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HomeMy WebLinkAboutWPO202000030 Calculations 2020-06-012415 IVY ROAD COMMERCIAL REDEVELOPMENT FINAL STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations June 1, 2020 PREPARED BY: COLLINS 0=NSINF=c1n1k' 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com Soils Mapping (Source: NRCS Web Soil Survey Online Database) Soils Table (Source: NRCS Web Soil Survey Online Database) Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent of Symbol AOI 19B Minnieville 3.G°/b loam, 2 to 7 percent slopes 36C Hayesville 4.111/a loam, 7 to 15 percent slopes 91 Urban land 92.9°b Totals for Area of 100.0wo Interest The NRCS web soil survey defines this development's soils as being primarily Urban Land. The following calculations conservatively consider 'Urban Land' as having a hydrologic group type of D. Precipitation Data (Source: NCIAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) Map •� Terrain v 2 4` � �w ♦ P� I Bellair Bird mood Golf y _ Course T - _ ry 1OOrn k •r OOft POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90"/fl CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, Volume 2, Version 3 PIDS-based precipitation frequency estimates with 90% confidence intervals (in inches)' Average recurrence inlereal (years! 1 2 5 10 25 50 100 2�� 560 100� 2�hr -. 30 .401 {3. 316 11;• {4.215525} {d. 6 6�19) {6. 6---7.57j ifi.97 8.751 {7. 6-10.1) {9. 2011.5j 12.4 {10.6- 3.7) 14.1 {11.8-15.5; DEQ Virginia Runoff Reduction Method for ReDevelopments Water Quality Calculations DEQ Virginia Runoff Reduction Method Re -Development Compliance Spreadsheet - Version 3.0 BMP Standards and Specifications M 2013 Draft BMP Standards and Specifications Project Name: 2415 IVY ROAD COMMERCIAL REDEVELOPMENT PLAN FINAL data input cells Date: 6/1/2020 constant values Linear Development Project? No calculation cells Site Information Post -Development Project (Treatment Volume and Loads Enter Total Disturbed Area (acres) 2.52 Check: BMP Design Specifications List: 2013 Draft Stds & Specs ® Linear project? No 0 Pre-ReDevelopment Land Cover (acres) Land cover areas entered correctly? ✓ Total disturbed area entered? It A Soils B Soils C Soils D Soils Totals Forest/Open Space (acres) -- undisturbed, protected forest/open space or reforested land 0.00 Managed Turf (acres) -- disturbed, graded for yards or other turf to be mowed/managed 0.99 0'99 Impervious Cover (acres) 1.53 1.53 2.52 Post -Development Land Cover (acres) A Soils B Soils C Soils D Soils Totals Forest/Open Space (acres) -- undisturbed, protected forest/open space or reforested land 0.00 Managed Turf (acres) -- disturbed, graded for yards or other turf to be mowed/managed 1.01 1.01 Impervious Cover (acres) 1.51 1.51 Area Check OK. OK. OK. 2.52 Constants Runoff Coefficients (Rv) Annual Rainfall (inches) 43 A Soils B Soils C Soils D Soils Target Rainfall Event (inches) 1.00 Forest/Open Space 0.02 0.03 0.04 0.05 Total Phosphorus (TP) EMC (mg/L) 0.26 Managed Turf 0.15 1 0.20 0.22 0.25 Total Nitrogen (TN) EMC (mg/L) 1.86 Impervious Cover 0.95 0.95 0.95 0.95 Target TP Load (lb/acre/yr) 0.41 Pj (unitless correction factor) 0.90 Land Cover Summary -Pre Land Cover Summary -Post (Fine Pre-ReDevelopment Listed Adjusted' Post ReDev. & New hi pervious Forest/Open Space Cover (acres) 0.00 0.00 Forest/Open Space Cover (acres) OTO Weighted Rv(forest) 0.00 0.00 Weighted Rv(forest) 0.00 %Forest 0% 0% %Forest 0% Managed Turf Cover (acres) 0.99 0.99 Manag(edacresTurf Cover ) 1.01 Weighted Rv(turf) 0.25 0.25 Weighted Rv(turf) 0.25 %Managed Turf 39% 39% %Managed Turf 40% Impervious Cover (acres) 1.53 1.53 Impervious Cover (acres) 1.51 Rv(impervious) 0.95 0.95 Rv(impervious) 0.95 %Impervious 61% 61% %Impervious 60% Total Site Area (acres) 2.52 2.52 Final Site Area (acres) 2.52 Site Rv 0.68 0.68 Final Post Dev Site Rv 0.67 Traatmanf Vnlrrma and NDtrinnt I nadi Final Post -Development Pre-ReDevelopment Treatment Volume 0.1418 0.1418 Treatment Volume 0.1406 (acre-ft) (acre-ft) Final Post -Development Pre-ReDevelopment Treatment Volume 6,175 6,175 Treatment Volume 6,124 (cubic feet) (cubic feet) Final Post- Pre-ReDevelopment TP Load 3.88 3.8 Development TP Load 3.85 (lb/yr) (lb/yr) (lb/,cr,/yr)'. I " I �E EII EIEM� Baseline TP Load (lb/yr) r 'Adjusted Land Cover Summary: Pre ReDevelopment land cover minus pervious land cover (forest/open space or managed turf) ac eage proposed for new imp,mo cover. 