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Dewatering: A Simple Explanation

The lightning capital of the world has the tendency to get flooded now and then especially during the spring and summer.  On a construction site, the excess of water poses a problem because it could delay the continuation of the project.  In times like these, dewatering is the solution.  In the simplest of terms, dewatering is the action of removing ground or surface water from a construction site.  You can complete excavation after the water is removed.  It is tough for heavy construction machinery to work on wet grounds. Of course, before doing any dewatering work, you must get a permit since there is a high possibility that other pieces of land that are not yours will be affected by the removal of water.

Types of dewatering

  1.  Deep wells

    • A deep well system is made up of several bored wells which are pumped by submersible pumps with a vacuum system.  The water goes into the well after a rainstorm then it is pumped into a settlement tank.  When a bunch of wells works together, they can lower the groundwater level.  The wells can get as deep as 30 feet below the ground.  This kind of dewatering is ideal for large excavations like dams, tunnels, and powerhouses.
  2. Wellpoints

    • This type of dewatering is used for excavation sites with shallow depths.  In Florida, the aquifer can pose a problem in dewatering as you do not want to dig too deep to hit even more water.  A wellpoint system consists of small diameters connected to a header pipe, drawing up water from the ground.   They are usually installed in lines or rings around the excavation site, and they are pumped into header mains like in a deep well.
  3. Sumps

    • This is probably the simplest form of dewatering in that it involves excavation of a temporary pit then sumps are installed so that water entering the site can be pumped.  This technique works well in course soil and gravel where water can be held.  If there is a lot of sediment going into the pumps, it can pose a problem for disposal as the dirt can get stuck causing a blockage and a few headaches.
  4. Geo Textile or Dewatering Bags

    • The name is interchangeable.  These durable geotextile bags are used to filter water by removing sediments.  They are typically used in dredging operations or places with a high water table near the shoreline.  One end of a hose is placed in the water and the second end is placed in the dewatering bag where the water is pumped.  This bag collects the sediment making it easier to dispose of and less likely that pollution will go back into the ground.site dewatering, swppp

Why is dewatering necessary?

Most construction sites just want to get rid of water, but they do not take into consideration where the extra water might end up.  The water gets removed then they put it back into the earth with all of the sediment.  Construction tends to change the natural set up of the land.  Being mindful of where the extra water can prevent erosion and any other problems that might occur.  It is best to follow BMPs when water is being pumped into our lakes, wetlands, or directly into our sewers.  It is important to choose the best location for discharge that is far away from bodies of water and our drinking water sources.

Find dewatering permits here.  If you have any questions regarding dewatering and BMPs, contact KCI, the environmental experts.