Seepage Undermines Flood Barriers

Flood barriers and sandbag dikes are undermined by water seepage which cannot only erode the soil on which the sandbags and barriers lay. They can also result in “floating” water-filled barriers depending on the height and weight of the barriers and the height of the water which has seeped underneath. The lifting of these barriers and the erosion of the soil underneath may cause both sandbag barriers and water-filled barriers to shift position ultimately “breaking” the wall and letting flood water through.

Precautions can be taken however to:

  • Reduce water seepage to the point where it is not a threat (soil conditions will be a factor here).
  • Catch water seepage and pump it back over the barrier wall before it becomes high enough to pose a threat.

A tarp or vapor barrier (construction sheathing) can be placed on the ground where the barrier is to be built…We assume you already know enough to fill in any divots, gaps, etc. in the ground and have cleared away debris which would cause your barrier to sit unevenly on the ground, perhaps even damaging the barrier material (we’re talking water-filled barriers here). Place or build your barrier atop the tarp or plastic sheathing… we’ll call it plastic sheathing from here on as it is likely to be used more often due to its cheaper cost. This will force seeping waters to travel a much further distance under the soil in order to soak past the barrier wall. The weight of the water on top of the sheathing will force the sheathing down and help to choke off water seeping between the soil and the sheathing.

Fold the sheathing back onto itself, place the barrier along the fold and then throw it back over the barrier. If the barrier is made of sandbags or layers of water-filled barriers, the sheathing will help prevent water from flowing between the layers of sandbags or plastic tubes. Though not guaranteed, the fold itself may catch water that might flow between the bottom of the barrier wall and the sheathing.

If the barrier wall is a sandbag dike and a trench has been dug to accept the first layer of sandbags, the sheathing will be laid atop the trench, and the first line of sandbags is then placed on top. The surplus sheathing is then placed over the top of the dike.

 

But What If Seepage Does Get Through?

As a precaution, we recommend a back-up system to catch any water coming from underneath the barrier.

One back-up system is to dig a trench and have a pump on hand to pump the water back out over the barrier wall. Time-consuming! Or dig a hole in a spot where water may congregate, and pump it out.

Another idea is to place a low-level water-filled barrier or a secondary low-level sandbag dike about 2  – feet behind your barrier wall, effectively constructing another wall to collect any seepage which can then

be pumped back over the main barrier.

Remember Those Downspouts!

Ok, so you built your barrier wall, and you surrounded your house with this wall, and you even made a secondary wall or dug a trench to catch seepage. You also armed yourself with a pump and one that runs on gas in the event of a power failure with sufficient gas on hand. You’re all set, right?

Mmmmm… maybe not quite. If it’s still raining, there’s something else you must do!

Attach hoses to your downspouts and make sure they are lapped over your barrier wall. Runoff from downspouts can have the same effect as seepage and lead to a deterioration and eventual failure of your barrier wall.