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Catastrophic floods, which resulted in millions of dollars in property damages and the loss of 33 lives, occurred in Central Texas during August 1-4, 1978, as a result of intense rainfall produced by the remnants of tropical storm Amelia. Rainfall in excess of 30 inches was unofficially reported at several locations, while the highest 24-hour amount recorded by the National•Weather Service was 29.05 inches at Albany in Shackelford County.Major flooding occurred on the Medina River and triputaries above Medina Lake and on the Guadalupe River and tributaries above Canyon Lake. Minor to severe flooding occurred on the tributaries of the Nueces River, on the Clear Fork Brazos River and tributaries, and on the Llano and Pedernales Rivers, which are tributaries of the Colorado River.Peak discharges at several streamflow stations exceeded the historic peaks, and the flood magnitude and frequency data for the Guadalupe River above Canyon Lake, the Medina River near Pipe Creek, and Clear Fork Brazos River indicate that the August 1978 flood had a recurrence interval in excess of 100 years. The highest unit discharge observed during this flood was 3,010 cubic feet per second from a 14.1-square-mil.e drainage area of Spring Creek, which is tributary to the Pedernales River.

Peak-discharge data from 28 stream-gaging stations with long-term records (10-33 years) and 60 stations with short-term records (less than 10 years) were used in multiple linear-regression procedures to obtain equations for estimating the peak discharge of floods with recurrence intervals of 10, 25, and 50 years on small rural streams in East Texas. The significant independent variables were drainage area, channel slope, and channel length. The relationships are presented in nomographs that can be used for ~stimating the peak discharges on small streams for floods of the selected recurrence intervals, provided that the magnitude of the independent variables is within the range of those used to develop the relationships.

This report is the ninth in a series of interim reports that describe the objectives, planning, instrumentation, progress, and status of the project. The report includes data collected during the 1972 water year.