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Home My WebLink AboutWPO202000034 Calculations 2022-07-01 4 BELVEDERE PHASE 5 H&H Calculations BELVEDERE PHASE 5 Tax Map Parcel 62-16D July 1st, 2022 LOCATION: liEALTH Albemarle, Virginia S DEVELOPER: 0 DUSTIN E.GREENE New Belvedere, Inc A 610 West Rio Road Lic.No.55833 Charlottesville, Virginia 22901 '14 ' Tv I PREPARED BY: S(VONAL ENA() Dustin Greene, PE Roudabush, Gale &Associates 999 Second Street SE Charlottesville, VA 22902 INDEX Executive Summary 2 Drainage Area Summaries, Tc's and Calculations 3 VRRM Spreadsheet 4 Letter of Availability 5 Post-developed Hydrographs 6-9 Routed Dry Pond 10-13 BELVEDERE PHASE 5 Executive Summary: The purpose of this amendment is to show that the private storm sewer system for lots 245- 254 was not constructed in accordance with the approved plans. The backs of the townhouses and yards are no longer draining to the retention basin as shown on sheet 3 of VSMP amendment#3 of belvedere phase IIB (WPO201600071). The rears of these lots now drain to the fire road dry pond as shown on sheet A18.2 of this VSMP (WPO202000034) submittal. Changes to the outlet structure ensure that the regulated storms are below the approved, post-developed flows, thus satisfying water quantity requirements. Per conversation with county engineer 6/7/22 0.18 lbs/yr of nutrient credits will be used to offset the phosphorous removal that would have been generated from the drainage going to the retention pond. The original nutrient purchase of 9.68 lbs of phosphorous per year and the remaining 0.18 lbs do not exceed the 10 lbs/yr of phosphorous that would trigger onsite compliance strategies along with offsite requirements. BELVEDERE PHASE 5 PRE-DEVELOPED POA#2 AREA=2.68 AC CN = 65 Tc= 9.9min POST-DEVELOPED SITE OUTFALL#2 AREA= 2.74 AC CN =69 Tc= 9.9min UPDATED POST-DEVELOPED SITE OUTFALL#2 AREA= 3.04 AC MANAGED TURF =2.64 AC (CN 65) IMPERVIOUS = 0.40 AC (CN 98) CN =69 Tc= 9.9 min Project Name: BELVEDERE PHASE 5 CLEAR ALL data input cells Date: 6/9/2022 constant values BMP Design Specifications List: 2013 Draft Stds&Specs calculation cells final results Site Information Post-Development Project (Treatment Volume and Loads) 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 0.20 0.20 Impervious Cover(acres) 0.10 0.10 0.30 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 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 Post-Development Requirement for Site Area TP Load Reduction Required(Ib/yr) 0.18 Rivanna River Nutrient Credit Bank Certificate No.James-039 June 24, 2022 Dustin Greene, PE Roudabush, Gale &Associates, Inc dgreene(a,ro udabush.com Re: Purchaser: New Belvedere, Inc. Project Name: Belvedere Phase 5 —(WPO-2020-00034) 6th Order HUC: 020802040203 Nutrient Credits: .18 Dear Dustin, This letter is to confirm the availability to your project(referenced above) of authorized Nutrient Credits sufficient to meet the your above referenced estimated requirements of Nutrient Credits at our Rivanna River nutrient offset credit bank facility(the`Bank").The Bank has been registered with the Virginia Department of Environmental Quality (DEQ). These Nutrient Credits are generated and managed under the terms of the Reduction Implementation Plan for the Bank dated November 2017, which was authorized by (DEQ)on September 5, 2018. The Bank has been authorized to provide Nutrient Credits for use in the James River watershed. These credits are transferable to those entities regulated under DEQ's Storm Water Management program in accordance with VA Code 62.1-44.15:27. The