SW4221201_Stormwater Narrative_20221207

Salem Brooke Subdivision Stormwater Narrative
Salem Brooke Subdivision is a 26 lot single family development on a 13.55 acre parcel
outside of Clemmons, Forsyth County, NC. The subdivision is being developed as low
density since the percent of impervious coverage is 21.17% which is well below the
State's requirement of being less than 24% BUA, and the density is 1.92 units per acre
which is less than the maximum 2 units per acre allowed for low density. In trying to
adhere to the low -density requirement of the State the subdivision is being developed
with ditch section roads using 3:1 side slopes with a 2' bottom width with ditch liner
and sodded with dense fescue. The pipe system for the development is limited to
cross pipes with rip rap aprons on the downstream side to keep the outlet velocity at
a non -erosive rate. To meet the State's low -density requirements per15A NCAC
02H.1003 (2) the following design requirements were used for the low -density project
and are listed and described below:
(a) DENSTIY THRESHOLDS:
The density for this project is less than 2 dwelling units per acre. The impervious
percentage for the net 13.51 acre tract (this excludes surface water area) is 21.17%
(2.86 acres).
(b) DISPERSED FLOWS:
Stormwater flows for this project will be mostly conveyed using ditch section flows
except where cross pipes are needed to convey stormwater across the NCDOT
designed streets. The outflows from these culverts will use rip rap aprons to reduce
velocities to be non -erosive. Calculations for all aprons have been provided in the
calculation booklet.
(c) VEGETATED CONVEYANCES:
Vegetated conveyances have been designed with side slopes no steeper than 3:1 with
a 2' bottom width to carry the runoff in roadside swales, curb outlets, and dispersed
flows to aid in treating the runoff. Calculations for the conveyances are contained
within.
(d) STORMWATER OUTLETS:
The only storm drainage used for the site, is a by-pass storm water system to convey
off -site stormwater, and 3 pipe culvert systems to convey stormwater across the
proposed streets into rip rap aprons, to reduce velocities, then to the natural buffer
areas for further treatment. Stormwater outlets have been designed so that they do
not cause erosion downstream of the discharge points from the peak flow from the
10-year storm event as shown in the attached calculations.
15A NCAC 2H.1003(4) VEGETATED SETBACKS:
Buffers have been provided on the existing perennial streams within the development.
These have been denoted and shown on the plans per the attached wetland report
provided by Pilot Environmental, Inc.
15A NCAC 2H.1003(7) DEED RESTRICTIONS AND PROTECTIVE COVENANTS:
The permittee shall record deed restrictions and protective covenants prior to the
issuance of a certificate of occupancy to ensure that projects will be maintained in
perpetuity consistent with the plans and specifications approved by the permitting
authority.