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HomeMy WebLinkAboutWPO202100010 Correspondence 2021-02-17 (2)® ROUDABUSH, GALE & ASSOCIATES, INC.1 February 17, 2021 Mr. Frank Pohl ATTN: David James Albemarle County Department of Community Development 401 McIntire Road Charlottesville, VA 22902 Project title: Belvedere Phase 3 Block 10 Water quantity requirements Dear Frank, Please find attached, an overview of the proposed Belvedere Block 10 Phase 3 development. This parcel is located at the outermost division of the Belvedere Neighborhood and located on a ridgetop overlooking the Rivanna River. This parcel is incased by critical slopes which severely limits the area of development and grading. The design layout incorporates the design standards required, not only by VDOT, but also largely incorporates the Grading Standards set forth by Albemarle County Zoning Ordinance. Due to the increase in the requirements of road design radii; the development has expanded into the previously designated Conservation and Preservation areas stipulated in the ZMA. The design team had to incorporate multiple retaining walls into the design to limit the disturbance to the slopes to the greatest extent possible; while still honoring the requirements set forth by the ZMA. It is our belief that we have balanced the development requirements of the Neighborhood Model District in accordance with ZMA200400007, with those of Virginia Department of Transportation (VDOT), as well as Albemarle County Design Standard in an effort to meet site requirements while honoring highest/best use of the parcel. Furthermore, our ability to alter the site layout is hampered by the existing ZMA and in order to limit the disturbance to the critical slopes as much as reasonably attainable. Therefore, the plan represents the maximum buildable envelope allowed by the code and it is not within our ability to alter the site layout since it is set by the existing ZMA. In accordance with Virginia Administrative code section 9VAC25-870-55 Stormwater management plan, these plans are designed to adhere to Virginia Code. Stormwater runoff within the Block 10 development will be collected and conveyed through a manmade stormwater pipe network to one concentrated outfall at the Rivanna. The nonerosive passage of the 2-year event will discharge at the normal river elevation (NRE) of the Rivanna, and adequate channel. Therefore, this project is in compliance of channel protection, as manmade improvements (section LA of 9VAC25-870.B) will be utilized all the way to the NRE of the river. This is the point of analysis of the system and the 1% rule (section 4.A) removes any need to further demonstrate capacity of the channel and negates any need for detention or energy balance. According to flood insurance study. No 51003CV000C, the South Fork Rivanna River's drainage area at the project outfall is approximately 268 square miles and the project drainage area is 9.87 acres — well below 1%. In reference to the flood protection, section 9VAC25-870-66-C.2.A, will be utilized to satisfy the requirements set in Virginia Code. The project is in compliance of flood protection since the entire 10-year peak flow is confined within pipes and conveyed to the discharge point which is below a FEMA mapped floodplain. On 09 February 2021, the design engineer visited the proposed location of the outfall for the storm sewer discharge point to the Rivanna River. The design discharge necessitates the determination of the Normal River Stage of the Rivanna at this point. A survey field crew accompanied the design engineer and collected field topography of the area of the discharge point. The designer selected a point to represent the Normal River Stage as shown in the photo below. The field crew determined that the elevation to be 321.05 (standard project datum). This elevation was used w large elevation. To conclude, this proposed development has one concentrated outfall. The outfall meets the minimum channel and flood protection requirements in accordance with Virginia Administrative Code Section 9VAC25-870- 66. The stormwater network adequately conveys its runoff through manmade pipes to a mapped floodplain where the site's drainage area is less than 1% of the receiving channel's total watershed. We trust this meets the Code requirements and we very much look forward to moving this project forward. As usual, we thank you for your help here and look forward to working with you to get this to fruition. Respectfully, Riki van-Niekerk, EIT Roudabush, Gale, and Associates Inc.