Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Hydraulic design of an optimised vertical-slot fishway targeted at multi-range fish-biology based design criteria for low, medium and high river flows. (#109)

Heath Robinson 1
  1. Public Works Advisory, Sydney, NSW, Australia

The trend towards reduced operational inputs and maintenance requirements requires fishways to be increasingly self-regulating.  This emphasizes the need for a robust understanding of fish migration ecology and the establishment of biology based hydraulic design criteria targeted at low, medium and high flow ranges.  Consequently, the hydraulic design of technical fishways such as the vertical-slot has increased in complexity with innovations needed to achieve optimised fish passage performance for a broad range of fish species and sizes, over a wide range of river flow conditions and with minimal compromises.

The challenges are amplified at a barrier site with a high maximum differential head across a fixed-crest rockfill weir, an associated large tailwater range and large variability in the upstream limit of fish movement making fishway entrance location difficult.

An innovative vertical-slot fishway has been designed for a large maximum differential head of 4.4m, that comprises two fishway entrances and a single fishway exit.  The objective was to optimise passage for fish in the size range of 20-700mm at river flows ranging between near zero and flood flows that cause weir drown-out.  The fishway is designed to be self-operating without external operational input or the need for mechanised control gates.  This contrasts with a more typical approach that may use multiple gated exits or potentially have compromised fishway entrance attraction conditions for a significant period.

The work covers low and high flow fishway entrance arrangements and fishway baffles with variable slot geometry aimed at delivering hydraulic performance that meets the targeted fish passage objectives inherent in the developed multi-range design criteria.

The long-term benefits for owners of an operationally simple fishway with minimized maintenance demands comes at the expense of a more challenging design process that requires a cohesive collaboration between fish biologists, experienced design engineers, asset owners and stakeholders.