SW4240401_Stormwater Narrative_20240605

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Stormwater Narrative
Whitehall Village South
This project consists of the proposed construction of townhomes, drives, sidewalks and utilities
for a total of 45 townhome units on a total of 6.874 acres. There is a total of 3.31 (48.1%) acres
of built-upon area. This project has an existing paved road (Whitehall Village Lane) that divides
the project into two (2) areas of development. There are two (2) stormwater control measures
(SCM) for this development. The first SCM is bio-cell #1 with a total drainage area of 1.56
acres, a built-upon area of 0.93 acres and a built-upon area percentage of 59.62%. The second
SCM is bio-cell #2 with a total drainage area of 4.04 acres, a built-upon area of 2.38 acres and a
built-upon area percentage of 58.91%. These two (2) SCM's are designed to control and treat the
runoff from the first one (1) inch of runoff and with a discharge rate for the one (1)-year, two (2)-
year and ten (10)-year, 24 (24)-hour storm event at or below the pre-development discharge rate.
This development's peak flow discharges for the one(1), two (2) and ten (10) year storms will be
less than or equal to the pre-development flows. All new site built-upon area will be routed
through the proposed SCM's.
The stormwater piping system will consist of polyvinyl chloride (PVC) and reinforced concrete
pipe (RCP). The stormwater piping system is designed to collect and transport the runoff from
the ten (10)-year, twenty-four(24) —hour storm event.
The runoff for the development will be treated and detained by two (2) bio-cells. The SCM's are
designed based on all requirements of the NCDEQ Stormwater Design Manual. The bio-cells
will be used for erosion control and will be restored to their original design once the site is
stabilized.
The bio-cells are designed using Hydrology Studio 2021 V 3.0.0.27. The pre-development time
of concentration was calculated using the TR55 Tc worksheet which is included with the
calculations. This is shown as 7.81 minutes for bio-cell #1 and 12.21 minutes for bio-cell#2. The
soil type for this area is NaB (Nathalie sandy loam) which is hydrological soil group B.
There are no proposed impacts to streams or wetlands associated with this development. All
design is in accordance with city, state, and federal regulations.