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Home My WebLink AboutCV TRACT 3 LOTS 1-3 DRAINAGE REPORT WITH ATTACHMENTSWHITE - DATERS & ASSOCIATES, INC. 24 Rahling Circle Little Rock, Arkansas 72223 Phone: 501-821- 1667 www.whitedaters.com CIVIL ENGINEERING - LAND PLANNING & DEVELOPMENT – SURVEYING – LANDSCAPE ARCHITECTURE Drainage Report December 7, 2022 Preliminary Plat Chenal Valley – Tract 3, Lots 1-3 Project Description Chenal Valley Tract 3 is a Commercial/Office Subdivision. This first 3 lot phase is on Chenal Parkway and contains approximately 8.5 acres. The project is currently wooded but bisected by watercourse and an existing sanitary sewer main that was constructed to serve previously developed subdivisions to the East. The project drains to West under Chenal Parkway at two locations. The areas upstream of this project are a mix of undeveloped wooded area and developed multifamily projects. Downstream of the project is the Chenal Golf Course and Chenal Valley residential subdivisions, Avingnon and Bretagne. At this time, there are no existing drainage issues/problems downstream of this project. After the May 30, 2013 storm event a downstream cart path culvert was overtopped. It has since been supplemented with an additional culvert and no recent overtopping has been reported. Lower portions of the project are considered flat for the general area, the upper portions of the project have slopes that range up to 10%. During construction of the new shared drives Lots 1 & 2 will be cleared and cut or filled to match the elevation of the adjacent streets and drives. A portion of Lot 3 will be cleared and similarly cut and or filled. Owner PotlatchDeltic Real Estate LLC 7 Chenal Club Boulevard Little Rock, Arkansas 72223 501-821-5555 Developer PotlatchDeltic Real Estate LLC 7 Chenal Club Boulevard Little Rock, Arkansas 72223 501-821-5555 Engineer Timothy E. Daters. P.E. White-Daters & Associates 24 Rahling Circle, Little Rock, AR 72223 501-821-1667 Address East of Chenal Parkway, south of Chenal Valley Drive (Address not yet assigned) CIVIL ENGINEERING - LAND PLANNING & DEVELOPMENT – SURVEYING – LANDSCAPE ARCHITECTURE Page 2 Existing Conditions This project is bounded on the north by Chenal Valley Drive, on the west by Chenal Parkway and on the south by the recent extension of LaMarche Drive. Developed upgradient areas include the Chenal Valley Fire Station, a portion of The Villas at Chenal, Valon Condominiums and portions of Pinnacle Park at Chenal Valley. These developed subdivisions drain into this project. None of the existing drainage patterns or improvements within these developed areas will be impacted by the development of this project. The north drainage area of this project (marked #1 on the attached map) has an area of 15 acres. This basin discharges under Chenal Parkway, flowing to the west to Avignon Court. It flows through the subdivision in a series of culverts and open ponds to the Chenal Valley Founders Golf Course, The other three drainage courses will be intercepted and conveyed in storm drains to the 5 foot tall x 10 foot wide concrete box culvert under Chenal Parkway. This box culvert discharges into a ditch that carries the flow around the south and west side of the #6 green on the Founders Course. Developed flow rates in the box culver are 445 CFS for the 25 year event and 525 CFS for the 100 year event. The Hydraulic Grade Line (HGL) for the 100 year event is 544.15 which is over 3 feet below the existing grade elevation of 548. Basin #2 has an area of 33 acres with a flow of 139 CFS. Basin #3 has an area of 47 acres with a flow of 198 CFS, Basin #4 from the south has an area of 21 acres with a flow rate of 88 CFS. These areas all drain under Chenal Parkway, around the #6 green and then between the #5 and #7 golf course fairways. The creek crossed the #5 fairway just in front of the #5 tee where it flows under the cart path and into the upper pond in the Bretagne Circle subdivision. There are a series of three ponds across the subdivision. The creek crosses the 14th hole fairway and flows into Rock Creek approximately 600 feet south of Chenal Valley Drive. Creeks on the Founders Golf Course are maintained by the Chenal Valley Country Club. There is no record of Chenal Parkway, or any of the downstream streets in the subdivisions noted ever being overtopped by storm water