Dewatering and construction dewatering are terms used to describe the action of removing groundwater or surface water from a construction site. Normally the dewatering process is done by pumping or evaporation and is usually done before excavation for footings or to lower water table that might be causing problems during excavations. Dewatering can also refer to the process of removing water from soil by wet classification.
Dewatering involves controlling groundwater by pumping, to locally lower groundwater levels in the vicinity of the excavation.
dewatering is used on most construction sites due to accumulated water in trenches and excavations or in places with an inadequate slope or high water table. In construction projects, this water should be removed to keep working as scheduled or to provide a safe workplace. Normally, builders tend to use water pumps to dewater these areas, but if they are not paying attention to the place where water is discharged, erosion and other problems may occur. It is important to follow best management practices when water is being pumped to lakes, wetlands or directly to storm sewer inlets.
The simplest form of dewatering is sump pumping, where groundwater is allowed to enter the excavation where it is then collected in a sump and pumped away by robust solids handling pumps. Sump pumping can be effective in many circumstances, but seepage into the excavation can create the risk of instability and other construction problems.
To prevent significant groundwater seepage into the excavation and to ensure stability of excavation side slopes and base it may be necessary to lower groundwater levels in advance of excavation. This is known as ‘pre-drainage’.
Pre-drainage methods include:
- Deep wells
- Vacuum wells
- Horizontal wells
Other specialist dewatering techniques are also sometimes used:
- Relief wells
- Artificial recharge
- Siphon drains
The selection of the dewatering technique or techniques at a particular site or country will depend on many factors. Groundwater Engineering’s team has decades of experience in dewatering projects, and we provide a complete design and installation service to control your groundwater problems.