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� Viaonan Place H�drotoev Reoort 8 Calcula4^^° N94-450� <br /> ■ WETPOND DF.SIGN <br /> r 1. Glcul�te the wetpond daign voluma <br /> The wetpond design volume outside of the Silver Lake drainage basin shall be equal to the <br /> � storm water runoff from the 6-month/24-hour design storm. The wetpond design volume <br /> is calculated by multiplying the total precipitation associated with the 6-month/24-hour <br /> design storm (0.99 inches)by the amount of impervious surface contributing tunoff to the <br /> ' wetpond (1.92 acres). <br /> The reyuired wetpond design volume is calculated to be: � <br /> I (0.99 in)(1.92 acres)(43560 ft2/Ac)(ft/12 in)= 6,900 CF <br /> I 2, Detennine the wetpond perm�nent storage volume rcquired �nd provided. <br /> Permanent Storage Volume Req�ired= 50%-6,900 CF=3,450 CF (minimum) <br /> Wetland Treatment Cell =(0.30)3,450 CF= 1,035 CF(minimum) <br /> I Open Water Cell a 3,450 CF-1,035 CF= 2,415 CF(minimum) <br /> Pertnanent Storage Volume Provided a 3,454 CF> 3,450 CF <br /> I Wetland Treatment Cell = 1,036 CF> 1,035 CF <br /> Open Water Cell =2,418 CF> 2,415 CF <br /> � 3. Determine the Ilve storage volume requircd and provided. <br /> Live Storage Vol. Req'd=Total Wetpond Design Volume-Pertnanent Storage Volume <br /> _ (6,900 CF -3,454 CF)=3,446 CF <br /> Live Storage Vol. Prov'd=3,543 CF(at water surface elevation 694.00') <br /> ( I. Route the 6-month/2�-hour deaign etorm through the wetpond to demonatrate that <br /> the full wetpond deaign volume ie provided in the pond. <br /> Using the SBUH Method with Type 1 A Rainfall Distribution and 24-hour duration for the <br /> I6-month storm (P=0.99"), the totel volume of runoff generated by the 1.92 acre basin <br /> tributary to the wetpond is deterntined to be 0.1250 Ac-ft or 5,445 CF(see attached Basin <br /> Summary). This is significantly less than the volume celculated using the City of Everett <br /> � Method 4-10.2(4a). Therefore, the wetpond will be designed to provide the total wetpond <br /> design volume computed using the City of Everett Method 4-10.2(4a). To show that the <br /> � full wetpond design volume is being reached during the 6-month/24•hour design storm, <br /> and assuming that the dead stotage ia full using Stage Storage Table for live storage area; <br /> the level pool routing analysis indicates that an orifice diameter of 1" would be necessary <br /> 1 to achieve this requirement. The top of the overflow riser will be set et elevation 694.00'. <br /> See the following level pool routing for the results of this analysis. <br /> I <br /> I <br /> f GROUP FOUR,INC. �b <br /> � <br />