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Home My WebLink AboutWPO201900039 Calculations 2022-01-134bKteverde 1/13/20" Seth Roderick, PE Monteverde Engineering & Design Studio 250 E Elizabeth St, Suite 114 Harrisonburg, VA 22801 Albemarle County Community Development Department Attn: John Anderson 401 McIntire Road North Wing Charlottesville, VA 22902 RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039 — AS-BUILTS Mr. Anderson, This letter and accompanying calculations are being in order to properly certify that discrepancies found between the referenced as -built survey and the original design file are satisfactory in relation to the functionality of associated stormwater management practices. Discrepancies noted and comparative testing results are described as follows: A. POND 1 (top of hill, POA A) Pond 1 was found to be graded bigger than originally prescribed on the plans, with a drainage area that included more impervious area than assumed in the original design, but less acreage overall. Portions of the original DA for Pond 1 were determined to drain instead towards Pond 2 / POA B, with another portion draining offsite as uncontrolled sheet flow to neither pond (retains overland sheet flow characteristics until landing at bottom of hill in existing farm pond). To account for these discrepancies, the additional area draining to POA B was added to the Pond 2 analysis (described below), while the POA A drainage was broken into uncontrolled and controlled subgroups. The 0.29 acres draining uncontrolled was determined to have a CN of 80 and a TC of 6 min. As stormwater travel distance is minimal and evenly spread across the perimeter of the area, it can be viewed as sheet flow. As such, no further efforts are needed in examination of channel protection requirements, while the area's hydrograph will be added to the analysis for total area's 10-Yr flood protection analysis. Note that due to differing times of Hillcrest Vineyard Tasting & Venue WPO 2019-00039 — AS-BUILTS January 13, 2022 concentration, the vast majority of the uncontrolled floes peak will have come and gone well before the pond's peak, so the uncontrolled aspect has little impact on total conditions. The remaining area draining to Pond 1, originally analyzed at 5.75 acres, was found to include 5.21 acres with a CN of 87 and a TC of 25.1 min. As the primary orifice to Pond 1 was drilled as directed after further analysis (6" orifice added at elevation 1072.2), and the riser top was cut to an elevation just above the 10-yr max elevation, the pond was found to handle the contributing drainage exceedingly well. Post -development runoff rates and pond analysis for as -built conditions are summarized below, while supporting calculations / hyrdrographs are attached. 10-Yr Pre -Development: 4.39 CFS 10-Yr Post -Development, Uncontrolled 1.70 CFS 10-Yr Post -Development, Pond (Actual) 2.38 CFS 10-Yr Post -Development, Total Combined 3.06 CFS 100-yr Elev = 1078.70 Top of Embankment = 1081.00 (2.30' of freeboard) B. LEVEL SPREADER The level spreader was found to be constructed at an approximate length of 69 LF, which is in excess of the originally prescribed 56 LF. As the extra length will provide a greater area to distribute the contributing storm event, which is now reduced with the 6" orifice, this discrepancy is deemed beneficial to the downstream conditions. No further analysis is required. C. POND 2 (bottom of hill, POA B) Similarly to Pond 1, Pond 2 was found to be constructed larger than prescribed