MOHAMOUD, Y. M., A. C. SIGLEO, AND R. S. PARMAR. Modeling the Impacts of Hydromodification on Water Quantity and Quality. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/116 (NTIS PB2010-104718), 2009.
Hydromodification activities are driven by human population growth and resource extraction and consumption including urbanization, agriculture, forestry, mining, water withdrawal, climate change, and flow regulation by dams and impoundments. These anthropogenic activities alter natural flow regimes and lead to reduced downstream water quantity and degraded water quality. Recently, USEPA and states recognized hydromodification as a stressor and a leading source of water quality impairment in streams and rivers. Hydromodification-induced stressors include chemical pollutants, pathogens, nutrients, suspended solids, and flow and habitat alteration. The diverse and interacting nature of hydromodification-induced stressors has made Total Maximum Daily Load (TMDL) development for impaired streams and rivers a major regulatory challenge. Because hydromodification integrates stressors that have combined, cumulative, and synergistic effects on water quantity and quality, TMDL modeling approaches are not well-suited for simulating the impacts of hydromodification. Modeling integrated stressors requires the development and application of predictive models and innovative modeling approaches, such as the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) modeling framework. Although BASINS has been in use for the past 10 years, there has been limited modeling guidance on its applications for complex environmental problems, such as modeling impacts of hydromodification on water quantity and quality. This report consists of two parts: Part 1 presents the development of a BASINS-based methodology that is applicable to modeling hydromodification. Part 2 is a case study of how the proposed modeling approach can forecast the impacts of urbanization on water quantity and quality.