HomeMy WebLinkAboutChenal Valley Phase 18-L Drainage Report 11 11 2022 execWHITE - 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 November 11, 2022
Preliminary Plat
Chenal Valley – Phase 18-L
Project Description
Chenal Valley Phase 19-L is a single-family residential subdivision. It includes 73 residential lots on
approximately 32.75 acres. The project is currently wooded but bisected by an existing sanitary
sewer main that was constructed to serve previously developed subdivisions to the west. The project
drains to north through double 72 inch diameter culverts under Chalamont Drive.
There is a large wooded buffer to the south of the project. The drainage basin to the south extends to
the ridge line of Shinall Mountain. Relatively small areas of developed residential subdivisions to the
east and west of this project drain into this project.
At this time, there are no existing drainage issues/problems downstream of this project. The drainage
course to the north of the 72 inch culverts silted in and was restored to it’s original shape in 2021.
Lower portions of the project are considered flat for the general area, the upper portions of the
project have slopes that range from 14% to 18%. Large areas of the project will remain undisturbed.
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 South of Chalamont Drive (Address not yet assigned)
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Existing Conditions
This project is bounded on the east by the DuQuesne Community Subdivision and on the west by the
Challain Place Subdivision. These subdivision drain into this project. None of the existing drainage patterns
or improvements will be impacted by the development of this project.
The 72 inch culverts under Chalamont Drive drain this project and portions of the two developed
subdivisions noted above. The culverts discharge into a tract between Corlay Court and Bronte Court
subdivisions. The culverts are designed for the 25 year developed conditions storm without overtopping
Chalamont Drive. There is no record of Chalamont Drive being overtopped since it was constructed in
2004. The 100 year event may likely overtop Chalamont Drive. The lowest lots in this project, upstream of
Chalamont Drive will be approximately 6-8 feet above the low spot in Chalamont Drive and will not be
impacted if the street is overtopped.
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 two phases. Phase 1 contains approximately 37 lots and Phase 2 the
balance. The entire project will be graded with Phase 1. The stormwater detention facility and downstream culverts
will also be constructed with Phase 1 of the project.
After development of the streets and utilities the lots will be sold to Home Builders or individuals for construction of
the individual homes.
Design Methodology
Time of Concentration for the analysis is 15 minutes which is conservative.. Runoff Coefficients are based on
current and 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 Water Detention was modeled using
Hydroflow Hydrographs. Storm drains and inlets were designed using Hydroflow Storm Sewers.
Predevelopment/Post Development Summary
Development discharge rates will increase slightly because of the increase in impervious surfaces. The majority of
the overall drainage basin will remain undisturbed. The major west to east water course along the northern end of
the project will remain largely undisturbed as will the main south to north water course through the eastern portion
of the project.
The detention facility constructed upstream of Cheran Court will provide sufficient reduction in peak flow so that
the post development discharge from the project to the culverts under Chalamont Drive will not exceed the
predevelopment rates of discharge.
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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 has been issued by the Corps of Engineers for this project. Prior to beginning
construction stream mitigation credits will be purchased.
Attachments
The following are included in this report.
Exhibit A Existing Basin Delineation Map
Exhibit B Storm Water Detention Preliminary Plan
Exhibit C Hydroflow Storm Water Detention Analysis
Exhibit D Hydroflow Drainage Report for the Pipe Networks
Exhibit E Preliminary Plat