If floodwaters are threatening your home, use sandbags to create a dike.
Pick a Spot
Build the dike on the side of your yard from which water will be flowing. Don’t erect the dike against a wall: The weight of the sandbags might compromise the building’s structure.
Fill the Bags
Put the first scoop of sand just inside the bag’s mouth to hold it open, then fill it halfway full before tying off the top.
Build the Barrier
Friction between sandbags and the ground holds the dike in place, so remove slippery substances like leaves. If you’re going to build your dike more than 3 feet (1 m) high, increase its stability by placing the bottom row of bags in a shallow trench that’s about 6 inches (15 cm) deep and 2 feet (61 cm) wide. Stagger the position of bags as you stack them, as if you were laying bricks. As a rule of thumb, the width of the dike at the bottom should be two or three times the overall height.
This tip is from OL's Ultimate Survival Manual. When disaster strikes, time is of the essence. The Ultimate Survival Manual has 333 skills that will get you out alive whether you're facing a disaster in the wilderness or an urban catastrophe.