9djusted total acreagei consistent with Pas[-ReDevelopment acreage (minus 2c eage of new impervious cover). !olumn I shows load reduction requriemeatfor new impervious cover (based on new levelopment load limit, 0.41 lbs/acre/year). TP Load Reduction Required (lb/yr) Land Cover Summary -Post Post-ReDevelopment Forest/Open Space Cover (acres) 0 .00 Weighted Rv(forest) 0.00 %Forest 0% Managed Turf Cover (acres) 1.01 Weighted Rv(turf) 0.25 %Managed Turf 40% ReDev. Impervious 1.51 Cover (acres) Rv(impervious) 0.95 %Impervious 60% Total ReDev. Site Area (acres) 2 62 ReDev Site Re 0.67 Treatment Volume and Nutrient Load Post-ReDevelopment Treatment Volume 0.1406 (acre-ft) Poest-ReDevelopment TreatmentVolume 6,124 (cubic feet) Poest-ReDeveJ­d) Load(3.85 (lb/yr Post-ReDevelo Load perare (lb/acre Maa. Reductio (Below 2" ReDevelopm TP Load Reduction Required for Redeveloped Area 074 (lb/yr) 0.74 Nitrogen Loads (Informational Purposes Only) Final Post -Development TN Load Pre-ReDevelopment TN Load (lb/yr) 27.15 (Past & New Impervious) 27.52 (lb/yr) Land Cover Summary -Post Post -Development New Impervious New Impervious Cover (acres) 0.00 Rv(impervi us) - Post -Development Treatment Volume -- (eic -ft) Post -Development Treatment Volume (cubic feet) Post -Development TP Load (lb/yr) TP Load Reduction Required for New 0 Impervious Area (Ib/yr) Drainage Area A Orainaee Area A Land tour, I ... e l ASoils I B Soils C Soils D Soils Totals Land Cover Rv F.... Open Space( acres) 0.00 0.00 Managed Turf(acres) 0.20 0.20 0.25 m pervious Cover lacresl EEL 0.26 0.26 0.95 Total 0.46 Stormwater Rest Management Practices MR = Runoff Reduction) VRRM R xv WRaad Final -NEW AREAS DA.A Total Phosphorus Available for Removal in D.A. A (lb/yr) 0.68 Post Development Treatment Volume in D.A. A (ft') 1,078 Runoff Managed Impervious Volume from Remaining Total BMP Phosphorus Phosphorus Load Untreated Phosphorus Remaining Practice Reduction Turf Credit Cover Credit Runoff Upstream a Runoff Volume Treatment Removal from Upstream Phosphorus Load Removed By Phosphorus Load Downstream Practice to be Credit (%) Area (acres) Area (acres) Practice (ft') Reduction (k) (ft') Volume (k') Efficiency (%) Practices (lb) to Practice (lb) Practice (lb) (lb) Employed 1. Vegetated Roof RR) La. Vegetated Roof #1 (Spec#5) 4s 0 0 0 0 +obi®c�as�s®sue o.00 o.00 o.00 60�g��e�p��®®®®��g�vgeg9®2809% �® ®®® e $i0®®® 0 eB@O®®Ca0 0 �Sa92809%ZB& 0.00 @O®0999 B® 0.00 0.00 1.b.Vegetated Roof#2(SPec#5) 0 0 2. Rooftop Disconnection (RR) 2.b.Simpl, Disconnection to C/D Soils �Pacifi`lk,rs C/D soils) (Spec 2a, To Dry Wall or French Drain H2, 21 To Rain Garden #" 3. Permeable Pavement (RR) 4. Grass Channel (RR) 4a. Gross Channel A/B Soils (Spec #3) 5. Dry Swale (RR) 6. Bioretention (RR) 5. Dry Swale (RR) 6. Bioretention (RR) 7. Infiltration (RR) 8. Extended Detention Pond (RR) Nitrogen Nitrogen Load Untreated Nitrogen Remaining Removal from Upstream Nitrogen Load to Removed By Nitrogen Load Efficiency(%) Practices(Ibs) Practice fibs) Practice fibs) (lbs) 1. Vegetated Roof (RR) 2. Rooftop Disconnection (RR) 3. Permeable Pavement (RR) 4. Grass Channel (RR) S. Dry Swale (RR) 6. Bioretention (RR) ®®®® 7. Infiltration (RR) 8. Extended Detention Pond (RR) VRRM_ReDa ,,Roetl Finel-NEWAREAS DA.A S.b. ED N2 (Spec.111 11 0 0 0 0 15 0.on 0.00 0.on 0.an 30 0.on 0.00 0.00 0.00 9. Sheetflow to Filter/Open Space (RR) TOTAL IMPERVIOUS COVER TREATED (ac) 0.26 AREA CHECK: OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AR EA CHECK: OK. TOTAL RUNOFF REDUCTION IN D.A. A (ft't) 403 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr) 0.68 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.33 TOTAL PHOSPHORUS REMAINING AFTER APPLYING RUNOFF REDUCTION PRACTICES IN D.A. A (lb/yr) 0.36 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS t Swale (no RR) 11. Filtering Practices (no RR) 12. Constructed Wetland (no RR) 13. Wet Ponds (no RR) 14. Manufactured Treatment Devices (no RR) TOTAL IMPERVIOUS COVER TREATED(ac) 