Implementation of Green Stormwater Infrastructure to Meet Water Quality Goals in Texas

The Fort Worth Central City (Panther Island) project is a major urban revitalization project located near downtown Fort Worth, Texas. The project began in 2002 as part of a master plan for the area that included flood control protection and assessed an area that encompassed 88 miles of the Trinity River and its major tributaries. As part of the project, a multi-phase effort is being undertaken to protect water quality in the Trinity River.The project effort includes several key elements to identify mitigation strategies based on science. The first element is a water quality model to assess the impact of development on water quality and green stormwater infrastructure (GSI) facilities and other best management practices (BMPs) to protect water quality. The second element is development of water quality requirements and implementation guidance. The third is a conceptual plan to evaluate opportunities to implement GSI. The project evaluated a wide range of green infrastructure options for developers to implement select strategies that provide resilient stormwater infrastructure while meeting project needs and goals.The impact of GSI / BMPs was evaluated using a coupled watershed and in-stream modeling framework to evaluate receiving water quality for critical water quality constituents (TSS, nutrients, bacteria and floatables) for potential to meet water quality goals for the Trinity River. The water quality modeling effort was intended to assess sources and pollutant loads and evaluate the impact of the BMPs to protect and maintain water quality in the Trinity River and Panther Island so the public can enjoy a high quality urban water resource. A watershed and an in-stream model were developed to evaluate the benefit of the GI implementation in the watershed upstream of and within Panther Island.The key parameters assessed by the models were nutrients, dissolved oxygen, chlorophyll, sediment and indicator bacteria. Pollutant generation rates and generalized land use category were compiled from local studies and supplemented where necessary based on accepted national references. Results from the watershed modeling show increases in loadings where development is expected to occur, including Panther Island. The proposed Central City / Panther Island plan was examined to identify potential locations for green stormwater infrastructure installation, including bioretention and permeable pavers.Development requirements were assessed to implement the required GSI / BMP efforts to protect water quality. An implementation guidance effort was undertaken to establish the necessary water quality features, level of treatment, and GSI effectiveness. The implementation guidance is intended to provide flexibility for developers, in addition to providing the required specificity and consistency that is needed for regulators. The guidance manual provides flexibility by using a component approach. The guidance manual provides detailed BMP design details and specifications for BMP component alternatives within the required categories. The handbook allows the developer to choose the type of component in each category and for their specific BMP to meet their site conditions.The project evaluated a wide range of green infrastructure options to select strategies that meet project needs and goals. GSI implementation scenarios were evaluated and the proposed Panther Island grading plan was examined to identify potential locations for green stormwater infrastructure installation. Water quality benefits associated with each of the green stormwater infrastructure practices were based on data available from the International Stormwater BMP database and modeled to evaluate the impact on the Trinity River at Panther Island.The project includes the development of a BMP / GI developer guidance manual handbook that is based on a scientific assessment, water quality modeling, and conceptual BMP layout. The manual provides detailed guidance and, also flexibility for developers. The project evaluated a wide range of BMP / GI options for developers to implement select strategies that provide resilient stormwater infrastructure while meeting project needs and goals.