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Comparing the Storage Efficiencies of the Highland Lakes and the Proposed LCRA-SAWS Project Lower Colorado River Reservoirs. Andrew Judd Semester Project for CE 394K.2 Surface Water Hydrology Instructor: Dr. Maidment University of Texas. INTRODUCTION. Lower Colorado River Authority (LCRA)
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Comparing the Storage Efficiencies of the Highland Lakes and the Proposed LCRA-SAWS Project Lower Colorado River Reservoirs Andrew Judd Semester Project for CE 394K.2 Surface Water Hydrology Instructor: Dr. Maidment University of Texas
INTRODUCTION • Lower Colorado River Authority (LCRA) • Project Centers around water transfer agreement • 150,000 ac-ft/yr to San Antonio • Income to LCRA for improving water supply system and conservation • One project component is 3-4 off-channel storage reservoirs for San Antonio supply Source: www.regionk.org Source: www.LCRA.org
OBJECTIVE • Majority of regional water supply storage in Highland Lakes • Lower Colorado Reservoirs to supply water to San Antonio • Without reducing storage volume in Highland Lakes Source: www.lcra.org Research Project: Compare storage efficiencies of Highland Lakes and proposed Lower Colorado reservoirs using historical data
Storage Efficiency • Ratio of surface flux volume per time to total reservoir volume • Constant reservoir volume and surface area assumed • Somewhat valid for Highland Lakes • Less valid for proposed Lower Colorado reservoirs Efficiency Equation (per time segment) in this analysis (per month)
Data Requirements and Sources Physical Characteristics of Reservoirs • Highland Lakes – LCRA provides data on website • Lower Colorado Reservoirs – obtained through request to LCRA Evaporation and Precipitation • NARR – good for many points over one time, not for single point over many times • NCDC – has plenty of precipitation data, very little evaporation data • Texas Water Development Board (TWDB) – has regionalmeasurement of monthly precipitation and evaporation quantities (1954 onward)
Evap & Precip Data Acquisition Regional Boundaries projected onto GIS map of Lower Colorado Region http://hyper20.twdb.state.tx.us/Evaporation/evap.html
Dimensional Data Acquisition • All areas and volumes converted to feet • Only 3 of the 6 Highland Lakes provide water storage • Higher volume to surface area ratio for Highland Lakes • Surface fluxes have greater effect on Lower Colorado Reservoirs
Proposed Lower Colorado Reservoirs • Reservoirs to have Ring Dike Structure • Capture excess flows in Colorado River (pumping) Source: LCRA & http://www.givlerengineering.com/jnres.htm
Storage Efficiency Analysis • Using Excel, compiled regional monthly evaporation and precipitation data • Evaporation/Precipitation balance • Efficiency Equation for each month (1954-2002) • Computed monthly storage efficiency for each storage system (weighted according to volume)
Storage Efficiency Analysis (cont.) Regional Evaporation correlated more than Precipitation
Storage Efficiency Analysis (Part 2) • Same storage efficiency, but different surface area to volume ratios • Summed E & P (1954-2002) • Highland Lakes has greater difference between evaporation and precipitation • Average storage efficiency not capturing full picture • Variability of storage efficiency also important factor • Calculated standard deviation of storage efficiency
Conclusions • Highland Lakes and Proposed Lower Colorado Reservoirs have comparable storage efficiencies • However, the storage efficiency of the Lower Colorado Reservoirs would be more variable due to greater sensitivity to climatic conditions