3214 BROADWAY BROADWAY KINECT APARTMENTS 2021-08-11

• • CITY OF EVERETT STORMWATER MANAGEMENT MANUAL • 3.3.7 BMP C206: Level Spreader • Purpose • To provide a temporary outlet for dikes and diversions consisting of an excavated depression constructed • at zero grade across a slope. To convert concentrated runoff to sheet flow and release it onto areas • stabilized by existing vegetation or an engineered filter strip. Conditions of Use • Used when a concentrated flow of water needs to be dispersed over a large area with existing stable • vegetation. • Level spreaders shall be used only where the slopes are gentle,the water volume is relatively low,and the • soil will adsorb most of the low flow events. • Items to consider are: • 1. The risk of erosion or damage if the flow becomes concentrated. • 2. An easement may be required if discharged to adjoining property. • 3. Most of the flow should be as groundwater and not as surface flow. • 4. Unsuitable where there is an unstable area downstream that cannot accept additional • groundwater. w Design and Installation Specifications • I. Use above undisturbed areas that are stabilized by existing vegetation. • 2. If the level spreader has any low points, flow will concentrate, create channels and may cause • erosion. - 3. Discharge area below the outlet must be uniform with a slope of less than 5H:I V. • 4. Outlet to be constructed level in a stable,undisturbed soil profile(not on fill). • 5. The runoff shall not re-concentrate after release unless intercepted by another downstream • measure. • 6. The grade of the channel for the last 20 feet of the dike or interceptor entering the level spreader • shall be less than or equal to 1 percent. The grade of the level spreader shall be 0 percent to ensure uniform spreading of storm runoff. • 7. A 6-inch high gravel berm placed across the level lip shall consist of washed crushed rock,2-to 4-inch or 0.75-inch to 1.5-inch size. • 8. The spreader length shall be determined by estimating the peak flow expected from the 10-year, • 24-hour design storm. The length of the spreader shall be a minimum of 15 feet for 0.1 cubic feet per second and shall be 10 feet for each 0.1 cubic feet per second thereafter to a maximum of • 0.5 cubic feet per second per spreader. Use multiple spreaders for higher flows. • 9. The width of the spreader should be at least 6 feet. • 10. The depth of the spreader as measured from the lip should be at least 6 inches and it should be • uniform across the entire length. • 11. Level spreaders shall be setback 100 feet minimum from the property line unless there is an • easement for flow or the flow is directed to a natural drainage course. • • Volume II—Construction Stormwater Pollution Prevention • 3-45 • 411