High Performing Turf Reinforcement Mats Provide Stormwater Control in Large Drainage Channel

摘要

In 2004, Illinois Department of Transportation District 2 Engineers were planning the extension of the Milan Beltway in the Quad Cities area of Northwestern Illinois, which include a long and highly visible drainage swale. Initial plans called for a rock riprap channel lining with cost estimates for this solution totaling about one million dollars. In addition to obvious concerns about the high price tag, the engineers were also concerned about aesthetics and maintenance of a rock lined channel. For all these reasons, the IL DOT engineers sought out a vegetated solution for this project. The channel adjacent to the beltway extension and the busy John Deere Expressway in Moline, Illinois needed to withstand the stormwater runoff created by the large roadways. During storm events the channel needed to withstand velocities of 20 ft/s and shear stress forces reaching 13 lbs/ft~2. 20,000 square yards of permanent Composite Turf Reinforcement Mats were installed in November of 2005. The late installation provided a real challenge to the project, requiring dormant seeding and leaving an unvegetated channel to withstand high flows through the winter months and into early spring. Moreover, 20 % of the upstream installation was not completed before winter. This area, just north of two 10 ft×10 ft box culverts, feeding the main channel, were left protected only by straw bale ditch checks. Several intense storms in late spring put the newly installed channel to the test. One storm produced 3.5 inches of rain within one day creating flashflood conditions, while a storm only a few weeks later produced 2 in/hr rainfalls resulting in standing water several feet deep. During these storm events, the upstream temporary straw bale ditch checks blew out totally, but the composite turf reinforcement mat provided the necessary erosion control to protect the channel. A site review in the spring of 2006 concluded that the lined channel had performed exceptionally well, and the site was fully vegetated within the first year. Compared to hard armor products the vegetated Turf Reinforcement Mats acted as a natural filter for stormwater runoff by allowing infiltration, entrapping sediments, and absorbing harmful pollutants, all while saving the Illinois DOT two-thirds of the original rock rip rap price tag.