The Geological Survey, in cooperation with the Texas Department of Water resources, began hydrologic studies in the Austin urban area in 1954. In cooperation with the city of Austin, the program was expanded in 1975 to include additional streamflow and rainfall-gaging stations, and the collection of surface water-quality data. In 1978, the program was expanded to include a ground-water resources study of the South Austin metropolitan area in the Balcones fault zone.

The objectives of the Austin urban hydrology study are as follows:

1. To determine, on the basis of historical data and hydrologic analyses, the magnitude and frequency of flood peaks and flood volume.
2. To determine the effect of urban development on flood peaks and volume.
3. To determine the variations in water quality during different seasons and flow conditions in representative watersheds with various types of urban development.
4. To quantitatively appraise the ground-water resources of the Edwards aquifer in hydraulic circulation with Barton Springs, the effect of urbanization on the quality and quantity of recharge and discharge, and the extent of contamination in the aquifer.

This report presents the basic hydrologic data collected in the Austin urban area for the 1986 water year (Oct. 1, 1985 to Sept. 30, 1986). Additional explanations of terms related to streamflow, water quality, and other hydrologic data used in this report are defined in the U.S. Geological Survey annual report Water Resources Data for Texas, TX-85-3, 1986.

Analyses of "Hydrologic data for urban studies in the Austin, Texas, metropolitan area" from 1975 to 1982 are presented in a report by Veenhuis and Gannett (1986). Two analyses were made to determine the effects of urbanization on flood peaks in streams in the Austin metropolitan area. The first analysis compares flood recurrence intervals of urban drainage basins to rural drainage basins. In the second analysis, data from one drainage basin in which considerable urban development occurred during the study period, were used. The data were analyzed for changes in rainfall-runoff and flood frequency relations due to urbanization.