Silt fence limits (NC DEQ 6.62)
The longest slope that may drain to a sediment fence, by the slope of the land above it. The area it can serve is that length times 100 feet for every 100 feet of fence.
| Land slope | Max. slope length | Area per 100 ft of fence | Acres per 100 ft |
|---|---|---|---|
| under 2% | 100 ft | 10,000 sf | 0.23 |
| 2 to 5% | 75 ft | 7,500 sf | 0.17 |
| 5 to 10% | 50 ft | 5,000 sf | 0.11 |
| 10 to 20% | 25 ft | 2,500 sf | 0.06 |
| over 20% | 15 ft | 1,500 sf | 0.03 |
- Standard-strength fabric on 14-gauge wire mesh: posts 8 feet apart at most. Extra-strength fabric without wire: 6 feet.
- Posts driven at least 24 inches; fence no taller than 24 inches above the ground.
- Trench 4 inches wide and 8 inches deep, with 12 inches of fabric along its bottom and side, backfilled and compacted.
- One continuous roll where possible; joints only at a post, overlapped 4 feet.
- Never across ditches, streams or other concentrated flow.
Temporary seeding (NC DEQ 6.10)
Rates per acre for the Piedmont; seeding dates differ in the mountains and on the coastal plain.
| Season | Seed, lb/acre | Lime | 10-10-10 | Straw |
|---|---|---|---|---|
| Late winter and early springJan. 1 – May 1, table 6.10a | Rye (grain) 120; Annual lespedeza 50 | 2,000 | 750 | 4,000 |
| SummerMay 1 – Aug. 15, table 6.10b | German millet 40 | 2,000 | 750 | 4,000 |
| FallAug. 15 – Dec. 30, table 6.10c | Rye (grain) 120 | 2,000 | 1,000 | 4,000 |
Straw is anchored by tacking with asphalt, netting or a mulch anchoring tool. At 4,000 pounds an acre and about 45 pounds a bale (Practice 6.14 calls 70 to 90 pounds one and a half to two bales), that's about 89 bales an acre. Weigh a few of your supplier's bales; they vary.
Wattles (NCDOT)
- Wattles are 10 feet long, 12 to 18 inches in diameter, excelsior for jobs of a year or less and coir for longer.
- In ditches under 2.5% grade, a wattle every 50 feet, on matting, with PAM where the plan calls for it.
- As slope breaks or barriers, no more than 20 feet apart, overlapped at least a foot.
- Each wattle takes 6 stakes: 2 upslope and 4 downslope.
A worked example
1,200 feet of wire-backed silt fence in 3 runs on a 6% slope, and 4 acres of late-winter temporary seeding:
- Posts: 1,200 ÷ 8 + 3 end posts = 153. Fabric: 13 rolls of 100 feet, with 4-foot laps. Wire: 1,200 feet.
- At 6% the slope above may be at most 50 feet, so the fence can serve 1.38 acres.
- Seed: 480 lb of rye (grain) and 200 lb of annual lespedeza. Lime 8,000 lb (160 bags), 10-10-10 3,000 lb (60 bags), straw 8 tons, 356 bales.
The topsoil calculator sizes a stockpile and the fence around it, and Site Bid carries each of these as a line in the estimate.
Sources
- NC DEQ, Erosion and Sediment Control Planning and Design Manual, Practice 6.62, Sediment Fence (effective 9/1/2023). Checked October 4, 2026.
- NC DEQ, Temporary and Permanent Seeding Specs, Practice 6.10, tables 6.10a–c. Checked October 4, 2026.
- NC DEQ, Practice 6.14, Mulching (effective 9/1/2023).
- NCDOT Roadside Environmental Unit, Wattle Application on Linear Projects. Checked October 4, 2026.
- Matting roll sizes and staple patterns vary by product; enter your product's.
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