Overview and role of soil in stormwater management

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Soils affect stormwater and stormwater management in two ways.

• Soil is a source of sediment and associated pollutants (e.g. metals, organic compounds) for stormwater runoff.
• Soil affects the types of stormwater management practices that can be implemented at a site (e.g. potential for infiltration, vegetation)

Soil erosion

Soil erosion and sediment runoff to waterways are significant problems in Minnesota. According to the Minnesota Pollution Control Agency (MPCA 2016), approximately 30 percent of the state’s rivers and streams are impaired by sediment. Poorly managed construction sites can be substantial sediment sources to these surface waters. Up to 100 tons of sediment per acre can be lost annually from unmanaged construction sites (EPA 1999).

The Universal Soil Loss Equation (USLE) and it's update, the Revised Universal Soil Loss Equation (RUSLE) are used to predict sheet and rill erosion. Soil loss, typically expressed on an annual basis in tons per acre, is affected by rainfall characteristics, soil erodibility, slope length and gradient, soil cover, and erosion control practices. Soil erodibility is the intrinsic susceptibility of a soil to erosion by runoff and raindrop impact. In general, the following affect soil erodibility.

• Increasing amounts of soil organic matter result in decreasing values of K
• Soil type effect on K: silt > silt loam = fine sand > loam > clay loam > clay > coarse sand. Note that wet clay soils that have expanded have increased risk.
• Coarse sand particles are too large to transport
• Clays are cohesive with good soil structure and it is difficult to dislodge soil particles
• Silts and fine sands are not cohesive and are easily transported
• Texture is the principal factor affecting Kfact, but structure, organic matter, and permeability also contribute
• The soil erodibility factor ranges in value from 0.02 to 0.69.

For more information on soil erodibility, link here.

Managing soil loss involves erosion protection and sediment control, with erosion protection being preferred.

Erosion protection practices

• Stabilization practices
• Erosion prevention practices - temporary seeding and stabilization
• Erosion prevention practices - natural and synthetic mulches
• Erosion prevention practices - tackifiers and soil stabilizers
• Erosion prevention practices - erosion control blankets and anchoring devices
• Erosion prevention practices - turf reinforcement mats
• Erosion prevention practices - Riprap

Sediment control

• Sediment control practices - Vehicle tracking BMPs
• Sediment control practices - Perimeter controls for disturbed areas
• Sediment control practices - Check dams (ditch checks, ditch dikes)
• Sediment control practices - Diversion barrier controls (cofferdams/temporary dikes)
• Sediment control practices - Storm drain inlet protection
• Sediment control practices - Outlet energy dissipation
• Sediment control practices - Sediment traps and basins
• Sediment control practices - Stabilized earth/soil berm
• Sediment control practices - Buffer zones
• Construction stormwater treatment - dewatering, including chemical treatment and sediment filtration