sale price for .18 pounds of phosphorous is $2,700.00.This pricing is valid through July 30, 2022. Hotel Street C• .ttal, LLC, Bank Sponsor By Its M• .4 ger • Thomas • ►es Ross II 540-687 0 71 TJRos ei lawfirm.com Rivanna River Nutrient Offset Trading Bank,31 Garrett Street,Warrenton,Virginia 20186 6 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc.v2020 Tuesday,06/28/2022 Hyd. No. 65 Post Dev to POA#2 Hydrograph type = SCS Runoff Peak discharge = 2.686 cfs Storm frequency = 1 yrs Time to peak = 12.03 hrs Time interval = 2 min Hyd. volume = 7,743 cuft Drainage area = 3.040 ac Curve number = 69 Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 9.90 min Total precip. = 3.02 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 Post Dev to POA#2 Q (cfs) Hyd. No. 65 -- 1 Year Q (cfs) 3.00 3.00 2.00 2.00 1.00 1.00 0.00 -- ' \- 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Hyd No. 65 Time (hrs) 7 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc.v2020 Tuesday,06/28/2022 Hyd. No. 65 Post Dev to POA#2 Hydrograph type = SCS Runoff Peak discharge = 4.367 cfs Storm frequency = 2 yrs Time to peak = 12.03 hrs Time interval = 2 min Hyd. volume = 11,893 cuft Drainage area = 3.040 ac Curve number = 69 Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 9.90 min Total precip. = 3.65 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 Post Dev to POA#2 o (cfs) Hyd. No. 65 --2 Year Q (cfs) 5.00 5.00 4.00 4.00 3.00 3.00 2.00 2.00 1.00 1.00 0.00 — 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Hyd No. 65 Time (hrs) 8 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc.v2020 Tuesday,06/28/2022 Hyd. No. 65 Post Dev to POA#2 Hydrograph type = SCS Runoff Peak discharge = 10.19 cfs Storm frequency = 10 yrs Time to peak = 12.03 hrs Time interval = 2 min Hyd. volume = 26,667 cuft Drainage area = 3.040 ac Curve number = 69 Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 9.90 min Total precip. = 5.52 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 Post Dev to POA#2 Q (cfs) Hyd. No. 65-- 10 Year Q (cfs) 12.00 12.00 10.00 10.00 8.00 8.00 6.00 6.00 4.00 4.00 2.00 2.00 0.00 -- S. - 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Time (hrs) Hyd No. 65 9 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc v2020 Tuesday,06/28/2022 Hyd. No. 65 Post Dev to POA#2 Hydrograph type = SCS Runoff Peak discharge = 23.11 cfs Storm frequency = 100 yrs Time to peak = 12.00 hrs Time interval = 2 min Hyd. volume = 60,002 cuft Drainage area = 3.040 ac Curve number = 69 Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 9.90 min Total precip. = 9.07 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 Post Dev to POA#2 Q (cfs) Hyd. No. 65-- 100 Year Q (cfs) 24.00 24.00 20.00 20.00 16.00 16.00 12.00 12.00 8.00 8.00 4.00 4.00 0.00 — 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Hyd No. 65 Time (hrs) 10 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc.v2020 Tuesday,06/28/2022 Hyd. No. 66 AB Fire Road Basin Hydrograph type = Reservoir Peak discharge = 0.761 cfs Storm frequency = 1 yrs Time to peak = 12.27 hrs Time interval = 2 min Hyd. volume = 7,735 cuft Inflow hyd. No. = 65 - Post Dev to POA#2 Max. Elevation = 427.40 ft Reservoir name = Fire road basin AB Max. Storage = 1,937 cuft Storage Indication method used. AB Fire Road Basin Q (cfs) Hyd. No. 66-- 1 Year Q (cfs) 3.00 3.00 2.00 2.00 1.00 1.00 0.00 - `- 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Time (hrs) Hyd No. 66 Hyd No. 65 Total storage used = 1,937 cuft • Pond Report 11 Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc.v2020 