flows. This Tract 3 project when developed will not negatively impact any downstream improvements. The Tract 3 project is part of the Regional Chenal Valley Detention Facility. Existing Area Drainage Problems Based on a physical inspection of the improvements in the vicinity of the project, this project when developed will not impact or exacerbate any existing drainage problems. Proposed Improvements Plans are for the subdivision to be constructed in one phase. With the construction of improvements to Chenal Parkway and the interior shared drives, storm drainage will be installed and all of Lots 1 & 2 will be cleared and graded to match the adjacent streets. A portion of Lot 3 will be cleared and graded as well. Ultimate development will be office or commercial uses. After development of the streets and utilities the lots will seeded and stabilized with grass cover. CIVIL ENGINEERING - LAND PLANNING & DEVELOPMENT – SURVEYING – LANDSCAPE ARCHITECTURE Page 3 Design Methodology Time of Concentration for the analysis is 20 minutes which is conservative. Runoff Coefficients are based on future land use and are consistent with those in the Little Rock Drainage Manual. Storm water runoff rates were computed with the Rational Method. Storm drains and inlets were designed using Hydroflow Storm Sewers. Predevelopment/Post Development Summary Development discharge rates will increase because of the increase in impervious surfaces. A significant portion of the overall drainage basin will remain undisturbed after development of Lots 1,2 &3, Tract 3. Development of this project will not significantly reduce the time of concentration for the overall drainage basin. A small detention facility may be constructed on the main east to west creek on the east side of the future extension of LaMarche Drive. Storm Water Pollution Prevention Plan & Erosion Control A Storm Water Pollution Prevention Plan (SWPPP) will be prepared and submitted to the Arkansas Department of Environmental Quality to obtain a Notice of Coverage. The SWPPP will be implemented and monitored in accordance with the plan. A Notice of Termination will be filed when sufficient areas of the site have been permanently stabilized. A three phase Erosion Control Plan will be prepared and approved by the City of Little Rock prior to any land alteration activities. 404 Permitting A 404 Permit Application will be prepared and submitted to the Corps of Engineers for this project. A wetland and Waters of the United Stated delineation has been completed. Prior to beginning construction, a permit will be issued and any necessary stream mitigation credits will be purchased. Attachments The following are included in this report. Exhibit A Existing Basin Delineation Map Exhibit B General Basin Identification Exhibit C Hydroflow Drainage Report for the Pipe Networks Exhibit D Preliminary Plat Exhibit E Downstream Flow Path 586 588554542545 44 608546548544546610546LOTS1-3,TRACT3CH ENALVALLEYDRAINAGE BASINM APAn Addition to th e City ofLittle RockDECEM BER 07,2022INLET 1INLET 2INLET 3INLET 4INLET 5INLET 6INLET 7INLET 8INLET 9INLET 10INLET 11A12=2.1 ACINLET 12EX DRAINEX DRAININLET 13INLET 14A2=1.0 ACA4=1.6 ACA3=0.4ACA5=0.5ACA7=0.3ACA6=0.2ACA10=0.7ACA11=0.5ACA8=0.2ACA9=33 ACA14=47 ACQ=88 CFSQ=2 CFS S T O R M F L O W STORMFLOWEXHIBIT A EXHIBIT B-1 EXHIBIT B-2 EXHIBIT C 5 86 588554542545 44 608546548544546610546LOTS1-3,TRACT3CHENALVALLEYDRAINAGEBASINMAPAnAdditiontotheCityofLittleRockDECEMBER07,2022INLET1INLET2INLET3INLET4INLET5INLET6INLET7INLET8INLET9INLET10INLET11A12=2.1ACINLET12EXDRAINEXDRAININLET13INLET14A2=1.0ACA4=1.6ACA3=0.4ACA5=0.5ACA7=0.3ACA6=0.2ACA10=0.7ACA11=0.5ACA8=0.2ACA9=33ACA14=47ACQ=88CFSQ=2CFSS T O R M F L O W STORMFLOW 588554542545 44 546548544546546N21°59'34"W240.59'N68°00'26"E10.00'N21°59'34"W481.88'S62°29'06"W310.86'S17°42'03"E344.09'S21°59'34"E338.14'S20°05'22"E301.07'N79°51'33"E140.64'N67°45'52"E71.59'R439.26'CD N 72°05'57" ELC118.62'R25.00'CD N 71°13'39" WLC36.14'N27°53'15"W80.00'LOTS1-3,TRACT3CH ENALVALLEYPRELIM INARY PLATAn Addition to th e City ofLittle RockDECEM BER 07,2022STORMFLOWST O R MF L O W PROPOSED RIGHT-TURN-IN LANEPROPOSED RIGHT-TURN-OUT LANEPROPOSED DRIVEWAY APRONEXISTING DRIVEWAY APRONPROP72"DRAI NPROP60"DRAIN5-FT SIDEWALK BY DEVELOPER5-FT SIDEWALK BY DEVELOPER5-FT SIDEWALK BY DEVELOPER#538NOVEM BER 14,2022EXHIBIT D TRACT 3CART PATH CULVERTSEXHIBIT E