Section 319
NONPOINT SOURGF PROGRAM SUCCESS STORY
Restoring Stream Reduces Nitrogen in an Urbanized Watershed
I H Uncontrolled stormwater runoff caused stream erosion and degraded
imprOVGQ rjparjan habitat in Maryland's Minebank Run and Lower Gunpowder
Falls watersheds. Maryland Department of the Environment (MDE) added Lower Gunpowder Falls
(including Minebank Run) to the state's Clean Water Act (CWA) section 303(d) list of impaired waters for
nutrients (phosphorus) in 1996. On the basis of benthic and fish assessments, MDE also classified the
waterbody as impaired for biological integrity in 2006. Project partners implemented numerous stream
restoration activities that led to visible and measurable water quality improvements. Until additional
improvements are documented, however, the segment will remain on the impaired waters list.
Problem
Minebank Run and Lower Gunpowder Falls are in
the scenic Cromwell Valley in eastern Maryland's
Baltimore County. Minebank Run is an urban
headwater stream that joins the Gunpowder River
just south of Loch Raven Reservoir, at which point
the watershed is called Lower Gunpowder Falls.
Minebank Run drains 2,135 acres and makes up
approximately 7 percent of Lower Gunpowder Falls'
29,470-acre watershed. The watershed was once
primarily used for agriculture but is now densely
developed in specific areas.
Minebank Run receives a high volume of runoff
from impervious surfaces in suburban residential
areas, office parks, highways and other areas
surrounding Towson, Maryland. MDE first added
the Lower Gunpowder Falls watershed, including
Minebank Run, to the state's CWA section 303(d) list
for phosphorus impairments in 1996. In 2006 MDE
also listed it as impaired because it did not meet its
designated use of aquatic life and wildlife support.
Before the restoration, Minebank Run exhibited
severe bank incision, a disconnected floodplain,
degraded fish and invertebrate habitat, loss of the
riparian zone, and high sediment and nutrient loads
from stormwater runoff. Stormwater conveyance
channels, built to remove stormwater from roads
quickly and not to protect hydrologic morphol-
ogy, caused flashy, high-volume flows that eroded
streambanks (Figure 1), exposed sewage trunk
lines and damaged park roads and access bridges.
Maryland Biological Stream Survey data confirmed
that the number and diversity of macrovertabrates
and fish were lower than they should be, indicating
that Minebank Run was in an unhealthy, degraded
condition.
Figure 1. High-volume stormwater flows damaged
this stretch of Minebank Run.
Project Highlights
Baltimore County Department of Environmental
Protection and Resource Management (DEPRM)
conducted two phases of restoration activities—the
first in 1999 and the second in 2005—on Minebank
Run, a subwatershed within the Lower Gunpowder
Falls watershed. In 1999 DEPRM worked to stabilize
highly erodible banks, construct point bars, and add
riffles and meander features with step-pool habitats
along 8,000 linear feet in a headwaters portion of
Minebank Run (Figure 2).
The project reduced the stream gradient to allow
the stream to overflow its banks and reconnect to
the floodplain. Reconnecting the floodplain allows
phosphorus and sediment to be deposited on the
floodplain rather than be carried downstream. It
also provides a greater residence time for nitrogen
to be removed by native vegetation uptake and
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Figure 2. DEPRM added riffles, meanders
and step-pool habitats during phase one
of the project.
Figure 3. Minebank Run at Loch Raven
High School, before restoration.
Figure 4. Minebank Run at Loch Raven
High School, after phase two of the
restoration project.
denitrification. The restoration involved planting
3,000 trees and 6,000 shrubs, which created a buf-
fer and encouraged the uptake of available nitrogen.
DEPRM began the second phase of restoration
in 2005 on a downstream reach of approximately
9,500 linear feet of Minebank Run. This phase had
similar objectives as the first but was more exten-
sive, involving removing a 500-foot concrete chan-
nel that coveys stormwater from Cromwell Road to
Minebank Run (Figures 3 and 4). The restoration, on
the grounds of Loch Raven High School, included
adding step-pools, increasing the stream's sinuosity
and planting riparian vegetation—all of which help
dissipate flow energy, reduce erosion, moderate
water temperatures and create stream channel and
riparian habitat. Once the projects were complete,
monitoring and geomorphologic evaluations were
conducted over several years by a variety of project
partners.
DEPRM armored stream banks at key locations to
protect existing infrastructure such as sewer lines,
bridges and roads. That has the beneficial effect
of making the stream more hospitable to benthic
macroinvertebrates and fish by decreasing flow
speed, preventing scour and minimizing damage to
aquatic habitat.
Results
The second phase of the Minebank Run project
included reconnecting the stream to the floodplain
and evaluating the results. A number of study part-
ners collaborated to assess the projects between
late 2003 and mid-2004. Results indicate that the
project measurably reduced the bioreactive nitrogen
(nitrate and nitrite) concentration in the surface
water and groundwater. Nitrogen concentrations
declined by 25 to 50 percent [1.5 milligrams per
liter (mg/L) to 0.8 mg/L], while denitrification rates
increased nearly twofold in test wells.
The project efforts removed an estimated
50,000 pounds (25 tons) of sediment typically
discharged from the stream annually. Associated
phosphorus reductions could range from 100 to
200 pounds annually. The projects have had many
beneficial effects by reducing flow and increasing
dissolved oxygen levels. The stream's physical and
hydrological conditions appear to have improved
substantially; however, measurable water quality
and biological improvements will likely not occur
a several years. In the meantime, DEPRM will
continue to monitor biological conditions in both
waterbodies.
Partners and Funding
DEPRM led the restoration and mitigation efforts.
Partners in the nationally recognized floodplain
denitrification study include the U.S. Geological
Survey, Institute of Ecosystem Studies, DEPRM,
and the University of Maryland's Center for
Environmental Science.
Some state and federal funding partners participat-
ed at different stages to assist with and document
the work. In 2003 Maryland's CWA section 319
program provided $150,000 to support DEPRM's
efforts; that was complemented by another
$100,000 in local match funding. Overall, Baltimore
County estimates that the costs for Phases I and II
were $2.2 million and $4.4 million, respectively.
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-09-001KK
November 2009
For additional information contact:
James George, Ph.D.
Maryland Department of Environment
410-537-3902 • jgeorge@mde.state.md.us
Candace L. Croswell, Baltimore County DEPRM
410-887-2904 • ccroswell@baltimorecountymd.gov
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