominant land use
in the area is single-family residential housing,
followed by commercial and industrial areas.
The stream's lower reach makes up a large part
EPA has approved a TMDL for biota across the entire Rouge River watershed, including Tonquish Creek
as an identified impaired stream. The biota target is the reestablishment offish and macroinvertebrate
communities that result in a consistent Acceptable or Excellent rating from P51 (ARC 2012).
Figure 51 shows the catchment boundaries within the Tonquish Creek subwatershed that were used for
the green infrastructure screening analyses. Those catchments are used to examine potential
stormwater source areas and evaluate BMP implementation opportunities.
4.3.1 Land Use and Land Cover
Land use and land cover information inventoried by SEMCOG can be used to develop runoff estimates
that reflect the mix of different land uses present across the Tonquish Creek subwatershed. The
SEMCOG inventory includes impervious cover estimates based on evaluation of parcel-scale data,
including building footprints, parking lot locations, and transportation corridors.
The SEMCOG land use information for the Tonquish Creek subwatershed is shown in Figure 52 and
summarized by catchment in Table 18. The primary land use in the subwatershed is single-family
residential housing, which covers approximately 42 percent of the entire drainage area. The
subwatershed also contains a number of high-density commercial areas, particularly in the Westland
Mall vicinity, along the Ford Road corridor, and around Plymouth.
The Table 18 summary highlights land use categories in each catchment that exceed the subwatershed
average, which is a useful indicator in targeting priority areas for green infrastructure planning. Another
way to view SEMCOG's land use data is by examining land cover patterns for each category (Table 19). In
addition to supporting development of subwatershed-scale runoff estimates, information presented in
this manner helps identify implementation options.
of the Holliday Nature Preserve
73
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PLYMOti
Rouge River Watershed
Tonquish Creek Subwatershed
RougeWatershed
Tonquish Subwatershed
SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266. Fax (313) 961-4869
www semcog org Copyright: SEMCOG. 2014
A
1:262.788
0 3
State Plane NAD83 HARN
December 2014
6
3 Miles
10
2 Kilometers
Figure 50. Location of Tonquish Creek pilot subwatershed within River Rouge watershed.
74
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~
Tonquish Creek Subwatershed
Tonquish Subwatershed Catchments
SEMCOG
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
k
1:71,608
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State Plane NAD83 HARN
December 2014
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Tonquish Creek Subwatershed
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:70,928
o
State Plane NAD83 HARN
December 2014
Land Use Categories
Agricultural
Single-family residential
| Multiple-family residential
Commercial
| Industrial
| Governmental / institutional
E Park, recreation, and open space
Airport
| Transportation, communication, utilities
Water
-------
Table 18. Tonquish Creek subwatershed land use
Land Use (percent)
Total
Impervious
Area
(percent)
Catchment Group /
Catchment ID
Area
(acres)
Single-family
Residential
Multifamily
Residential
Commercial
Institutional
Industrial
Road ROW
Parks, Open
Other
A
01/02 - North Branch
2,355
31%
2%
6%
9%
31%
21%
1%
0.1%
44%
B
10/11/12/13 - South Branch
1,835
64%
1%
3%
5%
2%
16%
9%
0.3%
33%
C
20/21 - Ann Arbor/Joy Road
179
53%
4%
20%
7%
—
15%
—
—
48%
22/23/24 - Upper Tonquish
1,377
56%
5%
7%
9%
2%
18%
1%
—
44%
D
30/31/32/33 - Koppernick
1,236
19%
3%
8%
1%
47%
15%
1%
6%
54%
34/35/36 - Middle Tonquish
2,007
38%
6%
7%
2%
18%
16%
13%
—
39%
40/41/42 - Willow Headwaters
1,189
75%
—
1%
11%
—
13%
—
0.4%
32%
E
43/44/45 - Upper Willow
458
45%
—
8%
24%
1%
17%
5%
—
42%
46/47/48/49 - Willow/Travis
1,558
41%
2%
19%
8%
4%
19%
5%
1%
43%
50/51/52 - Ford Tributary
397
32%
4%
40%
0.1%
-
24%
1%
-
57%
F
53/54/55 - Willow/1-275
235
30%
-
59%
-
3%
7%
-
-
30%
56/57/58 - Lower Willow
543
39%
4%
13%
4%
27%
13%
0.1%
—
41%
60 - Lower Tonquish
424
30%
28%
12%
—
—
5%
25%
1%
33%
G
61 - Morgan Creek
1,057
27%
11%
33%
8%
—
13%
9%
—
50%
62/63 — Tonquish Outlet
1,103
39%
15%
11%
9%
—
12%
14%
—
38%
Total
15,952
42%
5%
11%
7%
12%
16%
6%
1%
42%
Note
Yellow highlighted cells identify land use categories in each catchment that exceed the subwatershed average.
