2022 – Considerations on the use of forecast rainfall for dam operations

Phillip Jordan – HARC, David Stephens – HARC, John Pisaniello – University of South Australia, UniSA Business, Quan J Wang – The University of Melbourne, Department of Infrastructure Engineering, Rory Nathan – The University of Melbourne, Department of Infrastructure Engineering, Michael Cawood – HARC, Siraj Perera – Department of Environment, Land, Water and Planning, Victoria, Richard Mannix – HARC,Formerly Southern Rural Water, Joseph Matthews – AECOM,Formerly Southern Rural Water, Tansy Huang – Southern Rural Water

Dam owners and operators face continuing pressure from the community to operate dams to provide flood mitigation, which were built primarily for water harvesting purposes. In several Australian jurisdictions, dam owners may face legal liabilities if flood impacts occur downstream of their dam, particularly for gated structures, even if the flood is mitigated. Dam owners need to make decisions about whether they will apply rainfall forecasts in managing releases from dams, and if so, how and to what extent. The Bureau of
Meteorology continue to make advances in rainfall forecasting. Nevertheless, there are still significant uncertainties in flood forecasting.

The Victorian dam safety regulator, the Department of Environment, Land, Water and Planning, recently commissioned a Guideline for the use of rainfall forecasts to make releases from dams. This paper provides an overview of what was learnt from preparing the Guideline, which potentially has application to dam owners across Australia. The paper very briefly addresses the specific regulatory context that applies in Victoria, which differs from other jurisdictions. The paper then addresses useful approaches for planning and managing flood events for dam owners that are broadly applicable to Australian dam owners. These include development and implementation of sound procedures, including appropriate flood forecasting systems. Assessment is made of the rainfall forecast products that are currently available from the Bureau of Meteorology. An approach is outlined for forecast informed decision making and guidance is provided for flood operations review studies, which would inform flood operations procedures.