State Water Resources Research Institute Program (WRRI)
Start Date: 2008-03-01 End Date: 2009-02-28
Total Federal Funds: $16,245 Total Non-Federal Funds: $32,490
Principal Investigators: Zhi-Qiang Deng
Abstract: The U.S. Environmental Protection Agency and the states are faced with developing tens of thousands of TMDLs, each with a margin of safety (MOS). However, in almost all cases, MOS is defined arbitrarily, without consideration for the actual uncertainty in the likelihood of achieving water quality objectives. This can lead to two outcomes: (1) if MOS is too small, the TMDL has a high probability of not meeting its designated use; (2) if MOS is too large, the cost of implementing the TMDL will be much higher than necessary. Thus, a scientifically sound approach to determining MOS is required for all impaired water bodies, including the Amite River that is impaired by low dissolved oxygen (DO). The primary goal of this project is to develop and demonstrate a simple yet effective approach to identifying uncertainty sources and to quantifying the TMDL uncertainty arising from these sources through TMDL development for dissolved oxygen in the Amite River. The approach involves the determination of uncertainties in flow discharge and contaminant concentration. To achieve the goal four objectives are proposed: (1) uncertainty analysis for flow, (2) uncertainty analysis for DO concentration, (3) two-dimensional simulation of variability and uncertainty, and (4) TMDL calculations for dissolved oxygen in the Amite River. The objectives will be addressed through the combination of a statistical analysis and a deterministic model. The uncertainty involved in the flow will be estimated by means of probability distributions of discharge. The uncertainty involved in the concentration will be determined using a 1D mass transport equation and the first order error analysis method. A Copula method will be employed to determine the joint probability density distribution of contaminant concentration and flow discharge. The proposed research has broader implications for environmental restoration of impaired watercourses and watersheds in Louisiana. This project will improve understanding of uncertainty propagation in loading calculations, which will further the development of scientifically defensible load allocations for impaired rivers. Owing to the quantification of TMDL uncertainty the results of this study will help lower the risk of inadequately characterizing the margin of safety. The uncertainty-based TMDL calculations will also help with the development of stream restoration priorities and thereby loading reduction strategies as well as the selection of sources in which to target reduction efforts. The study includes the second-order uncertainty in uncertainty analysis and provides an efficient method for determination of twodimensional uncertainty for the first time. Although this study focuses on dissolved oxygen TMDL in the Amite River, the methods presented in this study will be generally applicable to TMDL calculations for other contaminants and nutrients as well.