Evaluating the Effectiveness and Maintenance of Low Impact Development Designs for Stormwater Management: A Case Study Along Lorton Road in Fairfax County

About the report:

Concerns about the quality of stormwater runoff from highways have increased steadily in recent years as more roads are built or widened. To mitigate the pollution of highway runoff on receiving waters, low impact development (LID) stormwater management systems have been employed as an environmentally sustainable alternative to treat stormwater in urban areas.

This research assesses the effectiveness of four LID systems, which include a bioretention basin, a grass channel, a compost-amended grass channel, and a bioswale, along Lorton Road in Fairfax County, over an extended monitoring period spanning multiple years. The primary objective is to investigate the stormwater quantity and quality performance of these LID systems. This study also evaluates their maintenance efficiency, factoring in various water quality parameters and economic costs, primarily emphasizing safeguarding public health and environmental preservation.

Results of this study indicate that the grass channel emerged as the most effective in terms of runoff and pollutant load reductions, despite serving a modest contributing drainage area and incurring higher average maintenance costs per catchment drainage area annually. In contrast, bioretention, which ranked second in volume and mass load reduction for pollutants, effectively serves the largest contributing drainage area and maintained consistent performance over time. Maintenance efforts enhanced the performance of the swales, with the compost-amended grass channel showing the most significant improvement, emphasizing the effectiveness of maintenance for this specific type of swale.

Three notable changes in practice are recommended. First, use multiple performance metrics to evaluate LID performance, such as considering contributing drainage area, footprint, and maintenance procedures. Second, consider other pollutants in addition to phosphorous. Third, exercise caution when employing compost amendments in swale soils to avoid nutrient losses, as evidenced by the negative impact observed in the compost-amended grass channel. Because the Department of Environmental Quality draft Stormwater Management Handbook is presently being updated, VDOT has an opportunity, through participation in the Stormwater Advisory Group, to advocate for these changes in practice.

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