The URL can be used to link to this page

Home My WebLink AboutWPO201300032 Correspondence 2021-07-30John Anderson From: John Anderson Sent: Friday, July 30, 2021 2:25 PM To: Dustin Greene; Jim Taggart Cc: Charlie A. Hurt, Frank Pohl Subject: RE: WPO201300032, Cascadia - Amendment #2 status Dustin, Thanks for your call to discuss email, below. Frank reminds me to check VDOT drainage manual and road classification, which indicate culvert beneath church access and beneath Rt. 20 are reviewed against 10-yr frequency event. My mistake. Disregard request for 25-yr event analysis. The 10-yr retention basin WSL is < emergency spillway elevation. Please check whether the 10-yr event inundates either the church access, or Rt. 20. If so, let's discuss —if not, please provide data. Thanks for your help with this -best, J. Anderson Enjoy the weekend. VDOT Drainage Design Manual, image below, p. 6 of .PDF at https://www.virginiadot. orgJbusiness/resources/LocDes/DrainageManual/chgpter9. pddf Table 9-2 Design Frequencies for Storm Drain Conduit Roadway Classification Design Speed (mph) Design Stony Frequency (year' Z) Principal Arterial With Shoulder All 25 Without Shoulder- 50 10 > 50 25 Minor Arterial, Collector, Local With or Without Shoulder All 10 .Rev. 3/19 Chapter 9-3 of 70 VDOT Road Classifications - httos://www.arcgis. com/bome/webmgp/v iewer. html?webmap=3eca6c9adb6649c988d98734f85baddb Stony Point Road (Rt. 20) is a minor arterial — road shown in -; ref. VDOT road classification legend at link website, above. N 0 300 600k From: John Anderson Sent: Friday, July 30, 2021 1:12 PM To: Dustin Greene <DGreene@roudabush.com>; Jim Taggart <JTaggart@roudabush.com> Cc: Charlie A. Hurt <Charlie@VirginiaLandCompany.com>; Frank Pohl <fpohl@albemarle.org> Subject: RE: WPO201300032, Cascadia - Amendment #2 status Dustin, Thanks for your call this morning. Jim, We spoke last week about this (Amendment #2 review). I expressed concern then that I had not responded. Another week has passed —I regret delay responding. I invite you and Dustin to call, if you'd like to talk about this. I am not operating absent oversight. I appreciate the county engineer's advice and perspective, since I was a bit distracted by 100-yr projected 147.73 cfs flow, when the relevant issues /standards are whether an existing culvert beneath site access to Broadus Memorial Baptist Church is adequate to convey the 25-year event, and whether the revised spillway design meets VSMH 1999 Min. Std. 3.03, Vegetated Emergency Spilfivays. To the first point: SWM-1 detail indicates the 10-yr elev. (WSL)=355.75' Emergency spillway elevation=355.93'. Emergency spillway is 0.18' (2.16") above the 10-yr WSL Please report 25-yr WSL: If>355.93', confirm exit portion of the emergency spillway contains the 25-yr event; if not, please revise spillway design to ensure it contains the 25-yr event for its entire length. Regardless of 25-yr WSL, compare Q25-yr for As -built (4eWQV) retention basin with existing pipe capacity, for culvert beneath site access to Broadus Memorial Baptist Church. In this context, please report: • Q25-yr discharge v. capacity (CFS) of existing culvert ( blue circle, 3rd image, below) • If Q25-yr exceeds capacity (CFS) of existing culvert, report whether 25-yr event overtops site access to Broadus Memorial Baptist Church, yellow arrow, 3rd image. • Report WSL (elevation) of 25-yr event against church site access embankment, if Q25-yr exceeds Ex. culvert capacity, and, presumably, is higher than crown of pipe. • If overtopped during 25-yr event, propose remedy to protect Church access, Stony Point Road (Rt. 20), and public RW (Rt. 20). Prevent inundation during 25-yr event. Given that the emergency spillway elevation is only 0.18' higher than the 10-yr WSL in the retention basin, it is important to evaluate Q25-yr, relative to church site access and Rt. 20. Top of Dom Elev = 358.00 8'� •Trosh rock to be installed on orifice as sl on detail 5/SW14 or approved equal. **Impervious core and cutoff trench shown for informational purposes only. Final design to be provided by geolechnical .rgency _ J SH 0► %C J� i or Core - Dustin E. Greene La. W. Ys1 1* ZONAL 1.5 yr. Elevation = 354.03' 2 yr. Elevation = 