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.
(SEE UPDATE BELOW - Plans changed dramatically)
