Update on the Arbuckle Reservoir

The Board of Directors of the Lower Colorado River Authority on Dec. 10, 2019, approved a $65 million increase in the lifetime budget of the Arbuckle Reservoir for remedial construction and related costs. The previous lifetime budget for the reservoir was $250 million, supplied by a Texas Water Development Board bond sale and a $2.4 million grant from the Texas Water Development Board. The debt service associated with the budget increase will be funded from LCRA’s Resource Development Fund.

Background
The Lower Colorado River Authority is building the first new water supply reservoir in the lower Colorado River basin in decades. The Arbuckle Reservoir is on 1,100 acres of land off the main channel of the Colorado River in Wharton County on the Texas Gulf Coast Prairie.

The Arbuckle Reservoir represents a massive new infrastructure project for Texas. Having a 5‑mile circumference, the reservoir is about 2 miles long and 1 mile wide. The reservoir will be capable of storing 40,000 acre-feet of water at a time. Because water in the reservoir can be used and the reservoir refilled multiple times per year, it will add up to about 90,000 acre-feet per year to the region’s water supply.

Given the soil characteristics of this area of Wharton County (intermixed layers of sand, sandy clays and pure clay), coupled with a high water table and the gentle east-to-west slope of the property on which the reservoir is located, LCRA was aware from the outset that groundwater seepage could be an issue. For this reason, an 80-foot-deep subsurface cutoff wall was constructed under the berm on the western side of the reservoir for the purpose of preventing groundwater transference.

Remedial Action
In November 2018, reservoir construction was substantially complete, and initial filling and testing started. In March 2019, after approximately four months of filling, staff observed groundwater seepage appearing on the western exterior of the reservoir. LCRA Dam Safety staff and engineers stopped the filling and emptied the partially filled reservoir. Subsequent engineering analysis and testing have determined that an additional subsurface seepage cutoff wall will be required to control groundwater transference and allow the reservoir to be refilled. Approximately 15,000 feet in length, this new 125-foot-deep subsurface cutoff wall will be constructed inside the western, northern and southern portions of the reservoir berm.

Building a new infrastructure project of this magnitude is highly complicated, and it is not uncommon for such an undertaking to take longer to complete and cost more than initially anticipated.

LCRA will use the additional funds for the construction of the new subsurface cutoff wall and other related items necessary to control seepage and allow the reservoir to operate safely. Staff anticipates the construction will take up to 26 months, and following filling and testing, the reservoir should be fully operational in late spring 2022.