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..

Sorry, but that is not a typo, and the bureacrats don't want to listen to anyone telling them it can't happen. Already been tried and shot down in District Court in Texas. A series of dam failures in the hill country set off this round of inspections and take no prisoners results. A 30 acre lake near Athens, Tx was drained after they lost their court case against TCEQ.

Forty-eight inches in six hours is crazy. You don't expect such crazy in Texas.

By the way, the last time I looked the state required a permit to build a dam if the water exceeded 200 acre-feet, not 500. But that was six years ago when my BOW was built, and even 200 wasn't an issue. Maybe 500 is subject to stricter scrutiny & regulation.

I think the safety inspections trigger at 500.

Maybe the 200 level was for scrutiny of environmental effects. I did have to fill out a form to get a permit for grass carp, though this year I am not gonna stock them. Too few weeds!

Dam Exemption
Effective September 1, 2013, dams that are located on private property, have a maximum impoundment capacity of less than 500 ac-ft, classified as low or significant hazard, located in a county with a population of less than 350,000 (as per 2010 census), and not located within the corporate limits of a municipality are exempt from safety requirements. Dam owners will still have to comply with maintenance and operation requirements. There is no exemption expiration date.

They raised us from significant to critical with no change in the dam or the area.

Just a thought, but how much over are you? My thought being, tell them to stick it, bring in some dirt, and decrease the lake size by just enough to get under their threshold. I bet it would be cheaper then having to meet their requirements, and then be subject to who knows what inspections and regulations down the road.

I remember talking to TCEQ before building our big pond. The 200 acre-feet limit was not crossed by our pond, so no issue. The 48 inches of rain measuring stick came from the Hurricane that dumped 36 inches in 12 hours way back in history. It was the event they are protecting to 150% in half the time as I recall. In my opinion, it is a very high bar indeed.

All this said, I am glad dams are being inspected. The damage water can do is incredible. The stored energy is impressive. But with the number of dams in Texas alone, they have a lot of work to do. Now, with all this said, springing a $120K bill on someone is a bit daunting, having a pathway to improvements over time seems more reasonable to me.

Also, thanks for the links to the documents.

Thats our gubmint dollars at work,, as a wise old man once said,, the most feared words in country are, "we're with the government and we're here to help". RR

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Ross,

Two things ... one posted by you ... and another posted by highflyer ... speak to me.


AND


Given these, I have to wonder if your community's dam could withstand the actual event that highflyer is referring. This is a known event with metrics that come from a very small window of geologic time. If you stop for a moment and wear the shoes of the task force burdened to prevent ANY dam failures in Texas private lakes ... I think that you would probably also base the yard stick on a known event with some level of overbuild (engineer's safety factor). The crap situation is that your location may not receive the known maximum event in 10,000 thousand years, or perhaps longer. BUT some location in Texas probably could within the next several decades. Given it is unknown where such events will occur ... what choice do they have but to make everyone comply with the standard?

$100,000 is fair sum of money but consider this. What would it cost in today's dollars to rebuild? How much would one human life be worth? Or a washed away home be worth? The risks do greatly outweigh the cost of buttressing the dam. I was once told that a good business agreement benefits everyone. While your community doesn't stand to profit from complying it could ensure the dam has a very long life and it could demonstrate, if the dam ever failed, that it worked willingly on compliance and made appropriate and recommended alterations. If the community plays games ... and the dam later fails ... there could be lots of liability and culpability floating around.

If the standard is 48 inches of rain in six hours, it is not reasonable. Reasonability is also why we don't have a four mph speed limit on highways, though that would cut auto deaths to almost zero.

Autos are a higher risk than private dams but the reasoning goes like this. Our economy can't function with 4 mile per hour speed limit. We all need higher speed limits than that. We address the risk by making better vehicles, improving roads, and requiring seatbelts. It's a risk we have to live with and as a whole we would never choose to go about our travels at 4 mph.

One the other hand. We all don't need anyone's private dam. While we can argue that we need higher speed limits despite the cost of life ... can we really argue that we need anyone's private dam? What is an acceptable loss of property and life that the public should bear from the failure of private water dams? The only answer to the public at large is "NONE". It's that simple and making everyone prepare for uncommon events is the only way to reduce the numbers to none.