Selecting cost-effective low-impact development (LID) treatments is essential for state departments of transportation (DOTs) to address the increasing demands for water quality and hydrologic management requirements. Vegetated filter strips along highways, an accepted LID Best Management Practice (BMP), are a cost-effective alternative to hydraulically engineered BMPs. However, this treatment may be limited by site constraints (i.e., limited right of way (ROW) and steep side slopes) and their effectiveness may vary depending on climate, soils, and other factors.
VCBs can overcome some of these limitations by promoting stormwater filtration, retention of runoff, and infiltration of stormwater into the underlying soils while potentially removing pollutants and reducing flow volumes. As a simple retrofit on roadside embankments, VCB’s low maintenance requirements have the potential to prove a good return on investment.
In order to provide state DOTs with an effective and economical BMP to assist state DOTs with effective uses of VCBs in highway projects, research was needed to evaluate hydrologic and water quality benefits of VCBs that can be used in a wide variety of roadway settings. This involved determining pollutant removal capability and capacity; the ability to detain and retain runoff; and the effect of climate, soils, compost composition, compost blanket thickness, and other parameters on performance.
Under NCHRP Project 14-39, “Using Vegetated Compost Blankets to Achieve Highway Runoff Volume and Pollutant Reduction,” the University of Maryland was asked to: (1) develop performance curves for surface-applied, VCBs on slopes of 3:1 or flatter that (a) remove pollutants of concern, (b) control erosion, (c) reduce volume, and (d) support vegetation when placed on an existing roadway embankment; and 2) provide construction specifications, standard details, and a decision matrix that provides guidance on the use, limitations, design, and implementation of vegetated compost blankets on existing roadway embankments.
The guidelines are intended to be a practical manual for state DOTs who select, design, and implement stormwater management facilities, which should be broadly applicable to a wide range of conditions and geography.
NCHRP Research Report 1040 presents a state-of-the-art investigation into vegetated compost blankets (VCBs) for stormwater control and the resulting impacts on the vegetative establishment, stormwater volume reduction, and water quality improvement. The research was based on a comprehensive analytical, field, and laboratory assessment. This report will be of immediate interest to design and maintenance engineers.
