Twar, talk to member TJ about soilfloc. It works great for leaks, but in your case, it also will 'firm' up the bottom by locking the sediments into the polymer and pulling it down into any pores in the bottom. Where I have put soilfloc in the shallows you can hardly push a stick into the sand as it is so rock hard and when you walk on it you get very little puffing of sediment from the bottom despite a sandy bottom that used to do this.
A single unit or even a half a unit as a test dose in the shallows might achieve what you are looking for.
