HomeMy WebLinkAboutStormwater ManagementClover Group Inc Stormwater Management Plan CGSTW-2025
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Stormwater Management Plan –
Engineering Submittal
Project Name: Porters Neck ADU Residential Development
Location: 406 & 408 Porters Neck Road, Wilmington, NC
Parcel Size: 2.01 Acres (87,556 sq ft)
Zoning District: R-15 Residential
Prepared For: Clover Group Inc.
1. Project Overview
This stormwater management plan supports a residential development consisting of sixteen
(16) Accessory Dwelling Units (ADUs), one (1) primary residence, and one (1) existing
utility building. The development features a gravel access road, gravel parking pads, and a
natural retention pond designed to handle on -site stormwater runoff. The site preserves
existing tree buffers and follows natural contours to support sustainable drainage.
2. Stormwater Regulatory Requirements
According to New Hanover County’s Stormwater Ordinance, any site disturbing more than
10,000 sq ft is subject to stormwater design review. This plan is prepared in compliance
with the NHC UDO Section 23, NCDEQ Stormwater Design Manual (2022), and EPA Phase II
MS4 requirements.
3. Built-Upon Area (BUA) and Volume Calculations
The effective impervious area is estimated at 27,760 sq ft, based on the following:
- ADUs: 16 x 800 sq ft = 12,800 sq ft (100% impervious)
- Primary Home: 2,000 sq ft (100%)
- Gravel Access Road: 600 ft x 20 ft = 12,000 sq ft (70%) = 8,400 sq ft
- Gravel Parking Pads: 16 x 300 sq ft = 4,800 sq ft (70%) = 3,360 sq ft
- Existing Office: 1,200 sq ft (100%)
Total Built-Upon Area: ~27,760 sq ft (~0.637 acres)
4. Design Storm and Retention Volume
Design Storm: 1.5 inches over 24 hours.
Runoff Volume = C x P x A = 0.637 acres x 1.5 in x (1 ft / 12 in) x 43,560 sq ft/acre = ~3,460
cu ft.
A retention pond must be sized to treat this volume, capturing the first flush from
impervious surfaces and releasing at pre-development rates.
Clover Group Inc Stormwater Management Plan CGSTW-2025
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5. Retention Pond Design
The proposed retention pond will meet the following specifications:
- Surface Area: 3,500–5,000 sq ft (~0.08–0.12 acres)
- Depth: 3.5–4 ft
- Volume: 3,500–4,000 cu ft
- Forebay for sediment control
- Primary outlet: 6” PVC orifice
- Emergency spillway: natural grade, riprap-lined
- 5 ft vegetated buffer around pond
- 10 ft gravel access path for maintenance
The pond will be located at the front-right corner of the site, aligned with topographic
runoff flow.
6. Low-Impact Development Features
This development incorporates LID strategies:
- Gravel roads and parking reduce runoff
- Existing tree buffers remain undisturbed
- Site grading follows natural topography
- Optional rain garden or swales along internal greenspace
7. Maintenance Plan
Clover Group Inc. will implement the following:
- Quarterly pond inspections
- Annual sediment removal from forebay
- Vegetation maintenance and buffer upkeep
- Documentation of maintenance activities for County review
8. Compliance Summary
The proposed design:
- Meets and exceeds stormwater treatment volume standards
- Complies with all local, state, and federal stormwater regulations
- Utilizes sustainable drainage principles
- Minimizes environmental impact and preserves natural site features
Prepare by: Clover Group Inc.
Bernard Miller
910-800-9682