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Home My WebLink AboutFDP202100014 Certified Engineer's Report 2022-03-04COLLINS 200 GARRETT ST, SUITE K CHARLOTTESVILLE VA 22902 MEMORANDUM TO: Albemarle County FROM: Scott Collins— Collins Engineering SUBJECT: Wintergreen Farm —Aerial Sanitary Sewer Crossing DATE: April 18, 2018 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com The original Wintergreen Farm construction plans were designed and approved for an aerial sanitary sewer crossing over an unnamed Tributary that has a floodplain associated with it (Based on FEMA mapping). Back in 2007, CE designed the Quadruple culvert crossing along this unnamed tributary at Ambrose Commons Drive, which is 2000 linear feet downstream of this aerial sanitary sewer crossing. Attached is the report on this crossing. The total drainage to this culvert was 1025 CFS for a 100yr flow analysis. Attached is also a cross section of the existing channel at the location of the aerial crossing (using field survey data). To be conservative, we used the same 100yr flow for this cross section that was used for the Ambrose Common Drive crossing. The cross-section of the stream was analyzed through flowmaster to determine the normal depth at this point in the stream. Based on the drainage flow along this tributary, the 100yr flow depth of the channel at the crossing is 4.88 ft. This is consistent with the attached HEC-GRAS analysis for the Ambrose Common Drive culvert crossing, which shows a critical flow depth and normal flow depth between 3 feet and 4 feet along this portion of the stream. It is also noted that the 4.88 feet at this cross section is very conservative, because it is using the same flow and drainage area for a point 2000 linear feet downstream. Using the normal channel depth for the 100yr flow at this cross section, the 100yr flow elevation at the location of the proposed aerial sanitary sewer crossing is 465.88. The invert of the sanitary sewer at the stream crossing is 466.55, as shown in the attached email. Therefore, there is almost 1' of height between the 100yr flow and the aerial sanitary sewer. The sanitary sewer is above the 100yr flow and therefore will have no effect on the hydraulics of the stream. If you have any questions or need any additional information, please contact me. Tha k you, 0 Cott Collins :OTT R. COLLIi Lie. No. 035781 y--1e-1 V Scott Collins From: John Anderson <janderson2@albemarle.org> Sent: Monday, April 16, 2018 12:37 PM To: Gregg P. O'Donnell; Scott Collins; Adam Long Cc: Frank Pohl Subject: SUB201500159 -Wintergreen Farm ('Off -Site Sanitary Sewer Plan'): FDP Application; FEMA Floodplain Elevation Certificate; Structural Engineer Certification (8" DIP Aerial San. Line Crossing), ETC. Please delete note just sent —ref. this, instead. Thanks Gregg, Thanks for taking time to speak with us, earlier today. We've copied Scott and Adam, the two I worked with on Wintergreen Farm plan review/s in 2016. FEMA website offers a wealth of information on development within 100-yr floodplains. Link: hOs://www.fema.gov/elevation-certificate. Thanks again Gregg. Feel free to call anytime: 434.296- 5832 0069. -best J. Anderson Scott, Adam, I look forward to working with Collins Engineering staff, again. Please feel free to call re. this note, or any CE project design that comes my way. In 2016, Collins Engineering (CE) worked with CDD /Engineering and ACSA on an `Off - Site Sanitary Sewer Plan' which is today being scanned into SUB201500159 (Road Plan), since it is part of the Approved road plan. Once scanned into the road plan, all sheets of the Off -site Sanitary Sewer Plan will be publicly viewable, including plan and profile images /snips, below. We need: • Floodplain Development Permit (FDP) Application completed for Wintergreen Farm to cover any and all phase of development with sanitary facilities constructed through in or across 100- yr floodplain as shown on Approved Road Plans (SUB201500159), whether owned by SM Charlottesville LLC, or Wintergreen Farm HOA Inc. • Base Flood Elevation (BFE) at 8" DIP Aerial San. Line over unnamed tributary to Biscuit Run. We understand design of ACSA improvements respond to ACSA long-range capacity needs (including decommissioning Redfields subdivision pump station), but review oversight on my part in 2016 —specifically, failure to establish BFE at point of aerial crossing of then -proposed 8" sanitary line between MH-119 and MH-113 —leaves Albemarle unable to evaluate BFE vs. vital infrastructure elevation at point of crossing. • Requested information prior to Road Plan bond release. ACSA