0.26 AR EA CHECK: OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AREA CHECK: OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE (lb/yr) 0.74 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr) 0.68 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.00 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A(lb/yY0.33 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A. A (Ib/yiI 0.33 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A. A (lb/yi 0.35 9. Sheetflow to TOTAL IMPERVIOUS COVER TREATED (ac) 0.26 AREA CHECK: OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AR EA CHECK: OK. TOTAL RUNOFF REDUCTION IN D.A. A (ft't) 403 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr) 0.68 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.33 TOTAL PHOSPHORUS REMAINING AFTER APPLYING RUNOFF REDUCTION PRACTICES IN D.A. A (lb/yr) 0.36 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS t Swale (no RR) 11. Filtering Practices (no RR) 12. Constructed Wetland (no RR) 13. Wet Ponds (no RR) 14. Manufactured Treatment Devices (no RR) TOTAL IMPERVIOUS COVER TREATED(ac) 0.26 AR EA CHECK: OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AREA CHECK: OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE (lb/yr) 0.74 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr) 0.68 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.00 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A(lb/yY0.33 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A. A (Ib/yiI 0.33 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A. A (lb/yi 0.35 9. Sheetflow to 14. Manufactured Treatment Devices (no RR) TOTAL IMPERVIOUS COVER TREATED(ac) 0.26 AR EA CHECK: OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AREA CHECK: OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE (lb/yr) 0.74 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr) 0.68 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.00 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A(lb/yY0.33 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A. A (Ib/yiI 0.33 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A. A (lb/yi 0.35 9. Sheetflow to TOTAL IMPERVIOUS COVER TREATED(ac) 0.26 AR EA CHECK: OK. TOTAL MANAGED TURF AREA TREATED(ac) 0.00 AREA CHECK: OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE (lb/yr) 0.74 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. A (Ib/yr) 0.68 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A (Ib/yr) 0.00 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A(lb/yY0.33 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A. A (Ib/yiI 0.33 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A. A (lb/yi 0.35 9. Sheetflow to Filter/Open Space (RR) TOTAL RUNOFF REDUCTION IN D.A. A (ft't) 403 NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A (lb/yr) 1 2.36 SEE WATER QUALITY COMPLIANCE TAB FOR SITE CALCULATIONS (Information Only) 10. Wet Swale (Coastal Plain) (no RR) 11 0.00 0 40 0.00 0.00 - 0.00 0.00 0.00 0.00 Practices (no RR) r1l.Filtering ructed Wetland (no RR) 13. Wet Ponds (no RR) 14. Manufactured BMP (no RR) 14. Manufactured BMP (no RR) SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. A Qb/yr� 2.36 NITROGEN REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. A Qb/yr) 0.00 TOTAL NITROGEN REMOVED IN D.A. A(Ib/yr) 2.36 Site Results (Water Quality Compliance) Area Checks D.A. A D.A. B D.A. C D.A. D D.A. E AREA CHECK FOREST/OPEN SPACE (ac) 0.00 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER (ac) 0.26 0.00 0.00 0.00 0.00 OK. IMPERVIOUS COVER TREATED (ac) 0.26 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA (ac) 0.20 0.00 0.00 0.00 0.00 OK. MANAGED TURF AREA TREATED (ac) 0.00 0.00 0.00 0.00 0.00 OK. AREA CHECK OK. OK. OK. OK. OK. Site Treatment Volume (ft3) 6,124 Runoff Reduction Volume and TP By Drainage Area D.A. D D.A. E TOTAL RUNOFF REDUCTION VOLUME ACHIEVED (fe) 403 0 0 0 0 403 TP LOAD AVAILABLE FOR REMOVAL (Ib/yr) 0.68 0.00 0.00 0.00 0.00 0.68 TP LOAD REDUCTION ACHIEVED (Ib/yr) 0.33 0.00 0.00 0.00 0.00 0.33 TP LOAD REMAINING (Ib/yr) 0.35 0.00 0.00 0.00 0.00 0.35 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) 2.36 0.00 0.00 0.00 0.00 2.36 Total Phosphorus FINAL POST -DEVELOPMENT TP LOAD(Ib/yr) 3.85 TP LOAD REDUCTION REQUIRED (Ib/yr) 0.74 TP LOAD REDUCTION ACHIEVED (Ib/yr) 0.33 TP LOAD REMAINING (Ib/yr): 3.52 REMAINING TP LOAD REDUCTION REQUIRED (Ib/yr): 0.41 Total Nitrogen (For Information Purposes) POST -DEVELOPMENT LOAD (Ib/yr) 27.52 NITROGEN LOAD REDUCTION ACHIEVED (Ib/yr) 2.36 REMAINING POST -DEVELOPMENT NITROGEN LOAD (lb/yr)l 25.16 SCS TR-55 Calculations U.S. Department of Agriculture Natural Resources Conservation Service FL-ENG-21A 06/04 TR 55 Worksheet 2: Runoff Curve Number and Runoff Project: 2415 Ivy Road Commercial Redevelopment Final Designed By: KKW, PE Date: 6/1/2020 Location: 2415 Ivy Road, Charlottesville, VA Checked By: SRC, PE Date: 6/1/2020 Check One: Present X Developed 1. Runoff curve Number (CNI Soil name and Cover description CN (weighted) _ Drainage Area Area Product of CN x Calculated Description hydrologic group (Appendix A) (Cover type, treatment, and hydrologic condition; percent impervious; unconnected/ connected impervious area ratio) CN (Acres) Area total product/ total area 'S' Value Impervious Areas -Paved 98 2.08 M 203.6 Impervious Areas -Gravel Parking 91 1.01 91.9 DA A-D (Pre-Dev.) D Impervious Areas -Dirt Parking 89 0.04 3.3 88 1.38 Lawns in Good Condition 80 1.03 82.6 Woods in Good Condition 77 1.18 91.1 Impervious Areas -Paved 98 0.70 68.4 DAA (Post-Dev.) D Lawns in Good Condition 80 0.32 25.7 88 1.35 Woods in Good Condition 77 0.39 30.1 Impervious Areas -Paved 98 0.26 25.3 DAB (Post-Dev.) D Lawns in Good Condition 80 0.20 15.7 90 1.10 Woods in Good Condition 77 0.01 0.4 Impervious Areas -Paved 98 0.53 51.9 DAC (Post-Dev.) D Lawns in Good Condition 80 0.38 30.3 85 1.71 Woods in Good Condition 77 0.55 42.5 Impervious Areas -Paved 98 1.62 158.9 DA D D Lawns in Good Condition 80 0.15 12.3 94 0.62 (Post-Dev.) Woods in Good Condition 77 0.23 18.1 2. Runoff 1-Year Storm I 2-Year Storm 10-Year Storm Drainage Area Description Frequency -years 1 2 10 n a Rainfall, P (24 hour)- inches 3.04 5.55 n/a Runoff, Cl- inches 1.84 2.41 4.18 DA A-D(Pre-Dev.) Runoff, Cl- inches 1.86 2.43 4.20 DA A (Post-Dev.) Runoff, Cl- inches 2.03 2.62 4.42 DA B (Post-Dev.) Runoff, Cl- inches 1.65 2.20 3.92 DA C (Post-Dev.) Runoff, Cl- inches 2.41 3.02 4.87 DA D (Post-Dev.) U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 3: Time of Concentration (Tt) or Travel Time (Tt) Project: 2415 Ivy Road Commercial Redevelopment Final Location: 2415 Ivy Road, Charlottesville, VA Check One: Present X Developed X Check One: Tc X Tt Segment ID: Sheet Flow: (Applicable to Tc only) 1 Surface description (Table 3-1) 2 Manning's roughness coeff., n (Table 3-1 3 Flow length, L (total L < 100) (ft) 4 Two-year 24-hour rainfall, PZ (in.) 5 Land slope, s (ft/ft) 6 Compute Tt = [0.007(n*L)o.a] / Pzo.s s.a Designed By: KKW, PE Checked By: SRC, PE Through subarea n/a DA A-D DA A DA B DA C DA D (Pre-Dev.) (Post-Dev.) (Post-Dev.) (Post-Dev.) (Post-Dev.) Light Woods Light Woods Light Woods Light Woods Light Woods 0.4 0.4 0.4 0.4 0.4 100 60 100 100 54 3.67 3.67 3.67 3.67 3.67 0.06 0.07 0.06 0.06 0.11 0.22 0.14 0.22 0.22 0.10 Shallow Concentrated Flow: 7 Surface description (paved or unpaved) Paved Paved Paved Unpaved Paved 8 Flow Length, L (ft) 155 155 224 95 410 9 Watercourse slope, s (ft/ft) 0.026 0.052 0.036 0.084 0.006 10 Average velocity, V (Figure 3-1) (ft/s) 3.3 4.6 4.6 4.6 1.4 11 Tt = L / 3600*V 0.01 0.01 0.01 0.01 0.08 Channel Flow: 12 Cross sectional flow area, a (ft) 13 Wetted perimeter, P. (ft) 14 Hydraulic radius, r = a/PW (ft) 15 Channel Slope, s (ft/ft) 16 Manning's Roughness Coeff, n 17 V= [ 1.49r2/3s05 ] / n 18 Flow length, L (ft) 19 Tt= L / 3600*V 20 Watershed or subarea Tc or Tt (Add Tt in steps 6, 11 and 19) Note: The shortest SCS Tc is 0.10 hrs. U_ N U_ N E E c v c v c o a c o a ru = N d N d u an u tin I- C: 4- � o .