Silt Fence Drainage-Area and Length Check

Whether a silt fence is long enough for the drainage area behind it (required length = tributary acres x 400, the quarter-acre-per-100-ft guideline) and whether the slope length stays under the AHJ limit. A 0.5-acre tributary needs 200 ft of fence; a 250 ft run catches up to 0.625 acre. Sheet flow only - a channel needs a check dam.

required_fence_len_ft = tributary_area_ac x 400 (a quarter acre of drainage per 100 ft of fence); max_area_ac = fence_length_ft / 400; length_adequate = fence_length_ft >= required_fence_len_ft; slope_ok = slope_length_ft <= max_slope_length_ft.

Silt-fence drainage-area guideline by name (quarter acre per 100 ft); first-principles arithmetic; the AHJ slope-length limit is user-entered.

The quarter-acre-per-100-ft figure is a generic published guideline; the AHJ maximum slope length is entered, not reproduced from a copyrighted table.

Estimate. AHJ and licensed professional govern.

Field names used by the API: tributary_area_ac, fence_length_ft, slope_length_ft, max_slope_length_ft, required_fence_len_ft, max_area_ac

• Drainage guideline quarter acre of drainage per 100 ft of fence (required length = acres x 400)generic SWPPP guidance
• Slope length 100 ft AHJ maximum default; the SWPPP spec and permitting AHJ governAHJ / SWPPP