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Sandbag Dike Construction
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Safety Tips for Leaders and Volunteer Workers
- Individuals with a medical condition that would make it dangerous for him/her to participate should avoid taking part.
- Register all persons involved and deliver the registration sheet to the community Emergency Coordinator.
- Wear protective gear such as steel toed boots, hat, safety glasses, gloves, sunscreen, etc.
- Ensure there are sufficient potable water and bathroom facilities. Take regular water breaks.
- Be attentive of large equipment moving in the area.
- Be aware of floodwater dangers:
- Varying water flow and strong undercurrents
- Floating debris
- Adhere to proper sandbag handling technique:
- Do not bend more than 20 degrees in any direction while handling sandbags. Person demonstrates sandbag lifting techninque, not bending more than 20 degrees in any direction.
- Keep heavy weights below shoulder height, above knees and close to the body. Limit reaching with arms when passing the sandbags. Person holds sandbag below shoulders and above knees.
- Pivot feet and do not twist through the back while handling sandbags.
- Do not throw sandbags.
- Fill sandbag to half its capacity (no more than 40 lbs) with sand, clay or silt.
- Fold or tie the flap (tying or sewing is not necessary).
- Do not drag the bags (this could cause lower back injury and bag to weaken).
- When forming a line to pass sandbags, face each other and stand no more than one to two feet apart. If there are not enough people to form a continuous line, use a wheelbarrow to move sandbags.
Building a Sandbag Dike
- Base area of dike should be clear of snow and ice.
- To avoid flood water moving under a dike, do not build a dike on porous land or on a septic field.
- The dike should be at least eight feet from building foundation. This prevents foundation damage and allows room for people and equipment to move. As well, this space allows more dike base width to be constructed should additional dike height be required. graphic of constructed dike 8 feet from structure
- To create a more secure dike, when possible, create a trench in the soil that is one sandbag deep by two sandbags wide.
- Dike size:
- Height: Sandbag dikes require at least two feet of freeboard. Freeboard is the area of the dike between the highest floodwater level and the top of the dike:
predicted floodwater rise above ground level + two feet of freeboard = required dike height
For example, if floodwater is predicted to rise four feet above ground level, the required dike height is at least six feet. (4' + 2' of freeboard = 6' high dike)
Sandbag dikes will compact when they get wet, which can reduce the available freeboard. The amount of compaction due to wetting increases with the size of the dike. Add at least five per cent to the required height of the dike to account for compaction. For example, add 3 - 4 inches for a six foot dike to account for compaction due to wetting.
- Width: The base of a sandbag dike is two feet wider than it's required height:
height + two feet = width at base
For example, a dike with a required height of six feet would have to be eight feet at its base. (6' + 2' = 8' wide at base)
- Sandbag dikes must be at least two feet wide across the top of dike.
- Due to the high pressure water can exert, consult your local authority for additional advice for dikes higher than six feet.
- Polyethylene sheets
- Proper use and placement of polyethylene sheets is important to reduce the rate of water seeping through the dike. Use six mil polyethylene in three metre wide rolls on the river side of the dike. Have the polyethylene sheet protrude over the ground on the river side of the dike. Be careful not to puncture the polyethylene sheet. (The polyethylene sheet will be weaved between the courses of sandbags.) Illustration of sandbag dike with polyethylene sheet weaved through.
- First course/bottom layer:
- Lay first course/bottom layer of bags parallel to river/water with the closed side of bag against river flow direction.
- The filled portion of the second bag sits over the empty portion of the previously placed bag. This is known as lapping.
- Lapping sandbags Drop the bags into place and tamp bags with feet to lodge them into place.
- Offset the bags from the previous row in the same course to form a brick pattern.
- Second and remaining courses:
- Rotate bags 90 degrees when laying second course of sandbags. Keep seal side of bag towards water/river. Ensure sandbags are well packed against each other and firmly in place.
- Change direction of bag from parallel to perpendicular to the river for each course of bags.
- Every second course of sandbags should be set back a quarter (1/4) of a sandbag width, both on the river side and the land side of the dike, producing a step-like appearance.
- Weave the polyethylene sheet between the courses of sandbags as to have at least two layers of sandbags protecting the polyethylene sheet from debris punctures. Maximum depth of the polyethylene sheet should be 3 sandbags or a quarter (1/4) of the cross section of the dike, whichever is less.
- If more height of polyethylene sheet is required, make polyethylene sheets overlap at least two feet.
- No matter how well you build a dike, extreme water pressure may cause water to seep through the dike or bubble up through the ground. It is advisable to have pumps with sufficient fuel and oil readily available to last the duration of the flood event and an escape plan.
Sandbag Dike Removal
- Sandbags should be removed with the same precautions as they were laid.
- Sand from sandbags should not be used for children's sand boxes or play areas, but could be used for landscaping purposes.