Joong Gwang Lee

A watershed-scale design optimization model for stormwater best management practices

U.S. Environmental Protection Agency developed a decision-support system, System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN), to evaluate alternative plans for stormwater quality management and flow abatement techniques in urban and developing areas. SUSTAIN provides a public domain tool capable of evaluating the optimal location, type, and cost of stormwater best management practices (BMPs) needed to meet water quality and quantity goals. It is a tool designed to provide critically needed support to watershed practitioners in evaluating stormwater management options based on effectiveness and cost to meet their existing program needs. SUSTAIN is intended for users who have a fundamental understanding of watershed and BMP modeling processes. How SUSTAIN is setup described here using a case study, conducted by actual data from an existing urban watershed. The developed SUSTAIN model was calibrated by observed rainfall and flow data, representing the existing conditions. The SUSTAIN model developed two BMP cost-effectiveness curves for flow volume and pollutant load reductions. A sensitivity analysis was also conducted by varying important BMP implementation specifications.

Costs and benefits of capturing urban runoff with competitive bidding for decentralized best management practices

[1] Urban storm water runoff is both a source of pollution and a potentially valuable resource. Centralized facilities traditionally have been used to manage runoff. Decentralized best management practice (BMP) options may be able to avoid the costs of purchasing expensive urban land needed for centralized facilities. We investigate the cost effectiveness of implementing BMPs in a Los Angeles area watershed with two voluntary incentive mechanisms: competitive bidding and a fixed subsidy. The subsidy mechanism has lower BMP placement costs but generates relatively large excess profits for landowners. The bidding mechanism has higher BMP placement costs but generates smaller excess profits and tends to be more cost effective for the regulator, particularly at higher runoff capture levels. We also compare the costs of bidding and centralized alternatives and find that the bidding alternative is significantly less costly than a centralized alternative for a range of storm water capture goals. Finally, we examine the value of infiltrated storm water and find that it is up to 38% of total BMP costs.

Modeling the Hydrologic Processes of a Permeable Pavement System

AbstractA permeable pavement system can capture stormwater to reduce runoff volume and flow rate, improve onsite groundwater recharge, and enhance pollutant controls within the site. A new unit process model for evaluating the hydrologic processes of a permeable pavement system has been developed in this study. The developed model can continuously simulate infiltration through the permeable pavement surface, exfiltration from the storage to the surrounding in situ soils, and clogging impacts on infiltration/exfiltration capacity at the pavement surface and the bottom of the subsurface storage unit. The exfiltration modeling component simulates vertical and horizontal exfiltration independently based on Darcy’s formula with elaborating Green-Ampt approximation. The developed model can be arranged with physically-based modeling parameters, such as hydraulic conductivity, Manning’s friction flow parameters, saturated and field capacity volumetric water contents, porosity, and density. The developed model was...

Determining the Optimal BMP Arrangement under Current and Future Climate Regimes: Case Study

AbstractAs watersheds are urbanized, the amount of impervious surfaces will be increased. As such, water infiltration will be reduced, and the volume of surface runoff will be increased. By retaini...

Long-term Performance Modeling of Vegetative/Infiltration BMPs for Highways

Nonpoint source pollution from highway stormwater runoff is a growing water quality concern and highway drainage systems are being re-evaluated for how well they can passively treat stormwater runoff. Vegetated buffer strips along fill slopes in the highway cross section can mitigate pollutants in stormwater runoff by infiltration and sedimentation. The existing models for vegetated buffer strips range from simple percent removal estimates to models with very complex routing and sediment transport algorithms for a single design storm. Instead of a design storm approach, the model proposed in this paper uses long-term precipitation data and a simple modeling framework to estimate concentration reduction and volume reduction through a vegetated buffer strip on an average annual basis. Data from field studies are used to support the spreadsheet-based model framework. In order to function effectively for passive stormwater treatment, buffer strips need an adequate vegetative cover. The model results clearly show the benefits of open drainage (vegetated swales) over closed drainage (curb and gutter systems).