Flow pattern in regional aquifers and flow relations between the lower Colorado River valley and regional aquifers in six counties of southeastern Texas

The lower Colorado River discussed in this report consists of the 318- river-mile reach from Mansfield Dam near Austin, Texas, to the Gulf of Mexico. The river is underlain directly or indirectly by six regional aquifers the Trinity Group, Edwards, Carrizo-Wilcox, Queen City, Sparta, and Gulf Coast; the Trinity Group aquifer is further subdivided into the lower Trinity, middle Trinity, and upper Trinity aquifers. Generalized potentiometric-surface maps of each regional aquifer show the ground-water-flow pattern near the river valley. Each regional aquifer discharges water to the lower Colorado River valley, particularly in the outcrop area of each aquifer. Only the Gulf Coast aquifer in central Wharton County appears to be recharged by water in the river valley. A summary map shows those subreaches of the lower Colorado River that gain water from the aquifers and those subreaches that lose water to the aquifers.