Dewatering Methods in Construction

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Dewatering Methods in Construction
When excavations do not have a sufficient onsite slope, they need to be dewatered. (close up of flowing water drops falling into water tank image by sasha from

In recent years, the methods of analysing and treating groundwater conditions have greatly improved. Construction dewatering is required when excavations do not have a sufficient onsite slope to provide a daylight drain. In these situations, rainwater or groundwater becomes caught within the excavation. Seepage, groundwater or rain can also be trapped in cofferdams and in all of these situations the water needs to be removed prior to the commencement of work.

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Care must be taken when simply pumping water from construction excavations and attention must be paid to the final destination of this water. Water follows a down gradient and, depending on the location of the construction site, may find its way into wetlands, streams or lakes. Attention must therefore be paid to correctly discharging the water in question. Sediment contained in the water must first be removed. Once it is pumped out of the excavation, this water must then be prevented from eroding soil and all natural resources, such as lakes and property. The discharged water must be stopped if the area it is being channelled to shows signs of becoming unstable or of eroding.

Contaminated Water

An oil/water separator or other suitable filtration method will be required prior to discharge if the collected water has been contaminated with petroleum products, oil or grease. A licensed transporter will be required to both contain and to transport the collected water away from the construction site if it has been contaminated by hazardous or toxic chemicals. In the case of contaminated water being trucked from the construction site, the requirements of federal, state and local agencies must be adhered to.


The dewatering of excavated areas on a construction site must include attention to both the removal of the collected water and the disposal thereof. A number of methods can be used to remove water from the construction site. These methods include using the bucket connected to specific pieces of construction equipment to mechanically scoop the water from the excavations. Water can also be pumped or siphoned from the collection sites. The use of a gravity drain through channels is yet another possibility. Ditch lining material must be utilised if the velocity of water flowing in the channels causes erosion. It is advisable not to attempt dewatering during periods of heavy rainfall. Water must not be discharged over or into bare areas or areas where new vegetation is attempting to establish itself. The dewatering process should be carefully and regularly monitored.

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