Water Supply Operations
LCRA’s operation of the Highland Lakes is governed by the 2020 Water Management Plan.
LCRA conducts water supply operations consistent with the Water Management Plan and all other applicable water rights and agreements. During water supply operations, needs for water are first met with the natural flow of the Colorado River – to the extent allowable – to reduce the amount of water used from the Highland Lakes. Water also may be released from any of the Highland Lakes as needed to manage floodwaters.
Releases from Lake Austin are made to meet downstream customer needs, and to supplement the flow of the lower river when needed to help meet environmental flow requirements. Customers that take water from the Colorado River downstream of Lake Austin include the City of Pflugerville, the Decker Creek Power Station, the Lost Pines Power Park, the Fayette Power Project, four irrigation operations (Lakeside, Garwood, Pierce Ranch and Gulf Coast), industrial customers in Matagorda County and others. Environmental flow requirements include TCEQ requirements to maintain instream flows along the lower Colorado River and supply freshwater inflows to Matagorda Bay and estuary.
Releases from Lake Travis are made when needed to replace water that is released from Lake Austin, and to supply water to customers that take water from Lake Austin, including the City of Austin, West Travis County Public Utility Agency and others.
Releases from Lake Buchanan are made when needed to replace a portion of the water that is taken or released from Lake Travis, and to supply water to customers along lakes Inks, LBJ and Marble Falls. Customers that take water from the Highland Lakes above Mansfield Dam include the City of Austin, City of Cedar Park, Travis County WCID No. 17, City of Leander, Lakeway Municipal Utility District, Thomas C. Ferguson Power Plant and others.
LCRA manages lake operations to optimize the capture of inflows to the lakes, reduce evaporative losses and reduce risks to life and property. The allocation of releases from lakes Buchanan and Travis are based on actual conditions at the time. Considerations include lake levels and capacities, inflows to each lake, the location of needs for stored water and planned operation and maintenance activities.
Lake Travis is downstream of Lake Buchanan, and it receives storm runoff from a larger and wetter watershed. When Lake Travis is closer to full than Lake Buchanan, releases from Lake Buchanan may be suspended or reduced so Lake Travis supplies a greater proportion of the needs for stored water. This creates more capacity in Lake Travis to capture storm runoff from the larger contributing watershed above Mansfield Dam, and it tends to optimize the capture of inflows to the Highland Lakes.
Lake Buchanan has a larger surface area than Lake Travis when the lakes are a similar percentage full. Consequently, Lake Buchanan tends to lose more water to evaporation than Lake Travis. As the level of Lake Travis goes down, LCRA gradually increases releases from Lake Buchanan. This helps reduce the amount of water lost to evaporation from the surface of Lake Buchanan.
During more extreme drought conditions, LCRA manages releases to ensure Lake Buchanan retains enough water to continue supplying water to areas between lakes Buchanan and Travis. When inflows to Lake Travis are greater than inflows to Lake Buchanan, LCRA may suspend releases from Lake Buchanan temporarily or reduce them to improve recovery of system storage and to increase the overall operational efficiency of the Highland Lakes.
Interruptible Water Supply for Agriculture
Water for 2021 first agricultural season will be allocated under Normal Water Supply Conditions, as described in Chapter 4 of the 2020 Water Management Plan. Up to 178,000 acre-feet of interruptible stored water from lakes Buchanan and Travis will be available for diversions at the Gulf Coast, Lakeside and Pierce Ranch irrigation systems during the first agricultural season.
The 2020 Water Management Plan protects the water supply for firm customers – mainly cities and industrial users – and allows LCRA to quickly adapt its operations as drought conditions change. The plan establishes three sets of water supply conditions – Normal, Less Severe Drought and Extraordinary Drought – to determine the availability of interruptible stored water, which is used by agricultural customers in the Gulf Coast, Lakeside and Pierce Ranch irrigation systems in Colorado, Wharton and Matagorda counties. Water for the Garwood Irrigation Division is supplied separately, under terms of the Garwood Purchase Agreement.
The 2020 Water Management Plan sets two dates – March 1 and July 1 – for determining the amount of interruptible stored water available for first and second crop. The determination is made based on several factors, including combined storage in lakes Travis and Buchanan and the prior three-month inflows.
On March 1, 2021, combined storage in lakes Travis and Buchanan was 1.501 million acre-feet, and the full allotment of interruptible stored water (178,000 acre-feet) allowed under the Water Management Plan is available for first agricultural season for the Gulf Coast, Lakeside and Pierce Ranch irrigation operations.
Water for agriculture may be released from the Highland Lakes each day, but only to the extent agricultural needs cannot be met with the natural flow of the Colorado River. The needs for agriculture and the flow of the river depend on weather conditions during the irrigation season.
Environmental Flow Criteria for Instream Flows
Environmental flow requirements for instream flow are set to Subsistence levels from March 2021 through June 2021.
The 2020 Water Management Plan describes three categories for instream flows in the Colorado River downstream of the Highland Lakes: “subsistence”, “base-dry” and “base-average”. Each category prescribes desired levels of flow of the Colorado River at Austin, Bastrop, Columbus and Wharton. Flow levels vary from month to month throughout the year to emulate the natural seasonal variations of flow in the lower river. See the Instream Flow Conditions and Environmental Criteria table on the River Operations Report.
The instream flow category is determined by the amount of water stored in lakes Buchanan and Travis on March 1, July 1 and November 1.
On March 1, 2021, the daily average combined storage of lakes Buchanan and Travis was 1.501 million acre-feet. In accordance with the 2020 Water Management Plan, because storage was less than 1.80 million acre-feet, environmental flow requirements for instream flow are set to Subsistence levels from March 2021 through June 2021.
See Chapter 4 of the 2020 Water Management Plan for a more complete description of the instream flow criteria.
Environmental Flow Criteria for Freshwater Inflows to Matagorda Bay
Environmental flow requirements for freshwater inflows to Matagorda Bay are set to the OP-3 category from March 2021 through June 2021.
The 2020 Water Management Plan describes five inflow categories for freshwater inflows to Matagorda Bay. The inflow category is determined by the amount of water stored in lakes Buchanan and Travis on March 1, July 1 and November 1. The lowest inflow category is “threshold,” which requires minimum monthly inflows of 15,000 acre-feet. The successively higher inflow categories are “OP-1” through “OP-4”. The lowest OP-1 through highest OP-4 categories call for minimum monthly inflows of 15,000 acre-feet, and higher two-month inflow totals that vary throughout the year.
On March 1, 2021, the daily average combined storage of lakes Buchanan and Travis was 1.501 million acre-feet. In accordance with the 2020 Water Management Plan, because storage was between 1.5 million acre-feet and 1.949 million acre-feet, environmental flow requirements for freshwater inflows to Matagorda Bay are set to the OP-3 category from March 2021 through June 2021.
LCRA’s obligation to release water from lakes Buchanan and Travis to meet freshwater inflow needs is subject to the availability of inflows to lakes Buchanan and Travis in excess of senior water rights.
See Chapter 4 of the 2020 Water Management Plan for a more complete description of the freshwater inflow criteria for Matagorda Bay.