Roadside swales are drainage ditches that also treat runoff to improve water quality, including infiltration of water
to reduce pollutant load. In the infiltration study, a quick and simple device, the Modified Philip Dunne (MPD)
infiltrometer, was utilized to measure an important infiltration parameter (saturated hydraulic conductivity, Ksat) at
multiple locations in a number of swales. The study showed that the spatial variability in the swale infiltration rate
was substantial, requiring 20 or more measurements along the highway to get a good estimate of the mean swale
infiltration rate. This study also developed a ditch check filtration system that can be installed in swales to provide
significant treatment of dissolved heavy metals and dissolved phosphorous in stormwater runoff. The results were
utilized to develop design guidelines and recommendations, including sizing and treatment criteria for optimal
performance of the full-scale design of these filters. Finally, the best available knowledge on swale maintenance
was combined with information obtained from new surveys conducted to develop recommendations for swale
maintenance schedules and effort. The recommendations aim toward optimizing the cost-effectiveness of roadside
swales and thus provide useful information to managers and practitioners of roadways. The research results and
information obtained from this study can thus be used to design swale systems for use along linear roadway
projects that will receive pollution prevention credits for infiltration. This will enable the utilization of drainage
ditches to their full pollution prevention potential, before building other more expensive stormwater treatment
practices throughout Minnesota and the United States.
Gulliver, John S.; Ahmed, Farzana; Natarajan, Poornima; Weiss, Peter T.; Nieber, John L..
Assessing and Improving Pollution Prevention by Swales.
St. Anthony Falls Laboratory.
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