Table 19. Tonquish Creek subwatershed land cover by land use category
Land Use Category
Area
(acres)
Impervious Surface Types (percent)
Pervious Area (percent)
Building
Pavement (road
surface, parking,
driveways, sidewalks)
Open
Tree Canopy
Single-family residential
6,739
14%
19%
31%
36%
Multifamily residential
756
18%
41%
24%
17%
Commercial
1,811
14%
44%
21%
20%
Institutional
1,049
8%
25%
41%
25%
Industrial
1,978
19%
34%
28%
19%
Road ROWs
2,592
0.2%
60%
26%
14%
Parks, Open Space
910
0%
5%
23%
72%
Other
117
4%
25%
62%
9%
Total
15,952
11%
31%
29%
29%
77
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4.3.2 Existing Conditions Related to Flashiness
The Rouge River Watershed Management Plan
describes an array of water quality concerns in
Tonquish Creek subwatershed. Poor
macroinvertebrate communities have been
observed at several sites in the drainage through
monitoring by both the Friends of the Rouge and
MDEQ (ARC 2012; Goodwin 2009). The Rouge
River plan noted that the developed area within
the Tonquish Creek subwatershed continues to
expand and that unmitigated stormwater inputs
could continue to degrade the stream as a result
of higher peak flows and decreased base flow. In
addition, Tonquish Creek is a tributary to the
section of the Middle Rouge River, which has degraded stream habitat caused by excessive flow
instability and accompanying bank erosion.
Although streamflow records for the Tonquish Creek subwatershed are not available, two locations
monitored by USGS on the Middle Rouge (one above and one below Tonquish) can be used to develop
flow estimates for this pilot subwatershed. Figure 53 depicts estimated daily average flows for Tonquish
Creek based on the difference in discharge between the two Middle Rouge gages. R-B Index values in
Tonquish Creek currently exceed 0.5 based on those estimates.
Tonquish Creek
Daily Flow Estimates (10/1 - 12/31/2003)
^¦Precip Estimated Flow
1000
100
200
250 3"
10
350
400
12/24/03
Figure 53. Estimated daily average Tonquish Creek streamflow patterns (10/1-12/31/2003).
78
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4.3.3 Stormwater Runoff Reduction Targets
The LSPC screening analysis offers a method to evaluate subwatershed-scale runoff patterns in the
context of current land use information. R-B Index estimates based on local meteorological information
and the SEMCOG land cover data were used to benchmark existing conditions for relative comparison
with different green infrastructure implementation strategies. This included identifying the impervious
cover that would need to be managed to meet the target R-B Index range.
Figure 54 presents the screening analysis results, which used baseline assumptions to examine the
change in R-B Index values as effective impervious cover is varied across the Tonquish Creek
subwatershed. The baseline curve assumes that no other green infrastructure opportunities are used.
Under this scenario, effective impervious cover would need to be managed to 11 percent to meet the
upper R-B Index target (i.e., 0.50). It is important to note that the effective impervious cover is less than
the total impervious cover reported in Table 18.