+, V, o •+:; Ln O w 00 w �.o 1-i 0.03 0.01 0.26 1 0.15 1 0.23 1 0.22 0.19 U.S. Department of Agriculture Natural Resources Conservation Service TR 55 Worksheet 4: Graphical Peak Discharge Method Project: 2415 Ivy Road Commercial Redevelopment Final Designed By: KKW, PE Location: 2415 Ivy Road, Charlottesville, VA Checked By: SRC, PE Check One: Present X Developed X 1. Data Drainage Area Description Drainage Area Description Drainage Area Description Drainage Area Description Drainage Area Description DA A-D (Pre-Dev.) DA A (Post-Dev.) DA B (Post-Dev.) DA C (Post-Dev.) DA D (Post-Dev.) Drainage Area (Am) in miles' = 0.0083 0.0022 0.0007 0.0023 0.0031 Runoff curve number CN= 88 88 90 85 94 Time of concentration (Tc)= 0.26 0.15 0.23 0.22 0.19 Rainfall distribution type= II II II II II Pond and swamp areas spread throughout the watershed= 0 0 0 0 0 2. Frequency -years 1 2 10 1 2 10 1 2 10 1 2 10 1 2 10 3. Rainfall, P (24 hour)- inches 3.04 3.67 5.55 3.04 3.67 5.55 3.04 3.67 5.55 3.04 3.67 5.55 3.04 3.67 5.55 4. Initial Abstraction, la- inches 0.28 0.28 0.28 0.27 0.27 0.27 0.22 0.22 0.22 0.34 0.34 0.34 0.12 0.12 0.12 5. Compute la/P 0.09 0.08 0.05 0.09 0.07 0.05 0.07 0.06 0.04 0.11 0.09 0.06 0.04 0.03 0.02 6. Unit peak discharge, Qu- csm/in Out of Range Out of Range Out of Range Out of Range Out of Range 7. Runoff, Q from Worksheet 2- inches 1.84 2.41 4.18 1.86 2.43 4.20 2.03 2.62 4.42 1.65 2.20 3.92 2.41 3.02 4.87 8. Pond and Swamp adjustment factor, Fp 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9. Peak Discharge, Qp- cfs where Qp=Qu Am Q Fp 10.03 13.13 22.75 Routed Through The SWIM Facility 0.95 1.23 2.07 2.46 3.27 5.83 4.93 6.18 9.97 WATERSHED SUMMARY Area, 1-year Flow, 2-year Flow, 10-year Flow, CN ac. cfs cfs cfs DAA-D(Pre-Dev.) 88 5.34 10.03 13.13 22.75 DA A (Post-Dev.) 88 1.41 1.51 2.10 4.76 DA B (Post-Dev.) 90 0.46 0.95 1.23 2.07 DA C (Post-Dev.) 85 1.46 2.46 3.27 5.83 DA D (Post-Dev.) 94 2.01 4.93 6.18 9.97 Totals= 5.34 9.85 12.78 22.63 Pre -Development Impervious Areas- Water Quality (Defined by the Limits of Disturbance) Existing Dirt Parking 1,636 sf Existing Gravel Parking 43,277 sf Existing Concrete Parking 1,739 sf Existing Asphalt Parking 13,121 sf Existing Sidewalk 1,457 sf Public Road 5,208 sf 66,438 sf Post -Development Impervious Areas- Water Quality (Defined by the Limits of Disturbance) Proposed Asphalt Parking & Circulation 53,464 sf Proposed Concrete Loading Area 1,719 sf Proposed Concrete Sidewalk 5,385 sf Public Road 5,208 sf 65,776 sf Overall Net Increase in Impervious Area -662 sf (Within the Proposed Limits of Disturbance) Water Quantity Site Coverage Pre -Development Drainage Areas A-D Coverage Summary Existing Dirt Parking 1,639 sf Existing Gravel Parking 43,968 sf Existing Concrete 4,118 sf Existing Asphalt 43,898 sf Existing Buildings 42,464 sf Existing Woods 51,543 sf Existing Lawn 44,980 sf 232,610 sf Post-ueveiopmemt urainage Area A coverage zoummary Proposed Concrete Sidewalk 1,645 sf Proposed Asphalt 28,758 sf Existing Buildings 0 sf Proposed Woods 17,034 sf Proposed Lawn 13,982 sf 61,419 sf Post -Development Drainage Area B Coverage Summary Proposed Concrete Sidewalk/Pavers 6,033 sf Proposed Asphalt 5,230 sf Existing Buildings 0 sf Proposed Woods 235 sf Proposed Lawn 8,539 sf 20,037 sf Post -Development Drainage Area C Coverage Summary Proposed Concrete Sidewalk 1,283 sf Proposed Asphalt 8,015 sf Existing Buildings 13,750 sf Proposed Woods 24,048 sf Proposed Lawn 16,502 sf 63,598 sf Post -Development Drainage Area D Coverage Summary Proposed Concrete Sidewalk 3,733 sf Proposed Asphalt 38,202 sf Existing Buildings 28,714 sf Proposed Woods 10,226 sf Proposed Lawn 6,680 sf 87,555 sf Channel and Flood Protection Compliance 9 VAC 25-870-66 Section B: Channel Protection "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet the criteria in subdivision 1, 2 or 3 of this subsection..." Section B.1: Manmade stormwater conveyance systems "When stormwater from a development is discharged to a manmade stormwater conveyance system, following the land -disturbing activity, either..." a. or b. shall be met: a. The manmade stormwater conveyance system shall convey the postdevelopment peak flow rate from the two-year 24-hour storm event without causing erosion of the system. Detention of stormwater or downstream improvements may be incorporated into the approved land -disturbing activity to meet this criterion, at the discretion of the VSMP authority. Q Pre -Developed = 13.13 cfs Q Developed = 12.78 cfs The total discharge to the point of analysis is 12.78 cfs, which is a conservative assumption as it assumes the peak flows from subareas A-D occur simultaneously. The reduced post -development 2-year flow of 12.78 cfs to the point of analysis is not erosive to the existing 15" corrugated metal pipe outfall. The LOA point per the 1% rule is within the existing manmade stormwater conveyance system, thus channel adequacy is provided in that the post -development peak flow from the two-year storm is improved from existing and non -erosive. 