Track the volume in the Highland Lakes' two water supply reservoirs

The graphic below shows the current storage level in lakes Buchanan and Travis — the only water supply reservoirs in the Highland Lakes chain. When the water in these lakes drops below specific “trigger points,” some users receive less water.

Enter numbers in the boxes to change total volume – and learn below how this
may trigger action to curtail water to specific users.

Buchanan  feet above msl
(Enter number between 912, the lake’s level when empty,
and 1,025, the top of Buchanan Dam.)

Travis  feet above msl
(Enter number between 502, the lake level when empty,
and 750, the top of Mansfield Dam.)

Trigger points:  How LCRA priortizes water during droughts
LCRA's state-approved Water Management Plan is designed to prioritize water during droughts based on the combined storage of lakes Travis and Buchanan. The lower the water drops, the stronger the actions required to limit water use. Below are specifics:

1. 2.01 million acre-feet: Lakes considered full. This translates to 681 feet above mean sea level (msl) for Lake Travis, and 1,020 feet (msl) for Lake Buchanan.
2. 1.897 million acre-feet: When the combined volume of the lakes falls below 94 percent of total capacity on either Jan. 1 or July 1, customers with “interruptible” water contracts — such as golf courses — are required to cease diversions. This does not affect large irrigation operations downstream.
3. 1.7 million acre-feet: If at or below this level on Jan 1, begin reducing releases for Matagorda Bay and estuaries.
4. 1.6 million acre-feet: If reached at any time during the year, request voluntary water conservation from all customers.
5. 1.1 million acre-feet: If the shortage intensifies so that the volume drops to less than 1.1 million acre-feet on Jan. 1, large irrigation operations downstream, including rice irrigation districts, are required to reduce diversions of water. Water also is curtailed for "instream flow" designed for environmental needs.
6. 900,000 acre-feet: If reached at any time during the year, request mandatory conservation from all customers.
7. 600,000 acre-feet: Begin pro-rata curtailment of firm water customers when Board declares a drought worse than "drought of record."
8. 325,000 acre-feet: If at or below this level on Jan. 1, cease all water to interruptible customers for the coming year.
9. 200,000 acre-feet: If reached at any time during the year, immediate and total cutoff of Highland Lakes’ water for rice irrigation.

Terms to know
*Acre-foot: The amount of water required to cover an area of one acre to a depth of one foot. One acre-foot of water is equal to almost 326,000 gallons.

Drought of record: The decade-long drought that affected Central Texas from the late 1940s through the late 1950s. (See LCRA history.) No other drought in recent history was as severe or as sustained. LCRA and other organizations use it as a benchmark to compare recent droughts and to prepare for future droughts.

Firm water: The amount of water lakes Buchanan and Travis could supply during a repeat of the most severe drought on record. Most of this water is committed for use by cities, industries, power plants and protection of aquatic life.

Interruptible water: Water that is available for use on a year-to-year basis, depending on how much water is stored in lakes Travis and Buchanan. Interruptible water is subject to curtailment during water shortages.

Mean sea level (msl): A point of reference to measure lake elevation. It refers to the elevation of the ocean halfway between high and low tide. Lake elevations are measured in feet above mean sea level.

Learn more: Overview: managing the water supply and state preferences |
Water Management Plan | What happens in a drought? | Water contracts
guarantee supplies even during severe drought (with pie chart graphic) |
Water conservation

Note on calculations: The volume of water in the lakes shifts constantly
because of the build-up of sedimentation, changes in river channels and other
factors. The calculations above are based on the latest hydrological surveys available.
Lake Buchanan’s volume is from an LCRA hydro survey in 1991 plus aerial
mapping in 1997 (based on National Geodetic Vertical Datum of 1929). Lake
Travis’ is from an LCRA hydro survey in 1992-1993 and aerial mapping
in 1997 (NGVD 29).

-- Published Feb. 1, 2006