An estimated range of potential effective impervious cover at the mouth of Tonquish Creek is shown in
Figure 54. This range is intended to address uncertainties associated with differences in land
use/impervious surface types in the Tonquish Creek subwatershed. The range shown in Figure 54 is
based on estimated ratios between effective impervious cover and total impervious cover derived from
the SEMCOG land cover data and USGS flow data examined for this project. To account for the array of
uncertainties (e.g., differences in land use/impervious surface types, background infiltration rate
assumptions), planners can estimate the amount of impervious area that needs to be managed for
stormwater using green infrastructure in priority catchments (as shown below).
Relationship Between Impervious Cover and R-B Flashiness
(Tonquish Screening Analysis)
Baseline
Estimate
Range of potential
effective impervious cover
at Tonquish mouth
x
o>
"O
£=
CD
¦
en
Target Flashiness
Range
0.3
o
20
40
60
80
100
Effective Impervious Cover (%)
Figure 54. Tonquish Creek subwatershed effective impervious cover and R-B flashiness screening
analysis.
79
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4.3.4 Areas of Opportunity and Priorities
Figure 55 shows the Green Infrastructure Vision for the Tonquish Creek subwatershed. The Potential
Conservation & Recreation Lands classification highlights areas that could be added to the network.
Potential Green Streets identifies major roads that have opportunities for improving soil health through
grow zones and/or implementing constructed practices. Finally, the top 10 percent by area of
institutional properties is highlighted as an initial priority along with the top 1 percent by area of private
parking lots. These opportunities are described in greater detail in the subsequent sections.
The SEMCOG land cover data provides a starting point from which to describe opportunities (Figure 56).
An important aspect is identifying potential impervious surface types that could be managed for
stormwater using green infrastructure. Within the Tonquish Creek pilot subwatershed, pavement (e.g.,
roads, parking lots, driveways, sidewalks, and so forth) represents nearly three-quarters of all
impervious surface types (Table 20).
Table 20. Tonquish Creek subwatershed impervious cover estimates by surface type
Catchment Group /
Catchment ID
Area
(acres)
Total
Impervious
Area (acres)
Percent of Total Impervious Area
Tree
Canopy
(percent)
Building
Road
Other
Pavement
A
01/02 - North Branch
2,355
1,036
27%
25%
48%
25%
B
10/11/12/13 - South Branch
1,835
613
24%
29%
47%
31%
C
20/21 - Ann Arbor/Joy Road
179
86
24%
20%
56%
29%
22/23/24 - Upper Tonquish
1,377
611
29%
28%
43%
24%
D
30/31/32/33 - Koppernick
1,236
664
31%
16%
53%
14%
34/35/36 - Middle Tonquish
2,007
784
27%
21%
52%
37%
E
40/41/42 - Willow Headwaters
1,189
379
24%
27%
49%
36%
43/44/45 - Upper Willow
458
193
28%
29%
43%
22%
46/47/48/49 - Willow/Travis
1,558
672
28%
29%
43%
23%
F
50/51/52 - Ford Tributary
397
225
24%
25%
51%
11%
53/54/55 - Willow/1-275
235
70
22%
14%
64%
43%
56/57/58 - Lower Willow
543
224
25%
21%
54%
34%
G
60 - Lower Tonquish
424
140
26%
12%
62%
43%
61 - Morgan Creek
1,057
531
25%
16%
59%
29%
62/63 — Tonquish Outlet
1,103
421
29%
21%
50%
37%
Total
15,952
6,652
27%
23%
50%
26%
80
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Tonquish Creek Subwatershed
Potential Green Streets
Conservation & Recreation Lands
Potential Conservation & Recreation Lands
Current Green Infrastructure
/ y Increase Tree Canopy
Gl Opportunities: Institutional Land
• Gl Opportunities: Parking Lots
A
1:74.491
o
Southeast Michigan Council of Governments o 2
1001 Vtoodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961 -4869 State Plane NAD83 HARN
www.semcog org Copyright: SEMCOG, 2014 December 2014
Green Infrastructure Vision
-------
Tonquish Creek Subwatershed
2010 Land Cover
y Impervious Surfaces. Buildings/Structures
| Impervious Surfaces Paved Drain to Sewer
Open Space - Grass/Scattered Trees Grass cover > 75%
| Trees Grass/turf understory Ground cover 50% - 75%
| Trees Grass/turf understory" Ground cover > 75%
