Pond Boss Forums POND CONSTRUCTION Building a dam Cinder-block dam with reinforced rebar?

I have an arroyo on my property in new mexico that I plan on constructing a 10’ wall dam across to retain water. The area is very sandy and full of prickly pear so i will most likely be using an RPE line with a geotextile underlayment to prevent intrusion by the prickly pear roots down the road.

I have a question as to the cinder block dam/retaining wall I plan on building. So long as it’s under 10-feet tall, i do not need an engineer’s stamp to create a water impoundment for my livestock and farming purposes according to New Mexico law. So, I want to make sure the method I use is sound for retaining the pond water to come after it is filled.

The area of the pond is roughly 80’ x 45’. After doing some online research, I seem to think that if I pound rebar through the holes of the cinder blocks and deep into the ground, and then backfill the cinder blocks with concrete as i build up the 10’ wall, that would be enough strength to hold back a pond that is 10’ deep at the dam but steadily gets shallower as it gets away from the dam (so that it will be like a beach entrance at the other end of the pond from the dam).

Does that sound like a solid enough construction method for this volume of water? Thanks in advance for your assistance!

Sounds good to me. Just assure that you tie it into the walls of the creek with concrete. Also, backfill behind it with rocks or concrete.

teeroy, welcome to PondBoss. Howdy neighbor. We're just a few hours away near Dolores,Co. My brother and sister in law, and our son and daughter in law are just down the hill by Fanta Se, as they like to call it. Our drive to visit them sometimes takes us through Espanola.
Dry dry dry where you are, isn't it!
What kinds of stock water impoundments are in your neck of the desert? Is there anything close to the size, as in volume, of the pond you're considering? I ask because a dam 10' tall may be more than you need to capture the meager snowmelt and monsoonal rain that falls by you.
I like your idea of using the block wall and rebar, then backfilling, with a liner to hold the bit of surface water you get there. My cautionary tale is that here, with our clay soils, our 3" to 2' of snow, and monsoon generated summer rain does not affect the depth of our 1/4 acre pond in any significant way. We get a small flow of runoff from rain; nothing from the snow melt. We've got 3 significant draws joining our pond with fewer than 50 acres of watershed. Our pond is irrigation water fed.
Good luck with your project. If you like, I can swing by on one of our trips to NM.
Roger

Your solution sounds quite easy and viable, yet nobody seems to build dams that way.

When I have some easy DIY project solution that the experts don't use, I later find out there is usually a reason they don't do it that way.

I am NOT an expert, but I believe there may be problems with your cinder block dam.

Cinder block walls are very strong at resisting vertical loads. They are not very strong at resisting lateral loads. If you build a 10' tall cinder block retaining wall to hold back soil, once that soil gets water saturated, it will almost always crack the block wall. I am worried that the hydrostatic pressure of your water column will crack your block wall. (It will certainly try to push it over. You will have to pour a very strong concrete footing.)

I also worry about the freeze/thaw cycles on your vertical wall that is NOT in compression to help it resist horizontal joint cracking. I expect your grout joints will crack.

Perhaps you can use your wall for strength, and use mastic to secure a vertical pond liner onto the wall for the actual permanent sealing?

I hope I am wrong, and your project will yield positive results. Your best advice to rely upon would be if some better building experts than I, drop into your thread.

Your plan suggests problems with as noted by Fishinrod that eventual lateral pressure cracking of the joints will occur. A liner placed on the inside of the wall could help reduce seepage from eventual joint cracking. My other concern is water pressure and movement can occur around the outside edge of the dam block structure and the eventual pressure and seepage will cause a gradual water movement pathway to occur round the outside of the wall. This is more likely to occur if there are any porus soils on the outside edges of the dam. Seepage will gradually continue to increrase over time. Lots of hydraulic pressure will occur at 9-10 ft deep to induce and gradually and slowly produce a seepage pathway that will over time increase to a significant flow rate. If long term structure of the dam block structure is important, I would consult with a soil engineer and or similar construction professional. Some government agencies (US Soil & Water? or Univ Extension Service) have soil engineers on staff or know about them for a free consult. Two professional opinions would be wise.

I wouldnt do it, ask AI for some calculations on what you are trying to hold and at the depth you are trying to hold back and youll find out it isnt practical or possible, i suspect you could do it with enough material behind it but in that case you'd just as soon leave the cinder blocks out and do it properly. Cinder blocks will allow for movement and seepage, it wont last long in my estimation...but then again try it and please report back on the results!

Without buttressing and making a bow shape, a 10ft tall block wall can be blown over by a strong wind, let alone water. The rebar would just assure it would all fall over together. I am thinking there would be a lot more to it than a simple line of block with rebar to hold back water.

I would imagine it being cheaper and easier to dozer up a proper dam/berm, then line the basin with impermeable material. It would probably look better too.

I agree. The block wall will tip over rather quickly. no matter how much reinforcement you put inside it. Look at all the dams that are built to retain water. NONE are made from block, NONE are built in a straight line.If you want to build a block wall, reinforce it with rebar and concrete, that's ok, but to get it to hold and not fall over with the water pressure you will have to backfill behind the block wall, and properly compact the soil while backfilling, which means getting moisture in it and compacting with a sheepsfoot roller. I would carry the soil out 30 feet behind the top of the10' block wall.

For the RPE liner, remember that you have to cover it with dirt to protect it from the UV rays. I am seeing lifespans of 3-10 years exposed and 20 years (or more) when they are covered with dirt and protected from the UV rays. In your location, I would suspect that exposed time to be even shorter than that.

It might just be cheaper to make the whole thing from dirt, THEN install the liner and cover the liner.

Im no expert but I do know this if you go with dirt, do it the right way , don’t cut corners , you’ll be better off,

I’ve seen one dam fail my grandad had done, but the guy that did it for him used a tree as part of the back wall, so eventually it rotted and it moved to another location, it’s formed a nice lil pool in the the spot where it ran to, I found it when I was looking for the place he had it put.

But my main point is if you used dirt , maybe some busted up brick, compacted the fire out of it, you’d be better off,

Mix in bentonite with your dirt n maybe busted brick combination, would be more price effective than block n rebar

Matter of fact if your budget allows you could buy a load or three of good dirt known for water retention, combine that with the bentionite, and whatever other materials you choose, I just spitballed broken up brick because it compacts hard and is relatively cheap , always someone willing to give it away from a remodel or demolition

I’m passing on the biggest lesson my grandfather taught me, don’t be cheap on something you want to last, if he had invested more into some of the projects I’m rehabbing they wouldn’t need as much rehab,

Invest In longevity