2009-12-10

Finally, dam repairs – seven years later

By Carol L. Smith

Seven years ago, the then Texas Natural Resource Conservation Commission (TNRCC) – now the Texas Commission on Environmental Quality, TCEQ – and Bexar County Judge Nelson Wolff, along with various other local and state emergency management officials stood near the Medina Dam giving a press conference in the pouring rain.

They reported that the Medina Dam was unstable and could possibly fail, that floodwaters had risen to within 18 inches of the top of the dam and that evacuations must begin immediately.

At long last, the BMA will begin the repairs needed to assure the Medina Dam’s stability and the safety of those who live in its shadow.

‘Mo $$$, mo’ $$$, mo’ $$$
During the 81st legislature, HB 4586 appropriated $4 million for structural improvements to the Medina Dam, with delivery of the money being contingent upon an interlocal agreement with an alphabet soup of agencies – the Bexar Medina Atascosa Water Control and Improvement District #1 (BMA), Bexar Metropolitan Water District (BexarMet), San Antonio River Authority (SARA), the Edwards Aquifer Authority (EAA), Bexar County and the Texas Water Development Board (TWDB).

According to BMA President Ed Berger, a final draft of the interlocal agreement is now being circulated among the parties and they hope to have the modifications to the dam completed by 2010.

This is a portion of the total $ 11.5 million that is estimated to be needed to complete the repairs and modifications to the nearly 100-year-old dam. Berger stated that the additional funding is being supplied “by the BMA, the TWDB and Bexar County.”

The need for these repairs became extremely urgent after the record setting, historic flood of July 2002. During this flood, water reached within 18 inches of going over the top of the Medina Dam, which caused widespread evacuations of the entire Medina Valley area below, including the cities of Rio Medina, Castroville and La Coste. This is the highest water level ever recorded at the Medina Dam.

In observations made in a joint dam safety inspection by Freese and Nichols Engineering and the TNRCC on July 5, 2002, the abutments on each side of the dam were “likely to initiate a failure.” In a joint report dated July 6, 2002, the overall conclusion “was that the integrity of the dam could not be assured”.

Repairs, modifications & accountability
The modifications to the dam needed to repair the abutments will be completed by URS Engineering, whose corporate headquarters are in San Francisco, CA. The URS firm provides planning, design and program and construction management services for all types of transportation and water resources infrastructure, as well as for healthcare complexes, schools, courthouses and other public buildings.

Berger explained that the renovations will incorporate “drilling into the bedrock, grouting and installing anchor cables,” to modify the abutments, stabilizing them against future flood events.

The TWDB stated in an email request for information on the project, that the proposed structural improvements by BMA “include a series of post tensions anchor cables at both abutments for stability and erosion protection at the downstream foot of the dam. The BMA anticipates construction to begin April 30, 2010 with a completion date of April 30, 2011.” The TWDB also reports that “A TWDB staff engineer has been assigned to the project and will review bid-contract documents, ensure that all permits and regulatory approvals have been obtained, review change orders and review requests from BMA to have grant funds released for the project.”

When asked who would be overseeing the repairs, Berger stated, “SARA will be running the project.”

It appears that the personnel with TWDB will administer the grant money appropriated through the legislature, making sure all documents, contracts and permits are administratively complete, while SARA employees will work with URS Engineering to complete the actual physical modifications.

Previous repairs & BMA conservation efforts
In 2004, the original outflow valves installed in 1912 at the base of the dam were replaced; however, the new valves proved defective, allowing water to continue to flow around them. A second set valves has since been added and are wired to the existing valves, enabling a complete shut off of all water flow.

BexarMet paid for the replacement of the original valves and has been embroiled in a lawsuit with the manufacturer about the defective valves since their installation. According to Berger, the valve repairs should be completed by the end of the year.

Other recent repairs to the BMA system include regrading and adding a concrete lining in the main water delivery canal. A $3,765,000 loan from the TWDB helped to pay for these repairs.

According to Berger, conservation efforts are essential to BMA’s plans for the future. The BMA owns an annual 66,000 acre-foot water right adjudication from Medina Lake. Most of the BMA’s water sales are for irrigation, although BexarMet owns a 20,000 acre-foot portion of the BMA’s annual water allotment. “In 2006 we used our entire adjudication, we’re not drawing anywhere near that now,” Berger said.

When discussing the current Medina Lake level of over 40’ below the spillway, he stated that “the last two years have been the worst drought ever and this year we only used 34,000’ and BexarMet took 8000’, a total of 42,000 acre feet. We want to keep water in that lake, so we can continue to supply water to our customers.”