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Stormwater Target Watersheds:Methods and Maps

February 2013

In Support of 2013 Solicitation for Proposals to Conduct Stormwater Retrofit Planning and Pre-Design

Funded by the National Estuary Program Watershed Protection & Restoration Grant Program

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Methods

1. Select Assessment Units (AUs) with High/Moderate High values for overall Water Flow

2. Select those that intersect/border urban growth areas (UGAs)

3. Add AUs with sound-wide H/MH value that intersect/border UGA

4. Remove AUs with >90% urban area

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1. Select AUs with High (H) and Moderate High (MH) Scores for Water Flow

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2. Select Those H & MH AUs that Intersect or Border UGAs

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H & MH AUs Remaining after Intersection

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3 & 4. Add AUs with Sound-wide importance; Select Any Remaining AUs with UGA That Is Either Immediately Upstream or Intersects H & MH AUs

Remove any areas of high imperviousness (i.e. >90% developed)

This UGA will directly affect a downstream AU of high or moderate high importance for Puget Sound

This AU of high or moderate high importance for Puget Sound intersects a UGA

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Final Target AU’s

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By using the characterization results for water flow we will be able to evaluate the relative degree of intactness (less degradation) and importance for water flow processes for these Watershed Management Units (WMU). A watershed that is more intact and has a higher importance should provide a greater “lift” in biological functions as stormwater restoration measures are applied.

Overlay Stormwater Target Areas with Watershed Management Units (black boundary)

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Summary Overlay of Stormwater Target Areas (pink) with Watershed Management Units (WMU – black outlines) for Puget Sound Watersheds

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Steps for Applying Watershed Integrity Index to Watershed Management Units

1) Divide the watershed roughly in half, thus creating an upper and lower watershed

2) Pick the dominant color or color combinations in the two halves, upper and lower watersheds, and match as closely as possible to one of the index diagrams

3) The color combinations are limited to dark green/light green; dark yellow/light yellow; orange/red. Ignore colors, for the time being, that do not match these set combinations.

4) Add a “+” or “-” to the score based on the presence of additional colors not matching the individual matrix diagram. For example, if the watershed is predominately “yellow” you would pick index 5, but add a “-” if more “red” was present as a secondary color. If “green” was present you would add a “+”.

In the example above the dominant color combination matching the diagram for the upper watershed would be “orange/red” and for the lower it would just be “yellow”. This would match the #2 index. The presence of the “green” non-dominant colors in the upper and lower watershed would indicate a shift in integrity towards the left of the index; thus a “+” would be added to the score.

Score = 2+

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Watershed Management Units & Watershed Integrity Index For Each WMU Containing a Target Stormwater Area

WMUs on the mainstem of the Nooksack were evaluated relative to their upper watershed in the Cascades which is judged to be relatively “intact” (i..e green colors, not shown on map) and were scored an “8”

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Watershed Management Units & Watershed Integrity Index For Each WMU Containing a Target Stormwater Area

WMUs on the mainstem of the Skagit were evaluated relative to their upper watershed in the Cascades which is judged to be relatively “intact” (i..e green colors, not shown on map) and were scored an “8”

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Watershed Management Units & Watershed Integrity Index For Each WMU Containing a Targety Stormwater Area

WMUs on major streams (Sammamish, Snohomish, Skykomish, Snoqualamie & Cedar Rivers ) were evaluated based on the cumulative upstream condition of those watersheds (e.g some of which extend into the Cascades).

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Watershed Management Units & Watershed Integrity Index For Each WMU Containing a Target Stormwater Area

WMUs major streams (Cedar, Green Rivers ) were evaluated based on the cumulative upstream condition of those watersheds (e.g some of which extend into the Cascades).

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Watershed Management Units & Watershed Integrity Index For Each WMU Containing a Target Stormwater Area

WMUs on major streams (Deschutes, Puyallup, White) were evaluated based on the cumulative upstream condition of those watersheds (e.g which extend into the Cascades).

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Watershed Management Units & Watershed Integrity Index

For Each WMU Containing a Target Stormwater Area

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Watershed Integrity Index with Watershed Management Unit

(WMU) Names

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WRIA 1

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WRIA 2

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WRIA 3, 4, & 5

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WRIA 6 & Upper 17

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WRIA 7

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Seattle & Lower WRIA 8

WRIA 9 & Upper WRIA 8

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WRIA 10_11

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WRIA 13_14

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WRIA 15

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WRIA 18

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WRIA 19

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Stormwater Retrofit Target Watersheds

With Watershed Integrity Index (1-9)for the

Watershed Management Unit (Black boundary)

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WRIA 1

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WRIA 2

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WRIA 3, 4, & 5

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WRIA 6 & Upper 17

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WRIA 7

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Seattle / Lower WRIA 8

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WRIA 9/ Upper WRIA 8

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WRIA 10_11

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WRIA 13_14

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WRIA 15

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WRIA 18

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WRIA 19