To be effective, sandbags must be properly constructed. The most common type of bag used is an untreated type of burlap sack. Another common type of sandbag is the commercial plastic variety made from polypropylene; while these bags are strong and reliable, they are not biodegradable. Given the daunting task of removing and disposing of hundreds of bags once the flood waters have receded, it is very that many of these nonbiodegradable bags will be left scattered over the region. It is thus better to use burlap sacks. Both kinds of sacks are widely available at hardware stores.
Sandbags must also be filled properly if they are to be effective. Filling a sandbag is a two-person job. One person should stand and hold the bag between his legs with his arms slightly extended. He should also fold the top of the bag over, forming a collar. This makes it easier to shovel sand into the bag. The other person should steadily shovel sand into the bag. While this operation is likely to be carried out in a panicked environment, it is important not to rush. Rushing may result in sandbags being too full or too empty, which may jeopardize the integrity of the barrier's structure.
Sandbags, while effective, are not a long-term solution to flooding. They will not seal out water indefinitely. Furthermore, depending on the type of bag used, they may begin to deteriorate before they have fulfilled their purpose. This is especially true if the bags are subjected to repeated wetting and drying, as in the case of repeated floods.
Sandbags are only appropriate to guard flooding up to about two feet in height. Higher water levels will require a more permanent type of barrier. Whatever barrier you use, it must be able to keep water back for long enough to allow it to drain away and/or evaporate.