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Home My WebLink AboutSW6231101_Design Calculations_20240224 Stormwater Wet Pond Design Criteria Project Name: Forest Ridge Commons - Ph. 1 SCM: Wet Pond 1 Calculate Runoff Coefficient A= 3.02 acres 131,734 sf Watershed area Ai= 2.01 acres 87,463 sf Impervious area la= 0.66 Impervious fraction Rv=0.05+0.9*la Rv= 0.65 Runoff Coefficient Calculate Runoff Volume Required to be Controlled Rd= 1 in Design storm rainfall depth (typically 1" or 1.5") V=3630*Rd*Rv*A WQV= 7,109 cf Volume of runoff that must be 1.96 Ac in controlled for specified design storm Calculate Required Pond Surface Area for Permanent Pool Elevation SA/DA= 2.34 Based 3 Avg. Perm. Pool Depth **See Table 10-1,10-2,10-3 for SA/DA SA= 0.071 Ac 3,079 sf Required Surface Area @ Perm Pool SC-3 Pond Volume Calculations Project Name: Forest Ridge Commons - Ph. 1 Outlet: Wet Pond 1 Permanent Pool Volume (Main Pool Only) Elev. Contour Accum. Stage Diff Area Incr. Vol. Vol. (ft) _(ft) (sf) (cf) (cf) 273.5 0.0 982 0 0 275 1.5 1,406 1,791 1,791 276 1.0 1,708 1,557 3,348 277 1.0 2,028 1,868 5,216 278 1.0 2,364 2,196 7,412 278.5 0.5 2,537 1,225 8,637 279 0.5 3,087 1,406 10,043 Perm Pool Elev. Forebay Only Volume Elev. Contour Accum. Stage Diff Area Incr. Vol. Vol. (ft) (ft) (sf) (cf) (cf) 274.5 0.0 50 0 0 275 0.5 344 99 99 276 1.0 346 345 444 277 1.0 348 347 791 278 1.0 350 349 1,140 278.5 0.5 452.3 201 1,340 279 0.5 761 303 1,643 16.4% Forebay To Main Volumes Check Temporary Pool Volume Elev. Contour Accum. Stage Diff Area Incr. Vol. Vol. (ft) (ft) (sf) (cf) (cf) 279 0.0 3,848 0 0 Perm Pool Elev. 279.5 0.5 4,867 2,179 2,179 280 0.5 5,346 2,553 4,732 280.5 0.5 5,836 2,796 ,52. Actual WQV 7,109 Min. Required WQV SC-7 Drawdown Orifice Sizing Calculations Project Name: Forest Ridge Commons - Ph. 1 Outlet: Wet Pond 1 Pond Storage= 7,528 cf Water Quality Volume Pond Depth(h)= 0.5 ft HO=H/3 Drawdown Time= 2.5 days 2-5 days Cd= 0.6 Coefficient of Discharge (typical 0.6) g= 32.2 ft/secA2 Gravity The Orifice Equation Q= Cd A Sqrt(2 g h) Rearrange to solve for A, the minimum orifice area needed to meet drawdown requirements Q= 0.03 cfs Based on pond volume and desired drawdown time A= 0.01024 sf 1.47 si Number of Orifices= 1 Minimum diameter to meet area d= 1.37 inch diameter orifice Use: 1.25 "diameter orifice 0.0085 sf Check Outflow time Q= Cd A Sqrt(2 g h) Q= 0.03 cfs Drawdown time= 3.00 days OK SC-5 Anti-Flotation Sizing Calculations Project Name: Forest Ridge Commons - Ph. 1 Outlet: Wet Pond 1 Riser Diameter= 0 in (circular) Dimensions of Riser= 5.5 5.5 ft Depth of pond = 6 ft Required Factor of Safety= 1.5 Cross Sectional Area of Riser Circular= 0.00 sf Rectangular= 30.25 sf Volume of Water Displaced Depth of pond * Cross-sectional area 181.5 cf Weight of Water Displaced (assuming weight of water= 62.4 lb/cf) 62.4 *Volume of water Displaced 11325.60 lb Minimum Weight of Anti-Flotaton Device FS *WoW Displaced 16988.40 lb Riser Base Provided 8 ft x 8 ft x 2 ft(depth) c-c-c-c-c-c- Weight of concrete assumed 150 lb/cf Weight of Base Provided = 19200.00 lb FS Provided = 1.70 OK SC-6 AVERAGE DEPTH CALCULATIONS Project Name: Forest Ridge Commons - Ph. 1 SCM: Wet Pond 1 Average Depth Equation 3 Vpp= 10,043 cf VSheIf= 153.3 cf ABottom of Shelf— 2,537 sf Davg= 3.9 ft Dmax Over Shelf= 0.5 ft Pperm PooI= 204.4 ft Wsubmerged part of shelf— 3 ft Vshelf= 153.3 cf Equation 3. Average depth when the shelf is partially or fully submerged and the shelf is being excluded from the average depth calculation VPP—Vshelf Davg= Abottom of shelf Where: Davg = Average depth(feet) Vpp = Main pool volume at permanent pool elevation(feet') Vshelf = Volume over the shelf only(feet3)—see below Abottom of shelf = Area of main pool at the bottom of the shelf(feet2) Vshelf= 0.5* Depthma,,over shelf*Perimeterparm pool•W Idthst6merged part of shelf Where: Depthmax over shelf = Depth of water at the deep side of the shelf as measured from the permanent pool(feet) Perimeterpem,pool = Perimeter of main pool at the bottom of the shelf(feet) Wdthsubmerged part of shelf = Width from the deep side to the dry side of the shelf as