May 7, 2024: “Texas is a land of perennial drought, broken by the occasional devastating flood.” This was reportedly stated by a National Weather Service meteorologist almost 100 years ago.
It’s still the case today; we saw it happen over the last week in the Brazos River Basin.
During April, most of the basin has seen much above-normal rainfall, which has produced runoff, significant floods in some areas, flooded roadways, stranded towns, and beneficial lake level rises in some areas.
The effects of the rain have varied across the Brazos River Basin. The climatological differences vary vastly for a watershed roughly the size of the state of Tennessee, extending from the Texas-New Mexico border down to the Gulf of Mexico.
Lake Limestone & the Navasota River
During the first week in May, record amounts of water flowed down the Navasota River into Lake Limestone, located in Limestone, Robertson, and Leon counties. The reservoir’s Sterling C. Robertson Dam released about 227,000 acre-feet of water from May 1 - 6, said Aaron Abel, Brazos River Authority water services manager. To help put that in perspective, an acre-foot is the amount of water needed to cover one acre (43,560 square feet) with one foot of water. One acre-foot is equal to 325,851 gallons of water, enough to cover a football field with a foot of water.
Lake Limestone was full when the rain event began, a welcomed relief after an extended period of drought. However, had the lake been completely empty on May 1, the entire reservoir would have filled, and releases would have still been necessary due to the high amount of inflows or water flowing into the lake.
The BRA’s three water supply reservoirs (lakes Possum Kingdom, Granbury, and Limestone) were not built to provide flood control storage during heavy rainfall events. This means when a reservoir is full, any additional water coming in must also go out to protect the dam’s gates and structure.
The amount of rain that hit that general area was so heavy that the Sterling C. Robertson Dam surpassed its record release rate of about 58,000 cubic feet per second (cfs) (set in April 2009) on May 2, 2024, releasing about 77,650 cfs. To put this in perspective, 1 cubic foot is equivalent to the volume of a small beach ball.
Lakes Belton, Stillhouse Hollow, and Proctor
The Little River watershed also received some much-needed rainfall. Listed under a Drought Contingency Designation of Stage 2 Drought Warning, the subwatershed had not received the beneficial rainfall seen in most other areas of the Brazos basin, with reservoir levels at far below normal with Lake Belton at 83% full and Lake Stillhouse Hollow 68% full.
During the five-day event, Lake Belton’s lake level rose above its conservation pool elevation of 594 feet above mean sea level (ft-msl) for the first time since Aug. 26, 2021, Abel said.
This was a significant drought in Lake Belton’s period of record, which lasted more than 32 months. The reservoirs’ lake level rose almost six feet on May 6, Abel said. Some areas within the Leon River watershed between Lakes Proctor and Belton received 6 - 15 inches of rain from April 30 – May 6.
As of May 7, the elevation of Lake Belton was 603.2 and climbing, some 9.2 feet above the top of its conservation pool elevation.
The Lampasas River, upstream of Lake Stillhouse Hollow, also received 6 - 15 inches of rain over the past week. Lake Stillhouse Hollow rose above its top of conservation pool elevation (622 ft-msl) this morning (May 7), Abel said. Since May 3, the reservoir has risen over 13.3 feet.
This is the first time the reservoir has been completely full since late September 2021. Lake Stillhouse Hollow reached its record low elevation since it was built in 1968 during this round of drought. In October 2023, the lake was 19.9 feet below the top of the conservation pool.
“We will begin the process to rescind our drought declarations at Lake Belton and the Stillhouse Hollow-Georgetown Subsystem,” Abel said. “We will move Lake Belton and the Stillhouse-Hollow Subsystem out of all drought declaration since we anticipate that these reservoirs will remain above the trigger level for Stage 1 Drought Watch for an extended period of time.”
Only one reservoir in the 11 lakes of the BRA’s Water Supply System remains under any level of drought designation, which happens to be the most severe category. Lake Proctor remains in Stage 4 Drought Emergency. However, the lake did see some beneficial improvements to its levels over the last few days, increasing around 2.5 feet since May 4. Lake Proctor remains around 9.7 feet low.
Totals
Between May 1 and May 6, the overall BRA Water Supply System made up of Lakes Possum Kingdom, Granbury, Whitney, Aquilla, Proctor, Belton, Stillhouse Hollow, Georgetown, Granger, Limestone, and Somerville, has experienced almost 650,000 acre-feet of inflows into the 11-reservoir system. This is a 7% increase in the total system water supply storage.
Since April 1, the overall BRA Water Supply System has experienced approximately 1.1 million acre-feet of inflows across the 11-reservoir system, an 11% increase in the total system storage since April 1.