Abstract

Bioswales are a promising stormwater control measure (SCM) for roadway runoff management, but few studies have assessed performance on a field scale. A bioswale is a vegetated channel with underlying engineered media and a perforated underdrain to promote improved hydrologic and water quality treatment. A bioswale with a rip-rap lined forebay was constructed along state highway NC 211 in Bolivia, North Carolina, USA, and monitored for 12 months. Thirty-seven of the 39 monitored rain events exfiltrated into underlying soils, resulting in no appreciable overflow or underdrain volume. The bioswale completely exfiltrated a storm event of 86.1 mm. The one event to have underdrain-only flow was 4.8 mm. The largest and third-largest rainfall depth events (82.6 and 146 mm, respectively) had a large percentage (85%) of volume exfiltrated, but also had appreciable overflow and underdrain volumes exiting the bioswale, resulting in no peak flow mitigation. Overall, this bioswale design was able to capture and manage storms larger than the design storm (38 mm), showing the positive hydrologic performance that can be achieved by this bioswale. The high treatment capabilities were likely due to the high infiltration rate of the media and the underlying soil, longer forebay underlain with media, gravel detention layer with an underdrain, and shallow slope.

Highlights

  • The United Nations predicts that by 2050, 66% of the world’s population will be living in urban areas [1]

  • The continued urbanization and consequent negative hydrologic impacts highlight the need for stormwater control measures

  • The studied bioswale was built in Brunswick County in Bolivia, North Carolina (NC), USA

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Summary

Introduction

The United Nations predicts that by 2050, 66% of the world’s population will be living in urban areas [1]. This increase in urban population will cause an increase in impervious cover resulting from urban sprawl. Changes in land cover likely alter storm hydrographs, resulting in increased runoff volumes, peak flows, and a decreased time to peak flow [7,8,9], causing an increased occurrence of flooding [10]. The continued urbanization and consequent negative hydrologic impacts highlight the need for stormwater control measures. Low impact development (LID) is a design philosophy to manage stormwater near its source [11]

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