Tuesday,06/28/2022 Pond No. 19 - Fire road basin AB Pond Data Contours-User-defined contour areas.Average end area method used for volume calculation.Begining Elevation=426.50 ft Stage/Storage Table Stage(ft) Elevation(ft) Contour area(sqft) Incr.Storage(cuft) Total storage(cuft) 0.00 426.50 120 0 0 0 50 427.00 2,607 682 682 1.50 428.00 3,711 3,159 3,841 3.50 430.00 5,084 8,795 12,636 5 50 432 00 6,559 11,643 24,279 7.50 434 00 8,275 14,834 39,113 9 50 436.00 10,296 18,571 57,684 11 50 438.00 12,656 22,952 80,636 13.50 440.00 15,799 28,455 109,091 Culvert/Orifice Structures Weir Structures [A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise(in) = 15.00 6 00 0 00 0 00 Crest Len(ft) = 12.57 0.00 0 00 0.00 Span(in) = 15.00 6.00 0 00 0.00 Crest El.(ft) = 432.50 0.00 0.00 0.00 No.Barrels = 1 1 0 0 Weir Coeff. = 3.33 3.33 3 33 3 33 Invert El.(ft) = 426.10 426.50 0.00 0.00 Weir Type = 1 --- --- --- Length(ft) = 186.47 0.70 0.00 0.00 Multi-Stage = Yes No No No Slope(%) = 11.79 0.00 0.00 n/a N-Value = .012 013 .013 n/a Orifice Coeff. = 0.60 0.60 0.60 0.60 Exfil.(in/hr) = 0.000(by Wet area) Multi-Stage = n/a Yes No No TW Elev.(ft) = 0.00 Note.Culvert/Onfice outflows are analyzed under inlet Qc)and outlet(oc)control. Weir risers checked for orifice conditions(ic)and submergence(s) Stage(ft) Stage/ Discharge Elev(ft) 14.00 440 50 12.00 438.50 10.00 436.50 8.00 434.50 6.00 432.50 4.00 430.50 2.00 428 50 0.00 426.50 0.00 2 00 4 00 6.00 8.00 10 00 12.00 14.00 16.00 18.00 20.00 22.00 Total Q Discharge(cfs) 12 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk,Inc v2020 Tuesday,06/28/2022 Hyd. No. 66 AB Fire Road Basin Hydrograph type = Reservoir Peak discharge = 1.017 cfs Storm frequency = 2 yrs Time to peak = 12.27 hrs Time interval = 2 min Hyd. volume = 11,884 cuft Inflow hyd. No. = 65 - Post Dev to POA#2 Max. Elevation = 427.91 ft Reservoir name = Fire road basin AB Max. Storage = 3,552 cuft Storage Indication method used. AB Fire Road Basin 0 (cfs) Hyd. No. 66--2 Year 0 (cfs) 5.00 5.00 4.00 4.00 3.00 3.00 2.00 2.00 1.00 1.00 0.00 — N.------- 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Time (hrs) Hyd No. 66 Hyd No. 65 Total storage used = 3,552 cuft 13 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk, Inc.v2020 Tuesday,06/28/2022 Hyd. No. 66 AB Fire Road Basin Hydrograph type = Reservoir Peak discharge = 1.550 cfs Storm frequency = 10 yrs Time to peak = 12.43 hrs Time interval = 2 min Hyd. volume = 26,659 cuft Inflow hyd. No. = 65 - Post Dev to POA#2 Max. Elevation = 429.44 ft Reservoir name = Fire road basin AB Max. Storage = 10,162 cuft Storage Indication method used. AB Fire Road Basin Q (cfs) Hyd. No. 66 -- 10 Year Q (cfs) 12.00 12.00 10.00 10.00 8.00 - 8.00 6.00 6.00 4.00 4.00 2.00 2.00 0.00 - 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Time (hrs) Hyd No. 66 Hyd No. 65 Total storage used = 10,162 cuft 14 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk®Civil 3D®2019 by Autodesk,Inc v2020 Tuesday,06/28/2022 Hyd. No. 66 AB Fire Road Basin Hydrograph type = Reservoir Peak discharge = 2.223 cfs Storm frequency = 100 yrs Time to peak = 12.63 hrs Time interval = 2 min Hyd. volume = 59,993 cult Inflow hyd. No. = 65 - Post Dev to POA#2 Max. Elevation = 432.37 ft Reservoir name = Fire road basin AB Max. Storage = 27,047 cult Storage Indication method used AB Fire Road Basin Q (cfs) Hyd. No. 66 -- 100 Year Q (cfs) 24.00 24.00 20.00 20.00 16.00 16.00 • 12.00 12.00 8.00 8.00 4.00 4.00 0.00 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Time (hrs) Hyd No. 66 Hyd No. 65 Total storage used = 27,047 cuft