What is Dewatering, When is It Used, and Methods

When learning what is dewatering, we learn more about how to separate solids from water, getting rid of sediments. Dewatering represents the process of removing water from soil or solid material by using filtration, centrifugation wet classification or other separation processes. Construction dewatering is a term that describes the process of removing groundwater from a construction site.

The dewatering process occurs by evaporation or pumping. Workers usually do it before excavation in order to decrease water table that can cause issues during excavation.

What is dewatering

Usually, dewatering is a technique implemented on most construction sites because it helps retrieve water accumulated in trenches. This water needs to be removed in construction projects to keep working as planned and provide a safe work environment. Workers generally use water pumps to dewater these areas. However, if the water is not discarded in a safe place, then erosion may occur. Hence, they should follow best management practices when they pump water into lakes or wetlands.

Dewatering precautions

In order to avoid soil erosion, dewatering activities must be done properly on the construction site. Furthermore, it is extremely important to choose the right location for discharge, even if the site is far away from a catch basin or a water body. You may also use some dewatering products that can help you remove sediment from the pumped water. Dewatering bags could be a great idea.

When you choose a discharge area for a dewatering process, you have to consider some aspects. For instance, you should never pump water directly into a slope. Furthermore, you should consider using a wooded buffer for dewatering activities. If the area where you discharge the water shows signs of erosion or instability, you need to discontinue dewatering.

You have to make sure that the channels you use for dewatering are stable. Another important aspect is to avoid dewatering under heavy rain. In this way, the infiltration rate would be at a minimum and water will move slower. Otherwise, the dewatering process will not function. It is best to avoid discharging water that has been contaminated with chemical products, grease or oil. Hence, in this case, you might need an oil/water separator.

Furthermore, when engaging in this process, you may need to fulfill some requirements and get additional permits from the local, state and federal agencies. You also need to understand the water table conditions in the area. In case the underground water is near the surface, your plan might not work. The most common dewatering technique implements the use of sump pumps. However, this can only handle small volume water.

A construction site

Dewatering methods

One of the most common dewatering methods is using dewatering bags. They are made of durable geotextile fabric which can filter water by removing sediments. Usually, dewatering bags are used on construction sites, dredging operations or areas with high water table near the shoreline. The dewatering bag should be sized relying on the type of sediment and the pump flow rate.

When you use dewatering bags, you have to make sure that you avoid several pipe discharges. This may cause the filter of the bag to fail. You have to manage water runoff properly, guiding it to a storm inlet.

Another method you could use to develop construction dewatering is by using drainage channels. These channels can carry away the water from the construction site to the discharge point. Another useful dewatering method is water pumping. Furthermore, you could also use siphoning or some large construction machinery buckets that can carry and dump water from the selected area.

Earth channels used for dewatering could also be protected with ditch linings. Furthermore, you could place additional protection to cut down on water velocities and also minimize erosion. Therefore, it is recommended to develop riprap revetment protection by using geotextile. In this way, you will prevent additional erosion at the discharge point.

Choose the method that fits best

Another method you could use is wellpoints. It uses lines or rings of closely-spaced wells which workers instal around the excavation site. Then, you need to connect the wellpoints to a headerpipe. Workers use wellpoint pumps which can handle both air and water. The system relies on the suction principle.

Therefore, drawdown using this method can be limited to about five to six meters below the wellpoint pump level. You will need to use multiple stages of wellpoints in case the site needs a deeper drawdown.

The educator well method is also an effective method. This is a dewatering process which can control pore water pressures in materials with low permeability characteristics, like slits or fissured clay. This method works via the venturi principle. In this case, high-pressure water circulates through eductors in each well, triggering a vacuum. Hence, this promotes drainage.

If you do not know which one of these dewatering techniques are appropriate for your excavation project, you could request some professional help. Try to talk to some experts in wellpoint systems and submersible pumps. If you only need a dewatering system for a limited time, you could as well rent some dewatering pumps, wellpoint pumps or trash pumps from specialized companies.

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Prevent water from affecting your site

When you think you may find a low permeability soil, you have to think of a solution to reduce the dewatering process. A possible technique could be by isolating the permeable strata from other sources of water. As a method of preventing water from entering your foundation or trench, you could use grout curtains, slurry walls or sheet piles.

Even if these techniques might not get rid of the problem, at least you could use them when the water table is high. You will still need to pump or remove water from the trench.

Summing up

Learning what is dewatering, it can help you with your construction, preparing the excavation site. In this way, you will have a secure construction site. You can use several dewatering methods, and you need to appropriately discard the excess water. Furthermore, you also need to make sure that you prevent the excess water from affecting your site.

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William E. Eubanks
 

I'm one of the main writers on the site; mostly dealing with environmental news and ways to live green. My goal is to educate others about this great planet, and the ways we can help to protect it.

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