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USGS Water-Year Summary 2024
08170500 San Marcos River at San Marcos, TX
LOCATION - Lat 29°53'20", long 97°56'02" referenced to North American Datum of 1927, Hays County, TX, Hydrologic Unit 12100203, on left bank at downstream side of bridge on Aquarena Springs Drive (Loop 82), 500 ft downstream from Spring Lake, and 4.2 mi upstream from Blanco River.
DRAINAGE AREA - 48.9 mi². of contributing surface drainage, however, most of the time flow is solely from San Marcos Springs.
REVISIONS HISTORY - WDR TX-04-5: Drainage area.
SURFACE-WATER RECORDS
PERIOD OF RECORD - July 1915 to Sept. 1921 (daily mean discharges below base discharge), May to Sept. 1956, Oct. 1994 to current year. Discharge measurements were made outside period of record since Nov. 14, 1894, and were published as miscellaneous measurements.
PERIOD OF RECORD, Water-quality.--
CHEMICAL DATA: Aug. 1994 to Oct. 1996.
BIOCHEMICAL DATA: Aug. 1994.
PESTICIDE DATA: Aug. 1994.
GAGE - Water-stage and water-velocity recorders. Datum of gage is 557.67 ft above NGVD of 1988. July 1915 to Jan. 1916, nonrecording gage at site 0.5 mi upstream from Interstate Highway 35, and Mar. 1916 to Sept. 1921, water-stage recorder about 0.7 mi downstream from Interstate Highway 35; datum relations unknown. May to Sept. 1956, water-stage recorder 0.7 mi downstream from Interstate Highway 35 and 2.1 mi upstream from Blanco River, at datum 536.82 ft above NGVD of 1929. Satellite telemeter at station.
REMARKS - Records good for the water year with no known regulation. Entire flow of river is from San Marcos Springs except during periods of local runoff. San Marcos Springs emerge from the Edwards and associated limestones about 1.1 mi upstream from Interstate Highway 35, in the Balcones Fault Zone. Some records listed in the "Period of Record" for surface water and water quality may not be available electronically.
