1. 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

2. 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 INTRODUCTION Source: www.LCRA.orgwww.LCRA.org Source: www.regionk.orgwww.regionk.org

3. 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 OBJECTIVE Research Project: Compare storage efficiencies of Highland Lakes and proposed Lower Colorado reservoirs using historical data Source: www.lcra.orgwww.lcra.org

4. Storage System Flows

5. Storage Efficiency Efficiency Equation (per time segment) in this analysis (per month) 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

6. Data Requirements and Sources 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 regional measurement of monthly precipitation and evaporation quantities (1954 onward) Physical Characteristics of Reservoirs Highland Lakes – LCRA provides data on website Lower Colorado Reservoirs – obtained through request to LCRA

7. Evap & Precip Data Acquisition http://hyper20.twdb.state.tx.us/Evaporation/evap.html Regional Boundaries projected onto GIS map of Lower Colorado Region

8. 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

9. 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

10. 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)

11. Storage Efficiency Analysis (cont.) Regional Evaporation correlated more than Precipitation

12. 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

13. Storage Efficiency Analysis (Pt 2 of Pt 2)

14. 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