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What Materials Work Best in a Sandbag for Blocking Floodwaters?


Researched by Alex K.


The purpose of this experiment was to see what materials work the best in a sandbag for preventing a flood. Fine and coarse gravel, plant soil, and mulch are not usually put in sandbags to stop floods. Most people do not have a lot of sand that they can put in sandbags.  That's why I'm doing this experiment, to see if fine and coarse gravel, soil, or mulch can have the same effect as sand.

I became interested in this idea when I heard about people losing their homes and lives to floods. The spring of 1996 had many terrible floods in the Yakima Valley.

The information gained from this experiment will help people prepare for floods and save their lives. 

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My hypothesis is that materials with more density will be more effective at blocking floodwaters. 

I base my hypothesis on Internet website that tells about flood protection with sandbags.

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The constants in this study are: 
size of sandbag 
shape of sandbag 
the water flow 
structure of sandbags 
time the water runs through the flood table

The manipulated variables are the different materials in the sandbags (sand, gravel, mulch, and soil).

The responding variable is what amount of water flows past the sandbags.

To measure the responding variable I will need a container that measures the amount of water that passes past the sandbags.

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.9144 square meters burlap 
1 kg. sand 
1 kg.  plant soil 
1 kg.  fine gravel 
1 kg.  course gravel 
1 flood table 
1 marking pen
3 2.84 liter bottles 
1 bucket 
1 sewing machine 
1 stop-watch
1 can paint bucket

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1 Make the sandbags by using 1 square yard of burlap. 
2 Cut each sandbag into 6x6 inch squares. 
3 Fold them in half and sew them into bags. 
4 Put a half-cup of the first material in the bags. 
5 To make the flood table, use 4x1x1 foot pieces of wood. Screw them together. 
6 Put a 1-inch piece of wood under the top of the table so it gets a slight incline. 
7 Place a bucket at the end of the flood table measure the amount of water that goes past. 
8 Place the sandbags on the flood table 2 and a half feet from the top. With a pen, mark where that is so you can get the same every time. 
9 Stack the sandbags so they are as tight as they can get. 
10 While stacking the sandbags, make sure there is 3 on top and three on bottom. 
11 Run a flood by steadily dumping 2.84 liters of water at the start of the flood table. 
12 Start a stop-watch when the first drop hits the flood box.
13 After 25 seconds, record how many millimeters of water goes past the sandbags. 
14 Run the test three more times with the same material. 
15 Use the next material. 
16 Repeat steps 8 through 15 using the following materials: sand, fine gravel, course gravel, and soil.

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The original purpose of this experiment was to see if different materials in sandbags besides sand would work if put in front of a flood. 

The results of the experiment were sand let the least amount of water past through the sandbags, an average of 848 milliliters of water in 25 seconds. Plant soil, the next best material, let 1,360 milliliters of water past through them. Then came fine gravel. It let through 1,439 milliliters. The material that let through the least amount of water was coarse gravel. It only held back 1,912 milliliters.

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My hypothesis was that materials with more density will be more effective at blocking floodwaters.

The results of the experiment were sand let the least amount of water past through the sandbags, an average of 848 milliliters of water in 25 seconds. Plant soil, the next best material, let 1,360 milliliters of water past through them. Then came fine gravel. It let through 1,439 milliliters. The material that let through the least amount of water was coarse gravel. It only held back 1,912 milliliters.

Because of the results of this experiment, I wonder if something solid like concrete, steel or metal would work as well or better. Also, I think that the more compacted the material is, the better it works.

If I were to conduct this project again, I would test more types of materials; like clay, sawdust, wood chips, etc. I would run a more accurate flood, make bigger sandbags, make a more waterproof flood table, run the test longer, make sure that all sandbags are the exact same size, and many more.

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Many thousands of people and homes have been killed or injured in floods. Sandbags help to prevent floods from damaging homes. They also help save peoples lives. 


