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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br /> 3,3.7 BMP C206: Level Spreader ' <br /> Purpose <br /> To provide a temporary outlet for dikes and diversions consisting of an excavated depression conswcted <br /> at zera grade across a slope. To converi concentrated nmoff to sheet flow and tclease it onto areu <br /> stabilized by exis4ng vegetatioo or an engineered 61ter strip. <br /> Conditions o/Use <br /> Used w6en a concenVated flow of water needs to be dispersed over a large azea with existing stable <br /> vegetation. <br /> Level sprcaders shall be used only wherc the slopes azc gcnde,thc water volume is relatively low,and thc <br /> soil will adsorb most of the low flow events. <br /> Items to consider aze: <br /> I. The risk of erosion a damage if the flow becomes concentrated. <br /> 2. M easement may be rcquirr,d if discharged to adjoining property. <br /> 3. Most of the 11ow should be as groundwa[er and not as sur(ace ilow. <br /> 4. Unsuitable where there is an unstable area dr,wnstream that cannot accept addidonal <br /> groundwater. <br /> Design and/nstallatlon Specifications <br /> L Use above undisturbed areas that are stabi6zed by existing vegetation. <br /> , 2. If the level spreader 6as any low points,flow will canceotrate,create c6annels and may cause <br /> erosian. <br /> 3. Discharge arca below Ihe outlet must be uniCorm with a slope of less than SN:I V. <br /> 4. Outlet to be constructed levcl in a stable,undisturbcd soil profile(not on fill). <br /> 5. The runoff shall nat re-cancenhate after release unless intercepted by another downsucam <br /> measure. <br /> 6. The grade of thc channel for the last 20 feet of the dike or interceptor cntering the level sprcadcr <br /> shall be Icss than or cqual to 1 percent. The gradc of t6e levcl spreader shall be 0 percent to <br /> ensure unifortn sprcading of stocm runoff. <br /> 7. A 6-inch hig6 gravel bertn placed across the Ievel lip s6all consist of washed crushed rock,2-to <br /> 4-inch or 0.75-inch to 1.5-inch sizc. <br /> 8. The sprcader length shall bc determined by estimating thc peak flow cxpectcd from thc 10•ycar, I <br /> 24-hour design storm. The length of the spreader shall be a minimum of I S feet for 0.t cubic fcet <br /> per second and shall be 10 feet for each 0.1 cubic(eet per second thereaflcr to a maximum o( <br /> 0.5 cubic feet per second per spreader. Use multiple spreaders for higher flows. <br /> 9. The width of the spteader should be at least 6 fect. <br /> I0. 'Che depth of thc spreadcr as measured itom the lip should be at least 6 inches and it should be <br /> unifo[m across thc entirc Icngth. <br /> l I. Level sprcaders shall be setback 100 feet minimum from the property line unless there is an <br /> easement for flow or the tlow is directed to a nahual drainage coursc. <br /> Volume 11—Constructron StormwaterPollution Prevention <br /> 3-45 <br />