Just looking for experienced small lake spillway design professional, preferably in the East Texas area but not opposed to outside the area. Need help designing a chute type spillway for an 18-acre, creek fed, earthen dam created lake that has been in existence since 1929. Thanks
I saw your various spillway pics from your other post. It appears they did some excellent work back in the day!
Is something getting close to failure, or are you just trying to add one more level of safety in case a hurricane remnant parks in your watershed?
The hydrograph data were generally created by people that were very good at their jobs. However, they are "theoretical" estimates of the water flows. I agree that you should try to get any info that your NRCS office can track down.
Depending on your concerns, you can also gather actual field data for your location. See how much a 3" rain at your property changes the inflow to the lake, and then compare that to a 3" rain that covers the entire watershed. After a few years of careful data collection you should have some excellent data records. "Experimental" data always trumps "theoretical" data. Of course, your experimental data will certainly be sparse and have some gaping holes, but it could still provide you with some valuable info to evaluate your concerns?
The bigger the watershed, the longer it takes for the inlet stream at your location to crest. Do you live at the property? You might be able to open your two flood pipes after a surprise thunderstorm begins and let out enough water to make a significant difference at your lake prior to peak discharge arriving (for example) 7 hours later.
Have you examined "automating" your flood control system? I have seen flood diversion systems with pipes around the same size as your pipes. The outlets are covered with big swing gates. The gates are weighted. For example, they have enough weight that they stay closed when there is 6" of water in the bottom of the pipe. However, if the water level rises a little, they are cracked open and start releasing a little water. If the water level keeps rising, then they continue to open a little farther and pass even more water in response. It is impressive to see the gates fully open during flood stage and banging against the top of the raging stream of water that is passing through!
In Kansas, you can hire a pond contractor (or DIY) for ponds up to a certain size, or dams of a certain height or volume of water impounded. Above those exclusions, every project must be designed by a certified civil engineer. Our state regulatory agency provides a list of independent engineers for lakes of that size. Perhaps you can look in the Texas regulations for building a large dam and see if they list some engineers or engineering firms that perform those projects. Obviously, those engineers would have to be able to design a proper chute type spillway when it was needed for the designed dam. That might get you to an experienced engineer for your project.
Good luck on your project of keeping your beautiful lake happy and safe!
Thanks for the input! Recently, the area received 14-16 inches of rain in 4 to 6 hours and the water overtopped the dam. The emergency spillway and primary spillways did their jobs and the dam showed very little wear, but part of the Emergency spill was washed out (the downstream-downslope portion). So, I want to add more assurance that the dam or spillway will not blow out with those types of extreme events. This lake has been in existence since 1929 (my great grandfather built it) and was originally equipped with a wooden spillway. The present 21 foot wide (flat portion), concrete lined trapezoidal chute spillway replaced the wooden spillway about 45 to 50 years ago and still functions as it should. In my entire life, I have never seen the extreme rains of the past 7 years or so (such as the event described above and hurricane Harvey that dumped over 60 inches of rain about 45 miles south of me back in 2017).
I started collecting rainfall data vs. lake level data and I'm now trying to make sense of it. Again, over my entire life, I have not seen the impacts to this lake that I am presently seeing. I am also looking over historical imagery, etc. to see what has changed in the watershed and also plan to call neighbors upstream to see what they are witnessing with these storm events.
I am researching automation of the sluice gate valves. I just need the vendors I have contacted to get back to me. Never thought it would be difficult to try to buy some expensive automation equipment but these companies must have more business than the need.
I contacted the State Dam Safety office and requested a list of dam/spillway engineers but that organization has still not emailed the list. I am also and engineer (ME Civil) but sure would like to have some real world experienced person help with this project.
Kind of crazy that of all the projects I've worked with over my life about 5 -10% of the effort is technical and the rest is just pushing to get simple things done and get information. The same applies with this project.
As it frequently happens, I am giving advice to someone with far more expertise on the topic than I have!
Having water overtopping the dam certainly answers my question about your main concern for your lake. I am glad you survived that frog strangler without damage to your dam.
I am sorry to hear about the damage to your emergency spillway. However, if it took a 50-year(?) rain event to damage it, then you might have the "proper" amount of protection for your pond. The budget for building a perfect system is always much higher than for just a 98% good enough system.
Another affordable option might be to raise the freeboard of your dam? You do have a huge capacity to pass water. If you could compact a few more lifts of material across the top of the dam, you might prevent over-topping for a 100-year rain event.
P.S. When I was talking about "automating" your flood control pipes, I was only using that term in the loosest sense. I have utilized automated/remote control valves in high pressure gas pipelines. They are an awesome technology, but they are expensive and they are NOT idiot proof. In my experience they are more likely to fail or perform poorly in the extreme conditions when they move out of their normal operating envelope. (Just when you need your automation the most.)
The flood control project around my city that I have observed for many years has hundreds of flood pipes with the outlet swing gates as I have described above. I very rarely see any required maintenance performed on them. I believe they were installed in the early '70s. That is a lower level of "automation" that might suit your needs. Those gate valves on your flood pipes are huge. The motors to move them automatically will necessarily be very large.
If you are already doing concrete repairs for your spillway, could you buy yourself some more freeboard by cementing in a large siphon within the emergency spillway. You could set it up to automatically start siphoning at your desired pond elevation. An 18" siphon pipe (for example) would be moving a lot of water at full siphon prior to peak discharge from the creek reaching your pond. Would that be enough to preserve enough freeboard that your dam does not get overtopped? It would certainly be much cheaper than a full chute type spillway.
Just throwing out more ideas for you to chew on since you understand all of the physical forces involved AND have eyeballs on your actual project site.
Hello from northeast Texas (north of Jefferson), NRCS office doesn't engineer for over 80 acres of drainage into proposed pond area, but he sent a flow chart for my area(378 acres). You maybe able to adjust to your acreage so you have a flow rate going into your pond. I'm not sure what I'll do with mine yet. Probably will dig out s bend in wet weather creek so I can check for clay & 1st have a pool to pump from.
