Sandbagging for Flood Protection (Part 2)

"A sandbag dike must be built properly to prevent or reduce flood damage."

** Filling Sandbage **
Fill the bags about one-half full and tie the bag near the top. if it is tied, which permits the sand to move easily in the bag to create a good dike. Overfilled bags and bags tied too low leave gaps in the dike, which allows water to seep through. Sandbags do not need to be tied unless they are transported. Filling sandbags usually is a two-person operation. One member of the team holds the bag on the ground slightly in front of his or her spread feet and the second shovels the sand into the bag. Use gloves to protect the bag holder's hands. The use of safety goggles is desirable, especially during dry and windy days. For large-scale operations. filling sandbags can be expedited by using bag-holding racks. funnels on the back of dump trucks used for sanding operations and various power loading cquipment. However. the special cquipment required is not always available during an emergency.


** Stacking Sandbags **
Lift bags using your legs and limit twisting of your back. Gently hanc the sandbat to the next person in a sandbag brigade or line.

A triangular or pyramid shape for the dike is not necessary if the height will be I foot or less. Support the wall of sandbags with "clusters" of bags every 5 feet to stabilize the sandbag wall so it does not tip over from the force exerterd by the floowater.

Place the first layer of bags lengthwise on the dike (parallel to the flow), lapping the bags so the filled portion of one bag lies on the unfilled portion of the next, with the tied or open end of the bag facing downstream. Offset adjacent rows or layers by one-half bag length to eliminate continuous joints, similar to what is done laying bricks. Compact and create a tight seal. Continue to walk on the bags as succeeding layers are placed.

The base of the dike should be about two to three times as wide as the dike is high to provide adequate strength and friction surface area. Water exerts a tremendous force against the dike. Estimate the pressure on the dike base by multiplying the water depth by 62 pounds. For example, the pressure theat 5 feet of water exerts on the base of a dike ia about 310 pounds per square foot. The force of 5 feet of water on a vertical wall is about 775 pounds per linear foot of wall. Flowing water striking the dike exerts even more more force on the dike. A triangular-shaped dike permits the weight of the water to push down on the dike to help hold it in place.


Plan of bottom Layer


Lapping sandbags


Place bags parallel to the flow of water


Fill the sandbag method

Thank you Detial From
"Kenneth Hellevang, Extension Engineer"
NDSU Extension Service North Dakota State University Fargo, North Dakota FEBRUARY 2011
For more information on this See www.ag.ndsu.edu

Sandbagging for Flood Protection (Part 1)

"A sandbag dike must be built properly to prevent or reduce flood damage."

** Managing Volunteers **
Since a dike will fail if not built correctly, training people on proper procedures for placing sandbags is very important. In the rush. voluntecrs will do something. but the result frequcntly is a dike that performs poorly or fails. Put a high priority on planning and organization. Identifying a supervisor for the project is recommended.


** Sandbag **
Bags are made form various materials, but the most common is woven polypropylenc. They usually measure about 14 inehes wide and 24 to 26 inches long. Other sizess of bags also are available, but bags are easier to handle if their weight with filling in them is limited to 35 to 40 pounds.

Sand is the easiest material for filling and shaping sandbags. Silt and clay in bags will form a good dike, but working with those materials is more difficult. Fill sandbags's ightly more than one-half full.

Contact your county emergcncy management officc for information on where to obtain sandbags.


** Site Selection **
When selecting the location for the dike. take advantage of natural land features that keep the dike as short and low as possible.

Avoid obstructions that would weaken the dike. Do not build the dike against a building wall due to the forces the dike may place on the building. Leave at least 8 feet to maneuver between the dike and buildings for observation. pumping secpage water and other activities.

Since friction holds a dike from sliding. create a good bond between the ground and the dike. Remove ice and snow since it will melt permitting water to flow under the dike. Remove anything else that is "slippery" If the dike is to be more than about 3 feet high. dig bonding trench where the dike will be placed if possible. The trench should be about 4 to 6 inches deep and 18 to 24 inches wide.


** Estimate Sandbags Needeed **
Build the dike at leat 1 foot higher than the projected crest tevel to allow for fluctuations in the water leve. Local experience will assist in determining the amount of freeboard to provide.

The U.S.A. Army Corps of Engineers recommends building a dike with a width at the base that is three times the dike height. For example. a 1-fool-high dike would have a base width of 12 feet. The corps indicates that each fool of finished dike length requires one bag cach foot of height requires three bags. and each 2.5 feet of width requires three bags. This results in each bag having placed dimensions. of about 4 inches high by 10 inches wide by 14 inches long.


Dimensions of a dike that is twice as wide as it is tall



Estimated cubic yards of sand needed per 100 feet of dike length for various dike heights and ratios of height to width. An additional 2 cubic yards will be needed for bags to hold the plastic.



User the following equation to estimate the number of bags required per linear foot of dike for a dike with a base width that is three times the height.
N = (3 x H) + (9 x H x H) / 2
N - Number of bags required per linear foot of dike
H - Dike height (feet)

Example:
Estimate the number of bags required per linear
foot for a dike 3 feet tall.
N = (3 x 3) + (9 x 3 x 3) / 2 = 45 bags

The estimated number of bags needed for 100 linear feet of dike is:
1 - foot - high dike: 600
2 - foot - high dike: 2,100
3 - foot - high dike: 4,500
4 - foot - high dike: 7,800

A common recomendation is to make the dike twice as wide as its height. This ia a minimum width-to-height ratio that should be used. The estimated number of bags needed for this ratio is in the following table. This is based on each bag having placed dimensions of about 4 to 5 inches high by 9 to 10 inches wide by 14 inches long.

The estimated number of bags needed for 100 linear feel of dike that it twice as wide as its height is:
1 - foot - high dike: 600
2 - foot - high dike: 1.700
3 - foot - high dike: 3,000
4 - foot - high dike: 5,500
5 - foot - high dike: 9,000

A cubic yard will fill about 100 30-pound sandbags or about 75 40-pound bags, assumning the sand weighs 110 pounds per cubic foot. Sand weighs 100 to 130 pounds per cubic foot, depending on moisture content and packing. A cubic yard is 27 cubic feel. Each 14-inch by 24-inch bag will hold about 0.4 cublc feel if filled about one-half full. Based on volume. each yard will fill about 67 bags one-half full.


Stacking sandbags wiht a base width three times the height


This volume is calculated based on a center section that is 9 inches wide and the remainder is in a triangular shape

Thank you Detial From
"Kenneth Hellevang, Extension Engineer"
NDSU Extension Service North Dakota State University Fargo, North Dakota FEBRUARY 2011
For more information on this See www.ag.ndsu.edu