#7 | U-shaped cofferdam | Moats – Water bodies

Dewatering: benefits and limits of the flexible Water-Gate© cofferdam


  • Adapts to all river bank configurations
  • Allows to work in sections according to the constraints of the site: installations in U, in L or
  • Allows work in areas not accessible to construction machinery
  • Allows work without the addition of exogenous materials
  • Time saving, quick set-up with limited staff


  • Maximum retention height 2 meters
  • Risk of stability on muddy ground: mud must be removed from the area provided for the cofferdam
batardeaux rivière canalisation
U-shaped cofferdam - Frederiksbord Castle - Installation completed
U-shaped cofferdam - Frederiksbord Castle - Start of pumping
U-shaped cofferdam - Frederiksbord Castle - End of pumping

Necessary conditions for the successful installation

  1. Probe the depth on the route planned for the cofferdams.
    Make sure to probe beyond the work area because the footprint (dimension of the lower canvas touching the ground) of the cofferdams is important.
  2. Check the possibility of lowering the height of the body of water (pond, basin, castle moat): block the upstream flow, open the outlet valve
  3. Calculate the maximum retention height necessary for the duration of the work, taking at least 20cm of margin (h value on the length diagram).
    It is possible to assemble cofferdams of different heights to adapt to the relief of the basin.
  4. Calculate the length of cofferdams required based on the dimensions of the work area (L and l values) and the h value.
  5. Remove the sludge from the location where the cofferdam will be installed to avoid the risk of slipping during pressurization. If the ground remains slippery, place rockery under the cofferdam before laying to increase the friction forces.
  6. Use powerful pumping means to pressurize flexible dams and to exhaust the site area. The pumping means depend on the height of the water and the porosity of the soil under the cofferdam.
U-shaped cofferdam | Calculation of the total length necessary according to the retention height and the dimensions of the site area.