Construction Dewatering – What You Need To Know
If you’ve ever dealt with excavation and shallow water tables, you’ve probably come across the term dewatering. Groundwater and construction aren’t friends – there’s hardly a jobsite out there that doesn’t require some water removal. Construction dewatering is an important preliminary task in which groundwater or surface water is removed from a site, typically by pumping or excavation. This process allows engineers to start with a stable footing for whatever they are building, as well as removing water from soil layers to inspect soil density, erosion, and sediment type. Learn more about dewatering practices, safety, and more below..
Got Water?
Dewatering is an important construction process that keeps the project moving while protecting workers when water accumulates in trenches or in locations with a slope or high water table. Typically, pumps are used to dewater key areas that siphon water off, but it’s important to account for where that water ends up. If you’re venting your pump to discharge the liquid back onto soil, you might have erosion and deposit issues. Lakes, wetlands, and storm sewers are also sites to send excess water, but be sure to follow local water mandates and best practices when moving water offsite.
When dewatering, one of the most important steps is selecting a location for discharge. Bodies of water and catch basins are the natural choice, but sometimes they aren’t available. Remember these tips when selecting a discharge area for dewatering:
- Start by sourcing all permits or requirement needed from state, local, or federal agencies to remove ground water
- Set up buffer areas between your excavation site and discharge area (wooded areas work best, if available)
- Build dewatering channels that are bolstered by grass or foliage to protect the ground
- Check the water coming out – don’t discharge water that is mixed with oil, grease, or chemical products
- Do not dewater in the rain, your water will move slower
- Pay attention to the soil being excavated, if signs of erosion or instability appear, stop immediately
- Do not pump water onto slopes or hills
Methods to Protect Your Site
In the simplest form, dewatering is typically handled using gravity drainage. Channels are dug to take water away from the worksite and water is collected downhill at the discharge point – simple and effective. Things like grass, vegetation, and even man-made linings can protect your drainage channels from erosion. However this method is slow, manual, and time-consuming when you have a lot of water to remove.
More often than not, dewatering takes place using pumps, siphons, and machinery buckets that remove water from the selected area faster than ditch drainage. While these methods are fast, they tend to remove large amounts of water and sediment very rapidly, which could wreak havoc on your jobsite depending on the soil type and consistency. It is strongly recommended to use ditch lining as well as geo-textile lined revetments to reduce the chance of further erosion.
One key element to use when dewatering your site is a dewatering or sediment bag. These non-woven, geo-textile material bags have the ability to trap fine silt and sediment particles while allowing water to flow out of the bag. That means you can attach a discharge hose to the bag and pump dirty, excavated water through the bag, filtering it while having a self contained unit of silt or debris ready to dispose of.
All in all, dewatering is an important construction process that sets the stage for everything to come. As with any excavation, removing water alters the characteristics of the surrounding soil. Be sure to follow the best practices above to not only make the the dewatering process simple, but also to demonstrate you’re a good environmental steward.
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