Case study

Borroloola Floodplain Mapping Study

ProjectBorroloola Floodplain Mapping Study
ClientNorthern Territory Department of Natural Resources, Environment, The Arts and Sport
LocationBorroloola, Northern Territory
Disciplines/ServiceHydrological modelling
Flood frequency analysis
2D hydraulic modelling
Design event Modelling
Flood hazard mapping
Key team members

Dr Sharmil Markar
Project Manager

Dr David Newton
Project Reviewer

Andrew Thompson
Flood Modeller

WRM ContactDr Sharmil Markar

The Challenge

The township of Borroloola, which is located some 720 km southeast of Darwin in the Northern Territory (NT), is situated on the northern bank of the McArthur River approximately 60 km upstream from the river mouth and about 10 km downstream of the tidal limit.

Borroloola was one of the communities identified in the NT Government’s 20 Growth Towns Initiative. Borroloola has a long history of flooding from the McArthur River and hence, the NT Government wanted to identify land liable for flooding for its land use planning.

The study results would assist the NT Government to develop safer and more resilient communities by improving planning for flood emergency events and develop land use plans by identifying flood-free land in the town.

Approach and Key Activities

A flood study had previously been undertaken for Borroloola in 1987. This study was dated and the national guidelines for undertaking flood studies had changed significantly. In addition, more accurate topographical and historical flood data had become available since the previous study.

The flooding characteristics in and around Borroloola were determined by flood modelling. An URBS runoff-routing hydrologic model was developed for the McArthur River catchment and calibrated to recorded flood data at three stream gauging stations for nine historical flood events. A TUFLOW two-dimensional hydraulic model was developed for the McArthur River channel and floodplain in the vicinity of the township of Borroloola and calibrated to recorded flood data for 5 historical flood events.

The calibrated URBS and TUFLOW models were used to estimate design flood discharges, flood levels, depths, velocities and extents in the McArthur River at Borroloola for the 5%, 2%, 1%, 0.5%, 0.2%, 0.05% annual exceedance probability (AEP) design flood events and the Probable Maximum Flood (PMF) event. The design discharges estimated by the URBS model were reconciled with discharges estimated from flood frequency analyses of recorded peak annual flood discharges at the Borroloola Crossing and M.I.M Pump stream gauges.

Outcomes and benefits

The NT Government received a comprehensive set of flood depth and hazard maps for a range of design events up to the PMF across the McArthur River floodplain for use in land use and flood emergency planning.

The flood model results identified the existing flood risk and flood hazards throughout the Borroloola town and environs including the Carpentaria Highway to determine the potential for development in the town area.