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Home My WebLink AboutWPO201900039 Certified Engineer's Report 2022-01-130*0 4oltteverde 1/13/2022 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 areas hydrograph will be added to the analysis for total areas 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 flows 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. ' h, Page 2 of 3 Hillcrest 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 deemed 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 cerely, Seth Roderick, PE Managing Partner Monteverde Engineering & Design Studio 0 h, Page 3 of 3 H GETH . R DERICK 9 d Lic. o. 04145404 O� Jqn 13, 2022 �� 10 AL ��~ Pond Report Hydraflow Hydrographs Extension for Autodesk® Civil 3138 by Autodesk, Inc. v2020 Thursday, 01 113 / 2022 Pond No. 1 - Detention Basin (As -Built) Pond Data Contours -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 (cuft) 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 1081.00 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 M 0.00 Crest Len (ft) = 9.42 Inactive 29.00 0.00 Span (in) = 18.00 2.00 M 0.00 Crest El. (ft) _ - 0.00 1079.80 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 I- 0.00 Weir Type = 1 Rect Broad -- Length (ft) = 75.00 0.00 0.00 0.00 Multistage = Yes Yes No No Slope I%) = 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 EAL(inlir" = 0.000 (by Contour) Multistage = n/a Yes Yes No TW Elev. (ft) = 0.00 Stage (ft) 10.00 6.00 4.00 2.00 0.00 ' 0.0 20.0 Total 0 Note: CulwrtfOnfice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for onfice conditions (ic) and submergence (s). 40.0 60.0 Stage / Discharge 80.0 100.0 120.0 140.0 Elev (ft) 1081.00 1079.00 1077.00 1075.00 1073.00 ' 1071.00 160.0 Discharge (cis) Hydrograph Report HydraBovi Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 7 Post Dev DA to Det Basin #1(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)] / 5.210 Q (cfs) 21.00 111IM1111 15.00 12.00 • rr JIM 3.00 0.00 0 2 4 Hyd No. 7 6 8 Thursday, 01 / 13 / 2022 Peak discharge = 20.52 cfs Time to peak = 12.13 hrs Hyd. volume = 74,258 cuft Curve number = 187- Hydraulic length = 991 ft Time of conc. (Tc) = 25.10 min Distribution = Type II Shape factor = 484 Post Dev DA to Det Basin #1 Hyd. No. 7 -- 10 Year Q (cfs) 21.00 18.00 15.00 12.00 • rr lllll. rr 3.00 0.00 10 12 14 16 18 20 22 24 26 Time (hrs) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 8 Det Basin #1 Rot (As -Built) Hydrograph type = Reservoir Peak discharge Storm frequency = M0 yrs Time to peak Time interval = 1 min Hyd. volume Inflow hyd. No. = 7 - Post Dev DA to Det Basin Max. Elevation Reservoir name = Detention Basin Max. Storage Storage Indication method used. Det Basin #1 Routed Thursday, 01/13/2022 = 2.378 cfs = 12.83 hrs = 74,246 tuft = 1077.45 ft = 38,397 cuft 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 Hydraflovi Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 15 As -Built Uncontrollef Hydrograph type = SCS Runoff Storm frequency = T0-779 Time interval = 1 min Drainage area = 0.290 ac Basin Slope = 0.0 % Tc method = User Total precip. = 5.38 in Storm duration = 24 hrs Composite (Area/CN) _ [(0.150 x 98) + (0.140 x 61)] / 0.290 Q (Cfs) 2.00 1.00 Peak discharge Time to peak Hyd. volume Curve number Hydraulic length Time of conc. (Tc) Distribution Shape factor As -Built Uncontrolled Hyd. No. 15 -- 10 Year Thursday, 01/13/2022 = 11.95 hrs = 3,503 cult = 80" = Oft = 6.00 min = Type II = 484 2 4 6 8 10 12 14 16 18 20 22 Hyd No. 15 Q (ofs) 2.00 1.00 � 0.00 24 Time (hrs) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 01 / 13 / 2022 Hyd. No. 17 Uncontrolled + l� Hydrograph type = Combine Peak discharge = 3.062 cfs Storm frequency = — Time to peak = 11.97 hrs Time interval = 1 min Hyd. volume = 77,750 cuft Inflow hyds. = 8, 15 Contrib. drain. area = 0.290 ac 4 (cfs) 4.00 S 11 2.00 1.00 Uncontrolled + Pond 1 Hyd. No. 17 -- 10 Year 0.00 0 4 8 12 16 20 24 Hyd No. 17 — Hyd No. 8 — Hyd No. 15 28 32 Q (cfs) 4.00 3.00 2.00 1.00 111111106- 0.00 36 Time (hrs) Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 01 / 13 / 2022 Hyd. No. 8 Det Basin #1 Route( Hydrograph type = Reservoir Peak discharge = 24.45 cfs Storm frequency = 100 yrs Time to peak = 12.30 hrs Time interval = 1 min Hyd. volume = 134,696 cuft Inflow hyd. No. = 7 - Post Dev DA to Det Basin Max. Elevation = -ft Reservoir name = Detention Basin Max. Storage = 49,969 cuft Storage Indication method used Q (cfs) 40.00 30.00 20.00 10.00 0.00 0 3 — Hyd No. 8 Det Basin #1 Routed Hyd. No. 8 -- 100 Year 6 9 12 15 18 21 24 Hyd No. 7 ® Total storage used = 49,969 cult Q (cfs) 40.00 30.00 20.00 10.00 WN-i- 0.00 27 Time (hrs) Pond Report Hydraflow Hydrographs Extension for Autodesk® Civil 3DO by Autodesk, Inc. v2020 Friday, 12 13 12021 Pond No. 5 - - Pond Data Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 