The dam doesn’t have to be high, a few of those larger boulders across the creek will do the trick.
Would take less than 15 minutes, and be there after a flood. When finished dredging you just take the plastic home with you, or leave it somewhere on your claim. The moment you put the plastic film in the water,it will cling to those rocks like glue on wall paper. The higher your dam, the further up the creek you can dredge with no problems. I used to dredge plenty of creeks, and every time I used a dam, makes the dredge float to. One thing I found with creeks. On starting the hole best to chuck every stone you can up on the bank,that way you pretty soon have deep water to pull the dredge into and the dam to help you along the way.
Right the anti murk net. Bit of a cunning one this and thought out by me. After many murking problems.in small creeks. This is what I used, but you could improvise I guess. I used an old fishing net .First thing I did was cut the net away, as all I wanted was the top rope with floats on it, and the bottom rope with lead weights on it .I cut of a section of the two ropes, long enough to go across any small creek,but really making it a bit longer doesn’t hurt, as the surplus can just lay on the bank. Right then off to Mitre Ten and buy a length of shade cloth or weed clothe. As long as it has very small aperture’s/holes in it, smaller the better. (Tight Weave), then bought some clips, which are also in the garden section. Right attach the cloth to the top and bottom section. Done, you now have an anti murk net. It will allow the water to flow through. Set up your dredge in your hole, and somewhere along where your suction hose is laying on the creek bed bottom. Lay the anti murk net across it. from bank to bank. The top rope will float, the bottom rope will lay snugly on the rocky bottom. With your suction hose sticking out. Dredge away, any murk no matter how stagnant your pond is, will stay on the other side and not come through. The flow through the cloth will ensure that. But even with no flow, very little murk will migrate through. Dredge away happily. Move when required. And there you have it Gavin.