Steep Slope Development and How It Effects the Environment Back

 

Steep slope disturbance can result in grave consequences to watercourses. Erosion and sediment from construction sites can impair water supplies, the biological integrity of a waterbody, and the local hydrology. Erosion and sediment impair water supplies by: increasing nutrient loading, impairing the ability of chlorine to disinfect the water supply, reducing the storage capacity of reservoirs, and increasing the treatment costs of any municipalities that filter their water supply. Erosion and sediment impair the biological integrity of waterbodies by filling streambeds and threatening macroinvertebrate habitat. Additionally, erosion and sediment alter hydrology by reducing the stream’s carrying capacity and increasing the likelihood of flooding.


For these reasons, construction activities on steep slopes should be severely limited. In the event that activities are required in close proximity to steep slopes, stabilization of the slopes should first be accomplished by grading to decrease runoff velocity over erodible soils, and site fingerprinting to minimize disturbance(1). Improper grading practices disrupt natural stormwater runoff patterns, resulting in poor drainage, high runoff velocities, and increased peak flows during storm events(2). For these reasons, permitting authorities should require a grading plan before approving grading activities. The plan should identify areas of the site to be graded and should address alteration of existing drainage patterns, and practices to stabilize, maintain and protect slopes from runoff. The grading plan also should include a schedule for grading disturbances as well as methods for disposal of borrow and fill materials(3).
Site fingerprinting is a low-impact development BMP that involves clearing and grading only those onsite areas necessary for access and construction activities. Extensive clearing and grading of sites promotes off-site transport of sediments and other pollutants(4). Site fingerprinting and the maintenance of temporary or permanent vegetated buffers during grading operations provide sediment control that reduces runoff and off-site sedimentation(5). Destruction of vegetated buffers on site perimeters and alteration of existing drainage patterns severely limits the effectiveness of land grading in stabilizing steep slopes and erodible soils.


EPA recommends periodic inspection of all graded areas and supporting erosion and sediment control practices, especially after rain events(6). Early detection and repair of failing control measures are critical in preventing small-scale eroded areas from becoming significant conveyances of stormwater runoff and its attendant pollutants(7).
EPA also recommends a Storm Water Contamination Assessment (SWCA) program to identify primary contaminants of concern for correction or prevention. The program is applicable in areas that contain materials or are subject to activities that may contribute pollutants to stormwater runoff from the site. The program is also valuable in identifying BMPs to control contamination from high-risk sources on a site-by-site basis.


All photos @Brian Alberghini

By Marc A. Yaggi, Senior Attorney and William Wegner, Watershed Analyst, Riverkeeper, Inc.

See U.S. ENVIRONMENTAL PROTECTION AGENCY, CONSTRUCTION SITE STORM WATER RUNOFF CONTROL, LAND GRADING

(last visited January 3, 2009).


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