| Trees Impervious understory
| Urban.Bare
Water Area
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:80,216
o
State Plane NAD83 HARN
December 2014
-------
The land use/land cover inventory data compiled by SEMCOG provides detailed information that can be
used to identify priority areas. Figure 57 summarizes the impervious surface composition for catchment
groups in the Tonquish Creek subwatershed. This chart conveys two types of information useful for
targeting green infrastructure implementation efforts: the quantity of impervious area and the density
of impervious cover in each catchment group. The quantity aspect identifies groups that contain higher
amounts of total impervious area. In the Tonquish Creek subwatershed, those are catchment groups A
(North Branch), D (Middle Tonquish), E (Upper Willow), and G (Lower Tonquish). The value in the oval
for each group represents the percent impervious cover (or the density aspect). The combination of
both aspects points to North Branch, Middle Tonquish, and Lower Tonquish as high priorities for
targeting green infrastructure, which does not mean that green infrastructure in other groups is less
important. Instead, it highlights the fact that managing impervious cover in these catchment groups
must play a major role in reducing stream flashiness in the Tonquish Creek subwatershed.
The impervious surface composition shown in Figure 57 provides other useful information for targeting
green infrastructure implementation. As indicated, Middle Tonquish (group D) is a high-priority group.
The greatest amount of impervious area in group D catchments is associated with commercial/industrial
land use followed by roads.
Tonquish Creek - Catchment Group Summary
Impervious Area by Land Use Type
1600
Group IC
Percentage
a Res idential
0 Commercial
/ Industrial
~ Institutional
A-0
B-1
C-2
D-3
E-4
F-5
G-6
-------
Institutional Properties
Green infrastructure on institutional properties offers several benefits, including a public display of the
types of practices suitable for implementation in the local community. Based on SEMCOG's analysis of
parcel-level information, more than 1,400 acres of the Tonquish Creek subwatershed are either publicly
owned or institutional property (Figure 58). Table 21 details the land cover breakdown by jursidiction.
Figure 59 highlights the extent of school district property in the Tonquish Creek subwatershed. School
districts can benefit from green infrastructure implementation through construction of schoolyard
habitats and native plant grow zones. In addition to the educational value, green infrastructure on
school properties can work to reduce long-term maintenance costs by improving drainage and replacing
high-maintenance turf with lower-maintenance trees, shrubs, and ornamental grasses.
Of the different types of impervious surfaces on publicly owned properties, pavement represents the
largest proportion. Recommended BMPs include bioretention, infiltration trenches, pervious pavement,
planter boxes, level spreaders, and vegetated swales. The Low Impact Development Manual for
Michigan also describes the range of design options available to accommodate site-specific situations
(SEMCOG 2008). The Site Development Stormwater Tool, which has been applied in Michigan, can be
used to guide more parcel-specific screening analyses (similar to that shown in Figure 23) to reflect
design configurations appropriate for each location (Christian 2014).
The level of implementation curves shown in Figure 24 and Figure 25 are based on southeast Michigan
climate data. These curves provide a general estimate of environmental benefits that could be derived
from constructed green infrastructure on institutional properties across all catchments in the Tonquish
Creek subwatershed. While individual opportunities might have unique site constraints, local challenges
can be addressed either with enhanced design for constructed practices (e.g., soil amendments,
increased BMP treatment capture depth) or by improving the infiltration benefit of pervious areas (e.g.,
grow zones, increased tree canopy).
