Case study

Katherine Flood and Flood Mitigation Studies

ProjectKatherine Flood and Flood Mitigation Studies
ClientNorthern Territory Department of Infrastructure, Planning and Logistics
LocationKatherine, Northern Territory
Disciplines/ServiceHydrological modelling
Flood frequency analysis
2D hydraulic modelling
Design Event Modelling
Flood risk management
Flood mitigation options
Levee design
Key team members

Dr Sharmil Markar
Project Manager

Hayden Guse
Hydrologic Modeller

Daniel Sheehy
Hydraulic Modeller

WRM ContactDr Sharmil Markar

The Challenge

Katherine has experienced significant flooding in the past, including in 1931, 1940, 1957, 1998 and 2006. The 1998 flood event, which is the largest on record with an annual exceedance probability (AEP) of less than 0.5%, inundated almost the entire town and caused extensive damage.

The key challenge for this project was to identify cost-effective flood risk management measures to reduce the risk of damage, disruption and costs associated with major flooding in Katherine.

Approach and Key Activities

The URBS hydrological model developed for major flood study in 2000 for the Katherine River catchment following the 1998 flood event was updated to a more recent version of the software and a number of refinements were made to improve its performance. The updated model was recalibrated and validated against five historical flood events (March 1984, February 1987, February 1991, January 1995 and January 1998). In addition, the model was validated against a post-2000 study flood event that occurred in April 2006.

The calibrated URBS model was used to determine design discharges for input into the TUFLOW hydraulic model, which was jointly calibrated with the URBS model for the 1998 and 2006 flood events. The calibrated hydraulic model was then used to estimate peak Katherine River flood extents, levels, depths and floodplain hazard areas for the 5%, 2%, 1%, 0.5% and 0.2% AEP design flood events as well as the PMF event. Design discharges were validated against flood frequency analyses of the annual peak series of the recorded data at the Katherine River Railway Bridge.

Hydraulic model was used to identify flood affected properties, potential structural flood mitigation measures for Katherine and any culturally sensitive sites or areas potentially affected by such measures.

Outcomes and benefits

The flood modelling results were also used to identify the existing flood risk and flood hazards throughout the Katherine town and to determine potential flood mitigation measures.

The flood modelling showed that it is possible to significantly reduce flooding of properties in Katherine during smaller more frequent floods, such as a 5% AEP flood event. However, structural mitigation options would not work for larger floods such as the 1% AEP or rarer flood events.

Potential mitigation measures include a combination of structural measures such as levees and drainage works, and non-structural measures such as land use and planning controls. The levee design proposed will include a combination of earth embankment and concrete wall.