caldwell county regional water and wastewater planning study

11.1.1 GBRA Mid-Basin ProjectThe Guadalupe-Blanco River Authority (GBRA) is proposing a project that willprovide 25,000 ac-ft to customers of Caldwell, Comal, Gonzales, Guadalupe, andHays Counties. The source of water will be primarily surface water from theGuadalupe River with a point of diversion below the confluence of the SanMarcos River. The water in the river at the proposed diversion point is notconsidered firm yield unless it is backed up with off channel storage or agroundwater source. Off-channel storage in Guadalupe County is beingconsidered for the Mid-Basin Project as well as a secondary source of supplyfrom the Carrizo and/or Wilcox Aquifers in west-central or northeast GonzalesCounty.A feasibility report has been prepared by HDR to assess the use of groundwater tosupplement surface water during dry periods. During dry periods, water would besupplemented with groundwater from the Carrizo/ Wilcox Aquifer to provide aconstant supply of 25,000 ac-ft/ yr.Groundwater availability from the study was determined using the CCWQCSGAM model. The pumping simulation model was run over a period of 55 yearsfrom 2010 to 2065. Pumping and well distribution from the proposed field wasanalyzed in three scenarios. Two pumping scenarios were capable of producingup to 25,000 ac-ft/ yr alone from the Carrizo. The other alternative utilized theCarrizo-Wilcox wells with river water. The layout of the well field was assessedusing current GCUWCD rules for well spacing and requirements of 1 ac-ft peracre.The study used a baseline scenario for comparative purposes and to illustrate thegroundwater level and projected draw down. Instream flow restrictions in thepumping simulations were based on the historical period from 1934 to 1989.Klotz Associates Project No. 0972.000.000January 201011-3Caldwell County Regional Water and Wastewater Planning StudyFinal Report