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Rivers rise with heavy rainfall, which could boost low lakes

Llano River May 3 2024

The Llano River rushes on a gray May 3 morning after heavy rainfall across its watershed caused a 19-fold increase in flow overnight. Staff photo by Dakota Morrissiey

The Colorado and Llano rivers are rising following heavy rainfall across their watersheds over the past 48 hours starting Wednesday, May 1. Both rivers could deliver badly needed relief to the Highland Lakes reservoirs of Buchanan and Travis.

The Llano River, which feeds into Lake LBJ and eventually Lake Travis, reached a peak flow rate of 1,428 cubic-feet per second at around 6 a.m. Friday morning, as measured by a Lower Colorado River Authority flow gauge in the city of Llano. The river was flowing at a rate of about 74 cfs at the same time on Thursday.

The Colorado River, which feeds the entire Highland Lakes chain of lakes from Buchanan to Travis, reached a peak flow rate of 1,255 cfs at around 8 a.m. Friday morning, according to an LCRA flow gauge near Bend. The river was flowing at about 150 cfs at the same time on Thursday.

Some areas in Burnet and Llano counties saw significant rainfall this week, according to LCRA rain gauges. Between 10 a.m. Wednesday and 10 a.m. Friday, Burnet received about 1.54 inches of rain, Kingsland about 1.07 inches, and remote portions of southwest Llano County about 1.8 inches. Marble Falls only got 0.33 inch of rain in the same time period.

While Highland Lakes counties had decent rainfall, the real gains for the rivers came from far heavier precipitation in counties farther north and west that hold countless creeks and draws that feed into the Colorado and Llano river basins.

At least 14 LCRA rain gauges in the Colorado River Basin north of Lake Buchanan in San Saba and Lampasas counties measured over 2 inches of rain in the same 48-hour period. Gauges measured 2.9 inches on McAnelly Creek, 2.68 inches on Kemp Creek, and 2.9 inches near the San Saba River west of the city of San Saba. 

Several LCRA rain gauges across Mason, Kimble, and Gillespie counties measured over an inch of rainfall in the same period. A few standout gauges showed significant precipitation, like the Salt Creek gauge in southern Mason County with 3.59 inches and the Sheep Run Creek gauge with 2.94 inches.

The Colorado River’s increased flow could boost the levels of Lake Buchanan, which is currently 48 percent full. The lake sits at 995.59 feet above mean sea level, which is significantly lower than its historical April average of 1,012.77 msl. When full, the lake is at approximately 1,020 msl. The lowest it was ever recorded was 983.7 msl in September 1952.