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2.1.6 Element 6: Protect Slopes <br /> West of the Cascade Mountains Crest <br /> Describe how slopes will be designed, constructed, and protected to minimize erosion. <br /> Temporary pipe slope drains must handle the peak 10-minute flow rate from a Type 1A, 10- <br /> year, 24-hour frequency storm for the developed condition. Alternatively, the 10-year, 1-hour <br /> flow rate predicted by an approved continuous runoff model, increased by a factor of 1.6, may <br /> be used. <br /> The hydrologic analysis must use the existing land cover condition for predicting flow rates from <br /> tributary areas outside the project limits. <br /> For tributary areas on the project site, the analysis must use the temporary or permanent project <br /> land cover condition, whichever will produce the highest flow rates. <br /> If using the Western Washington Hydrology Model (WWHM) to predict flows, bare soil areas <br /> should be modeled as "landscaped area". <br /> Describe how you will reduce scouring within constructed channels that are cut down a slope. <br /> East of the Cascade Mountain Crest <br /> Describe how slopes will be designed, constructed, and protected to minimize erosion. <br /> Temporary pipe slope drains must handle the expected peak flow velocity from a 6-month, 3- <br /> hour storm for the developed condition, referred to as the short duration storm. <br /> Describe how you will reduce scouring within constructed channels that are cut down a slope. <br /> Will steep slopes be present at the site during construction? <br /> ® Yes❑ No (Note: Steep slopes are limited to soil removal activities for Phase 1). <br /> List and describe BMPs: <br /> There will be steep slopes during the removal of the spoil pile. All runoff from the spoil pile will <br /> be contained within the spoil pile area. Exposed dirt will be covered with plastic during rain <br /> events to keep scouring from occurring. Water that is contained within the spoil pile area will be <br /> channeled and pumped to the sediment pond which will then be chemically treated. <br /> • Plastic Covering (BMP C123) <br /> Installation Schedules: <br /> Plastic will be installed on an as needed basis depending on the weather. <br /> Page 1 17 <br />