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HomeMy WebLinkAboutStormwater (2) Stormwater Management Report For Fox Run Phase 4 Harnett County JOHN W. HARRIS, P.E. CONSULTING ENGINEER, Inc. 7909 OCOEE COURT RALEIGH, N.C. 27612 (919) 789-0744 PROJECT NARRATIVE: Site Design: The site for this project is phase 4 of the Fox Run Subdivision (which will be subdivided into 15 lots) and is also the connection of Prairie Lane to Trotters Ridge via Jockey Ridge. The minimum lot size will be 15,000 square feet. The front setback is 35’ and the rear is 25’. The side setback is 10’ and the corner side setback is 20’. We will extend the existing road Prairie Lane 1,000’ and Jockey Ridge will be extended 310’. The right-of-way will be 50’ and the edge of pavement will be 20’ for Prairie Lane and 18’ wide for Jockey Ridge. A. Development name and location Fox Run Subdivision Located off Docs Road in southern Harnett County B. Developer/owner and consultant contact information Mike Barbour 919-775-2500 919-774-8884 511 E. Main Street Sanford, NC, 27332 C. Site description including the following: D. The proposed section of Prairie Lane of Fox Run Subdivision phase 4 is located along and off of Docs Road in Lillington, NC. The developer is Mike Barbour; 511 E. Main Street Sanford, NC 27332. The engineer for the project is John W. Harris, P.E., Consulting Engineers, Inc; 5112 Bur Oak Circle, Raleigh, NC 27612. Survey information was provided by from Eakes Surveying; 8024 Eakes Road Sanford, NC 27330. The site is approximately 13.59 acres and is zoned RA-20R. E. Existing Conditions: F. On phase 4 the road is already rough graded and has a 6” waterline on the north side of the road and two fire hydrants. There is a 24” RCP under the road at the low point as indicted on our plans. For Jockey Ridge, a path will need to be cleared, graded, and paved to extend Jockey Ridge to intersect with Prairie Lane as required by Harnett County. 1. Vicinity map USGS Map SITE BnB VaB VeB = Vaucluse gravelly loamy sand, 2 to 8% slopes VeE = Vaucluse gravelly loamy sand, 15 to 25% slopes Soils information was obtained from Harnett County GIS. The site has four different soil conditions. Vaucluse loamy sand, (VaB) has slopes, Vaucluse gravelly loamy sand, Soils Map BnB = Blaney loamy sand, 2 to 8% slopes = Vaucluse loamy sand, 2 to 8% slopes VeB = Vaucluse gravelly loamy sand, 2 to 8% slopes VeE = Vaucluse gravelly loamy sand, 15 to 25% slopes Soils information was obtained from Harnett County GIS. The site has four different soil conditions. Blaney loamy sand, (BnB) has 2 to 8% slopes (VaB) has 2 to 8% slopes, Vaucluse gravelly loamy sand, slopes, Vaucluse gravelly loamy sand, (VeE) has 15 to 25% slopes. Soils information was obtained from Harnett County GIS. The site has four different soil 2 to 8% slopes, Vaucluse gravelly loamy sand, (VeB) has 2 to 8% 15 to 25% slopes. Aerial Map 1. Description of all water courses, impoundments, and wetlands on or adjacent to the site or into which storm water directly flows The project has one main water courses that transect the site. The property is immediately upstream of a future subdivision. This downstream property known as Totters Ridge was designed by John Harris P.E. Consulting Engineer, who knew of the future phases of Fox Run and he has designed the Totters Ridge drainage system to account for the future developed upstream drainage run-off. The site does not have any wetlands. G. Statement noting whether the site is located within the conservation zoning or a watershed district. It is our understanding that this site is not located within either a conservation zoning or watershed district. H. Impervious area calculations The impervious surface areas are presumed to be the following: Impervious Area Calculations 2850 S.F. per Lot x 15 Lots = 42750 S.F. (.98 AC.) 1000 Linear ft. Street @ 20’ Wide = 20,000 S.F. (0.46 AC)) 1.44 AC. (Impervious): 13.59 AC.Total = 10.6% 0.00 Wetlands I. A description of the proposed storm water management system including: 1. Best Management Practices (BMPs) and preliminary sizes and locations, including post development drainage map delineating the flows diverted to each BMP. Since the site is considered low density and is below 24% (actually +/- 10%) of impervious surface, structural BMP’s are not required. 2. Description and concept for diversion of off-site storm water Off-site surface storm water shall be handled via the existing conveyance channels and with NCDOT approved storm water drainage design methods at the road crossing. It is important to note that this project lies near the top of its drainage basin, thus the upstream quantity of off-site drainage is extremely minimal. 3. Pre-development and post-development discharges for the 10 year and 25 year storms. If the increase in the pre-development discharge is less than 10 percent (10%), then an additional may not be required unless deemed necessary by the DRB. The final design will utilize a Low Impact Design (LID) scenario where storm water is not allowed to concentrate for long runs in roadside ditches. This concept will increase the flow concentration time of surface water and will create a more natural groundwater recharging system that reduces post- development run-off. The following chart provides the storm water run-off for Pre and Post conditions. J. Downstream Analysis, if required: N/A 1. Provide topography with the following identified: The Topography is shown. a. Drainage areas for the development The major drainage area for the site is noted in the Hydrology Computation sheet. b. Drainage areas for downstream drainage structures These major drainage areas are also shown on the topography. c. Provide photographs of downstream structures N/A 2. For existing streams and ditches, the analysis should focus on increases in velocity and flooding within the stream. Both the 10 yr and the 25 year storms produced only a minimum of 5 cfs of additional storm water run-off. This is considered minor. It is noted that the downstream property known as Totters Ridge was designed by John Harris P.E. Consulting Engineer, who knew of the future phases of Fox Run and he has designed the Totters Ridge drainage system to account for the future developed upstream drainage run-off. 3. For existing culverts, the analysis should focus on increases in headwater and flooding at the structure. N/A 4. Identify the point at which the drainage area of the development or redevelopment becomes less than 10 percent (10%) of the total watershed. 5. All negative impacts of existing improvements and developments shall be identified, if there are no negative impacts, the analysis specifically state and demonstrate that there are not adverse impacts in the increase in site runoff. There are no adverse impacts in the increase in site run-off. 6. If downstream measures are found to be inadequate, detention or other improvements will be required to minimize downstream impacts. N/A No downstream structures within a reasonable distance at this time.