Vertical slot type fishway structures operate by carefully controlling internal hydraulic conditions, allowing fish to move upstream. While the design of small vertical slot fishways can be straight forward, the hydraulics of larger fishways is more complex, especially when combined with variable headwater and tailwater levels. Other design elements, like non-uniform slot geometry, use of supplementary fishway flow sources, multiple fishway exits and entries, non-uniform cell sizes, and non-uniform bed slope can further complicate fishway hydraulics.
The interplay of complex hydraulics behaviour and multiple (and at times contradictory) design criteria criteria can result in unexpected fishway performance at particular headwater and tailwater combinations, and can significantly complicate the fishway design and analysis process.
This presentation describes an approach to vertical slot fishway hydraulic modelling designed to address these inherent complexities. This system utilises an exhaustive modelling approach, where each fishway configuration is simulated under hundreds of thousands of individual hydraulic conditions, the results of which form a database that is used to map fishway functionality according to the design criteria. This approach to fishway analysis has been implemented in a computer program called the Vertical Slot Fishway Functional Envelope Model (VS2FEM).
Use of this modelling approach allows for the efficient development of more highly optimised fishway designs and allows optimum fishway function to be aligned with the most frequent occurring hydraulic conditions. It can also be used to evaluate existing fishway structures, investigate the implications of modelling uncertainty, or used to develop operational guides for management of configurable fishways.