SW4211202_Stormwater Narrative_20220307

STORMWATER
NARRATIVE
For -
Ivy Brook Subdivision
Hickory Tree Road
Davidson County, North Carolina
ADI Project No. 21-016
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Developer:
Isenhour Homes, LLC
3411 Healy Drive
Winston-Salem, NC 27103
Prepared by:
Allied Design, Inc.
4720 Kester Mill Road
Winston-Salem, NC 27103
[phone]
[e-mail]

STORMWATER NARRATIVE
IVY BROOK
TABLE OF CONTENTS
A. Introduction
B. Methodology
C. Site Design and Assessment
D. Conclusion
Appendix
A. Outlet Stabilization Calculations
B. Ditch Calculations
C. NOAA Rainfall Data
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STORMWATER NARRATIVE
IVY BROOK
A. Introduction
Ivy Brook is a proposed 19.2-acre, 21 lot, single-family, residential development
located off Hickory Tree Road in Davidson County. In accordance with the
requirements of NCDEQ Post Construction Stormwater program, the project will
require a stormwater management permit.
The resulting project density is less than 2 lots per acre. Also, based on anticipated
development on the lots, the calculated BUA Percentage for the property will be less
than 24%. Consequently, the project can be permitted under the "Low Density" (LD)
provisions of the program. This will exempt the project from design and construction
of permanent, stormwater quality control measures.
Development under the LD option will require that the project meet with the minimum
design criteria outlined in 15A NCAC 02H .1003. More specifically the project: must
meet the Density Thresholds, must utilize Dispersed Flow; must provide Vegetated
Conveyances, and may be allowed to use Curb Outlet Systems. Guidance for
development under The Low Density option is taken from the NCDEQ Stormwater
BMP Manual, Chapter E-1, "Low Density".
B. Low Density Design Considerations
1. Development Threshold
The project density should be less than 2 dwelling units per acre. The total
project area for the subdivision is 19.2 acres. The number of proposed lots is
21. The resulting yield is 1.1 dwelling units per acre, well below the density
threshold of 2 dwelling units per acre.
2. Dispersed Flow
As outlined in the Dispersed Flow requirements of the NCDEQ Stormwater
Manual this project must be designed to maximize dispersed flow through
vegetated areas and minimize channelization. Downspouts from the proposed
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STORMWATER NARRATIVE
IVY BROOK
homes will spill onto grade and not be piped. This will allow infiltration and
reduced erosion as runoff drains toward the roadway side ditches and swales
between homes.
3. Vegetative Conveyances
Stormwater runoff that cannot be maintained as shallow flow will be
transported by Vegetated Conveyances. These conveyances will be lined with
vegetation and designed to carry runoff from the 10-year storm at a non -
erosive velocity. Side slopes will be 3.1 maximum, the longitudinal slopes will
be held as flat as possible and a 2' minimum bottom width will be provided.
5. Vegetated Setbacks
No streams exist within the project limits. Consequently, vegetative setbacks
are not being provided.
6. Stormwater Outlets
Stormwater outlets shall be designed such that discharge from the 10-year
storm will be released at non -erosive velocities. Outlet stabilization will be
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STORMWATER NARRATIVE
IVY BROOK
designed in accordance with the erosion control design manual will be
provided at the stormwater outlets.
C. Conclusion
This Stormwater Narrative concludes that the project is being developed in
accordance with the Low -Density provisions of the MDC. The design of the
stormwater drainage system intentionally releases stormwater water at the same
two pre -developed locations. The intent was to maintain pre -developed patterns
as closely as possible. This plan intends to provide dispersed flow and avoid
concentrated discharge. This report and the site construction documents
demonstrate that:
1. The project meets the density threshold requirement of less than 2 dwelling
units per acre.
2. The project utilizes dispersed flow to allow shallow release of stormwater
runoff, minimizes channelization and releases channelized flow through a
vegetated area.
3. Where vegetated conveyances are utilized, they are designed to be non -
erosive for the 25-year storm (exceeds the 10-year storm requirement), are
constructed with 3.1 (or flatter) side slopes, have a 2' minimum bottom
width.
5. Vegetated setbacks are not required.
6. Stormwater outlets will include appropriately sized outlet stabilization.
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STORMWATER NARRATIVE
IVY BROOK
Appendix
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