Every grading permit comes with a condition: you must prevent sediment from leaving your site during construction. It sounds simple. In practice, erosion and sediment control (ESC) is one of the most frequently cited violations during construction, and inspectors have no patience for sites that discharge muddy water into the storm drain system.

This article covers the primary erosion and sediment control BMPs used during construction, how they work, where they go, and the common mistakes that turn a compliant site into a violation.

Why It Matters

During construction, exposed soil is the single largest source of sediment pollution in stormwater. A one-acre construction site can produce 35 to 45 tons of sediment per year — 10 to 20 times the amount produced by agricultural land and 1,000 to 2,000 times the amount from forested land. That sediment clogs storm drains, fills detention basins, buries aquatic habitat, and carries attached pollutants (phosphorus, metals, hydrocarbons) into receiving waters.

The Clean Water Act, through the NPDES Construction General Permit (CGP) in most states, requires erosion and sediment control on all construction sites that disturb one acre or more. Many jurisdictions have local grading ordinances that apply to even smaller sites. The requirements are not suggestions. Violations can result in stop-work orders, fines of $10,000 to $50,000 per day, and personal liability for the site superintendent and the project owner.

Erosion Control vs. Sediment Control

These are two different things, and the distinction matters:

• Erosion control prevents soil from detaching in the first place. Examples: mulching, hydroseeding, erosion control blankets, soil binders, plastic sheeting, and preserving existing vegetation. These are always the first line of defense because it is cheaper and more effective to keep soil in place than to catch it after it moves.
• Sediment control captures soil that has already become mobile. Examples: silt fences, fiber rolls, sediment basins, inlet protection, stabilized construction entrances. These are the backup, not the primary defense.

A compliant ESC plan uses both. Erosion control on all exposed surfaces. Sediment control at the site perimeter and at every discharge point.

Primary BMPs

Silt Fence

A woven or non-woven geotextile fabric attached to stakes, installed along the site perimeter at the downslope edge. The fabric ponds sediment-laden water behind it, allowing the sediment to settle out before the water flows through or over the fabric.

Installation requirements: The fabric must be trenched into the ground a minimum of 6 inches and backfilled. Stakes at 6-foot maximum spacing. The fence must follow the contour, not run up and down the slope. Maximum contributing drainage area is typically one-quarter acre per 100 linear feet of silt fence. Silt fence is not designed to hold back flowing water — it is a filtering device for sheet flow only.

Common mistakes: Not trenching the bottom (water goes under the fence instead of through it). Running silt fence across a concentrated flow path (the flow overtops or undermines it). Not maintaining it — sediment buildup should be removed when it reaches one-third the height of the fence.

Fiber Rolls (Wattles)

Cylindrical rolls of straw, coconut fiber, or excelsior, typically 8 to 12 inches in diameter and 20 to 25 feet long. They are staked to the ground surface along the contour to slow sheet flow and trap sediment.

Best applications: Slope faces, where they are installed horizontally at regular intervals (typically every 15 to 25 feet of slope length) to break up the flow path and prevent rill erosion. Also used at the perimeter of disturbed areas and around drain inlets.

Installation: Dig a shallow trench (2 to 3 inches deep), lay the roll in the trench, and stake it with wooden stakes at 3- to 4-foot intervals. Overlap adjacent rolls by at least 6 inches. Turn the ends uphill to prevent flanking.

Stabilized Construction Entrance

A pad of 3- to 6-inch crushed aggregate, typically 50 feet long, 20 feet wide, and 12 inches thick, at every point where vehicles leave the site onto a paved road. The purpose is to knock mud off tires before vehicles track it onto public streets.

Requirements: Most permits require that the entrance be the only point where vehicles can leave the site. A rumble strip of larger rock at the exit point improves effectiveness. If tracking still occurs despite the stabilized entrance, a tire wash station may be required. Sediment that does get tracked onto the road must be swept up (dry sweeping or vacuum), not washed into the storm drain.

Inlet Protection

Every storm drain inlet within and immediately downstream of the construction site must be protected to prevent sediment from entering the storm drain system. Common methods include:

• Gravel bags — sandbags filled with 3/4-inch gravel, stacked around the inlet to form a filter berm. Simple, effective, and easy to maintain.
• Filter fabric and frame — a geotextile filter stretched over a wire or wood frame placed around or over the inlet grate.
• Proprietary devices — manufactured inserts (Dandy Bags, Ultra-Drain Guards) that drop into the inlet and filter incoming water.

Sediment Basin

A temporary basin that collects runoff from the disturbed area, detains it long enough for sediment to settle, and discharges relatively clear water. Required on larger sites (typically 10 acres or more of contributing drainage) and sites with high sediment risk.

Sizing: The Construction General Permit typically requires a sediment basin to provide 3,600 cubic feet of storage per acre of contributing drainage. The outlet structure must include a skimmer or riser that decants water from the surface (where it is clearest) rather than from the bottom. A dewatering plan is required for basins that will be pumped.

Erosion Control Measures

Hydraulic Mulch and Hydroseeding

Sprayed-on mulch (wood fiber, cellulose) or seed-and-mulch slurry applied to disturbed areas. Provides immediate cover to reduce raindrop impact erosion and promotes vegetation establishment for long-term stabilization. Typically required on any disturbed area that will be inactive for 14 days or more during the rainy season.

Erosion Control Blankets (ECBs)

Manufactured rolls of straw, coconut fiber, or excelsior held together with netting. Installed on slopes to provide erosion protection while vegetation establishes. Biodegradable versions (which break down over 12 to 24 months as the vegetation takes over) are standard for permanent slopes. Synthetic versions are available for channels and areas with high shear stress.

Soil Binders

Chemical stabilizers (polyacrylamide, guar gum, or proprietary products) sprayed on exposed soil to bind the surface particles together and resist erosion. Useful for large flat areas like building pads that will be exposed for weeks or months. Reapplication is needed after rain events or vehicle traffic.

Inspection and Maintenance

The Construction General Permit requires ESC inspections before and after every rain event, and at least weekly during non-rain periods. The qualified SWPPP practitioner (QSP) or designated inspector must document:

• Condition of every BMP (intact, damaged, bypassed, full)
• Any discharges from the site and their visual quality (clear, turbid, discolored)
• Any areas of erosion, rill formation, or sediment deposition
• Corrective actions taken and the schedule for completion

Most ESC violations occur not because the BMPs were not installed, but because they were not maintained. A silt fence that has been knocked down by equipment. Inlet protection buried under tracked mud. A stabilized entrance that has lost its aggregate and is now a mud pit. Maintenance is the difference between a compliant site and a violation.

Seasonal Considerations

Most jurisdictions have a defined wet season (typically October through April in California, year-round in the Pacific Northwest) during which ESC requirements are more stringent. In California, the risk level assigned to your project (Risk Level 1, 2, or 3 under the CGP) determines the additional requirements during the wet season, including effluent monitoring (turbidity sampling) for Risk Level 2 and 3 sites.

If you are grading during the wet season, plan for it. Install perimeter controls before you start grading, not after. Stage the work so that the minimum area is exposed at any time. And have a rain event action plan (REAP) that specifies exactly what the crew does when rain is forecast: which areas get covered, which BMPs get checked, who is responsible for the 48-hour post-storm inspection.