Flood inundation mapping in the Murray-Darling Basin: River Murray Flood Inundation Model
The Challenge
Before human modification, floodplain riparian species established in relation to a natural flow regime where trees along river banks were inundated once every 1-2 years and floodplain trees, once every 3-5 years or even 10 depending on the species. With river regulation, the flow regime is now highly modified and reduced as a result of extraction to support irrigation and human life. The Murray-Darling Basin Plan aims to share water equitably between users and the environment, to help protect the ecological function of the river basin.
Under the Basin Plan, it is vital to understand what vegetation gets inundated, where and how long it is inundated for as these species are flood dependent and require specific, species dependent overbank inundation. A flood inundation model which can demonstrate the extent of flooding for every 1 ML of flow a day, allows Basin water managers to model modified river flows under the Basin Plan and assess the area of floodplain that will be inundated and determine which species which will benefit from the flooding. Such a model allows for spatial and quantitative analysis of the flood extents to be used as an input into the management decision process.
Flooded Red Gums in Yanga National Park, New South Wales
Our Response
Our capability
CSIRO provided the capabilities and innovation to undertake this task, using a multi-disciplinary team of hydrologists, spatial scientists and ecologists. In recent years, the modelling has laid the foundation to attract an additional $2M in funding to extend the modelling beyond the River Murray into other major rivers and tributaries to further support environmental management across the whole Murray-Darling Basin, in partnership with the Murray-Darling Basin Authority.
Science and Innovation
A complex model which integrates a combination of digital elevation data with satellite images of historical flow events, to calculate flood extents and water heights was developed referred to as the River Murray Flood Inudation Model (RiM-FIM). The modelling utilises river gauge hydrographs to assist in the selection of cloud-free satellite imagery for a given inundation event, which are then interpolated at 1,000 ML day-1 intervals for a specific gauge. This enables the model to predict the general depth of the water surface across the landscape for a specific gauge height.
Aerial view of floodplain inundation extent over a part of New South Wales. PHOTO: Tanya Doody
Results
RiM-FIM is a research and decision-support tool for environmental management in the River Murray. The model has been critical to underpin environmental objectives and targets within the Murray-Darling Basin Plan and management of natural resources, along the length of the River Murray. It has provided the foundation to Government Policy which aims to manage the river system and its associated social and economic benefits.
The Murray-Darling Basin Authority, among other Government departments has used the RiM-FIM modelling tool to determine floodplain areas impacted by various management scenarios which has informed the development of the Basin Plan and its implementation strategies. The model underpins many investigative studies undertaken by the MDBA (such as ‘Constraints Management” project, the ‘environmentally sustainable level of take’ project as well as underpinning flow-ecology relationships in the Murray-Darling Basin Plan. It has been used to inform risk management by natural resource organisations and underpins an online tool for public flood safety in South Australia. The Victorian Government used the model to help determine how to best sustainably use River Red Gum forests in Victoria to develop new River Red Gum forest management policy. Related journal papers have >100 citations indicating strong scientific uptake.
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Additional Information
- Overton, IC, McEwan, K, and Sherrah, JR (2006) The River Murray Floodplain Inundation Model – Hume Dam to Lower Lakes. CSIRO Water for a Healthy Country Technical Report 2006. CSIRO: Canberra.
- Overton IC. 2005. Modelling floodplain inundation on a regulated river: intergrating GIS, remote sensing and hydrologic model. River Research and Applications. 21(9), 991-1001.