Update on the Arbuckle Reservoir

The LCRA Board of Directors approved a $65 million increase in the lifetime budget of the Arbuckle Reservoir for remedial construction and related costs on Dec. 10, 2019. 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 TWDB. The debt service associated with the budget increase will be funded from LCRA’s Resource Development Fund.

Background
LCRA 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 reservoir site, 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- to 175-footdeep subsurface cutoff wall is being constructed inside the western, northern and southern portions of the reservoir berm. Groundwater testing is underway to determine if additional mitigation is needed prior to being fully operational.

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.

Following filling and testing, the reservoir is expected to be operational in 2024.