9 VAC 25-870-66 (Flood Protection Analysis #1) Section C: Flood Protection "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and hydraulic methodologies:" Section C.2.b.: The point of discharge (the site outfall), "releases a postdevelopment peak flow rate for the 10- year 24-hour storm event that is less than the predevelopment peak flow rate from the 10-year 24-hour storm event. Downstream stormwater conveyance systems do not require any additional analysis to show compliance with flood protection criteria if this option is utilized." Section C.3 Limits of Analysis The flood protection analysis terminates at the subareas since subsection C.2.b is met. Pre -Development Hydrographs Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DAA-D(Pre-Dev.) 0.26 0.26 0.09 0.0154 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.26 11.3 0.35 11.6 0.49 11.9 0.75 12.0 1.14 12.1 2.09 12.2 4.03 12.3 7.51 12.4 10.03 12.5 9.14 12.6 6.69 12.7 4.59 12.8 3.19 13.0 1.77 13.2 1.25 13.4 1.03 13.6 0.89 13.8 0.78 14.0 0.71 14.3 0.62 14.6 0.54 15.0 0.49 15.5 0.45 16.0 0.40 16.5 0.35 17.0 0.32 17.5 0.31 18.0 0.29 19.0 0.25 20.0 0.22 22.0 0.18 26.0 0.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 SCS TR-55 Pre -Development Unit Hydrograph (DA Pre A-D) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DAA-D(Pre-Dev.) 0.26 0.26 0.08 0.0201 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.34 11.3 0.46 11.6 0.64 11.9 0.99 12.0 1.49 12.1 2.74 12.2 5.28 12.3 9.83 12.4 13.13 12.5 11.96 12.6 8.76 12.7 6.00 12.8 4.17 13.0 2.32 13.2 1.63 13.4 1.35 13.6 1.17 13.8 1.03 14.0 0.93 14.3 0.81 14.6 0.70 15.0 0.64 15.5 0.58 16.0 0.52 16.5 0.46 17.0 0.42 17.5 0.40 18.0 0.38 19.0 0.32 20.0 0.28 22.0 0.24 26.0 0.00 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 SCS TR-55 Pre -Development Unit Hydrograph (DA Pre A-D) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA A-D(Pre-Dev.) 0.26 0.26 0.05 0.0349 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.59 11.3 0.80 11.6 1.12 11.9 1.71 12.0 2.58 12.1 4.74 12.2 9.14 12.3 17.02 12.4 22.75 12.5 20.72 12.6 15.18 12.7 10.40 12.8 7.22 13.0 4.01 13.2 2.83 13.4 2.34 13.6 2.02 13.8 1.78 14.0 1.60 14.3 1.40 14.6 1.22 15.0 1.12 15.5 1.01 16.0 0.91 16.5 0.80 17.0 0.73 17.5 0.70 18.0 0.66 19.0 0.56 20.0 0.49 22.0 0.42 26.0 0.00 25.00 20.00 15.00 10.00 5.00 0.00 SCS TR-55 Pre -Development Unit Hydrograph (DA Pre A-D) Post -Development Hydrographs Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA A (Post-Dev.) 0.15 0.15 0.09 0.0041 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.07 11.3 0.09 11.6 0.13 11.9 0.20 12.0 0.30 12.1 0.56 12.2 1.07 12.3 2.00 12.4 2.67 12.5 2.43 12.6 1.78 12.7 1.22 12.8 0.85 13.0 0.47 13.2 0.33 13.4 0.27 13.6 0.24 13.8 0.21 14.0 0.19 14.3 0.16 14.6 0.14 15.0 0.13 15.5 0.12 16.0 0.11 16.5 0.09 17.0 0.09 17.5 0.08 18.0 0.08 19.0 0.07 20.0 0.06 22.0 0.05 26.0 0.00 3.00 2.50 2.00 1.50 1.00 0.50 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post A) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA A (Post-Dev.) 0.15 0.15 0.07 0.0054 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.09 11.3 0.12 11.6 0.17 11.9 0.26 12.0 0.40 12.1 0.73 12.2 1.40 12.3 2.61 12.4 3.49 12.5 3.18 12.6 2.33 12.7 1.60 12.8 1.11 13.0 0.62 13.2 0.43 13.4 0.36 13.6 0.31 13.8 0.27 14.0 0.25 14.3 0.21 14.6 0.19 15.0 0.17 15.5 0.16 16.0 0.14 16.5 0.12 17.0 0.11 17.5 0.11 18.0 0.10 19.0 0.09 20.0 0.07 22.0 0.06 26.0 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post A) 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA A (Post-Dev.) 0.15 0.15 0.05 0.0093 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.16 11.3 0.21 11.6 0.30 11.9 0.45 12.0 0.69 12.1 1.26 12.2 2.43 12.3 4.52 12.4 6.04 12.5 5.50 12.6 4.03 12.7 2.76 12.8 1.92 13.0 1.06 13.2 0.75 13.4 0.62 13.6 0.54 13.8 0.47 14.0 0.43 14.3 0.37 14.6 0.32 15.0 0.30 15.5 0.27 16.0 0.24 16.5 0.21 17.0 0.19 17.5 0.19 18.0 0.18 19.0 0.15 20.0 0.13 22.0 0.11 26.0 0.