I'm renovating a 45 year old dam located in southeastern South Dakota. It originally covered 12.89 acres and held 33.83 acre feet but is now silted in. I think we can end up with about a ten acre lake with most of the depth in the eight foot range and 2 acres in the 15 foot range. Since we have so much silt to move, it seems that the best way to do this is to make deep channels and domes/ridges that would be about two feet below the high water mark. We have an 883 acre watershed composed of half pasture (grass) and half cropland (beans, corn, and alfalfa) so we think that the lake will stay full most of the time. The surrounding terrain is fairly open so there will be quite a lot of wave action (especially in the summer with strong south winds). The maximum straight line for wind to act on is about 400 yards.

I have two questions. How deep to we need to make the channels to avoid huge amounts of submergent vegetation? How far down underwater does the erosive action extend? I don't want them to wash the tops of the domes/ridges back into the channels.

The dam itself is in good shape. Any other ideas would be greatly appreciated.
Thanks
Mike

great questions baltic pit, and welcome to PB.

seems to me the depth needed to avoid excessive aquatic veg. will depend ultimately on the average water clarity of the pond. what is the average clarity of managed or unmanaged ponds around you?

for my 1 acre pond (which is not really applicable to you), weeds grew as deep as 10 feet prior to when i started aerating. after starting aeration, the water column was able to grow more microorganisms and maintained phyto bloom longer which reduced sunlight penetration and weeds mainly took hold in 3-4 feet water or less.

i would make sure mounds are well compacted and 2 feet sounds a bit shallow for the types of sustained winds you get in SD. just guessing here but you may find erosive action to extend that deep, and you probably want your mounds at 4 to 5 feet down. mounds at 2 feet will also grow alot of weeds....but again, just a SWAG.....maybe others will chime in on this.

sounds like a great place.

baltic pit, it's good to see your first post. Is weed growth on top of the mounds a bad thing? It would probably be cattails but they would certainly reduce wave action, provide forage and protection for small fish and lots of structure. The big thing is that you don't want is these domes washing back down and refilling your trenches. I hope you get lots of replies as I'm interested in these questions also.

what that sort of land use, you may not have very clear water at all. Also what is the usual wind speed you experience?