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Dewatering With Submersible Pumps

Construction projects are always at risk of being flooded by groundwater, rainwater or other runoff. Large quantities of water may be entering the site from various places depending on the location and environment of the construction site. Dewatering is a crucial issue, especially when excavation is taking place below a water table, and dewatering with submersible pumps is usually considered the best way to deal with this problem.

Before choosing a dewatering pump, it is essential to consider the type of construction, location of the site, the surroundings and environment. Usually the waste water will contain some sort of solid matter, and it is necessary to focus on the type and concentration of the matter in the water in order to choose a pump type suitable for the operation. Generally three types of pumps are used for these operations.

  • Drainage pumps: Most construction sites use these pumps to draw up water with little or no deposits, such as water in clay. These pumps can usually handle ground and solids mixed in with the water, but only up to a particular size. The strainer holes in the pump will dictate to what extent solids can be pumped. Sans is heavy and abrasive, and must be mixed with a high concentration of water in order to be pumped successfully.
  • Sludge pumps: These are more powerful pumps that can pump liquids with a higher concentration of solids or earth deposits. It is used to pump thick sludge or mud.
  • Slurry pumps: These pumps are even more powerful than sludge pumps and can deal with high concentrations of heavy solids in the water, such as gravel or cement. In order to strengthen the pumps, the hydraulic elements of these pumps are made with materials which are stronger than the usual metals. To avoid blockages, these pumps are usually outfitted with an additional agitator to prevent slurry from settling in the pipes or the pump.

You may be tempted to get one big pump for the entire site in order to save money, but it is better to get a few smaller pumps and use them in various places that need dewatering at the same time. The pumps can be switched on and off to match the flow. There are also pumps available that can gauge the depth of the water and switch the pump on or off as required. The pump will not run constantly, and this will reduce electricity costs.

Ease of Use

Electrical submersible pumps are easy to use as they can just be connected to an electrical outlet and pumping can start immediately. The smaller pumps weigh relatively little, between sixteen to twenty five kilograms, and they are easy to move to the locations where they are needed. Always check holes directly after excavation as this is the time that they are most likely to fill up with water.

When dewatering with submersible pumps, it is important to ensure that a pump pit is made in a suitable area and that a suitable pump is installed to pump the water off site. The pump should have a firm footing, such as a plank or pierced oil drum in order to prevent it from sinking away into the mud or slurry.


Solids in the water such as sand or gravel may cause problems, and depending on the concentration it may be advisable to create a pit to act as a sedimentation tank before the water can be pumped away. Prepare a hole large enough to contain the required amount of water and wait for a few hours after pumping for solids to accumulate at the bottom. The cleaner water at the top can then be pumped out with a submersible water pump, while the remaining sludge can be pumped out with a slurry pump and transported away to a suitable location. It is usually forbidden to use municipal drains for these purposes.

In short

  • Construction sites must be dewatered to ensure that they do not flood the surrounding area.
  • Ensure that the correct pump is chosen for the type and concentration of sediment in the water. Usually a submersible drainage pump will be suitable.
  • Instead of using one large pump, rather use a few smaller pumps to keep up with the location of water flow.
  • A pit can be created into which the water from the smaller pumps can be pumped. If there are a lot of solids in the water, this pit can be used as a sediment tank to prevent the pumps from clogging.
  • Use pumps with float switches to save costs on electricity.
  • Ensure that no water is pumped into municipal drains without written permission from the local municipality. It is very seldom allowed and you may have to organise a tank transporter to collect and dispose of the water and sludge.

If you need a pump for your construction site, or you need to do dewatering with submersible pumps, feel free to contact HEMS Pumps. We have a wide variety of pumps for sale and for rent, and can find you a suitable solution for any pumping problem!

Written byJayme Wium


Pump Supplier in Mpumalanga

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