Joe, I'm pretty new to this too and I built a 1/2 acre pond a few years. Here in Ohio the recommended minimum depth is 8'. I decided to go to slope the sides down to 10' deep to delay later silt removal on 2/3 of the pond. I would be a little more concerned with this happening to your pond because you have about double the watershed as I do. The extra depth is also nice for swimming. Two of my banks are 3:1 while two are 5:1. I can walk out of the 3:1 relatively easy and these banks look nicer as the water drops. I do not have weed problems on either of the banks but the 5:1 slope above water level is more comfortable to mow and walk on. 1/3 of the pond was dug only to about 6' at full pool and gets no shallower than 4' during very dry spells. It makes for good spawning and I do not have weed problems. About a 1 1/2 years after construction during a low water spell, I added about a 5' width of geotextile fabric and #2 limestone to stop bank erosion and improve the appearance. I only wish I had done it sooner.
The below picture is facing the 5:1 slopes with the shallow end at the right during construction
Here is the 3:1 slopes after placing the stone
Full pool 3:1
8" below full pool 5:1, as you can see the more gradual slope shows +/- grade more.
