Christopher: Personally, I'd recommend that you NOT moonscape the exposed slope of your dam. Doing so would increase the potential for erosion; thus reducing the pond's depth adjacent to the dam and/or producing a lot of murky water (which could have some negative consequences for your phytoplankton population).
If you want to reduce your mowing labor and frequency, try using glyphosate (any formulation) at a very LOW use-rate. Properly applied, low-rate glyphosate applications serve to stunt the growth of many plant species - without killing them. Several tall grasses are actually controlled by these low use-rates.
Do you ever notice the TX-DOT spray-rigs running the shoulders of our highways and backroads?
Roadside Sprayer Guess what they're spraying.. In most cases, they're applying about 12 - 24 oz. of ROUNDUP PRO - PER ACRE - in approx. 40 to 50 gal. of water. Common bermudagrass is very tolerant to such low use-rates. Not so with Johnsongrass and several other grass species (corn, grain sorghum/milo respond similarly to Johnsongrass ~ very sensitive to glyphosate).
You might "consider" trying this chemical-mowing treatment - sparingly at first, until you see the results (about .25 oz/gal.). Otherwise, I'd seriously caution the use of glyphosate for total vegetation control in such areas.
