Another thing you will need to consider is permitting for a dam that big. You may have to deal with state permits and Army Corps of Engineers Permits, if the dam is to be constructed in a draw that is listed as a linear wetland.
If you get the USDA NRCS involved in the design, they have various levels of approved designs that the local guys can do. If the dam empounds over a certain number of acre-feet of water, it will need to be designed and approved at a regional level.
States are generally concerned about potential impacts on downstream areas (either blocking water flow, or damage potential if the structure were to fail). Thus check to make sure a local government agency won't limit your plans.
I love your enthusiasm for doing the project yourself, but building a dam is not as easy as just piling up and packing some dirt to block a water flow. Even if you have a properly designed dam, with appropriate primary and secondary spillways, and plenty of freeboard, that is only half of the equation. Being able to read soils and what is buried beneath them, is more of an art than a science. Compaction of the dam and around the principle spillway are critical. Having an experienced and trustworthy contractor will be its weight in gold. If you want to help, you might be able to provide some sweat equity. I'd just caution you about building a dam this large as your first attempt.
Tim Pinney is a contractor from TX that often posts here. Look all his posts up and digest as much as you can. Then try to find a Tim Pinney in Utah (or invite him up).
Another consideration is that with that much surface area you need to protect the dam (and probably a large part of the shoreline) from erosion. We have 2, 25 acre lakes and a 30 mph wind creates 3 ft waves. Large rock or sharp angled rip rap is necessary.
Bill
