Green Infrastructure for Highway Stormwater Management: Field Investigation for Future Design, Maintenance, and Management Needs

Abstract

Many types of structural stormwater best management practice (BMP) have been employed since the late 1990s in the hope of mitigating the impervious surface hydrology (indicated by, e.g., high runoff volume and peak flow rates, sewer and ditch runoff conveyance, and short time to peak flow) and deteriorating water quality due to land development and human activities. It is time to examine the status of the BMP deployment from an infrastructure perspective and reflect the best strategies for low-impact development (LID). This paper presents a 22-month field investigation for 279 structural BMPs and 227 major outfalls (defined as storm drain outfall pipes with an equivalent diameter of 91 cm or larger) along highways in Prince George’s County, Maryland, an area that has LID BMP research and employment history for decades. This study offers a snapshot about the state and effectiveness of structural BMPs in mitigating highway runoff in this region. The results indicate that the majority of structural BMPs deployed along the regional highway system are infiltration trenches and stormwater ponds, both of which need extensive maintenance. Due to safety concerns for traveling vehicles, fast runoff conveyance and end-of-pipe treatment are sometimes required in highway systems, prompting challenges for the LID designs. Stormwater discharged from 51% of the major outfalls is not treated, indicating strong demands for stormwater green infrastructure expansion and retrofit. This paper identifies general problems and maintenance needs of different highway structural BMP designs as well as providing recommendations for improvement to engineers and highway administrators.