Water Quality and Environmental Flows Maintaining Quantity for Quality’s Sake

1. Water Quality and Environmental Flows Maintaining Quantity for Quality’s Sake Presented By: Jennifer Benaman Quantitative Environmental Analysis, LLC November 1, 2005

2. Project Overview Water for San Antonio Water for rural communities Higher water levels in Highland Lakes Lake Buchanan Austin Instream flows to maintain aquatic habitat San Antonio Water for agriculture (up to 150,000 ac-ft/yr) Freshwater inflows for Matagorda Bay file name LSW11_ _._ _

3. Maintain higher water levels in Highland Lakes How will the project conserve and develop 330,000 acre-feet of water? Use Groundwater for Agriculture when Surface Water Insufficient • Provide beneficial Inflows P P Colorado Columbus Build Off-Channel Storage Wharton Wharton • Conserve Agricultural Irrigation Water Matagorda Bay City Matagorda Bay file name LSW11_ _._ _

4. State Legislative Requirements • As per HB 1629, the project must • Protect and benefit basin interests • Be consistent with state regional water plans • Provide inflows adequate to maintain ecological health and productivity of Matagorda Bay • Maintain current instream river flow protections • Ensure San Antonio practices stringent conservation measures • Provide broad public and scientific review process • Benefit stored water levels in Lakes Travis and Buchanan file name LSW11_ _._ _

5. Environmental Study Teams • Matagorda Bay Health • Respond to the mandate that bay inflows remaining after any Project diversions will be adequate to maintain the health and productivity of the Matagorda Bay System • Aquatic Habitat/Blue Sucker • Study the impact of the LSWP on the riverine habitats in the river below Austin • Water Quality • Study the impact of the LSWP on the water quality of the river file name LSW11_ _._ _

6. Matagorda Bay Health Evaluation • Detailed analysis of inflows to the bay system, both from the Colorado River and the coastal drainage system into the bay which stem in part from return flows from irrigation areas • Salinity modeling of the bay system including the marsh systems on the northern boundary of Matagorda Bay and East Matagorda Bay • The effects on bay habitat of various freshwater inflow regimes • The effects of changes in inflow on bay food supply (nutrients and sediment) • Development of statistical relationships between inflow and biota • Synthesis of these various components of “bay health” file name LSW11_ _._ _

7. River Water Quality Implications • Current LCRA Water Management Plan • Release stored water from Highland Lakes for downstream irrigators during summer • Net effect: summer flows higher than “natural” • Potential Effect of LSWP • Irrigators obtain water from local (downstream) sources. • More frequent low flows in summer Changes in the timing, duration, and frequency of low flows may affect water quality file name LSW11_ _._ _

8. River Model Approach Longhorn Dam Smithville • Use state-approved QUAL-TX • Focus on critical low flow condition • Expand TCEQ grid • Collect additional data to constrain model • Calibrate to new data, scale to warmer temperatures • Future critical condition anticipated to be in summer • Perform future simulations in coordination with expected flow regime TCEQ grid New grid file name LSW11_ _._ _

9. New Data Collection • Water quality under “low-flow”/warm conditions • Dye tracer for hydraulic characterization • Diel DO for daily dissolved oxygen fluctuations • Bay habitat mapping • Salinity data for model development in the bay file name LSW11_ _._ _

10. For Additional Information www.lcra.org/lswp file name LSW11_ _._ _