A New Decision-Making Tool for Texas Dam Owners

Second in a series

As we discussed last month, a recent study published by the Texas Commission on Environmental Quality (TCEQ) could affect many Texas dam owners. The study updates the probable maximum precipitation (PMP) data, and in many cases it has changed the amounts of rainfall that dams are required to accommodate. New dam projects, including rehabilitation designs and hydrologic assessments, will be required to use this data starting in July 2017.

A matrix within the TCEQ study report succinctly illustrates the average PMP changes by geographic region, watershed size and critical storm duration. (The study is available to download from the TCEQ Dam Safety page. This matrix is on PDF Page 125, and a full map of the zones is on Page 86.)

We can observe several trends from the matrix. Compared with the previous data, the largest PMP reductions are:

• In smaller watersheds
• For shorter critical durations
• Throughout West Texas

These changes are consequential because the watershed data is used to predict the probable maximum flood (PMF), which in turn is used to evaluate dam safety and determine design requirements. Dams that had been considered inadequate under the old data may now meet dam safety criteria or have reduced rehabilitation costs.

Dam owners would still need to have a study conducted to re-evaluate their dam’s specific requirements and learn what upgrades are needed. This matrix serves as a helpful tool for deciding whether such a study is worthwhile.

Your Next Steps

Freese and Nichols’ team of engineers and hydrologists can help you determine how the new PMP data affects your dam and advise you on your next steps. To learn more, contact me at patrick.miles@freese.com or 817-735-7236.

Check back next month as this series continues with a case study, or subscribe to this blog now to receive updates in your inbox.