on the plans, but also with a slightly larger contributing watershed (including some area originally designed for Pond 1, with other assumed to drain offsite to the north; 0.64 ac total increase in area toward Pond 2). Through analysis of the pond, it was found that the allowable discharge rate per energy balance dropped slightly due to an increase in post -development RV associated with the larger drainage area, but the additional volume in the pond slows the analyzed release rate sufficiently to meet requirements. No further modifications to the outlet riser or orifices are deemed necessary. odowlh, Page 2 of 3 FhHcrest Vineyard Tasting & Venue WPO 2019-00039 - AS-BUILTS January 13, 2022 It was also noticed that the emergency spillway may not be properly functional, due to a low point existing elsewhere on the embankment. As more than 2.0' of freeboard was calculated to exist during the 100-yr event, however, this design still meets minimum standards for such facilities (i.e., no emergency outlet is required). It is recommended, but not required, that the embankment be modified to properly direct overflow directly to the spillway (note that the Owner has agreed to remedy this, but no further as -built verification is deeined necessary due to minimum standards already having been met). Post -development runoff rates and pond analysis for as -built conditions are summarized below, while supporting calculations / hyrdrographs are attached. Qa = 0.8 (Q-pre.site x RV-pre.site)/ RV-post.site + Offsite bypass Qa = 0.8 (0.515 x 4046) / 10,873 + (3.858 cfs) Qa = 4.01 cfs 1-Yr Allowable, Pond 4.01 CFS 1-Yr Post -Development, Pond 3.79 CFS 10-Yr Pre -Development 32.01 CFS 10-Yr Post -Development, Pond 28.59 CFS 100-Yr Elev = 1002.13 Top of Embankment = 1004.30 (2.27' of freeboard) In sum, while the facilities were not constructed to the original spec, they were analyzed to be more than sufficient to accommodate the anticipated storm events as required by code. I am comfortable certifying such with my seal, as stamped below, given the survey data presented. Any questions to this matter, please feel free to let me know. Si acerely, Seth Roderick, PE Managing Partner Monteverde Engineering & Design Studio �fr v SETH . R DERICK 9 � Lic. o. 041454W 0;e� Jan 13, 2022 $� �Ss'ONAL ECG~ Page 3 of 3 Pond Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 01 / 13 / 2022 Pond No. 1 - Detention Basin (As -Built) Pond Data Contour; -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 1071.00 ft Stage / Storage Table Stage (ft) Elevation (ft) Contour area (sgft) Incr. Storage (cult) Total storage (cult) 0.00 1071.00 200 0 0 1.00 1072.00 4,204 1,773 1,773 2.00 1073.00 5,540 4,856 6,630 3.00 1074.00 6,226 5,879 12,509 4.00 1075.00 6,942 6,580 19,089 5.00 1076.00 7,710 7,322 26,411 6.00 1077.00 8,432 8,068 34,478 7.00 1078.00 9,179 8,802 43,280 8.00 1079.00 9,950 9,561 52,841 9.00 1080.00 10,765 10,354 63,195 10.00 11,607 11,182 74,377 Culvert / Orifice Structures Weir Structures [A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise (in) = 18.00 2.00 6.00 0.00 Crest Len (ft) = 9.42 Inactive 29.00 0.00 Span (in) = 18.00 2.00 6.00 0.00 Crest El. (ft) = 1077.70 0.00 0.00 No. Barrels = 1 1 1 0 Weir Coeff. = 2.60 3.33 3.33 3.33 Invert El. (ft) = 1068.90 1071.00 4.072.20 0.00 Weir Type = 1 Rect Broad - Length (ft) = 75.00 0.00 0.00 0.00 Multi -Stage = Yes Yes No No Slope (%) = 3.00 0.00 0.00 n/a N-Value = .012 .012 .013 n/a Orifice Coeff. = 0.60 0.60 0.60 0.60 Exfil.