Everyone who floats The Grand Canyon knows about the dam tides. Water levels fluctuate radically with the demand for power from the Glen Canyon Dam. So you tie-up your raft in the normal way, and in the morning, after the water level has dropped, this is what you find.
The same thing happens in Hells Canyon on the Snake River. I awoke one morning on a Snake trip to find one of our rafts perched precariously on top of a boulder, four feet out of the water. Getting a heavily-loaded beached raft back into the water can be a lot of work.
So here's how we avoid the problem.
We call this a bungee anchor. The blue bungee is sold under the name of Anchor Buddy. You can find it at just about any marine supply store. It stretches out to about 35 feet.
Here's Hoss deploying his bungee anchor. He's throwing it as far out from the back of the raft as he can, and he'll leave enough slack in the tie-up line to let the Anchor Buddy pull the raft out away from shore.
The anchor Hoss uses is called a "folding grapnel anchor," and it also came from a marine supply store. It has the advantage of being light weight, and the flukes fold up, so it is compact to store. The disadvantage is that the flukes can snag in the rocks. I had to sacrifice mine when it got snagged so firmly that I couldn't get it loose. Note the brown cord attached to the bottom of the anchor. That will allow Hoss to pull his anchor after it is snagged--something he figured out after I lost mine. The alternative is to use the mushroom anchor like in the third photo. It may be less secure, but it is also less prone to snag.
Here's how it looks after the bungee anchors are deployed. There's enough elasticity in the bungee to let us pull the rafts to shore to load or unload. When finished, the bungee will pull the raft back out into deeper water.