In almost all circumstances for an 8-acre pond, I think the proper design would include an emergency spillway.
My point, was if you have 300 acres of drainage above your dam site, your are going to need a lot of extra freeboard on the dam and a very large emergency spillway to handle a large rain event or the remnants of a hurricane.
If you have only 45 acres, then your design requirements are much reduced.
Your watershed drainage estimate should also include the land off of the property. Water flows do NOT respect boundaries unless there are ditches directing the water elsewhere.
Where are you roughly in SC? I believe all of the state usually gets over 40" of rain per year. The coast and the NW corner may get over 60". That is great for filling ponds, but also bad for trying to overtop dams.
The reason I mentioned two ponds, is that I put up a thread a long time ago asking members if they would prefer one large pond, or multiple ponds? And if multiple ponds, what sizes?
Many members recommended for multiple ponds. Lots of reasons, including: easier fish management, ability to have multiple fish food chain types on the same property, not all of your eggs in one basket, etc. I think 8 acres would be clearly better for recreation like water or jet skiing. Or if you are going to spend a ton of money and go for a truly trophy-level bass pond.
Finally, you need to start checking the applicable regulations. For example, in Kansas I can build a pond with a capacity of not more than 15 acre-feet and be exempt from most of the state regulations. Your pond would be MUCH larger at 64 acre-feet (if you had an average depth of 8')! If that dam was breached during a storm it might create a hazard for people downslope of your hollows, or even along the creek that is present at some point. Stuff like that moves your dam engineering requirements up several levels!
Now might be a good time to meet with the NRCS agent for your county. The agent should be able to give you an overview of the important regulations for your area. If you can get a meeting, bring the legal description of the property. The agent might even be able to look at the satellite view and give you the LIDAR topographic map which is accurate to inches. The agent will also have an understanding of the soil types you may encounter and if rocky ledges are going to be a problem. They used to even have cost-sharing programs for building ponds. However, most of those programs have ended.
Good luck on your pond adventure.
This is all good information to have.
I'm not into jet skis or anything like that LOL. I just want to fish. I just thought that for growing bigger bass that one bigger pond would be better. I had planned on building some forage ponds as well so that I could constantly be dumping forage into the main pond, but we're talking about smaller ponds less than an acre in size. I just want to make sure that the bass have plenty to eat. I don't want to go to all of this trouble and have a pound full of bass looking like Heathcliff just pulled a fish carcass out of the garbage can (some of the younger readers may not get that one LOL).
I don't think that not having enough water is going to be a problem. We get about 50 inches of rain here every year in Spartanburg County. I don't have a problem investing in the emergency spill ways. Heck I would probably even go overboard in that department to make sure that we didn't have a dam breach. That is probably the biggest disaster that I could imagine. I am hours and hours from the coast, so it would have to be one heck of a hurricane to come get me here.
