Hydromodification Base Strategy Additional Examples Document January 16, 2019

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1 Hydromodification Base Strategy Additional Examples Document January 16, 2019 Hydromodification Planning Tool Web Map The draft Hydromodification Planning Tool Web Map is intended to be a screening tool for hydromodification requirements outside of areas with existing sub-basin plans (e.g., North Bethany, River Terrace). Several upgrades have been made to the map to improve its usability and function since it was initially released on January 4, Additional usage guidance for the Map is provided below. Use the information i tool to provide additional instructions on how to use the various tools in the map such as search and measure, turn on and off specific GIS layers, and display legend items. For example, some layers are only available once zoomed into a site, while others (such as Hydromodification Protection Levels) can be seen at all scales. You can click on a feature to find out more about it. This box will pop up and provide information on the feature that you clicked on, as well as other features in the close vicinity. If you find that you aren t getting information on the feature that you re interested in, use the arrow in the blue header to cycle through all selected features until you get the one you want.

2 Additional Base Strategy Methodology Examples Additional Example #1 Pearl Street, Beaverton 1.05 ac lot at end of cul-de-sac Zoned R-10; 4 lot subdivision Impervious Area = 17,385 sq. ft. Project Size Category = Small Development Class = Developed (i.e., not Expansion Area) Hydromodification Protection Level = Low (See trace of piped stormwater conveyance system and Receiving Reach on lower map. You may need to zoom in to see details, such as the stormwater swale just upstream of the Point of Discharge to the Receiving Reach which is 350 feet long (based on 1 st order receiving stream). Preferred Hydromodification Approach = Enhanced LIDA Receiving Reach Point of Discharge to Stream Existing Piped Conveyance Stormwater Discharge from Site

3 Additional Example #2 Unincorporated Washington County west of Portland Community College Rock Creek campus and north of NW West Union Rd. Taxlot 1N ~40 buildable ac lot in new urban expansion area Assumed several 100+ lot subdivisions (in phases) with small commercial area Impervious Area > 600,000 square feet across all phases Project Size Category = Large Development Class = Expansion Area (but doesn t alter Preferred Hydromodification Approach) Hydromodification Protection Level = High (Based on eventual stormwater discharge to High Protection zones in 3 rd order Holcomb Creek (north) or 5 th order Rock Creek (east), though this doesn t alter Preferred Hydromodification Approach) Preferred Hydromodification Approach = Flow Duration Curve Matched Detention. This project has a Size Class of Large, so it is not necessary to use the Map to determine the Hydromodification Protection Class or Development Class. All Large projects result in the same preferred Hydromodification Approach; Flow Duration Curve Matched Detention.

4 Additional Example #3 Unincorporated Washington County SE of intersection of SW 185 th and SW Farmington Road; Taxlot 1S224AA acre lot Zoned R-15; 14 lot subdivision Impervious Area = 46,432 The Point of Discharge to the Receiving Reach is to a 1st order stream. Trace flow path from the point stormwater leaves the project site through the existing stormwater conveyance (open ditch and storm system) to the Point of Discharge as shown on next page. This may require panning the Map to see sufficient detail in the storm system. Project Size Category = Medium Development Class = Developed Hydromodification Protection Level = Low Preferred Hydromodification Approach = Peak Matched Detention Example continues on next page.

5 Point of Discharge to Stream Receiving Reach Existing Conveyance Stormwater Discharge from Site