The theme for Engineers Australia’s 41^st HRWS is ‘Living with extremes’ and will showcase a representation of the water resource industry’s exploration around extreme weather events, which are expected to increase in frequency due to climate change.

Technical Presentations

A Structured Flood Mitigation Approach – A case Study: Road Level Crossing Removal Project
Gus Naghib (Associate Engineer – Water Resources NSW), Tim Rhodes (Technical Principal – Water Resources VIC)

Many civil projects require flood modelling to be undertaken to confirm that the proposed project will have minimal flood impacts on adjacent properties and water courses. Authorities and councils require stringent flood criteria to be met through modelling to issue approvals.

It can be very challenging to comply with the various criteria due to a combination of very fine tolerances in modelling, a wide variety of modelled storm event shapes and sizes, and long computational run times.

The solution typically involves some combination of flood storage, peak flow timing, and hydraulic grade line controls. It is important to identify the dominant variable or variables that are to be targeted to solve the problem and achieve project compliance.

Effect of Dual Bridge Piers – Learnings from CFD, ducks and 2D modelling
David Cox (Principal Engineer – Water Resources QLD), Tim Rhodes (Technical Principal – Water Resources VIC), Freddie Takhtemina (Technical Principal – Dams & Hydropower VIC), Carlos Gonzalez (Technical Principal – Water Resources QLD), Urs Z Baeumer (TMR)

The shadowing effect of dual bridge piers is not well understood. There is an industry shift towards modelling these complex situations with Computational Fluid Dynamics (CFD) as we construct new bridges in close proximity to existing bridges.

This relationship between loss and distance apart works well for bridge abutments, however, is less understood for piers. For many projects, we want to be able to answer the simple question ‘how much will my pier losses increase in my flood model if I put the new bridge next to the old one?’

Downstream fish passage on dam spillways: truths, myths, and realities during prototype operation
Carlos Gonzalez (Technical Principal – Water Resources QLD), (Hubert Chanson – UQ)

The movement of fish in natural rivers is affected by in‐stream man‐made structures, including dams and weirs that may prevent fish passage and cause fish mortality and injuries. While research on upstream fish passage has been active, the effects of downstream fish passage over dam spillways and weirs has received much less attention.

We discuss and compare downstream fish migration mortality data, captured during recent events on several spillway structures with smooth and stepped inverts, as well as natural fish mortality rates, recreational fishing and fish mortality induced by navigation.

Extreme Floods: Reducing conservative estimates through revising non-linearity assumptions
Tim Rhodes (Technical Principal – Water Resources VIC)

Extreme flood estimates constitute a key input to dam risk assessments, and they are subject to a high degree of uncertainty due to both a limited understanding of the meteorologic drivers and catchment runoff generation processes. Current estimation methods routinely apply an assumption of nonlinearity which results in increased peak flows. In essence, doubling rainfall results in more than double the runoff peak flow. There is little strong evidence to support the nonlinear assumption in the extreme flood range.