Low Impact Development (LID) techniques that are economical and appropriate for the highway environment are important tools for state departments of transportation (DOTs) faced with increasingly demanding 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. Their use is limited however, by site constraints such as limited right-of-way and steep side slopes, and their effectiveness may vary greatly depending on climate, soils, and other factors. Vegetated compost blankets (VCBs) can overcome some of these limitations by promoting stormwater filtration, retention of runoff, and infiltration of stormwater into the underlying soils, potentially removing pollutants and reducing flow volumes. VCBs have the potential to be relatively low cost and low maintenance, which makes them attractive to state DOTs. VCBs also can be a relatively simple retrofit on a roadside embankment.
Research was needed to evaluate hydrologic and water quality benefits of VCBs, which 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.
The objectives of this research were 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.