has bonded sanitary system elements, separately, but ACSA is not the local Floodplain Administrator; Albemarle County Engineer is. • At crossing, we need CE (or others) to provide PE -sealed Floodplain Elevation Certificate showing bottom of pipe elevation (8" DIP, 112.97 LF San. Line) relative to 100-year base flood elevation (BFE). Were this pipe below grade, there would be less of an issue, but elevated and located within the 100-yr floodplain, we need to evaluate clearance between bottom of pipe and BFE. • Please confirm As -built condition and elevation of 8" DIP San. Line match CE design at this location. o Elev. Certificate, Sec. A, block A4: please state `Accessory -8" DIP Aerial San. Sewer Line (,SUB201500159)'. o Elev. Certificate, Sec. B, block B9: please provide base flood elevation (BFE) to nearest O ; if estimate, provide basis of estimate (historic, flood study /report /similar, interpolation (county GIS), engineering judgment, etc.) o Elev. Certificate, Sec. C, block C2e: please list lowest elevation of Aerial pine, to nearest hundredth (0.00'). Additional Aerial crossing As -built condition: provide or confirm Structural Engineer Certrfcation, slope, design elevation, long span pipe, circular columns, etc. CE to confirm location /TMP # of 8" Aerial San. Line crossing — TMP #76S-03-OS-IF? Link to Floodplain Elevation Certificate /Instructions (.PDF): hMs://www.fema.gov/media-librarv-data/1520628026490- Ofb72da8Oac68cafel7394f6b5f5Oaf1/FF086033 ElevCert RE 1Mar2018 pdf Link to Floodplain Development Permit Application: http://www.albemarle.ore/upload/images/forms center/departments/Community Development'forms/Engineering_ and WPO Forms/Floodplain Development Permit.odf Thanks Adam, thanks Scott John Anderson, PE, Civil Engineer II • (434) 296-5832 -x3069 Community Development Dept. I Engineering Division County of Albemarle 1 401 McIntire Road Charlottesville, Virginia 22902-4596 Snips /Images: SLJB201500159 /plan —`Off-Site Sanitary Sewer' —Aerial crossing circled blue --2v4Or MH-124 MH-i3,3 49 a co aao R FLOIDDPLA (02, z 170- to 47 476 MH-220 py SUB201500159 /profile —'Off-Site San Ltw3r Sewer' CE to confirm As -built condition; provide Structural EngLineer Certi cation fi_ 3 NOTE: LONG SPAN PIPE SHALL BE n REQUIRED FOR THE AERIAL CROSSING x 20 0c arn� O' N � 2220 00 0 O va �00 a r Nmr O r r o O O1O r m a p� O N N `D ONoca ^ N t0 x a '2 i> p ^��tno zz 475 475 � 00 0 I xa2»> 2tA O_ ZZ Z xF�» r tit d' Z Z i 470 / 470 8" DIP \ LF o.6z% s17.97 - 811 SDR-26 PVC 465 / - 4i.57 LF (ar7 i.i7% 465 -. BE / PIPE SUPPORTS FOR AERIAL CROSSING SHALL ITEM #59C-8, STAINLESS STEEL STANCHION SADDLE SUPPORT BY FM STAINLESS, LLC. _ PIER DESIGN SHALL BE CERTIFIED BY A STRUCTUAL 460 ENGINEER. PIERS TO BE CIRCULAR COLUMNS. U m m a N iO a to a n a -0+25 0+00 0+50 2+00 2+50 2+00 MH-!60 - MH-3-13 Albemarle County GIS Approx. Location 8" Aerial San. Line crossing, circled, blue (TMP #76S-03-OS-IF, likely) 4 I Wintergreen Farm Sanitary Sewer Crossing Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Channel Slope 0.01500 Wit Discharge 1025.00 ft /s Section Definitions Station (ft) Elevation (ft) -1+00 467.90 -0+80 466.60 -0+60 466.50 -0+40 465.00 -0+20 464.00 -0+10 461.90 -0+04 461.40 0+00 461.00 0+02 461.20 0+10 462.20 0+20 464.80 0+40 465.80 0+60 466.80 0+80 468.00 1+00 470.00 Roughness Segment Definitions Start Station (-1+00, 467.90) Options current Hougnness Weighed Method Open Channel Weighting Method Closed Channel Weighting Method Ending Station Pavlovskii's Method Pavlovskii's Method Pavlovskii's Method (1+00, 470.00) Roughness Coefficient OI4pral Bentley Systems, Inc. Hoestad Methods SeambibFE1dlaMaster V8i (SELECTseries 1) [08.11.01.03] 4117/2018 9:37:37 PM 27 Siemens Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 1 of 2 Wintergreen Farm Sanitary Sewer Crossing Results Normal Depth 4.88 ft Elevation Range 461.00 to 470.00 ft Flow Area 192.72 fta Wetted Perimeter 109.09 It Hydraulic Radius 1.77 ft Top Width 108.36 ft Normal Depth 4.88 ft Critical Depth 4.34 ft Critical Slope 0.03109 ft/ft Velocity 5.32 tt/s Velocity Head 0.44 It Specific Energy 5.32 It Froude Number 0.70 Flow Type Subcritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 it Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Downstream Velocity Infinity ft/s Upstream Velocity Infinity ft/s Normal Depth 4.88 ft Critical Depth 4.34 ft Channel Slope 0.01500 ft/ft Critical Slope 0.03109 It/ft Bentley Systems, Inc. Haestad Methods ShcfitlliCEliteMaster V8i (SELECTseries 1) 108.11.01.031 4M712018 9:37:37 PM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 2 of 2