Thursday, March 28, 2024

Drought impacts causing lake releases

Posted

BRAZOS RIVER AUTHORITY

 

 

Aaron Abel is the water services manager for the Brazos River Authority. Abel, a hydrologist and water resource planner, has more than 22 years of experience in water management. 

 

We may have officially entered fall, but continued high temperatures, water use, evaporation, and a lack of rain have impacted lake levels throughout Texas, including Possum Kingdom Lake, Lake Granbury and the other reservoirs in the BRA's water supply system.

If you visited a lake during the drought of 2010-2014, you know our current situation is not as dire as during that period. PK and Lake Granbury, though low, still have more than 85 percent of water stored behind their dams. Other areas of the basin are not doing as well.

For the past several months, low flows in the Brazos River have prompted the need to release water from several Brazos River Authority System reservoirs to meet water supply needs in the lower Brazos basin. Since June 6, we've made releases from Lakes Whitney, Somerville, Limestone, and currently, from Lake Belton. But as the supply in these reservoirs’ declines, our hydrologists are challenged to balance local needs with other areas that are running short of water.

It's been more than 11 years since the BRA has had to release water from Possum Kingdom Lake and Lake Granbury to help supply other areas of the Brazos basin. But without drought conditions improving, releases are unavoidable.

Why do we have to release water? 

All surface water in Texas is owned by the state and held in trust for use by its citizens. The state legislature tasked the BRA with managing a specific amount of that water and making it available through contracts to municipal, industrial, mining, irrigation, and agricultural interests for beneficial use. 

The idea behind a water supply reservoir is to capture and store water during wet times for use during periods of drought when rainfall and river flows are down. Though many consider the reservoir located near their home as belonging to their city, county or region, the water stored in the 11 reservoirs permitted to the Brazos River Authority function as a "system" or a series of linked storage facilities with the capability of supplying water both locally and to other areas within the system via release into a river or tributary or in some cases via pipeline.   

During times of drought, BRA hydrologists analyze, in part, the system as a whole, considering local water supply needs, available storage in each reservoir and multiple other factors to determine which reservoir has enough water to allow a stored water release to occur. The goal is not to empty a lake and then move to the next one. Instead, our hydrologists work to distribute the water stored in the lakes as evenly and efficiently as possible to balance the drought impacts across the BRA System of reservoirs.

Based on current forecasts, the water supply needs in the lower basin will require a release of water stored in Possum Kingdom Lake. The current forecast estimates the release would draw the lake down about 3 feet during the month of October. The release would account for almost 2 feet of the decline, and the remaining foot would be a result of meeting local water supply needs, evaporation rates during that time and maintaining the balance between Possum Kingdom and Lake Granbury in accordance with the BRA PK-Granbury-Whitney Water Management Study finalized in 2011.

The levels in Lake Granbury will also be affected by downstream water supply needs. With PK's forecast decline of three feet, Lake Granbury would drop about two feet, with about a foot of that decline attributed to the water supply release and one foot to local use and evaporation.  

October is typically one of the two wettest months for the area, so rainfall of any type could modify the current lake level prediction. If we receive rainfall, these forecasts will change.

The BRA has a Drought Contingency Plan that is designed to work, with efforts by other state and local agencies, to manage water during times of scarcity. Currently, both PK and Lake Granbury are under Stage 1 Drought Watch, which requests a 5 percent reduction in water use. To view the BRA's Drought Contingency Plan, go to https://bit.ly/3rhQJGO

And if you'd like to watch our hydrologists speak more about the drought, go to our YouTube page at https://bit.ly/3BSkdjf

www.brazos.org