Case study

Tennant Creek Stormwater Investigation

ProjectTennant Creek Stormwater Investigation
ClientNorthern Territory Department of Lands and Planning
LocationTennant Creek, Northern Territory
Disciplines/ServiceHydrological and hydraulic modelling
Stormwater network modelling
Key team members

Rhys Cullen
Project Manager

Hayden Guse
Flood Modeller

WRM ContactRhys Cullen

The Challenge

The town of Tennant Creek, located approximately 450 km north of Alice Springs and 890 km south of Darwin, experienced a significant rainfall event in January 2017, which exceeded the capacity of the underground stormwater drainage network, resulting in extensive overland flow along roadways and through some allotments.

Drainage characteristics in Tennant Creek are complex, particularly during large flow events. There are interactions between in-channel flows, overbank flows, overflows draining over roads as well as flows through culverts and other stormwater infrastructure.

The key challenge was to develop an understanding of the drainage behaviour and limitations of the Tennant Creek trunk stormwater and open drain network, including identification of locations where the capacity of the network would initially become exceeded, and locations which would become adversely affected by overflowing stormwater, potentially resulting in inundation of allotments and buildings. In order to do this, it was important to ensure the conveyance of the trunk drainage, overland flowpaths and roads was represented adequately.

Approach and Key Activities

WRM developed detailed models of the Tennant Creek trunk stormwater catchments, which included both underground and above ground drainage infrastructure. Detailed survey of the road network, overland flowpaths and drainage channels was incorporated into the model. This required significant manipulation of the 3D survey surface and underlying photogrammetry digital elevation model.

The models were calibrated against observed flooding from the January 2017 storm event, with an excellent agreement between predicted and observed flooding achieved.

The models used to define design event flooding from the Tennant Creek stormwater drainage networks for a range of annual exceedance probability’s (AEPs). The models were used to identify overland flowpath locations and extents, and locations where runoff exceeded the capacity of the stormwater drainage network and inundated roads and properties.

Outcomes and benefits

The flood modelling and mapping enabled the identification of suitable developable land on the floodplain to satisfy the growing population of Alice Springs. The models were also used to develop a drainage strategy that was sympathetic with the natural environment and provided sufficient flood immunity to the future community.