The Copa® Flume weir was designed to suit a particular hydraulic situation and was found to work so well that it has been extended to other industry areas.
It is particularly well suited to flow regulation applications where other approaches could result in potential upstream flooding.
The flume weir is designed to divert the desired flow through a side or central pipe for all incoming flow conditions up to a preset maximum flow depth. Once the maximum flow depth is reached the extra flow is allowed to overtop the weir.
The flume weir operates by inducing subcritical flow up to the treatable flow rate and then maintaining a supercritical regime for flows above the treatable flow rate and in doing so results in a negligible effect on hydraulics of the system at full flow capacity.
Generally, subcritical flow and supercritical flow is distinguished by the Froude Number. If the Froude Number is larger than 1, the flow is supercritical. Similarly, for subcritical flow, the Froude Number is smaller than 1.
The theory behind minimum energy is to reduce energy losses through a channel transition (widening, narrowing etc) by maintaining the Froude Number as close as possible to the approach flow. When the minimum energy principle is applied to a supercritical channel widening, it results in the bed level of the channel requiring to be raised.
Hence, a bed profile can be carefully designed that does not impact the flow regime. A widening combined with a raised bed results in a flow depth reduction and an increase in velocity. The overall effect of the total energy is minimal.