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4D <br />a H <br />9Hcn <br />H H <br />H H <br />M f7 <br />H xl <br />axo <br />AS H Ii1 <br />VJ H <br />H <br />z <br />OHd <br />H^ag <br />9H� <br />t z <br />HH <br />g� H <br />C3 d fn <br />Crl <br />2.'H Co <br />H O CA <br />OOOOS ENGINEERS, INC. <br />a7� <br />CIVIL ENGINEERING SURVEYING PLANNING <br />d 205 '46TH AVE. N.E.. SUITE 200 - BELLEVUE. WA SB007 <br />)206) 665-7677 OR 454-3743 <br />WETM14D 5('L(NG <br />TFtE 5ASIS FOF-SI-e(NG-V(E WECR3NDS ACE AS FOL-VOA) <br />JOB NO. Gll2— <br />OAT E -_ <br />BY — <br />4.3.14.3 Wet Ponds in the Silver Lake Watershed shall be <br />designed to provide a 24 hour residence time for a 2 <br />year rainfall event (1.55 inches of precipitation.). <br />Wet ponds outside the silver Lake watershed shall be <br />designed to provide a 12 hour residence tine for a 2 <br />year rainfall event (1.20 inches of precipitation). <br />4.3.14.4 Wet ponds Design Criteria <br />a) At least 50 percent of the required wet pond <br />volume shall be permanent (dead) storage. <br />b) At least 30 percent of the surface area of the <br />permanent pond shall be planted with wetland <br />vegetation (such as cattails or bulrush). <br />e) The maximum depth of dead _torage shall he 12 <br />inches for the portion of the wet pond planted <br />with wetland vegetation with 6 inches <br />preferred. <br />d) The side slopes shall be no steeper than 3 <br />horizontal to 1 vertical (5:1 preferred). <br />e) A 10' wide flat safety bench, 6 inches to 12 <br />inches below the permanent water surface shall <br />be provided around the perimeter of the pond. <br />f) The length percent width ratio shall be at <br />least 3:1. <br />g) Grit removal shall be provided upstream of the <br />wet pond by a 72 inch diameter catch basin with <br />a 48 inch deep sump.. Alternatively a Forebay <br />with a 15 minute residence tire in a two year <br />storm (0,25 inches of precipitation) may be <br />provided. <br />h) At least one baffle shall be provided across <br />the width of the pond. <br />i) Wet ponds designed solely for water quality <br />Improvement shall be designed to reach its full <br />design volume at a frequency of once every two <br />years. For wet ponds incorporated into on -site <br />detention ponds, a multi orifice (or comparable <br />method) shall be provided to ensure that the <br />wet pond design depth is equalled or exceeded <br />once every two years. <br />j) The open water portion of the wet pond shall <br />have a dead storage depth of three to six feet. <br />SHEET 9 0 <br />