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USGS Water-Year Summary 2024
08150700 Llano River near Mason, TX
LOCATION - Lat 30°39'38", long 99°06'32" referenced to North American Datum of 1927, Mason County, TX, Hydrologic Unit 12090204, on right bank 98 ft downstream from downstream bridge on U.S. Highway 87, 1.0 mi upstream from Beaver Creek, 9.1 mi southeast of Mason, 10.2 mi downstream from James River, and 61.1 mi upstream from mouth.
DRAINAGE AREA - 3,247 mi² of which 5 mi² probably is noncontributing.
REVISIONS HISTORY - WDR TX-75-3: 1968 (P). WDR TX-81-3: Drainage area. WDR TX-01-4: 1980.
SURFACE-WATER RECORDS
PERIOD OF RECORD - Mar. 1968 to May 1993, Oct. 1997 to current year.
GAGE - Water-stage recorder. Datum of gage is 1,225.60ft above NAVD88 as determined by GNSS survey. Prior to Jan. 18, 2023, the datum of gage was 1,225.36 ft. above NGVD of 1929. Datum lowered 5.0 ft. on Jul. 07, 2021. Datum of gage prior to this date was 1230.36 ft. above NGVD of 1929. Prior to Jan. 19, 1971, at site 190 ft. upstream at same datum (pre Jul. 2021). Radio telemeter at station. Satellite telemeter at station.
COOPERATION - Lower Colorado River Authority provides operation and maintenance of the gage and verification of stage-discharge relation at low stages. U.S. Geological Survey maintains stage-discharge relation at medium to high stages, computes and publishes streamflow record.
REMARKS - No known regulation or diversion.
EXTREMES OUTSIDE PERIOD OF RECORD - Maximum stage since at least 1875, about 46 ft. at previous datum (51.00 ft. current datum), June 14, 1935, discharge, about 380,000 ft³/s, from information by Texas Department of Transportation; at site 17.0 mi downstream discharge was 388,000 ft³/s by slope-area measurement. Discharges for other floods are 258,000 ft³/s, 1952; 218,000 ft³/s, 1889.
EXTREMES FOR PERIOD OF RECORD - Maximum discharge: 260,000 cfs, gage height 37.00 ft., at previous datum (42.00 ft. current datum), Sept. 8, 1980.
