Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Texas dam safety

We have a 45 acre community lake that is about 300 acre feet at normal pool.

Texas Commission on Environmental Quality (TCEQ) regulates dams in the state. If you break their threashold (https://www.tceq.texas.gov/assets/public/compliance/field_ops/damsafety/DamSafetyGuidance090113.pdf) they will be around to inspect your dam. We are just over the threashold of 500 acre feet at maximum (top of dam). Based on a required engineering study, our spillway is inadequte to contain a 50% maximum flood event. Now TCEQ defines a maximum flood event as 48 inches of rain in 6 hours. Think about that for a minute. Hurrican Harvey produced 60 inches, but it was over 4 days. The engineering study computed that our 40 foot spillway would need to be 170 feet wide to handle this rain event. That is wider than our dam. Since we can't create a spillway that wide, and we can't raise the dam 7 or 8 feet, our only solution is to armour the dam. This entails stripping all the vegetation from the dry side and installing engineered soil retaining mats anchored into the dam, replacing the top soil, and reseeding. All in about $120,000 project plus $6000 for engineering studies.

Wow that sounds like something California would require

You might try the old bureaucrat switcheroo.

Create a proposal for a sediment settling pond at the very upper end of your community lake. Figure out where to place the small dam to get the big lake below the 500 acre-feet limit.

There is a chance you could get approvals AND do that project for $20,000. It might actually be a win-win situation. A settling pond would keep your big lake cleaner following storm events and would slow your silting rate.

It would also be marginally safer. If the big dam fails in a flood, then the 50 acre-feet (or whatever) above the settling pond dam would not go rushing downstream.

Might as well make a good plan for submission. Create a design to have the capability to dredge or excavate the silt out of the settling pond in the original proposal and argue that you are significantly extending the life of your community lake.

Good luck on your big project!

Rod

BS, I have never heard of 48 inches in 6 hours. Ask them when that has happened. Well,there was Noah, but that wasn’t in Texas.

I agree with Dave. Is that a typo on your part, or a typo in their report?

I think 48 inches in 6 DAYS may be the maximum flood event calculation.

Nederland in the Houston area probably set the record for texas in a single day ... 31.35 inches. Image from Wiki

I think it was 2002, our second big flood event (1998 the first) for Bexar and surrounding counties, getting about 28 inches, I was caught at home, it had already been raining for some hours and was a flash flood event for all of Bexar county and the hill country beyond. The rain was torrential, like 1998, and for the same type event...moisture from bad 'ss hurricanes off of Baja sneaking across the two mountain ranges of Mexico and pouring down in central Texas...in October! The same effects as that for the model max, a gulf coast hurricane stalled out over the hill country. I had links to some really cool NOAH and NWS sites...they had live satellite feeds of "precipitable moisture," kilograms per square meter, I think on 100 meter squares, zoomable right down to about four square miles around me, this link is showing 25 (min) to 35 (max) kg/m^2 (color coded) rushing overhead at what looked like near a hundred miles an hour! (I will search for those links on an old computer). Outside was the sound of roaring falls as inches of water ran off the hills and rolled over lesser hills. Spectacular! All in a fog. With that event in mind, I'm happy my watershed is small. I am looking at catching our driveway run-off into a drain and pipe to the pond, with a valve to cut it off...I think a three inch rain, somewhat rare, but..., could replace half the water in the pond, but I wouldn't want that much..