Erosion control for construction and developing sites will have a major impact on the total pollution loads in receiving waters. Current estimates show that approximately 1500 sq mi of the United States is urbanized annually. All of this land area is exposed to accelerated erosion.
Following are basic guidelines and principles of erosion control. Reduce the area and duration of soil exposure. For example, various mining operation stages should be scheduled so that clearing, grubbing, scalping, grading and revegetation occur concurrently with extraction, so that a minimum area is exposed at one time.
Protect the soil with mulch and vegetable cover. For example, covering the soil surface with wood chips reduces construction site soil loss by 92%. Vegetation also has a marked effect on water quality. Temporary fast-growing grass can reduce erosion by an order of magnitude; sod ding can reduce erosion by two orders of magnitude. Straw mulch application can be combined with grass seeding for permanent surface protection.
Reduce the rate and volume of runoff by increasing the infiltration rate. A properly roughened and loosened soil surface will benefit plant growth, enhance water infiltration, and slow surface runoff.
Diminish runoff velocity with planned engineering works. A key concept in controlling soil erosion is to intercept runoff before it reaches a critical area and divert it to a safe disposal area. Interception and diversion are accomplished through various structures, including earth dikes, ditches, and combined ditch and dike structures (Figure 9.21.1).
Protect and modify drainage ways to withstand concentrated runoff from paved areas. To reduce the rate of flow and the resulting detachment and transport of soil particles in natural and manmade drainageways, grade can be controlled by the construction of flumes or other flow barriers across the channel. Bends in the channel, either natural or manmade, also impede flow.
Trap as much sediment as possible in temporary or permanent sedimentation basins.
Maintain completed works and assure frequent inspection for maintenance needs.
Principal cropland erosion control practices and BMPs for pollutants are summarized in Table 9.21.2.
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