The URL can be used to link to this page

Home My WebLink About20130667 Ver 2_Stormwater2 n LSpreader_20150824Smith, Cherri L From: Buchholz, George <buchholz @mcadamsco.com> Sent: Friday, August 21, 2015 11:06 AM To: Smith, Cherri L Subject: RE: SAW- 2013 -01773 DD Alexander Place, LLC, Adara Alexander Place Apartments Attachments: Stormwater2 n LSpreader of PCN - Alexander Place.pdf TISVINOTAITIMM I returned your message and left a message to see if you had any other questions. Please give me a call if you do. George Buchholz, Environmental • Water Resources Office: it it 3' • 000 ext 284 Direct: 919-287-0890 Mobile: 919-475-3874 McAd • • �I . .... ....... .... „ ...ry .o....k ......... .... M... ........ .F..so. ....m........... Designing Tomorrow's Infrastructure & Communities From: Smith, Cherri L ( mailto:cherri.smith @ncdenr.RovI Sent: Thursday, August 20, 2015 12:56 PM To: Buchholz, George <buchholz @mcadamsco.com> Subject: RE: SAW- 2013 -01773 DD Alexander Place, LLC, Adara Alexander Place Apartments Could you also revise Questions 1a, 1b, 2a, and 2b in the Stormwater Section of the application and email that page to me? Thanks. Jason Robinson in this office is reviewing the diffuse flow plan for this project. I'll check and see where he is in that review. Cherri From: Buchholz, George rmailto :buchhoizCaDmcadamsco.comI Sent: Wednesday, August 19, 2015 4:02 PM To: Smith, Cherri L Subject: RE: SAW- 2013 -01773 DD Alexander Place, LLC, Adara Alexander Place Apartments Hi Cherri, I forgot about that. Sorry. Attached is the revise section of the PCN. Basically I added at the end of the first paragraph the following: -.. • s ME . - •- • because of discharging into a floodplain. However, water quality diffuse flow volume is being provided through the vegetated level spreader filter strip." George Buchholz, REM, PWS Environmental Consultant Water Resourc- Office: it it G ^. .00 Direct: 919-287-0890 Mobile: 919-475-3874 McAdamsCo.com Designing Tomorrow's Infrastructure & Communities From: Smith, Cherri L ( mailto:cherri.smith @ncdenr.Rovj Sent: Wednesday, August 19, 2015 11:44 AM To: Buchholz, George <buchholz @mcadamsco.com> Subject: RE: SAW- 2013 -01773 DD Alexander Place, LLC, Adara Alexander Place Apartments George, thanks — I think you were also going to revise the stormwater section of the application and email that to me. Cherri From: Buchholz, George rmailto:buchhoiz(d )mcadamsco.comI Sent: Tuesday, August 18, 2015 2:12 PM To: David L Shaeffer ( david .i.shaeffer(cbusace.armv.mil); Smith, Cherri L Subject: SAW- 2013 -01773 DD Alexander Place, LLC, Adara Alexander Place Apartments Cherri, Per your request, attached are profile and cross sectional views of the road crossing for the Adara Alexander Place Apartments project. We probably should have provided this at the time of the PCN submission. It should be noted, that the PCN has permanent stream impact (culvert) of 64 LF and a permanent stream impact (dissipator pad) of 29 LF for a total stream impact of 93 LF. The profile view has a permanent stream impact (culvert) of 50 LF and a permanent stream impact (dissipator pad) of 20 LF for a total stream impact of 82 LF. The difference in values is due to the curvature of the existing stream, see Inset 3 Plan View. For the purposes of the PCN submittal the total stream impact should be 93 LF to account for the curvature of the existing stream. If you have any questions, or need anything else for this project, please contact me at the numbers below or email me. George Buchholz, REM, PWS Environmental Consultant Water Resources & Infrastructure Office: 919 - 361 -5000 ext 288 Direct: 919- 287 -0890 Mobile: 919- 475 -3874 McAdamsCo.com Designing Tomorrow's Infrastructure & Communities E. Stormwater Management and Diffuse Flow Plan (required by DWQ) 1. Diffuse Flow Plan la Does the project include or is it adjacent to protected riparian buffers X Yes No identified within one of the NC Riparian Buffer Protection Rules? 