SWM POND DESIGN CALCULATIONS DRAWDOWN TIME Project Name: Milton Meadow and 1321387 Ontario INC. Prepared by: R.K. Municipality: City of Milton Checked by: A.F. Project No.: 10-334 Last Revised: 1-May-14 Date: 1-May-14 Pond S44 Detention Time Calculations t = (0.66C2h1.5+2C3h0.5)/2.75Ao (MOE Eq'n 4.11) t= 345258 t= 95.9 drawdown time in seconds drawdown time in hours d= 0.11 A0= 0.0095 h= 0.945 diameter of the orifice (m) cross-sectional area of the orifice (m2 ) maximum water elevation above orifice (m) Drainage Area= 21.60 Qext det= 0.0246 ha (includes pond block area) proposed extended detention release rate (m3/s) Qtarget= 0.0238 based on target release rate (0.0011m3/s/ha) and 21.6ha drainage area C2= 1927 slope coefficient from the area-depth linear regression C3= 4040 intercept from the area-depth linear regression Pond area-depth relationship: Elevation 208.40 209.40 N.W.L. Ext. Detention Area 4040 5967 Depth 0.00 1.00 The drawdown time for Pond S44 is 95.9 hours (4 days) Hickenbottom (Perforated Riser Pipe) Calculation Pipe Diameter Hole Diameter Number of Holes 300 75 20 (mm) (mm) Hole Spacing 50 (mm) Max. # of holes per row # of rows required Min. Perf. Pipe Length 7 3 0.43 (m) Area Check: Area of holes Equivalent Diameter 88357 335 (mm2) (mm) Therefore, the perforated riser pipe does not control the extended detention release rate. Provided Perf. Pipe Length 1 (m) P:\Projects\10-334\Reports\FSR - Century Grove\1st Submission CG\Design\SWM\[Drawdown time calculation S44.xlsx]Pond S44 Urbantech Consulting, A Division of Leighton-Zec Ltd. 25 Royal Crest Court, Suite 201 Markham, Ontario L3R 9X4 TEL: 905.946.9461 FAX: 905.946.9595 www.urbantech.com
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