Browsing by Subject "freshwater inflows"
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Item Characterizing the Impact of Land Use and Land Cover Change on Freshwater Inflows(2009-05-15) Ferijal, TeukuFreshwater inflows are a crucial component for maintaining estuarine health, function and productivity. Streamflows, the primary source of freshwater inflows, have been modified and altered from their natural flow by population growth and anthropogenic impacts on the contributing watersheds. The Guadalupe Estuary is a primary habitat for many endangered species. The Guadalupe River Watershed, which supplies 70% of freshwater inflows, experiences rapid urbanization and agricultural development. This study proposed to characterize the impact of land use/cover change in the Guadalupe River Watershed on freshwater inflows to the Guadalupe Estuary. Pre-whitening, Mann-Kendall and bootstrap techniques were used to test for significant trends on streamflow and precipitation. Analyses suggested more trends in annual and seasonal minimum and mean streamflow than would be expected to occur by chance in the periods of 1930-2005 and 1950-2005. No significant trends were found in the period of 1970-2005. Significant trends were more prominent in the upper watershed and decreased as analysis moved downstream in the period of 1950-2005. Trend tests on precipitation data in the period of 1950-2005 revealed more significant trends than would be expected by chance in mean annual and winter precipitation. Analyses of Landsat images of the watershed using an unsupervised classification method showed an increase in forest, urban and irrigated land by 13, 42 and 7%, respectively, from 1987 to 2002. Urbanized areas were mostly found in the middle part of watershed surrounding the I-35 corridor. More than 80% of irrigated lands are distributed over the San Marcos and Middle Guadalupe River Watersheds. Soil and Water Assessment Tool (SWAT) model was applied for the Guadalupe River Watershed. Calibration and validation using data recorded at USGS 08176500 indicated the model performed well to simulate streamflow. The coefficient of Nash- Sutcliffe, determination and percent bias were 0.83, 0.96 and 3.81, respectively, for calibration and 0.68, 0.75 and 29.38 for validation period. SWAT predicted a 2% decrease in annual freshwater inflow rates from the effect of land use/cover change from 1987 to 2002. Reservoirs increased freshwater inflows during low flow months and decreased the inflows during high flow months. Precipitation variability changed characteristics of monthly freshwater inflows.Item Decision support tools for managing freshwater inflowsSprague, PaigeItem Modeling the effect of land cover land use change on estuarine environmental flows(2009-05-15) Sahoo, DebabrataEnvironmental flows are important to maintain the ecological integrity of the estuary. In a watershed, it is influenced by land use land cover (LULC) change, climate variability, and water regulations. San Antonio, Texas, the 8th largest city in the US, is likely to affect environmental flows to the San Antonio Bay/Guadalupe Estuary, due to rapid urbanization. Time series analysis was conducted at several stream gauging stations to assess trends in hydrologic variables. A bootstrapping method was employed to estimate the critical value for global significance. Results suggested a greater number of trends are observed than are expected to occur by chance. Stream gauging stations present in lower half of the watershed experienced increasing trend, whereas upper half experienced decreasing trends. A similar spatial pattern was not observed for rainfall. Winter season observed maximum number of trends. Wavelet analysis on hydrologic variables, suggested presence of multi-scale temporal variability; dominant frequencies in 10 to 15 year scale was observed in some of the hydrologic variables, with a decadal cycle. Dominant frequencies were also observed in 17 to 23 year scale with repeatability in 20 to 30 years. It is therefore important to understand various ecological processes that are dominant in this scale and quantify possible linkages among them. Genetic algorithm (GA) was used for calibration of the Hydrologic Simulation Program in FORTRAN (HSPF) model. Although, GA is computationally demanding, it is better than manual calibration. Parameter values obtained for the calibrated model had physical representation and were well within the ranges suggested in the literature. Information from LANDSAT images for the years 1987, 1999, and 2003 were introduced to HSPF to quantify the impact of LULC change on environmental flows. Modeling studies indicated, with increase in impervious surface, peak flows increased over the years. Wavelet analysis pointed, that urbanization also impacted storage. Modeling studies quantified, on average about 50% of variability in freshwater inflows could be attributed to variation in precipitation, and approximately 10% of variation in freshwater inflows could be attributed to LULC change. This study will help ecologist, engineers, scientist, and politicians in policy making pertinent to water resources management.