(in/hr) = 0.000 (by Contour) Multi -Stage = n/a Yes Yes No TW Elev. (ft) = 0.00 Stage (ft) 10.00 8.00 6.00 4.00 2.00 000 Note:Culvert/Orifice outflows are analyzed under lnlet(Ic) and oudet(oc) wnirol. Weir users checked for orifice oonditions(ic) and submergence(a). Stage / Discharge Elev (ft) 1081.00 1079.00 1077.00 1075.00 1073.00 107100 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 • Total 0 Discharge (cfs) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 313® by Autodesk, Inc. v2020 Hyd. No. 7 Rc: -t Dev DA to Det Basin -"'I (As -Built) Hydrograph type = SCS Runoff Storm frequency = 10 yrs Time interval = 1 min Drainage area = 5.210 ac Basin Slope = 0.0 % Tc method = TR55 Total precip. = 5.38 in Storm duration = 24 hrs Composite (Area/CN) = [(3.630 x 98) + (1.580 x 61)1 / 5.210 Q (Cfs) 21.00 18.00 15.00 12.00 MR! MM 3.00 M Thursday, 01/13/2022 Peak discharge = 20.52 cfs Time to peak = 12.13 hrs Hyd. volume = 74,258 cuft Curve number = ;W' Hydraulic length = 991 ft Time of conc. (Tc) = 25.1? i" 1in Distribution = Type 11 Shape factor = 484 Post Dev DA to Det Basin #1 Hyd. No. 7 -- 10 Year Q (cfs) 21.00 U, 15.00 12.00 o f, 3.00 tnn u [ 4 6 8 10 12 14 16 18 20 22 24 26 Hyd No. 7 Time (hrs) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 01 f 13 12022 Hyd. No. 8 Pet Basin #1 Routed (As -Built) Hydrograph type = Reservoir Peak discharge = 2.378 cis Storm frequency = 10 yrs Time to peak = 12.83 hrs Time interval = 1 min Hyd. volume = 74,246 cuft Inflow hyd. No. = 7 - Post Dev DA to Det Basin Max. Elevation = 1077.45 ft Reservoir name = Detention Basin Max. Storage = 38,397 cuft Storage Indication method used. Det Basin #1 Routed Q (cfs) Hyd. No. 8 -- 10 Year Q (cfs) 21.00 21.00 18.00 18.00 15.00 15.00 12.00 12.00 9.00 9.00 6.00 6.00 3.00 3.00 0.00 - 0.00 0 4 8 12 16 20 24 28 32 36 Time (hrs) Hyd No. 8 — Hyd No. 7 Total storage used = 38,397 cult Hydrograph Report HydraBow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 15 A5-Built Uncontrnlied Hydrograph type = SCS Runoff Peak discharge Storm frequency = 10 yrs Time to peak Time interval = 1 min Hyd. volume Drainage area = 0.290 ac Curve number Basin Slope = 0.0 % Hydraulic length Tc method = User Time of conc. (Tc) Total precip. = 5.38 in Distribution Storm duration = 24 hrs Shape factor Composite (Area/CN) = ((0.150 x 98) + (0.140 x 61)] / 0.290 1.00 Thursday, 01 / 1312022 _ 1.702 cfs = 11.95 hrs = 3,503 cuft = 80' = 0 ft = 6.00 min = Type II = 484 As -Built Uncontrolled Hyd. No. 15 -- 10 Year 2 4 6 8 10 12 14 16 18 20 22 Hyd No. 15 Q (cfs) 2.00 1.00 0.00 24 Time (hrs) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 17 Uncontrolled + Pond 1 Hydrograph type = Combine Storm frequency = ,IO—ga Time interval = 1 min Inflow hyds. = 8, 15 Thursday, 01/13/2022 Peak discharge = 3.062 cfs Time to peak = 11.97 hrs Hyd. volume = 77,750 cult Contrib. drain. area = 0.290 ac Uncontrolled + Pond 1 Q (Cfs) Hyd. No. 17 -- 10 Year Q (Cfs) 4.00 4.00 3.00 3.00 2.00 2.00 1.00 1.00 1 0.00 0.00 0 4 8 12 16 20 24 28 32 36 Time (hrs) — Hyd No. 17 —Hyd No. 8 —Hyd No. 15 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 8 Det Basin #1 Routed Hydrograph type = Reservoir Peak discharge Storm frequency = .100 yrs Time to peak Time interval = 1 min Hyd. volume Inflow hyd. No. = 7 - Post Dev DA to Det Basin Wax. Elevation Reservoir name = Detention Basin Max. Storage Storage Indication method used. Q (cfs) 40.00 30.00 20.00 10.00 Det Basin #1 Routed Hyd. No. 8 -- 100 Year Thursday, 01 / 13 / 2022 = 24.45 cis = 12.30 hrs = 134,696 cuft = E1078.70 ft = 49,969 cuft 