The U.S. Geological Survey collected hydrologic (rainfall, streamflow, and reservoir content) and water-quality data in the Seco Creek watershed, south-central Texas. Most of the data from 15 sites were collected as part of a study in cooperation with the U.S. Department of Agriculture and the Texas State Soil and Water Conservation Board to evaluate the effects of agricultural best-management practices on surface- and ground-water quantity and quality in the 255-square-mile watershed. Nearly 400 best-management practices at 58 sites were implemented by landowners in the watershed during March 1990-September 1995.

Most of the data are from the early 1990s, the period during and after implementation of best-management practices. Data from five sites include water quality and are summarized in tables and graphics in the text; and data from all 15 sites are summarized on a diskette.

Maximum annual rainfall among the sites for which data are presented in the text (excluding one site) for the during-and-after-implementation period (March 1990-September 1995) was 53.27 inches in water year 1992. Maximum annual total streamflow among the sites for the period was 63,400 acre-feet, also in water year 1992. At the one site with water-quality data (under base-flow conditions) for both the before-implementation period and the during-and-after implementation period of best-management practices, percentiles (5, 25, 50, 75, 95) for specific conductance, nitrate concentration, and fecal coliform density were less for the during-and-after-implementation period than for the before-implementation period.