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Collapsed Lake Dunlap Dam rebuilt for increased stability and maintenance access Posted on August 09, 2023


Transcript

Charles Hickman - Executive Manager of Engineering, Guadalupe-Blanco River Authority

Back in 2019, we experienced a failure of one of the spill gates here at the Dunlap Dam that certainly led to the immediacy of the need for the design and construction project. But there was a number of factors that GBRA had been discussing with the lake community for several years that also contributed to the need for the project.

These dams were built in the 1920s, way before modern dam safety criteria existed. So, a critical component of this project was bringing these dams into compliance with modern dam safety standards. That involved adding a lot of concrete to the primary spillway to make the dam more stable. A big part of the project was also adding concrete to the earthen embankment. So that way, when that overtopping happens, the erosive forces are less likely to cause damage to the structure. 

So, one of the unique components of this project is the replacement of 1890s spill gate technology. When we looked and canvased other dams across the country and the world, we found very few examples of where that technology remains. Also, this dam has pretty unusually wide spill gates. The spill gates are 85 feet wide. And so, that presented a few challenges in the design. 

There were certain parts of this dam that were just inaccessible for some of the maintenance activities that needed to be done. So, a critical component of delivering this project was adding that maintenance capacity. And that's this bridge we're standing on today—was an addition that was done so that there's a crane that can come out, deploy a de-watering system, and be able to do future maintenance activities with the hydroelectric system in operation and the lake full for recreational access. 

And so, it's a over a $36 million project to perform this type of rehabilitation work. The financing for the project was secured through a loan commitment from the Texas Water Development Board through their Clean Water State Revolving Fund program. Our financial analysts, when looking at this project, determined that accessing the funding through that program would lead to a savings of over $16.5 million dollars of interest payments through the 30-year life of this loan. You know, the funding of this project was provided by taxpayers who are residents around the lake. Getting that loan commitment from the Water Development Board was a critical piece for them feeling comfortable that they were getting this project delivered in the most affordable manner. And ultimately, that loan program led to a reduction of around $600,000 per year in their tax burden.

Dain Larsen – Water Supply and Infrastructure Asst. Director, Texas Water Development Board

The Clean Water State Revolving Fund is used for projects such as expanding or adding new sewer lines to the community, constructing new wastewater treatment plants, or upgrading existing ones. Other uses that communities have for the program are developing reuse projects. This is to provide water that's available for parks and golf courses. Clean Water SRF funding can be used for other projects, such as stormwater, and that's how we used it in the Lake Dunlap project. The Lake Dunlap project was a response to an emergency situation in which the dam collapsed. And so this was a good use of the funds to help a very urgent situation.

Charles Hickman - Executive Manager of Engineering, Guadalupe-Blanco River Authority

So, this project got underway in May of 2021. It was originally planned to be a two-year construction project, but as you can imagine, working on a structure that's almost 100 years old with limited as-built information, there were a few challenges discovered on the way that extended that timeline. Right now, we're nearing the ending phases of the project.

I think the speed with which we got from the crisis situation of the spill gate failure to starting a construction project is a real testament to the collaborative capacity of this community.



This article is posted in Water Planning / Financial Assistance / Water Supply .