990.00 ft Stage / Storage Table Stage (ft) Elevation (ft) Contour area (sgft) Incr. Storage (cult) Total storage (cuft) 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 / Orifice Structures Weir Structures [A] [B] [C] [PrtRsr] [A] [B] [C] [D] Rise (in) = 24.00 8.00 0.00 0.00 Crest Len (ft) = 12.56 0.00 0.00 0.00 Span (in) = 24.00 8.00 0.00 0.00 Crest EI. (ft) _ - 0.00 0.00 0.00 No. Barrels = 1 2 0 0 Weir Coeff. = 3.33 3.33 3.33 3.33 Invert El. (ft) = 990.00 990.7.Q 0.00 0.00 Weir Type = 1 -- -- -- Length (ft) = 112.00 0.00 0.00 0.00 Multi -Stage = Yes No No No Slope I%) = 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 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 (ic) and outlet (oc) control. Weir risers checked for onfice conditions (ic) and submergence (s). Stage I Storage I Discharge Table Stage Storage Elevation CIvA CIvB CIvC PrtRsr WrA WrB WrC WrD Exfil User Total It cuft It cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs 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 Hydraflovi Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 10 Post Dev Project Area Hydrograph type = SCS Runoff Storm frequency = 1 yrs Time interval = 1 min Drainage area = 3.790 ac (prev 3.15) Basin Slope = 0.0 % Tc method = TR55 Total precip. = 2.97 in Storm duration = 24 hrs * Composite (Area/CN) = [(3.150 x 71) + (0.260 x 98) + (0.380 x 61)] / 3.790 Q (cfs) 3.00 2.00 1.00 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 -- 1 Year 120 240 360 480 600 720 840 960 Hyd No. 10 Friday, 12 / 3 / 2021 = 2.161 cfs = 736 min = 10,873 cult = 72* = Oft = 35.50 min = Type II = 484 Q (cfs) 3.00 2.00 1.00 0.00 1080 1200 1320 1440 1560 Time (min) Hydrograph Report Hydraflm Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 20 pond 2 as -built Hydrograph type = Reservoir Peak discharge Storm frequency = 1 yrs Time to peak Time interval = 1 min Hyd. volume Inflow hyd. No. = 13 - Total Drainage to B Max. Elevation Reservoir name = Pond 2 - As -built Max. Storage Storage Indication method used Q (cfs) 6.00 5.00 4.00 S 11 r 11 1.00 pond 2 as -built Hyd. No. 20 -- 1 Year Friday, 12 / 3 / 2021 = 3.791 (<4.06 CFS) = 759 min = 38,689 cuft = 994.1Oft = 3,539 cuft Q (cfs) 6.00 5.00 4.00 3.00 2.00 1.00 I I I I I I I I I 1 0.00 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 20 —Hyd No. 13 ®Total storage used = 3,539 cuff Time (min) Hydrograph Report Hydraflovi Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 10 Post Dev Project Area Hydrograph type = SCS Runoff Storm frequency = 10 yrs Time interval = 1 min Drainage area = 3.790 ac (prev 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 Q (Cfs) 8.00 . M 4.00 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 120 240 360 480 600 720 840 960 Hyd No. 10 Friday, 12 / 3 / 2021 = 7.665 cfs = 735 min = 34,318 cult = 72* = Oft = 35.50 min = Type II = 484 Q (cfs) 8.00 lllll.1( 4.00 2.00 0.00 1080 1200 1320 1440 1560 Time (min) Hydrograph Report Hydraflm Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 20 pond 2 as -built Hydrograph type = Reservoir Peak discharge Storm frequency = 10 yrs Time to peak Time interval = 1 min Hyd. volume Inflow hyd. No. = 13 - Total Drainage to B Max. Elevation Reservoir name = Pond 2 - As -built Max. Storage Storage Indication method used Q (cfs) 35.00 30.00 25.00 15.00 10.00 5.00 pond 2 as -built Hyd. No. 20 -- 10 Year Friday, 12 / 3 / 2021 = 28.59 Cfsl (<32.01 CFS) = 746 min = 164,583 cuft = 997.71 ft = 30,012 tuft Q (Cfs) 35.00 30.00 25.00 20.00 15.00 10.00 5.00 I I i i i, I I I I I 1 0.00 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Time (min) Hyd No. 20 —Hyd No. 13 ®Total storage used = 30,012 cult Hydrograph Report Hydraflovi Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 10 Post Dev 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 * Composite (Area/CN) = [(3.150 x 71) + (0.260 x 98) + (0.380 x 61)] / 3.790 Q (cfs 18.00 15.00 12.00 M . �� 3.00 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 -- 100 Year 0.00 - 0 Friday, 12 / 3 / 2021 = 16.51 cfs = 734 min = 72,983 cult = 72* = Oft = 35.50 min = Type II = 484 Q (cfs) 18.00 15.00 12.00 M 3.00 rasa 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Hyd No. 10 Time (min) Hydrograph Report Hydraflm Hydrographs Extension for Autodesk® Civil 3136 by Autodesk, Inc. v2020 Hyd. No. 20 pond 2 as -built Hydrograph type = Reservoir Storm frequency = 100 yrs Time interval = 1 min Inflow hyd. No. = 13 - Total Drainage to B Reservoir name = Pond 2 - As -built Storage Indication method used. Peak discharge Time to peak Hyd. volume Max. Elevation Max. Storage Friday, 12 / 3 / 2021 = 45.51 cfs = 757 min = 399,715 cult = 94,889 tuft pond 2 as -built Q (cfs) Q (cfs) Hyd. No. 20 -- 100 Year 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 10.00 000 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 = 94,889 cult