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.
The right dewatering plan can be used to be in compliance with some of the Best Management Practices related to the SWPP plan.
Construction 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.
Construction dewatering from open excavation or trenches can be done by several methods. However, the most simple of all is gravity drain using drainage channels carrying away water from the area to be worked to the discharge point. Other feasible ways for dewatering are water pumping, siphoning and/or using large construction machinery buckets to scoop and dump water from the selected area. Earth channels used for dewatering could also be protected with ditch linings, and additional protection should be placed to reduce water velocities and minimize erosion. It is recommended to build riprap revetment protection with geotextile to prevent additional erosion at the discharge point.
When it is known that a low permeability soil can be found, a possible solution to reduce the dewatering process is isolating the permeable strata from other sources of water. Sometimes, sheet piles, slurry walls, and grout curtains can be used as a method of preventing water from entering into you trench or foundation. Although this solution will not get rid of the problem, it is a very good plan to use when the water table is high, as you will still need to pump or remove water from the foundation or trench due to rainfall and water trapped in the area. Depending on the system use, a complete engineering analysis will be required to analyze how this process affects other areas.