Table 21. Tonquish Creek subwatershed publicly owned property by jurisdiction
Jurisdiction
Area
(acres)
Impervious Surface Types (acres)
Pervious Area (acres)
Building
Pavement
(parking, driving
surfaces, sidewalks)
Open
Tree
Canopy
City of Livonia
52
2
5
17
28
City of Plymouth
22
3
5
4
10
City of Westland
58
0
2
2
54
Canton Township
69
0
8
14
47
Plymouth Township
191
2
23
102
64
Detroit Metro Water Department
10
0
2
6
2
Wayne County
294
0
9
11
274
State of Michigan
67
5
15
25
22
School Property
647
58
162
284
143
Total
1,410
70
231
465
644
84
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Canton Township
City Of Livonia
City of Plymouth
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Plymouth Township
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Tonquish
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-------
Tonquish Creek Subwatershed
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1:71,608
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State Plane NAD83 HARN
December 2014
| | Tonquish Subwatershed Catchments
School Property
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Roadways
Green infrastructure, both natural and constructed, can be strategically used along roadway corridors to
provide recreational, social, and aesthetic amenities to surrounding communities in addition to
providing local and regional environmental benefits. Within the Tonquish Creek subwatershed, roadway
types include freeways (e.g., 1-275, M-14), arterial and collector roads (e.g., Ford Road, Warren Road),
local and residential streets, and alleys.
Roads—including those under the jurisdiction of the local communities, Wayne County, and MDOT—
represent 2,592 acres, or nearly 40 percent, of the total impervious surface area of 6,765 acres in the
Tonquish Creek subwatershed. Open spaces within the road ROWs represent potential opportunities to
increase green infrastructure, depending on the array of site-specific factors.
The aerial imagery and land use displayed on Figure 51 and Figure 52 shows the extent of the roadway
network in the Tonquish Creek subwatershed. As indicated, nearly 10 percent of the entire 15,952-acre
land area is comprised of roadway impervious surfaces. The SEMCOG parcel data identify major
roadways as potential opportunities for increasing green infrastructure in the subwatershed (Figure 60).
Table 22 summarizes the existing land cover and general jurisdictional ownership of the roadway
network in subwatershed.
Open spaces within the road ROWs represent potential opportunities to increase green infrastructure,
depending on the array of site-specific factors. In addition to the Low Impact Development Manual for
Michigan, the Green Streets Guidebook: A Compilation of Road Projects Using Green Infrastructure also
provides information on suitable practices for use in road ROWs (SEMCOG 2008, 2013). Recommended
BMPs include bioretention, permeable pavement, bioswales, and native plant grow zones.
Similar to the discussion of institutional properties earlier in this section, the benefits of green
infrastructure (both constructed practices and the use of grow zones) across all catchments in the
Tonquish Creek subwatershed can be estimated using the level of implementation curves (Figure 24 and
Figure 25). The screening analysis (e.g., Figure 23) guided by spreadsheet methods (e.g., Site
Development Stormwater Tool) can be used to account for site-specific design adjustments appropriate
for each location.
Table 22. Tonquish Creek subwatershed road ROW land cover
Jurisdiction
Area
(acres)
Pavement
(acres)
Pervious Area
(acres)
Open
Tree Canopy
Wayne County & Local
2,031
1,314
415
302
MDOT
561
250
260
51
Total
2,592
1,564
675
353
87
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Tonquish Creek Subwatershed
3 State Tiunkfine 100ft ROW
County Pnmary 60ft ROW
County Local 30ft ROW
I | Tonquish Subwalorshod Catchments
Southeast Michigan Council of Governments
1001 VNfoodward Avenue. Suite 1400. Detroit, Michigan 48226-1904
Phone (313) 961-4266, Fax (313) 961-4869
www.semcog.org Copyright: SEMCOG, 2014
A
1 69.963
o
Slate Plane NADS3 HARM
Decern b«r 2014
-------
Parking Lots
Publicly and privately owned parking lots comprise
a significant portion of impervious surface area in
the Tonquish Creek subwatershed. The SEMCOG
parcel data identify two institutional and six
privately owned parking lots, which provide optimal
opportunities for increasing green infrastructure in
the subwatershed (Figure 61). Recommended BMPs
include bioretention, infiltration trenches, pervious
pavement, and increasing tree canopy.
