USGS Water-Year Summary 2021
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.
- WDR TX-04-5: Drainage area.
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 1929. 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.