Developing homogeneous sequences of river flows and performing comparative analyses of flow characteristics

The objectives of the dissertation research are (1) to improve and expand capabilities for developing naturalized or otherwise homogenous river flows representing specified conditions of basin development for input to models for simulating river/reservoir system management and (2) to investigate characteristics of observed, naturalized, and simulated regulated river flows of relevance to water management, especially integration of environmental flow standards in water management in Texas. Key research results and conclusions are as follows:;SWAT was applied to the Sabine, Neches, and GSA River Basins to develop daily and monthly natural-condition flows at relevant sites from available rainfall records. Alternative calibration strategies were developed, tested, and compared. SWAT was combined with the maintenance of variance method, type 2, called MOVE2, to develop a new methodology for filling in gaps of missing naturalized monthly flows. Comparative testing of alternative variations of flow synthesis methods was performed.;The drainage area ratio method for transferring flows for gauged to ungauged sites was investigated and an alternative more refined method proposed. A comparative assessment of alternative methods for transferring flows is presented using available flow data. The drainage area ratio method is shown to be inaccurate for very small or very large drainage area ratios. SWAT was applied to develop daily flow pattern hydrographs for the Sabine, Neches, and GSA WAMs for use in disaggregating monthly naturalized flows to daily. Various issues were resolved and the daily pattern hydrographs were implemented in the WAMs. Rainfall-runoff modeling with SWAT is demonstrated to be a feasible approach for developing daily pattern hydrographs for the WRAP/WAM models and complexities are explored.;The Dundee Hydrological Regime Alteration Method (DHRAM), which incorporates the Indicators of Hydrologic Alteration (IHA) methodology, was applied to assess the hydrological alterations of daily river flow sequences between user-defined impacted and un-impacted periods in the case study river systems. Frequency metrics for regulated versus naturalized flows from the WAMs are compared to assess long-term changes in flow characteristics.;Changes in flow characteristics range from being negligible at some sites to very large at other sites. Frequency analysis of unappropriated flows resulting from WAM simulations with versus without Senate Bill (SB3) instream flow standards were performed to evaluate the impacts of the environmental flow standards on water availability. Impacts on unappropriated flows range from no impacts at some sites to very significant impacts at other sites.