As noted in Figure 61, groups F and G are high-
priority areas for green infrastructure to reduce
stormwater volume in the Tonquish Creek
subwatershed. This recommended high-priority
area is based on both the amount and density of impervious cover. Commercial land use dominates
total impervious cover in this area and is one reason that green infrastructure implementation for the
priority parking lots will be an important component to reduce stream flashiness in Tonquish Creek.
Incorporating stormwater volume reduction practices into the priority parking lots would represent a
major step towards reducing the amount of effective impervious cover that needs to be managed using
green infrastructure in this pilot subwatershed.
Similar to the discussion of institutional properties earlier in this section, the benefits of green
infrastructure across all catchments in the Tonquish Creek subwatershed can be estimated using the
level of implementation curves (Figure 24 and Figure 25) included in this report. The screening analysis
(e.g., Figure 23) guided by spreadsheet methods (e.g., Site Development Stormwater Tool) can be used
to account for the site-specific design adjustments appropriate for each location.
4.3.6 Pilot Watershed Summary
The Tonquish Creek subwatershed assessment illustrates the value of the outcome-based strategic
planning framework to determine the role green infrastructure can play in working towards WQ5
attainment by addressing documented stormwater problems. The pilot assessment describes overall
existing conditions related to flashiness in the subwatershed (Figure 53). The approximate amount of
impervious cover that needs to be managed to achieve the stream flashiness goal is identified (Figure
54). Land use/land cover detail is provided in the form of maps (Figure 52 and Figure 56) and tables
(Table 18, Table 19, and Table 20). Priority catchments are defined using impervious cover composition
and density information (Figure 57). Recommendations are summarized based on areas emphasized in
SEMCOG's Green Infrastructure Vision for Southeast Michigan (SEMCOG 2014).
89
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Tonquish Creek Subwatershed
All Parking Lots
Tonquish Subwatershed Catchments
Southeast Michigan Council of Governments
1001 Woodward Avenue, Suite 1400, Detroit. Michigan 48226-1904
Phorte (313) 961-4266. Fa* (313) 961-4669
www.semcog.org Copyright: SEMCOG, 2014
A
1:69.963
o
State Ptarie NAD83 HARN
December 2014
Priority Parking Lots Identified in Gl Vision
0 Institutional Parking Lots
0 Private Parking Lots
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5 Conclusions
The overall purpose of this project was to determine the role of green infrastructure in working towards
meeting WQS in southeast Michigan and in protecting western Lake Erie. Stormwater runoff volume
reduction targets were identified using stream flashiness to connect aquatic biology and stream channel
concerns with TMDLs and stormwater management activities. Those targets were based on local
monitoring data and provide a baseline from which to examine alternatives for green infrastructure
techniques that achieve WQS and protect biological communities using an outcome-based strategic
planning process.
The approach was applied to three pilot subwatersheds selected by SEMCOG staff and several members
of the Southeast Michigan Green Infrastructure Partners. Each pilot subwatershed has land use/land
cover characteristics representative of green infrastructure planning challenges and opportunities in
southeast Michigan. The green infrastructure assessment for each pilot project described existing
hydrologic conditions in the subwatershed. The amount of impervious cover needing green
infrastructure improvements to achieve the stream flashiness goal was identified.
A detailed analysis of SEMCOG's land use/land cover data defined priority catchments within each pilot
subwatershed based on impervious cover composition and density. Opportunities were examined using
desktop screening analyses to estimate the relative benefit of different implementation strategies
highlighted in SEMCOG's Green Infrastructure Vision (SEMCOG 2014). The green infrastructure options
evaluated to achieve stream flashiness and stormwater reduction targets include native plant grow
zones, increasing tree canopy, and the use of constructed practices (e.g., bioretention, pervious
pavement, bioswales).
The green infrastructure target setting process for this project is transferable to other southeast
Michigan watersheds. In a separate project, the framework is being extended to other Detroit-area
subwatersheds in support of efforts to develop a water quality program strategy that aligns MDOT
transportation infrastructure goals with watershed management plans. In addition, this framework will
serve as a baseline from which to evaluate progress for urban watershed restoration across the region.
91
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