Forest and Wetlands Important for Protecting Water Quality and Watershed Integrity
Background:

The objective of the analysis is to identify forests and wetlands important in protecting water
quality and sustaining watershed integrity. This "watershed value" is based on physical and
biological functions that store precipitation, retain and assimilate nutrients, moderate runoff,
protect soils and maintain important critical landscape functions such as those of riparian buffers.
These functions, when present, serve to protect water quality. It is well accepted that forests and
wetlands are the best land cover for sustaining the integrity of watershed functions and in
providing high quality water; therefore the analysis attempts to identify a nexus between a forest
or wetland and the parameters that enable these lands to sustain watershed functions.

Additionally, it attempts to place a value on wetlands or forests that if lost, would have significant
potential to degrade watershed integrity/water quality.

Data Layers:

Local parameters (scored for each 36.73 meter pixel):

Proximity to water
Soil Erodibility
Slope

Wetland function
Net primary productivity
Forest Fragmentation patch size
Hydrogeomorphic regions
Floodplains

Regional Parameters (Summarized by HUC-11 and scored for each 36.73 meter in the
watershed):

Stream density

Percent of watershed forested
Percent of imperviousness
Water quality
Drinking water supply

Methodology:

Data was collected for each parameter and an Arc-Info grid raster layer was created and rescaled
to 36.73-meter resolution and clipped to represent the Chesapeake Bay watershed. Then each
parameter was classified into ranges based on its influence on watershed integrity/water quality
and assigned a score (0-4). The parameters were also assigned a weight to emphasize those
parameters with greater influence on water quality/watershed integrity. For each individual
parameter, the weight was multiplied by the score and a number was assigned to each grid cell.
Finally, the corresponding numbers for each grid cell were summed in order to score forests and
wetlands for their importance or value in protecting watershed integrity/water quality.


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Parameters used in to identify the important lands for protecting water quality, along with the rank assigned to the value range
and the weight assigned to the parameter.

Resource Lands Assessment Topic:

Identification and prioritization of areas important to water quality areas for the Resource Lands Assessment

(Forest and W etlands)

Conservation Priority Index

Ranking of value ranges



Param eter

Data Source

Scale

4

3

2

1

W eight

li in I'll x Mr.11 I'.i r;i in i-1 l i s (lnr;i 1)



L S G S MI D

1 :1 0 0 k





1 SO - 270 m

2 7 0 m

5

Erodible Soils

STATSGO (kfact)

1 :250K

> .30 (High)

.2 - .3 (Moderate)

< .2 (None to Slight)



2

Net Prim ary Productivity

USFS

1 km

4

3

2

1

3

Slope

DEM



>15%

15 - 10%

5-10%

< 5%

3

1 IMIllinli.il |' .| l.i III i-l c |s (l"l'.lll

W etland Function *

NWI - cumulative
score of w ater-
related functions

1 :1 00K

score >.3.5

score = 3.0

score <3.0



5

Forest Fragm entation - Patch Size

(HA)

CBP

1 :1 00K

> 1000

400 - 1000

100 - 400

<100

2

FEMA 100 year flood plain

FEMA



Yes







2

- - - ' ~













:

l< i-iiinn.i I \\ .i ii-i-s|ii-d I'.i r.i in i-li-I's

Stream Density-m eters/sqkm

NHD

1 :100K

> 1.042

0.77 - 1.042

0.524 - 0.769

0 - 0.523

4

% Forested

MRLC 1997

1 :1 00K

40 - 65%

30 - 40; 65 - 75%

15 - 30; 75 - 85%

< 1 5 ; > 8 5 %

3

% Impervious Surface

MRLC 1997

1 :1 00K

5 to 1 5 %

< 5%

15 to 25%

> 25%

2

W ater Q uality

Sparrow/DU

1 :100K

Good

Fair

Very Good

Poor

5

Municipal Surface W ater Supplies

USGS - pop.
Served/ # of intakes

1 :1 00K

High/H igh,
High/Med,
Med/High,
Low/High,
H igh/L o w

Med/Med

Med/Low, Low/Med

Low/Low

4


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