STORMWATER

A number of new products have entered the stormwater mitigation and erosion control marketplace. Everything from plastic drain basin protectors, manufactured fiber products and several unique streambed stabilizing technologies are now available. Interlocking concrete blocks, in combination with filter fabrics, can be used to clearly define a drainage swale or constructed wetland and also improves maintenance accessibility. Old-fashioned storm drains, silt fence and bales of hay will continue to be used. The manufactured fiber products are more resistant to harsh weather conditions and actually promote the growth of beneficial vegetation. Silt fencing requires frequent monitoring as excess silt or damage during construction could compromise the material. In the past, storm drain protection usually amounted to a piece of filter-fabric draped over the grating. This can be effective, as long as silt and debris are kept off of the fabric. Once silt and debris deposit on the fabric, it simply falls through, so much for protection. A better solution is a flexible filter, rigid frame, insert that goes under the grate.

Why don’t we see more of this new technology? Typically, contractors and engineers tend to use the “tried and true” equipment. We are all guilty of resisting change.

On a recent trip, south of the Mason-Dixon Line, I observed a plastic drainage system being installed as part of the road bed construction. The engineer explained that many intersections are low-lying and tend to form large puddles during rain events. Using this under-pavement drain and shoulder drains allowed the stormwater to infiltrate the surrounding soils and runoff much quicker than simply relying on storm sewers. Paper, plastic and other refuse have a tendency to block storm drains when they are needed most. Some cities have to retrieve “man-hole” covers following a rain event. The force of water backing up in a storm sewer can actually lift and transport those heavy covers. (Another reason for not driving through a flooded intersection.)

Separation of solids from the stormwater remains an important feature in modern design. Some applications simply use screens or grates, others have begun to use swirl pattern designs. These devices push the solids to the side, allowing the stormwater to flow through unimpeded. Lifting the cover provides access for maintenance and cleaning. Regardless of the design, a schedule of cleaning and preventive maintenance will be necessary.

Parking lots present a difficult situation. Large impervious areas tend to concentrate stormwater flows. The scouring action will clean the parking lot, however, grit and refuse are combined with the water. By filtering the stormwater and directing the flow into chambers under the parking lot, clogging of the infiltration devices can be minimized and sufficient volume will reduce the impact from runoff. Stormwater draining from a roof should be dealt with in a similar manner.

Have you noticed the number of pervious driveways being installed around town? It seems to be catching on!

Steve Luckett

WPCA Coordinator