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- Water-Year Summary reports summarize a year of hydrologic data in a printer-friendly format.
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USGS Water-Year Summary 2024
08170000 San Marcos Springs 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 - Not applicable. This is a springflow station.
SURFACE-WATER RECORDS
PERIOD OF RECORD - May 1956 to current year. Records prior to Oct. 1997 published as "San Marcos River Springflow at San Marcos".
PERIOD OF RECORD, Water-Quality.--
CHEMICAL DATA: July 1965, Oct. 1995 to Oct. 1996.
BIOCHEMICAL DATA: July 1965.
GAGE - Water-stage recorder. Datum of gage is 557.67 ft above NGVD of 1929. May 1956 to Sept. 1988, water-stage recorder 0.7 mi downstream from Interstate Highway 35 and 2.1 mi upstream from Blanco River, datum 536.82 ft above NGVD of 1929. Oct. 1988 to Sept. 1994, water-stage recorder at ground-water well No. LR-67-09-110, 0.2 mi southwest of intersection of FM 2439 and McCarty Lane and 3.7 mi south of San Marcos, datum 678.50 ft above NGVD of 1929. Satellite telemeter at station.
REMARKS - Record is good for the 2016 water year except those for estimated daily discharges, which are fair. Some records listed in the "Period of Record" for surface water and water quality may not be available electronically. Springflow is equal to flow at San Marcos River at San Marcos (station 08170500) except during periods of local runoff. Springflow is separated from runoff using modified Institute of Hydrology base-flow separation program BFI 4.14 (March 2006) (go to:
http://www.usbr.gov/pmts/hydraulics_lab/twahl/bfi/texaswater95/comalsprings.html ). Selected springflow values computed using the program are revised on the basis of further examination of the base-flow records. The springflow for all days with springflow separations are considered computed daily mean springflow values and only days in which the river flow was estimated, are shown as estimated. San Marcos Springs emerge from the Edwards and associated limestones about 1.1 mi upstream from Interstate Highway 35, in the Balcones Fault Zone.
