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Win-Win: Using Sediment and Erosion Control Technology to Overcome Regulatory Challenges AND Increase Project Benefit

Sediment and erosion control (SEC) technology typically comes to the forefront in tackling over-increasing NPDES regulations, land disturbance requirements, and other routine issues. However, for a residential development in Chesterfield, Missouri, the creative application of SEC technology played a critical role in solving larger regulatory permitting issues. Federal regulatory requirements were satisfied in a technically challenging setting, and without burdening the project. SEC solutions actually added to the overall project objectives and site aesthetics, as well as lowered project expenses.

The Reserves at Chesterfield Village is an upscale residential development bordering perennial Chesterfield Creek. Chesterfield Creek and its wooded buffer are protected by the U.S. Army Corps of Engineers (CE) as environmental mitigation area. Special permission from the CE was required to discharge stormwater into the creek through the mitigation area. Authorization from the CE hinged on two key aspects. First, that disturbance be limited to only two areas. Secondly, that the discharge areas be restored to near-natural conditions.

Preliminary engineering plans specified six stormwater discharges to the creek. Concentrating stormwater into only two discharges increased the potential for stormwater erosion. The steep slopes above the creek would be prone to runoff erosion following disturbance. A creative mix of SEC technologies was employed to meet the conditions set by the CE for minimizing disturbance and restoring the site. These included widespread use of turf reinforcement mats (TRM)s, contour wattling, native vegetation, and tree preservation and replanting. Instead of piping, an existing 400-ft. natural swale was modified to conduct 16 c.f.s of stormwater. Modifications include TRM, velocity checks, and laminar flow converters. At both discharge areas, stormwater enters the channel into constructed rock grade control zones. These are designed to prevent channel head cutting and bank erosion. They also function like natural rock riffles, increasing aquatic habitat potential.

Construction was completed in fall of 2007. The project area has since experienced record precipitation. Both discharge areas have functioned as designed under extreme conditions. Without the employment of SEC technology, the battering by spring rains and design-event flows would likely have resulted in significant erosion of slopes and discharge points. However, the project successfully met the regulatory mandates for protecting and restoring the mitigation area. Moreover, the natural appearance of the vegetated discharges adds to the pastoral setting promoted by the developer. And best of all, the "green" SEC methods that were used saved substantial costs over conventional piping or concrete swale design.