0.00 ' 0 3 6 9 12 15 18 21 24 — Hyd No. 8 — Hyd No. 7 Total storage used = 49,969 cuft Q (cfs) 40.00 30.00 20.00 10.00 0.00 27 Time (hrs) Pond Report a Hydrallow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Friday, 12 13 / 2021 Pond No. 5 - (Pond 2..s As.buNt Pond Data Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 990.00 ft Stage / Storage Table Stage (it) Elevation (ft) Contour area (sqft) Incr. Storage (tuft) Total storage (cult) 0.00 990.00 25 0 0 1.00 991.00 86 52 52 2.00 992.00 310 186 239 3.00 993.00 1,526 841 1,080 4.00 994.00 3,711 2,539 3,619 5.00 995.00 5,671 4,656 8,275 6.00 996.00 7,550 6,587 14,862 7.00 997.00 9,349 8,433 23,295 8.00 998.00 11,230 10,274 33,569 9.00 999.00 12,990 12,098 45,667 10.00 1000.00 14,760 13,864 59,531 11.00 1001.00 16,628 15,683 75,214 12.00 1002.00 18,676 17,640 92,855 13.00 1003.00 20,918 19,784 112,639 14.00 1004.00 23,304 22,098 134,737 Culvert I Orifice Structures Weir Structures [A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise (in) = 24.00 0.00 0.00 Crest Len (ft) = 12.56 0.00 0.00 0.00 Span (in) = 24.00 i♦ 0.00 0.00 Crest El. (it) = 4000,00 0.00 0.00 0.00 No. Barrels = 1 / 0 0 Weir Coeff. = 3.33 3.33 3.33 3.33 Invert El. (ft) = 990.00 0.00 0.00 Weir Type = 1 -- - - Length (ft) = 112.00 0.00 0.00 0.00 Multi -Stage = Yes No No No Slope 1%) = 7.90 0.00 0.00 n/a - N-value = .012 .013 .013 n/a Orifice Coeff. = 0.60 0.60 0.60 0.60 Ex01.(in/hr) = 0.000 (by Wet area) Multi -Stage = n/a Yes No No TW Elev. (ft) = 0.00 Note: CuNerlOdfice outflows are analyzed under inlet(ic) and outlet(oc) control. Weir risers checked for orifice contll6ons(ic) and subrnaWnce(a). Stage / Storage / Discharge Table Stage Storage Elevation Clv A Clv B Clv C PrlRsr Wr A Wr B Wr C Wr D Ex01 User Total ft tuft ft cis cfs efs cis cis cis cfs cis cfs eft efs 0.00 0 990.00 0.00 0.00 -- -- 0.00 - - -- -- -- 0.000 1.00 52 991.00 0.60 is 0.57 is -- -- 0.00 - -- --- --- -- 0.573 2.00 239 992.00 3.39 is 3.30 is - - 0.00 -- - - --- - 3.305 3.00 1,080 993.00 4.72 is 4.71 is -- - 0.00 -- -- - - -- 4.713 4.00 3,619 994.00 5.78 is 5.78 is -- -- 0.00 -- -- - - -- 5.782 5.00 8,275 995.00 6.69 is 6.62 is -- -- 0.00 -- - - -- - 6.616 6.00 14,862 996.00 7.36 is 7.36 is - -- 0.00 - -- -- -- - 7.363 7.00 23,295 997.00 8.12 is 8.05 is - - 0.00 -- -- -- - - 8.050 8.00 33,569 998.00 8.76 is 8.68 is -- - 0.00 -- - -- -- -• 8.684 9.00 45,667 999.00 9.38 is 9.28 is - -- 0.00 -- - -- -- - 9.276 10.00 59,531 1000.00 9.84 is 9.84 is -- - 0.00 --- -- -- -• - 9.842 11.00 75,214 1001.00 45.26 is 3.44 is - - 41.82 -- -- -- -- - 45.26 12.00 92,855 1002.00 49.86 is 1.23 is - -- 48.62 s -- - - -- -- 49.85 13.00 112,639 1003.00 52.29 is 0.73 is - -- 51.52 s - -- - - -- 52.25 14.00 134,737 1004.00 54.48 is 0.51 is - -- 53.96 s - -- - - -- 54.47 Hydrograph Report Hydraflow Hydrogrephs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Friday, 12 / 3 / 2021 Hyd. No. 10 Post Dev Project Area Hydrograph type = SCS Runoff Peak discharge = 2.161 cfs Storm frequency = 1 yrs Time to peak = 736 min Time interval = 1 min Hyd. volume = 10,873 cuft Drainage area = (3,790 ag (prev 3.15) Curve number = 72* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 35.50 min Total precip. = 2.97 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484 Composite (Area/CN) = [(3.150 x 71) + (0.260 x 98) + (0.380 x 61)1 / 3.790 Q (cfs) Post Dev Project Area Hyd. No. 10 -- 1 Year 3.00 2.00 1.00 WUMP Q (Cfs) 3.00 2.00 1.00 IVW 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 10 Time (min) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Aulodesk, Inc. v2020 Friday, 1213 12021 Hyd. No. 20 pond 2 as -built Hydrograph type = Reservoir Peak discharge = 3.791 cis (<4.06 CFS) Storm frequency = ,1 yrs Time to peak = 759 min Time interval = 1 min Hyd. volume = 38,689 cuft Inflow hyd. No. = 13 - Total Drainage to B Max. Elevation = 994.10 ft Reservoir name = Pond 2 - As -built Max. Storage = 3,539 cult Storage Indication method used. Q (cfs) 6.00 5.00 4.00 3.00 2.00 1.00 dW pond 2 as -built Hyd. No. 20 -- 1 Year Q (cfs) 6.00 5.00 4.00 3.00 2.00 1.00 M 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Time (min) — Hyd No. 20 --^ Hyd No. 13 Total storage used = 3,539 cult Hydrograph Report HydraOow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 10 ;pGicf I iPPw PrniPrf Area Hydrograph type = SCS Runoff Storm frequency = 10 yrs Time interval = 1 min Drainage area = ,3 79 0 a (prey 3.15) Basin Slope = 0.0 % Tc method = TR55 Total precip. = 5.38 in Storm duration = 24 hrs Composite (Area/CN) = [(3.150 x 71) + (0.260 x 98) + (0.380 x 61)] / 3.790 Io 4.00 DIO r Hyd No. 10 Peak discharge Time to peak Hyd. volume Curve number Hydraulic length Time of conc. (Tc) Distribution Shape factor Post Dev Project Area Hyd. No. 10 -- 10 Year Friday, 12 / 312021 = 7.665 cfs = 735 min = 34,318 cuft = 72" = Oft = 35.50 min = Type II = 484 Q (Cfs) 8.00 . 11 4.00 em .TiTin 360 480 600 720 840 960 1080 1200 1320 1440 1560 Time (min) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Friday, 12 13 / 2021 Hyd. No. 20 pond 2 as -built Hydrograph type = Reservoir Peak discharge = 28.59 cfs (<32.01 CFS) Storm frequency = 10 yrs Time to peak = 746 min Time interval = 1 min Hyd. volume = 164,583 cult Inflow hyd. No. = 13 - Total Drainage to B Max. Elevation = 997.71 ft Reservoir name = Pond 2 - As -built Max. Storage = 30,012 cuft Storage Indication method used pond 2 as -built Q (cfs) Hyd. No. 20 -- 10 Year Q (cfs) 35.00 30.00 25.00 20.00 15.00 10.00 5.00 000 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Time (min) — Hyd No. 20 — Hyd No. 13 Total storage used = 30,012 cult Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Hyd. No. 10 ,PGse nev Project Area Hydrograph type = SCS Runoff Storm frequency = 100 yrs Time interval = 1 min Drainage area = 3.790 ac (prev 3.15) Basin Slope = 0.0 % Tc method = TR55 Total precip. = 8.69 in Storm duration = 24 hrs Friday, 12/3/2021 Peak discharge = 16.51 cfs Time to peak = 734 min Hyd. volume = 72,983 cuft Curve number = 72' Hydraulic length = 0 ft Time of cone. (Tc) = 35.50 min Distribution = Type II Shape factor = 484 . Composite (Area/I _ [(3.150 x 71) + (0.260 x 98) + (0.380 x 61)] / 3.790 Post Dev Project Area Q (cfs) Hyd. No. 10 -- 100 Year Q (cfs) 18.00 18.00 15.00 15.00 12.00 12.00 9.00 i 9.00 6.00 6.00 3.00 3.00 0.00 000 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 10 Time (min) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Friday, 12 / 3 / 2021 Hyd. No. 20 ,pond 2 as -built Hydrograph type = Reservoir Peak discharge = 45.51 cfs Storm frequency = 100 yrs Time to peak = 757 min Time interval = 1 min Hyd. volume = 399,715 cuft Inflow hyd. No. = 13 - Total Drainage to B Max. Elevation = [1002.13 it Reservoir name = Pond 2 - As -built Max. Storage = 94,889 cult Storage Indication method used. pond 2 as -built Q (cfs) Hyd. No. 20 -- 100 Year Q (cfs) 90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 000 90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Time (min) — Hyd No. 20 -- Hyd No. 13 I Total storage used = 94,889 cult