354.23' 10 yr. Elevation = 355.75' 100 yr. Elevation = 356.99' To the second point: Although p. 3.03-2 of VSMH, 1999, states `that an armored emergency spillway over the top of an embankment should be designed by a qualified professional,' Engineering maintains that the hydraulic design guidance that follows at item 5, p. 3.03-6 applies; namely: `The exit channel should have a straight alignment and grade and, at a minimum, the same cross-section as the control section.' Please identify the control section of the revised emergency spillway; then, provide exit channel width that, at a minimum, is the same cross-section as the control section. Please find VSMH, 1999, Min. Std. 3.03 Attached. Also, since the proposed revised emergency spillway width is increased from 16' to 40' at the spillway inlet channel, yet narrows to 16' at the toe, Engineering requests Amendment provide an emergency spillway section (detail) at the spillway exit channel, to ensure Q 100-yr does not leave confines of the revised emergency spillway at the toe. Last, the county engineer offered perspective that a berm (proposed grade shown on plan sent with email 7/1/2021 8:25 AM) is inappropriate, since berms, if breached, fail. Engineering requests conventional tie-in grading along west edge near inlet channel of emergency spillway, instead of a berm. A berm suggests the emergency spillway may be perched too high relative to immediately adjacent embankment grade/s. Failure and erosion are primary concerns with a berm at the edge of an emergency spillway. berm: blue circle I � I TIE INTO EXISTIN�,-� EMERGENCY / SPILLWAY / -I , / l / n � I intend to send a typical plan review memo, but should you have chance to consider this note in the meantime, feel free to call to discuss items above, VSMH requirements, or any error/s on my part. Thanks for your help and patience. best, J. Anderson John E. Anderson, PE I Civil Engineer 11 Department of Community Development I County of Albemarle, Virginia 401 McIntire Road I Charlottesville, VA 22902 434.296.5832 ext. 3069 4 I, F S1 T J s 3' MATCH EXISTING r RIP RAP CLASS IA TIE INTO EXISTIN4—' ) EMERGENCY SPILLWAY i - F I I 1 11 1 1 I 1 1 1 � 11 \ \ I 1 \ 1 \ \ V \ \ om: Dustin Greene <DGreene@roudabush.com> -nt: Thursday, July 1, 20218:25 AM r John Anderson <janderson2@a1bemar1e.org> Con embonkmenl9" - --- -�-" lie riprop into the top edge of the existing riprop ditch for o 3,0' NI smooth tronsition for flons L MODIFIED PERMANEN JW14 NOT TO SCAM 5 Cc: Charlie A. Hurt <Charlie@VirxiniaLandCompanv.com> Subject: RE: WP0201300032, Cascadia -Amendment #2 status John, These documents were dropped off at Community Development 6/18/21. The owner dropped off the resubmittal payment on 6/28/21. Please review these updated documents and I will give you a call. The dam tests area scheduled for July 21s`, 2021. Best Regards, Dustin Greene, PE Roudabush, Gale & Associates, Inc (o) 434-977-0205 ex - 724 (Direct) 434-328-1069 (m)415-420-8238 dareene@roudabush.com Physical Address: 999 Second Street SE Suite 201 Charlottesville, VA 22902 BOUDAWN GALE QAS9OOAI$M Mailing Address: 435 Merchant Square Suite 300-159 Charlottesville, VA 22902 From: John Anderson <janderson2@albemarle.orl > Sent: Thursday, July 1, 20218:17 AM To: Dustin Greene <DGreene@roudabush.com> Subject: WP0201300032, Cascadia - Amendment #2 status Dustin, I am a bit concerned by voicemail left 6/30/21, 8:22 AM. You explained work is proceeding on SWM pond at Cascadia, and reference only a few remaining Amendment #2 comments. There is risk proceeding without an approved Amendment. CV indicates that last review comments were sent 5/6/21. We have not received a resubmittal, to my knowledge. Though there are just a few remaining comments, the review process is incomplete. Amendment #2 is not approved. Work is not authorized. An email or phone call are not ordinary process for completing a WPO Plan Amendment review. Please re -submit at earliest convenience, and we will review as soon as possible. Thanks, take care, best, J. Anderson John E. Anderson, PE I Civil Engineer 11 Department of Community Development I County of Albemarle, Virginia 401 McIntire Road I Charlottesville, VA 22902 434.296.5832 ext. 3069