measured at permanent pool(feet) SC-8 Stormwater Wet Pond Design Criteria Project Name: Forest Ridge Commons - Ph. 1 SCM: Wet Pond 2 Calculate Runoff Coefficient A= 8.41 acres 366,362 sf Watershed area Ai= 6.31 acres 274,772 sf Impervious area la= 0.75 Impervious fraction Rv=0.05+0.9*la Rv= 0.73 Runoff Coefficient Calculate Runoff Volume Required to be Controlled Rd= 1 in Design storm rainfall depth (typically 1" or 1.5") V=3630*Rd*Rv*A WQV= 22,134 cf Volume of runoff that must be 6.10 Ac in controlled for specified design storm Calculate Required Pond Surface Area for Permanent Pool Elevation SA/DA= 2.72 Based 3 Avg. Perm. Pool Depth **See Table 10-1,10-2,10-3 for SA/DA SA= 0.228 Ac 9,947 sf Required Surface Area @ Perm Pool SC-3 Pond Volume Calculations Project Name: Forest Ridge Commons - Ph. 1 Outlet: Wet Pond 2 Permanent Pool Volume (Main Pool Only) Elev. Contour Accum. Stage Diff Area Incr.Vol. Vol. (ft) (ft) (sf) (cf) (cf) 251.25 0.0 7,618 0 0 252 0.8 8,225 5,941 5,941 253 1.0 9,047 8,636 14,577 254 1.0 9,887 9,467 24,044 255 1.0 10,743 10,315 34,359 255.5 0.5 11,179 5,481 39,840 256 0.5 13,407 6,147 45,986 Perm Pool Elev. 9,947 Min. Req'd SA Forebay Only Volume Elev. Contour Accum. Stage Diff Area Incr.Vol. Vol. (ft) (ft) (sf) (cf) (cf) 251 0.0 654 0 0 252 1.0 948 474 474 253 1.0 1245 1,097 1,571 254 1.0 1579 1,412 2,983 255 1.0 1952 1,766 4,748 255.5 0.5 2153 1,026 5,774 256 0.5 3199 1,338 7,112 15.5% Forebay To Main Volumes Check Temporary Pool Volume Elev. Contour Accum. Stage Diff Area Incr.Vol. Vol. (ft) (ft) (sf) (cf) (cf) 256 0.0 16,606 0 0 Perm Pool Elev. 256.5 0.5 20,090 - 9,174 9,174 257.25 0.8 21,722 15,680 24,854 Actual WQV 22,134 Min. Required WQV SC-7 Drawdown Orifice Sizing Calculations Project Name: Forest Ridge Commons - Ph. 1 Outlet: Wet Pond 2 Pond Storage= 24,854 cf Water Quality Volume Pond Depth(h)= 0.416667 ft HO=H/3 Drawdown Time= 2.5 days 2-5 days Cd= 0.6 Coefficient of Discharge (typical 0.6) g= 32.2 ft/secA2 Gravity The Orifice Equation Q= Cd A Sqrt(2 g h) Rearrange to solve for A, the minimum orifice area needed to meet drawdown requirements Q= 0.12 cfs Based on pond volume and desired drawdown time A= 0.03702 sf 5.33 si Number of Orifices= 1 Minimum diameter to meet area d= 2.61 inch diameter orifice Use: 2.5 "diameter orifice 0.0341 sf Check Outflow time Q= Cd A Sqrt(2 g h) Q= 0.11 cfs Drawdown time= 2.72 days OK SC-5 Anti-Flotation Sizing Calculations Project Name: Forest Ridge Commons - Ph. 1 Outlet: Wet Pond 2 Riser Diameter= 0 in (circular) Dimensions of Riser= 5.5 5.5 ft Depth of pond = 6.5 ft Required Factor of Safety= 1.5 Cross Sectional Area of Riser Circular= 0.00 sf Rectangular= 30.25 sf Volume of Water Displaced Depth of pond * Cross-sectional area 196.625 cf Weight of Water Displaced (assuming weight of water= 62.4 lb/cf) 62.4 *Volume of water Displaced 12269.40 lb Minimum Weight of Anti-Flotaton Device FS *WoW Displaced 18404.10 lb Riser Base Provided 8.5 ft x 8.5 ft x 2 ft(depth) c-c-c-c-c-c- Weight of concrete assumed 150 lb/cf Weight of Base Provided = 21675.00 lb FS Provided = 1.77 OK SC-6 AVERAGE DEPTH CALCULATIONS Project Name: Forest Ridge Commons - Ph. 1 SCM: Wet Pond 2 Average Depth Equation 3 VPP= 45,986 cf Vshelf= 647.75 cf ABottom of Shelf= 11,179 sf Davg= 4.1 ft Dmax Over Shelf= 0.5 ft Pperm Pool= 518.2 ft Wsubmerged part of shelf— 5 ft Vshelf= 647.75 cf Equation 3. Average depth when the shelf is partially or fully submerged and the shelf is being excluded from the average depth calculation VPP—Vshelf Davg= Abottom of shelf Where: Davg = Average depth(feet) Vpp = Main pool volume at permanent pool elevation(feet') Vshelf = Volume over the shelf only(feet3)—see below Abottom of shelf = Area of main pool at the bottom of the shelf(feet2) Vshelf= 0.5* Depthma,,over shelf*Perimeterparm pool•W Idthst6merged part of shelf Where: Depthmax over shelf = Depth of water at the deep side of the shelf as measured from the permanent pool(feet) Perimeterpem,pool = Perimeter of main pool at the bottom of the shelf(feet) Wdthsubmerged part of shelf = Width from the deep side to the dry side of the shelf as measured at permanent pool(feet) SC-8