I'm not sure what part of the state you are in, but your dirt looks like most dirt in my area (Winchester area).
I'm assuming that the builder did not put the topsoil aside when starting the excavation so they could put it on top of the dam when finished.
I'd suggest starting with a load of topsoil or compost spread on top of it. Southern States sells "contactor's mix" which includes a wide variety of fast germinating and fast growth grasses that could be overseeded in the fall with better grasses. In the meantime, you will get reasonable looking, but somewhat temporary grass.
Places like Tractor Supply and Harbor Freight have inexpensive Chinese-made 2" semi-trash pump kits with hoses. They are actually pretty good. They are great for running two or three 50' directional sprinklers on tripods.
That is basically what I've done several times. Our red clay isn't great for growing great grass.
These days I use the pump and sprinklers in my garden and my wildlife food plots.
Ken
