I have a feeling things will hold pretty well in the case of poorly-compacted soils. One thing I have seen here is ponds that fill up really fast after excavation tend to be "seepy". It is like the soil in the dam never gets a chance to settle, and then the slowly flowing water suspends the particles as it flows through.
Stop the flow, remove the water from between the particles, and the dam can settle better.
For me, being able to mow and clean up the backside of the dam will be a huge plus. I spent last fall nuking willows and pulling unwanted trees by hand. It would be nice just to mow the darned thing and keep the cattails off of it.
