If you have access to sandbags or other materials, the National Weather Service says you can use them to protect your home from flood waters if you have sufficient time to do so. Filling sandbags can take more time than you may think.
The Army Corps of Engineers says the most commonly used bags are untreated burlap sacks available at feed or hardware stores.
When filling sandbags you should work in pairs, with one person holding the bag while the other shovels in the fill material.
The most common mistake made is overfilling bags. The first shovel of fill should be placed on the lip of the bag to help hold the bag open. The shoveler should use rounded scoops of fill until the bag is approximately 1/3 full.
The use of sandbags is a simple but effective method of preventing or reducing damage from floodwater and debris.
Suggestions for constructing sandbag structures are:
1. Close-weave burlap bags 18" x 30" are recommended for all sandbag construction when available.
2. Fold the empty top of the bag at a 45-degree angle to keep sand from leaching out.
3. Place each bag over the folded top of the preceding bag and stomp into place.
4. Stagger the second layer of bags over the seams of the preceding layer.
5. Stomp all bags to form a tight seal.
6. The last sandbag in a line is referred to as a Key Sack. The empty top of this bag is folded under and stomped into place.
How to place sandbags
According to the Army Corps of Engineers you should remove any debris from the area where the bags are to be placed.
Fold the open end of the unfilled portion of the bag to form a triangle. If tied bags are used, flatten or flare the tied end. Place the partially filled bags lengthwise and parallel to the direction of flow, with the open end facing against the water flow.
Tuck the flaps under, keeping the unfilled portion under the weight of the sack. Place succeeding bags on top, offsetting by one-half (1/2) filled length of the previous bag, and stamp into place to eliminate voids, and form a tight seal. Stagger the joint connections when multiple layers are necessary.
In locations where the water may rise and there is no current lay a visquine plastic sheet on the ground and up to your home's walls and build a half pyramid out of sandbags. Cover doors and vents with plywood.
For more information you can download this sandbag brochure made by the California Dept. of Water Resources.
Sources: http://www.water.ca.gov/floodmgmt/docs/flood_fight_methods.pdf, https://www.wsask.ca/Global/Lakes%20and%20Rivers/Flood%20Watch/How%20To%20Use%20Sandbags.pdf