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post A) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 100-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA A (Post-Dev.) 0.15 0.15 0.03 0.0169 Hydrograph Time 100-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.29 11.3 0.39 11.6 0.54 11.9 0.83 12.0 1.25 12.1 2.30 12.2 4.43 12.3 8.25 12.4 11.02 12.5 10.04 12.6 7.35 12.7 5.04 12.8 3.50 13.0 1.94 13.2 1.37 13.4 1.13 13.6 0.98 13.8 0.86 14.0 0.78 14.3 0.68 14.6 0.59 15.0 0.54 15.5 0.49 16.0 0.44 16.5 0.39 17.0 0.35 17.5 0.34 18.0 0.32 19.0 0.27 20.0 0.24 22.0 0.20 26.0 0.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post A) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA B (Post-Dev.) 0.23 0.23 0.07 0.0015 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.02 11.3 0.03 11.6 0.05 11.9 0.07 12.0 0.11 12.1 0.20 12.2 0.38 12.3 0.71 12.4 0.95 12.5 0.87 12.6 0.63 12.7 0.43 12.8 0.30 13.0 0.17 13.2 0.12 13.4 0.10 13.6 0.08 13.8 0.07 14.0 0.07 14.3 0.06 14.6 0.05 15.0 0.05 15.5 0.04 16.0 0.04 16.5 0.03 17.0 0.03 17.5 0.03 18.0 0.03 19.0 0.02 20.0 0.02 22.0 0.02 26.0 0.00 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post B) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA B (Post-Dev.) 0.23 0.23 0.06 0.0019 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.03 11.3 0.04 11.6 0.06 11.9 0.09 12.0 0.14 12.1 0.26 12.2 0.49 12.3 0.92 12.4 1.23 12.5 1.12 12.6 0.82 12.7 0.56 12.8 0.39 13.0 0.22 13.2 0.15 13.4 0.13 13.6 0.11 13.8 0.10 14.0 0.09 14.3 0.08 14.6 0.07 15.0 0.06 15.5 0.05 16.0 0.05 16.5 0.04 17.0 0.04 17.5 0.04 18.0 0.04 19.0 0.03 20.0 0.03 22.0 0.02 26.0 0.00 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post B) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA B (Post-Dev.) 0.23 0.23 0.04 0.0032 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.05 11.3 0.07 11.6 0.10 11.9 0.16 12.0 0.23 12.1 0.43 12.2 0.83 12.3 1.55 12.4 2.07 12.5 1.89 12.6 1.38 12.7 0.95 12.8 0.66 13.0 0.37 13.2 0.26 13.4 0.21 13.6 0.18 13.8 0.16 14.0 0.15 14.3 0.13 14.6 0.11 15.0 0.10 15.5 0.09 16.0 0.08 16.5 0.07 17.0 0.07 17.5 0.06 18.0 0.06 19.0 0.05 20.0 0.04 22.0 0.04 26.0 0.00 2.50 2.00 1.50 1.00 0.50 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post B) Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA C (Post-Dev.) 0.22 0.22 0.11 0.0038 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.06 11.3 0.09 11.6 0.12 11.9 0.18 12.0 0.28 12.1 0.51 12.2 0.99 12.3 1.84 12.4 2.46 12.5 2.24 12.6 1.64 12.7 1.12 12.8 0.78 13.0 0.43 13.2 0.31 13.4 0.25 13.6 0.22 13.8 0.19 14.0 0.17 14.3 0.15 14.6 0.13 15.0 0.12 15.5 0.11 16.0 0.10 16.5 0.09 17.0 0.08 17.5 0.08 18.0 0.07 19.0 0.06 20.0 0.05 22.0 0.05 26.0 0.00 3.00 2.50 2.00 1.50 1.00 0.50 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post Q 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA C (Post-Dev.) 0.22 0.22 0.09 0.0050 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.09 11.3 0.12 11.6 0.16 11.9 0.25 12.0 0.37 12.1 0.68 12.2 1.31 12.3 2.45 12.4 3.27 12.5 2.98 12.6 2.18 12.7 1.49 12.8 1.04 13.0 0.58 13.2 0.41 13.4 0.34 13.6 0.29 13.8 0.26 14.0 0.23 14.3 0.20 14.6 0.18 15.0 0.16 15.5 0.15 16.0 0.13 16.5 0.12 17.0 0.11 17.5 0.10 18.0 0.10 19.0 0.08 20.0 0.07 22.0 0.06 26.0 0.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post Q 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA C (Post-Dev.) 0.22 0.22 0.06 0.0089 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.15 11.3 0.21 11.6 0.29 11.9 0.44 12.0 0.66 12.1 1.22 12.2 2.34 12.3 4.36 12.4 5.83 12.5 5.31 12.6 3.89 12.7 2.66 12.8 1.85 13.0 1.03 13.2 0.72 13.4 0.60 13.6 0.52 13.8 0.46 14.0 0.41 14.3 0.36 14.6 0.31 15.0 0.29 15.5 0.26 16.0 0.23 16.5 0.21 17.0 0.19 17.5 0.18 18.0 0.17 19.0 0.14 20.0 0.13 22.0 0.11 26.0 0.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post Q 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA D (Post-Dev.) 0.19 0.19 0.04 0.0076 Hydrograph Time 1-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.13 11.3 0.17 11.6 0.24 11.9 0.37 12.0 0.56 12.1 1.03 12.2 1.98 12.3 3.69 12.4 4.93 12.5 4.49 12.6 3.29 12.7 2.25 12.8 1.56 13.0 0.87 13.2 0.61 13.4 0.51 13.6 0.44 13.8 0.39 14.0 0.35 14.3 0.30 14.6 0.26 15.0 0.24 15.5 0.22 16.0 0.20 16.5 0.17 17.0 0.16 17.5 0.15 18.0 0.14 19.0 0.12 20.0 0.11 22.0 0.09 26.0 0.00 6.00 c nn 4.00 3.00 2.00 1.