Bioretention for Highway Stormwater Quality Improvement in Texas: Final Report (0-5949-4)

This final report summarizes five years' worth of work in evaluating the applicability and performance of bioretention best management practices (BMPs) for highway environments in Texas. Within the five-year time frame, the research team did a literature review, conducted pilot experiments, and constructed a field demonstration site. The field site was tested with two different designs: (1) dry (or non-internal water storage [IWS]) and (2) internal water storage types. The field site is near the intersection of SH 21 and SH 6 in Bryan, Texas. The site includes a water hydrant for irrigation and synthetic runoff tests. The report includes introduction, research methods, test results, discussion, drawing examples, designs and maintenance guidelines, a special specification, a planting plan guide, a summary of the site selection process, and test data. In summary, bioretention BMPs can reduce peak flow and increase detention time. Non-IWS design moderately removed suspended solids; less effectively removed copper and zinc, less effectively removed total nitrogen, and moderately removed total phosphorus. The IWS layer significantly improved all performances, including hydraulic and water quality. The significance of this research project is that bioretention BMPs are a promising method for highway application in hot, semi-arid areas. Furthermore, the IWS layer is a viable application to improve bioretention performances.