Urban Runoff and Pollutant Reduction by Retrofitting Green Infrastructure in Storm Water Management System

摘要

Construction of impervious surface by replacing natural vegetation increases surface runoff and is traditionally managed by channeling storm water to an outlet. However, traditional methods create problems such as downstream erosion and flooding, reduction in ground water storage, and increase in pollutant loads. This study presents an analysis on reduction of runoff quantity and pollutant loads by retrofitting urban stormwater management system. Retrofitting was done by using combinations of green infrastructures such as rain cisterns, infiltration trenches, permeable pavement, and roof disconnections. A part of University of Nevada Las Vegas campus area was selected as study area. A design rainfall of 6-hour duration with a return period of 100 years was used to analyze flooding and design retrofits. Storm water management model was used to model infiltration and flow routing in the existing storm water network with system of conduits and storage units. Runoff and pollutant response was analyzed by dividing the area into subcatchments based on existing structures and stormwater inlets. Pollutant loads were modeled using buildup and washoff equation for two different land uses and routed through drainage systems. Results were validated by using the runoff quantity and pollutant loads from previous studies. Cost estimates of retrofits were calculated using stormwater calculator. Green infrastructures such as permeable pavement, infiltration basin, rain cisterns, and rooftop disconnections were suggested as retrofits to solve the problem of flooding. The results showed that impermeable pavements and infiltration basins were most effective for parking lots and reduced the runoff by as high as 90% and pollutant loads by 57%. The runoff coefficient was reduced significantly up to 94% for catchments with high percentage of replaceable impervious cover such as parking lots. Roof cisterns were suggested as an option to control runoff from buildings. The total installation cost of retrofits was estimated to be 5.2 million dollars. Retrofitting with green infrastructures could be helpful for planners to reduce runoff and pollutant loads.