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post D) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA D (Post-Dev.) 0.19 0.19 0.03 0.0095 Hydrograph Time 2-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.16 11.3 0.22 11.6 0.30 11.9 0.46 12.0 0.70 12.1 1.29 12.2 2.48 12.3 4.63 12.4 6.18 12.5 5.63 12.6 4.13 12.7 2.83 12.8 1.96 13.0 1.09 13.2 0.77 13.4 0.64 13.6 0.55 13.8 0.48 14.0 0.44 14.3 0.38 14.6 0.33 15.0 0.30 15.5 0.28 16.0 0.25 16.5 0.22 17.0 0.20 17.5 0.19 18.0 0.18 19.0 0.15 20.0 0.13 22.0 0.11 26.0 0.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post D) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA D (Post-Dev.) 0.19 0.19 0.02 0.0153 Hydrograph Time 10-yr Discharges (hrs.) (cfs) 0.0 0.00 11.0 0.26 11.3 0.35 11.6 0.49 11.9 0.75 12.0 1.13 12.1 2.08 12.2 4.01 12.3 7.47 12.4 9.97 12.5 9.09 12.6 6.65 12.7 4.56 12.8 3.17 13.0 1.76 13.2 1.24 13.4 1.02 13.6 0.89 13.8 0.78 14.0 0.70 14.3 0.61 14.6 0.54 15.0 0.49 15.5 0.44 16.0 0.40 16.5 0.35 17.0 0.32 17.5 0.31 18.0 0.29 19.0 0.24 20.0 0.21 22.0 0.18 26.0 0.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 SCS TR-55 Post -Development Unit Hydrograph (DA Post D) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Proposed Dry Retention Basin Routing Ivy Commercial Dry Retention BasinFlow printout INPUT: Basin: Ivy Commercial Dry Retention Basin 4 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 556.48 272.00 0.0 558.00 863.00 30.4 560.00 2106.00 137.0 561.00 2840.00 228.2 Start—Elevation(ft) 556.48 Vol.(cy) 0.00 4 Outlet Structures Outlet structure 0 Orifice name: Barrel area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 556.480 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Low -Flow Orifice area (sf) 0.087 diameter or depth (in) 4.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 556.480 multiple 3 discharge into riser Outlet structure 2 Orifice name: Mid -Flow Orifice area (sf) 0.049 diameter or depth (in) 3.000 width for rect. (in) 0.000 coefficient 0.500 invert (ft) 558.750 multiple 4 discharge into riser Page 1 Ivy Commercial Dry Retention Outlet structure 3 Weir name: Riser diameter (in) 24.000 side angle 0.000 coefficient 3.300 invert (ft) 559.670 multiple 1 discharge into riser transition at (ft) 0.608 orifice coef. 0.500 orifice area (sf) 3.142 4 Inflow Hydrographs Hydrograph 0 Curve name: 1-yr 24-hr. SCS Design Storm Curve time incr (minlhrs) 0.10 time limit (minlhrs) 30.00 file: 1 YEAR-0.02 hr intervals.txt volume (cy) 393.87 routed true time in hours true Hydrograph 1 Curve name: 2-yr 24-hr. SCS Design Storm Curve time incr (minlhrs) 0.10 time limit (minlhrs) 30.00 file: 2 YEAR-0.02 hr intervals.txt volume (cy) 509.93 routed true time in hours true Hydrograph 2 Curve name: 10-yr 24-hr. SCS Design Storm Curve time incr (minlhrs) 0.10 time limit (minlhrs) 30.00 file: 10 YEAR-0.02 hr intervals.txt volume (cy) 889.53 routed true time in hours true Hydrograph 3 Curve name: 100-yr 24-hr. SCS Design Storm Curve Page 2 Ivy Commercial Dry Retention time incr (minlhrs) 0.10 time limit (minlhrs) 30.00 file: 100 YEAR-0.02 hr intervals.txt volume (cy) 1620.80 routed true time in hours true OUTPUT: Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks: inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 1 Routing Summary of Peaks: inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 2 Routing Summary of Peaks inflow (cfs) discharge (cfs) water level (ft) storage (cy) Hydrograph 3 Routing Summary of Peaks: inflow (cfs) discharge (cfs) water level (ft) storage (cy) 1-yr 24-hr. SCS Design Storm Curve 2.670 at 12.40 (hrs) 1.509 at 12.60 (hrs) 558.711 at 12.60 (hrs) 57.946 2-yr 24-hr. SCS Design Storm Curve 3.490 at 12.40 (hrs) 2.095 at 12.60 (hrs) 559.170 at 12.60 (hrs) 81.408 10-yr 24-hr. SCS Design Storm Curve 6.040 at 12.40 (hrs) 4.760 at 12.60 (hrs) 559.886 at 12.60 (hrs) 128.261 100-yr 24-hr. SCS Design Storm Curve 11.020 at 12.40 (hrs) 9.125 at 12.50 (hrs) 560.542 at 12.50 (hrs) 183.060 Mon Jun 01 07:43:41 EDT 2020 Page 3