I'm new to the group. I have lots of vague plans and will likely have lots of future questions. I'll start with the most challenging.
I'm buying 200 acres in a mountainous region of the Chihuahuan Desert in SW Texas. The property has two main arroyos and one steep walled canyon. Both arroyos are dry except immediately after rains. The arroyo through the canyon has a few tinajas that hold water about 1/3 of the year, depending on rain. Both have large catchment areas. I plan to build a series of trincheras and gabions to slow the periodic flash floods and capture silt for habitat restoration and hopefully establishing year round water.
The smaller arroyo has an ancient pond basin where a rock ridge use to form a natural dam. At some point in the distant past, the water broke through the ridge. Any water flowing down the arroyo now races through the opening (about 10' wide) to never be seen again.
Now the question: How thick of a concrete dam would be required to plug the gap in rock ridge and restore the ancient pond to a depth of five feet?
My thoughts, based more on aesthetics than any engineering knowledge, is as follows:
Dig down to bedrock (basically just brush away a few inches of sand and gravel) in the gap and along the upstream side of the flanking walls.
Set forms to create a concrete dam about seven feet high with the upstream wall on the upstream side of the rock ridge.
Have the dam base and side walls extend about three feet to either side and one foot in front of the natural break.
Slope the upstream damn wall at about 70 degrees.
Make the top of the damn about two feet wide.
Set the spillway at about five feet high and eight feet wide (two feet below tops of dam sidewalls and about one foot in from the natural rock ridge on both sides).
Slope the spillway at about 45 degrees with a level extension at the base to prevent undercutting.
Reinforce with lots of rebar.
Pour all concrete at once.
This is very preliminary and will likely be scaled back after I price out the concrete. I may try to save money by making it less thick and/or infilling with native stone.
The water depth will be five feet at the base of the damn and may be deeper toward the center (depending on depth of bedrock). The surface area when full will be approximately 1.5 acres. I'll have a 4" PVC drain line that I can open up to create a small amount of downstream flow or couple to a 1/2" water line for watering new plantings far downstream from the dam.
Any thoughts, suggestions, or warnings would be appreciated.
Check out the dams that were done in what is now the Hueco Tanks State Park east of El Paso. They were done in the 1950s or early 60s before the state got it. Many many thousands were spent on the dams and trucked in clay, and they never held water due to the caliche. I recently spent a week there and heard all the stories.
Correct Bill. Just trying to capture some water. Mud turtles live in the arroyo (buried deep underground when dry) and will take up residence. If the water becomes permanent, I may stock some minnows, but don't foresee it sustaining any larger fish.
I also have plans for a larger dugout pond at another spot. It may be large, deep, and permanent enough for stocking some something more interesting. Not at that point yet.
Failure is always an option. Worst case scenario, I'll capture a huge amount of silt, sand, and gravel that will retain and slowly release some water downstream.
The second option is just to plug the hole with a permeable gabion type dam. Skip the dream of a surface pond and be satisfied just to slow the flow and capture silt hold subsurface water.
Of course, if the concrete dam and pond works, I'll have to dig out the silt, sand, and gravel periodically.
Correct Bill. Just trying to capture some water. Mud turtles live in the arroyo (buried deep underground when dry) and will take up residence. If the water becomes permanent, I may stock some minnows, but don't foresee it sustaining any larger fish.
I also have plans for a larger dugout pond at another spot. It may be large, deep, and permanent enough for stocking some something more interesting. Not at that point yet.
In that case, assuming the pond doesn't leak, IMO I would get an estimate of evaporation rate at the site before spending any money. Maybe a 5 gallon bucket of water at the site to measure? IMO depth is your friend not so much surface area. If you lose a few inches a week to evaporation you will need to have a retention pond much deeper than you might think to get through the dry times.
As for the pond going dry between rains, that's not a problem. In fact, I fully expect it. I'm working to restore and improve habitat, not create an aquaculture, at least not in THIS pond. Currently, this arroyo drains of all surface water within 24 hours of rain and is typically bone dry even several inches below grade within two weeks. If I can hold and slowly release water for even a few weeks after a good rain, that will dramatically improve the vegetation near the pond and downstream.
I've seen areas in similar environments that have been dramatically transformed by a series of one and two foot gabion dams (completely permeable, just trap silt and slow flow). In some cases, permanent or semi-permanent surface flow has been restored after decades with no surface flow other than brief flash-floods.
Welcome to the forum. If the concrete dam would utilize the natural rocks at each side, I would drill and epoxy rebar into those rocks and use a bonding agent on those rocks right before the concrete was coming out of the chute, and any other place where the concrete will be touching natural rock. You don't want the water finding a way around the concrete between the rocks and washing out a hole over time.
Good points on the rebar to the natural rock and the bonding agent. I had planned to drill the rock and epoxy in the rebar, but had not considered using a bonding agent. I'll update the plan accordingly.
