The GNA CSO HYDROBEND bending weir is designed to have the same flow capacity as a standard overflow weir operating under the same maximum design head and weir length, but is designed so that overflow will only occur when the maximum design water level is reached.

  • The increase in water level before overflow begins represents the net increase in the in-system storage.
  • The increased storage results in reducing the volume and frequency of overflows, thereby increasing the likelihood of capturing and treating the most highly polluted flows instead of discharging them to the receiving waters.
  • In the event that receiving waters rise to levels higher than the maximum design level, The GNA CSO HYDROBEND will act as a back-flow preventer thereby ensuring that the treatment plant will not treat river, lake or ocean water

The GNA CSO HYDROBEND will remain in the neutral (closed) position, as long as the preset design maximum upstream water level is not achieved, which translates into a considerable increase of the available in-system storage volume. Once the maximum storage capacity is achieved the device reacts instantly and adjusts itself so that the maximum upstream water level is maintained and the overflow discharge exactly matches the additional inflow.

The key component of the self-adjusting GNA CSO HYDROBEND is an eccentric control disc, which is designed to supply a permanent balance of forces between the hydrodynamic pressure of the flowing water acting on the overflow face of the bending weir and the counterbalancing weight. The bending weir reacts instantaneously and automatically adjusts itself in order to maintain a constant design overflow water level. Should the additional inflow be greater than the design peak discharge, the GNA CSO HYDROBEND will remain fully open and act as an emergency overflow.


Hydraulically Operated Bending Weir


Special flowrate vs. water level requirements are accomodated by the hydraulically operated bending weir real time monitored and controlled by PLC either locally or from remote SCADA.

The GNA CSO HYDROBEND may be installed in any new or existing overflow structure to increase storage capacity. The bending weir is shipped ready to install. It is simply dropped in place and anchored to the existing concrete structure.


  • Distribution of water in irrigation systems.
  • UV disinfection units for waste water treatment.
  • Oil and floatable objects removal systems for municipal and industrial waste water treatment.

Advantages of the GNA CSO HYDROBEND

  • Construction costs are considerably reduced because retention basins may be down sized.
  • The GNA CSO HYDROBEND allows the use of 100 % of the available in-system storage volume.
  • At no additional cost, the device also acts as a backflow preventer.
  • The GNA CSO HYDROBEND requires little or no servicing because it is constructed entirely of stainless steel.
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