How to build a sandbag dike-

 A properly built sandbag dike can reduce or prevent flood damage. To make a dike 1-foot high, you need to use 800 sandbags. To make a dike 2-foot high, you need 2,000 bags; and for a 3-foot high you need 3,400 bags. When filling them make sure and fill them only half way full.
Site Selection- When deciding to make a sandbag dike you should place it in a place where it has all the natural advantages. You should try to keep it as low and short as possible. Also avoid anything that would weaken the dike. Leave about 8 feet in between the dike a building.
 Stacking the Sandbags- when you are stacking your sandbags, you should remember to have the base of your dike 3 times as wide as it is high. You should over-lap the sandbags so that the full part of the sandbag is lying on the half-empty part. The second layer of the dike should look like the first layer.
Sealing the Dike- To seal a dike you need a sheet of plastic to improve water tightness. Put sandbags on top and bottom of the dike to weight the plastic down. Try not to puncture it.

Sand- Sand is a mass of minerals. It is made of very fine grains. Sand is made of Mica, feldspar, magnetite, and other minerals. It is very important to soil. Sand is formed through the process of erosion. When sand is first formed it is very sharp. After a while it becomes smaller and more rounded by wind and water. Sand is used to make many things. 
Gravel- Gravel is a very loose material made of small rock and mineral fragments. Gravel is larger then sand particles. Gravel is deposited along lakes, rivers and oceans. Beach gravel is very round and smooth because it gets worn down. When gravel is used in industry, it is mixed with a dark tar-like substance, then is used to build roads, railroads, airfields landing strips, and much more.
Soil- Soil is made of sand, silt, clay, etc. Sand is an important resource; all life on earth depends on soil. Soil is developed through centuries of materials collecting together; and through erosion. 
Mulch- Mulch can be many different things like grass, straw, manure, hay, clover, chaff, alfalfa, corncobs, leaves, sawdust, wood chips, and more. Mulch helps decay and enrich the soil. It helps keep air in and water from evaporating out. Mulch also keeps weeds from growing. When placing mulch on the ground place it 2 to 3 inches thick. 


A flood is a body of water that comes over dry land and carries topsoil away and leaves the land bare. Floods are usually harmful to people and homes. Floods are sometimes helpful by making the land very fertile. 
Seacoast floods- Seacoast floods usually kill hundreds of thousands of people, and destroy millions of homes. Seacoast floods usually result from hurricanes and big storms. A giant sea wave caused by an earthquake is called a Tsunami.
River floods- Most rivers overflow once every two years. Too much rain at one time sometimes floods rivers. Sudden melting of snow and ice does too. When this happens the riverbed has ten times as much water as the river can hold. Heavy rain or thunder storms usually cause flash floods. They mostly occur in the mountains. Flashfloods come fast and unexpectedly.  People don’t have time to get ready and react to them. Some rivers, like the Hung He in China, have killed nearly a million people.
Tropical Storms floods- Tropical Storm floods usually form over warm water of the tropics and are loaded with moisture. When storms make their  way to land, they bring inches of rain. This causes streams and rivers to overflow.

 Floods can be helpful to the environment by making the land very fertile. They can also be dangerous to houses and deadly to people. Sandbags give people a chance to prepare themselves for a flood that could kill them. If you make a properly built sandbag barrier, you can help in the prevention of a floods danger. Materials like sand, gravel, and soil may help in flood protection. Seacoast, river, and tropical storm floods are just some kinds of floods that can be deadly and disastrous. 

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"Floods" Compton’s Interactive Encyclopedia  2000

"Gravel" Encarta 98

"Mulch" Encarta 98

Rango, Albert "flood" The World Book Encyclopedia, 95 vol., F-9 pg. 237-238

Sandbagging for Flood Protection,

"Sand" Encarta 98

"Sandbags" Grolier’s encyclopedia 98 

"Soil" Encarta 98 

Waters, John, Flood! Crestwood house, Macmillan Publishing Company, pg. 10- 



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