Sandbags provide valuable defence against flood waters. However, if the defences are built wrong, they will fail. Sandbag walls can keep water out for short periods of time which can be improved on by using them in conjunction with plastic sheeting.
They are cheap and easy to obtain. However, they are relatively ineffective when you compare them with purpose-designed flood protection products such as flood boards, non-return valves for plumbing and air brick covers.
How to Obtain Sandbags
Now while here in the UK during floods, authorities will often have sandbags that they provide you with, this isn’t always the case and will depend on how severe the floods are as they only have a very limited supply. You can’t assume that the authorities will provide you with sandbags in a flood emergency!
It is ultimately the responsibility of the property owners to take the appropriate action to protect their property from flooding. You should contact your local authority in advance to find out what their policy is and how you can get access to sandbags before flooding starts. There may be a charge for this service.
If your local authority doesn’t supply sandbags, you can buy unfilled sandbags and a supply of sand from most DIY stores and Builders Merchants, but remember that if there is a flood expected in your area demand may exceed supply as people rush to buy them. For this reason it is a good idea as with your other preps, to get them in stock as early as possible.
Consider all entry points that water could get through, not just doorways, such as – airbricks, utility service points, cable entry points. Use other solutions for entry points where sandbags won’t work (such as silicone sealant).
You’ll need at least 6 sandbags to keep out 20cm depth of water for a standard door opening. Each sandbag will need approximately 15kg of sand.
How to Build a Sandbag Wall
Start off by removing any debris from the area where the sandbag wall is to be built. If purchasing sand, consider a level place near the center of the wall for your sand pile. This will make it much easier when it comes to filling the sandbags.
Take a note of the following two points:
- The length of the wall you need to build
- The height of the wall you need to build
Use the following table to estimate the number of bags required:
|Height in Feet||Bags/10 Feet|
You can expect to use about 40lbs of fill material per sandbag. Multiply your number of sandbags (above) by 40lbs to get total amount of material required.
Gather Your Supplies
You will need the following items at the ready:
- Sandbags and sand
- Plastic Sheeting
- Safety Glasses
Filling the Sandbags
You will need at least two people for construction of your sandbag wall. One person will be needed to hold the bags open while the other should carefully shovel the sand into each bag.
It is easier when filling the bags to fold the top of the bag over slightly, creating a collar to firmly grip on to. You should also be sure not to fill the bags right up to the top. They should only be filled to just over one-half of their capacity. Over filling the sandbag will make it too heavy to manipulate and will significantly weaken the berm.
If you have a third person assisting, they can stack the filled sandbags. It would be ideal if the team rotated positions, so as not to cause muscle fatigue from performing the same act over and over.
Please consider, in advance, the time it takes to build sandbags. You can expect to fill sandbags at a rate of 20 per hour per person.
If you are building a sandbag wall away from a building to prevent flood waters from a nearby river, you should start at the downstream end of the sandbag operation about one foot landward from the river or levee’s edge and continue upstream. The wall should be built parallel to the flow of water. Low areas should be placed first, before placing bags the full length of the wall.
The first row of sandbags should be placed tightly against one another. The unfilled top of the bag should be folded under the bag when placing them. After each row, you should tramp down the wall, by walking along the layer, to form a tight seal and to prevent slippage.
For each row, stagger the sandbags offset by one half a bags length on top of the bottom layer (similar to the way bricks are layered). This way you won’t have one continuous joint.
Pyramid Placement for One Foot Tall or Less
The pyramid placement can be used when you need to increase the height of sandbag protection greater than one foot off the ground.
Start by placing the sandbags to form a pyramid with the base being three times as wide as it is high. On the first, third and fifth layers, place the bags crosswise (header course). On the second, fourth and sixth layer, the sandbags should be placed lengthwise (stretcher course).
Use this rule of thumb in determining dimensions of the pyramid:
• 1 bag in length equals about 1 foot.
• 3 bags in width equals about 2 ½ feet.
• 3 bags in height equals about 1 foot