Q&A for How to Dam a River

Very large boulders for most of the dam, and pack a lot of dirt on top of that. If you really want the dam to be waterproof, then you can lay a sheet of tarp on top of the dam.

You should dig out a big reservoir and then build a wall surrounding the reservoir.

If your dam is going to build up large amounts of pressure, then far into the walls. But at the same time, if your river bed and walls are made rock or hard clay/mud, then the sides would not have to go very far in. The best idea would be about 1 foot to half a foot (a couple of centimeters).

Create a small trench under the planed area of the dam, and fill that with bricks or cement (or both). You could also replace your wooden log supports with bricks that are cemented together. The sides could be done in the same way. Dig a trench vertically, and fill it in with concrete, so your dam goes partially into the sides of the river bed. You could build a reservoir style dam at the front so that the sides are covered in brick/concrete. Finally, simply choosing a location with a hard or solid river bed is best, this prevents water from seeping underneath or from the sides (which can lead to your entire dam collapsing).

It can take only some hours to build a small dam in a small stream/river. A larger dam, perhaps to raise the level of a pond, or a large stream may take a few months, and a very large dam, to block up a river, large stream or lake could take a year or more. This entirely depends on the number of workers, any complications along the way, what you want the dam for and also the materials and availability of those materials you are using.

First, make sure the boulders won't shift or are unbalanced. If they are not stable, they may shift, creating cracks in the concrete. Put some stone wedges (random rocks can suffice) under the boulders. dig any soft material out of the bed. Creating a small trench that marks the area of your dam. This will make sure your dam does not collapse. Add some large stones, leaving space in between for concrete to fill the spaces. If your dam is to be very tall, (taller than 1.2 meters) adding bricks or stones for the basic structure is needed cement your bricks together, wait until it dries. Simply pour your cement over your stones filling the trench. If there are any gaps, fill those in too.