Simplified Analysis Method for Natural Dispersion of Highway Storm Water Runoff in Rural Areas

Abstract

Storm water quantity control has long been a challenge for highway designers. Traditionally, centralized best management practice designs are often cost prohibitive and inefficient in many rural highway applications. The use of existing vegetated rights-of-way as a method of treating storm water, a component of the broader storm water treatment concept more generally referred to as low-impact development, has become a primary focus of the Washington State Department of Transportation. To design and use such storm water management controls adequately, however, further research and correlation between numerical infiltration–runoff models and field experiments were needed. This paper focuses on evaluating natural dispersion performance through the use of simulated rainfall runoff data collected with a field-scale rainfall simulator and a numerical model to study the effects of slope length, angle, and impervious contributory area on natural dispersion applications. A simple new equation was developed to analyze natural dispersion performance on the basis of multiple variables. The research and resulting evaluation procedure indicated that the use of natural dispersion as a storm water quantity control strategy is applicable to many roadside areas in Washington State.