1 b If yes, then is a diffuse flow plan included? If no, explain why. The City of Raleigh is a delegated authority for NCDWR Stormwater Management Plans. The review and approval of the SWMP is part of the City of Raleigh's review process. Two courtesy X Yes No copies of the stormwater design notebook is included, and a copy of the final approved stormwater management plan will be provided to NCDWR. Copies of the Level Spreader Calculations for Level Spreaders SB1 and SB2 are attached. 2. Stormwater Management Plan 2a What is the overall percent imperviousness of this project? 44% 2b _Does this project require a Stormwater Management Plan? X Yes No 2c If this project DOES NOT require a Stormwater Management Plan, explain why: Per City of Raleigh regulations, stormwater management on this site shall address two primary issues: (1) peak discharge rates and (2) water quality management. Stormwater runoff from the proposed project area will discharge directly to a FEMA - regulated floodplain (Little Brier Creek, Basin 18, Stream 16). In agreement with the City of Raleigh, detention for large storm events is not required because of discharging into a floodplain. However, water quality diffuse flow volume is being provided through the vegetated level spreader filter strip. ADAFA ALEXANDER PLACE LEVEL SPREADER CALCULATIONS DDV-14000 SBI - Level Spreader LEVEL SPREADER SIWG The purpose of the level spreader is to provide a non-erosive outlet by converting concentrated flow into sheet flow and release it uniformly over the vegetated filter strip. The level spreader length should be designed such that during the I " storm event, a non-erosive velocity (in this case, 10 feet per cfs) is released from the level spreader into the vegetated filter strip. Design Hydrology C = 0.87 The splitter box is designed such that the box provides sufficient driving head to pass the I "per hour i = 1.00 in/hr A= 4.18 ac Q = 3.63 cfs Required Level Spreader Length = 10 LF per cfs Min. Level Spreader Length = 36.3 feet Proposed Level Spreader Length = 40.0 feet SPUTTER BOX DESIGN The splitter box is designed such that the box provides sufficient driving head to pass the I "per hour storm event through a smaller pipe at the invert of the box without activating the bypass. Flows in excess of the I "per hour storm will be bypassed. Orifice Equation Orifice Diameter = 15.00 in Q = Cd * ri * r 2 * 1(2 * g * h) Cd 0.6 r = 0.625 ft 0 32.2 ft/s' Q = 3.63 cfs Head from Centroid (h) = 0.38 ft Level Spreader Pipe Radius = 0.63 ft Level Spreader Pipe Invert Out = 355.40 ft Min. Bypass Pipe Invert Out = 356.40 ft J.V. LOPERFIDO, El 8/21/2015 ADARA ALEXANDER PLACE LEVEL SPREADER CALCULATIONS DDV-14000 SB2 - Level Spreader LEVEL SPREADER SIZING The purpose of the level spreader is to provide a non-erosive outlet by converting concentrated flow into sheet flow and release it uniformly over the vegetated filter strip. The level spreader length should be designed such that during the I "storm event, a non-erosive velocity (in this case, 10 feet per cfs) is released from the level spreader into the vegetated falter strip. Design Hydrology C = 0.83 The splitter box is designed such that the box provides sufficient driving head to pass the I "per hour i = 1.00 in/hr A = 3.90 ac; Q = 3.25 cfs Required Level Spreader Length = 10 LF per efs Min. Level Spreader Length = 32.5 feet Proposed Level Spreader Length = 35.0 feet SPLITTER BOX DESIGN The splitter box is designed such that the box provides sufficient driving head to pass the I "per hour storm event through a smaller pipe at the invert of the box without activating the bypass. Flows in excess of the I "per hour storm will be bypassed. Orifice Equation Orifice Diameter = 15.00 in Q = Cd * TE * r 2 * V(2 *g *h) Cd = 0.6 r= 0.625 ft 9 = 32.2 ft/s' Q = 3.25 cfs Head from Centroid (h) = 0.30 ft Level Spreader Pipe Radius = 0.63 ft Level Spreader Pipe Invert Out = 350.40 ft Min. Bypass Pipe Invert Out = 351.33 ft J.V. LOPERFIDO, El 8/21/2015