Duane, What I have noticed with my pond which has some areas that happened to come out (not designed) with a berm like you are suggesting is it probably won't work well and will probably increase erosion. What will happen at the berm is the water will be damned on refilling causing a break in your berm at the weaker points. When the weaker points break huge amounts of eroding water will flow thru, this path of water movement will continue ie Grand Canyon.

If you do opt to construct the berm I would suggest that you ensure that the walls have sufficient thickness to hold the water.

Don