Yep. "Navigable by statute" is a tricky and strange issue out here. I almost bought a big chunk of land along Terlingua Creek (a dry creek subject to extreme flash floods with permanent water limited to a few very short sections fed by springs). The "creek" is only navigable by kayak by maniacs with huge balls for a few hours after massive rain events, then drains back to dry. Nevertheless, it is "navigable by statute" based on width from bank to bank, even though both banks and the bed are almost always dry.
I decided there wasn't much point in owning land where the public had a permanent recreation easement and where I could not modify the creek by so much as a shovel full.
The land I've now settled on has arroyos that all fall way below the criteria to be considered navigable by statute. I'll still consult with TCEG and TPWD for advice and possible grants. Based on how they've worked with some other locals down here, I expect more help than hindrance ... hopefully.
I'm sure old Clay appreciated the drinks. Best damn mayor in Texas. I'll take a crazy old drunken goat over a typical politician any day.
He was a good mayor. IIRC, there were about 30-40 people living in Lajitas when I was there, and they all disappeared into the hills during the chili cook off.
The country down there is almost mentally cleansing. Good luck with your plans.
I was inspecting the site again today. Sadly, I noticed a number of fissures in the native rock that had escaped earlier notice.
Chances seem very high that my dam would hold but the rock on either side would leak like a sieve (best case) or be blown out completely (worst case).
I think I'll change plans and install a highly permeable gabion dam instead. It won't form any type of pond, but will slow the flow, capture sediment to build up the stream bed, and slowly release water downstream. It will be the first in a series of several gabion and trinchera type sediment dams along about a half mile of this arroyo.
I'll then build a large earthen dam downstream from the gabions and trincheras. The resulting pond should cover about 2.5 acres and have a maximum depth of fifteen to twenty feet. The dam itself will only need to be about 8' high. Most of the depth will be dug out. The primary spillway will be a series of culverts two feet below the top of the dam on the upstream side. They'll have a 45 degree bend so they can slop down through the dam and exit level at the natural creek bed. Emergency spillway will be a wide overflow channel around one side of the dam with a gentle slope down to the creek bed.
This larger pond, shouldn't collect much sediment, thanks to the series of upstream sediment dams.
About 50 yards downstream from the dam is the confluence of this arroyo with another, much larger, arroyo. Just beyond that, the combined arroyos enter a vertical walled canyon with a few seasonal tinajas (natural rock basins holding temporary or permanent water).
I plan to enhance the tinajas by adding some natural looking and broadly sloped masonry dams ranging from two to three feet high. I'll keep the main tinaja (8' wide x 12' long x 5' deep) topped off at all times. I'll use water from the main pond in good times, and water from my well when necessary.
I want the main tinaja to serve as a permanent water hole for wildlife and an occasional splash pool for myself. The canyon wall has a cave (8' high x 8' wide x 20' deep) with a natural rock porch and a smaller side cave. It's about halfway up the canyon wall and well above the highest water mark. It was used by prehistoric Native Americans. I plan to deck it out as a neolithic man cave. A buried water line with a hidden solar powered water pump will create a natural looking "spring" near the mouth of the cave that will trickle down to the tinaja.
I'm hoping I can stock some native minnows, catfish and perch in the large pond, but need to make sure it will hold permanent water first. I may also try stocking the tinajas with minnows, but would probably need to restock them after every major rain event. Flash floods through that canyon can be torrential and would likely carry any fish in the tinajas far downstream. Flash floods will also scour out any sediment from the tinaja basins, as long as I maintain proper slopes on the masonry dams. Otherwise, they'll just become gravel pits
Look and see if anybody does epoxy injection. It's a technique used to repair cracked concrete. Basically you take a tube with a foot on it, glue it over the crack and repeat. Typically the tubes are placed the concrete slab thickness apart on the crack. Take more epoxy and cover the crack. The next day the epoxy is injected into the crack, keep injecting until you see it flowing under the next tube. Pull the injection machine off of that tube, cap it, and move to the next tube.
When you are done, let it set up for a day, then use a torch and a scraper, grinder or some other tool to remove the epoxy that was used to seal the cracks, and the tubes come with it.
It's an approved fix for concrete. It has been used to waterproof a floating highway, basically glue the L.A. Coliseum back together after the Northridge earthquake, seal foundations, building slabs, parking structures, etc., etc.
I don't know what will be more cost effective for you. Or if it will work, but it could be something to look at. The epoxy is actually stronger than the concrete, and the machine that I am familiar with uses air over hydraulic to achieve around 20,000 psi injection pressure.
Interesting suggestion on the epoxy injection. After looking at the fractured natural rock outcrop that used to form a natural dam, I'd rather leave it alone and just place a large gabion at its upstream base. "Repairing" it and adding a concrete dam would take too much away from its natural character. I think I'll be quite happy with just the series of sediment dams and the one larger pond way downstream. That larger pond will be easier to build, more likely to last, and be considerably larger and deeper.
Focusing on just the one pond, instead of stretching my resources to build two, seems to be the wiser play.
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