Physically-based modeling of hydrologic processes in Texas

Hydrological modeling has a long history in solving various surface water problems such as flood management and water conservation. In relation to water resources management, the variations of climate and physiography of Texas result in different regions with unique characteristics in surface water and groundwater resources. Hydrologic modeling plays a major role in assessing these characteristics through balancing the water budget that defines the water excess (floods) and water scarcity for water supply and irrigation. Also, water quality is crucial to the fresh water budget, thus studying water quality distribution is another point of interest to evaluate water resources. The interaction between surface water and groundwater as part of the hydrologic cycle can also be assessed by hydrologic models in term of watershed contribution to the groundwater recharge.;This study contributed to physical modeling of hydrologic processes in Texas in different ways. First, vigorous validation of physically-based distributed-parameter modeling over watersheds of different sizes was performed. Second, detailed comparison of this approach against conceptual modeling was performed to understand the advantages and disadvantages of each approach over a range of rainfall events and watershed characteristics. Third, a physically-based distributed parameter was used to improve the hydrologic simulation component of a widely accepted water quality model in simulating nutrient transport over the entire San Antonio River basin. Fourth, the physically-based distributed-parameter model was used to produce very high resolution (in time and space) estimates of recharge for the Edwards aquifer. Different hydrologic models are used in this dissertation to study different topics that relate to surface water and other hydrologic cycle components in different watersheds in Texas through different events and their different causes and effects in various watersheds. Some of them are semi distributed and lumped models such as Soil and Water Assessment Tool (SWAT), Hydrologic Modeling System (HEC-HMS) and physically based distributed model Girded Surface- Subsurface Hydrologic Assessment GSSHA taking the advances of GIS, NEXRAD product, remote sensing and other products such as gridded land use and soil map to achieve the highest accuracy of these models. Two different models: SWAT and GSSHA are used for water quality assessment in San Antonio River basin because the rainfall runoff simulation is needed to derive the surface water quality process, especially along the streams. The accuracy of the predictions of hydrologic models has significantly improved. The demand to solve more complicated hydrologic, hydraulic and water quality problems are increasing due to population growth and rapid development and expansion of agricultural activities.