Author(s): Julian Martin; Christine Lauchlan Arrowsmith; Warwick Bishop; Dean Judd
Linked Author(s): Warwick Bishop
Keywords: Hydraulic structures; Anabranch management; Large woody debris
Abstract: Anabranching river networks such as the Lake Hume to Yarrawonga Reach of the River Murray in Australia characteristically contain anabranch channels that develop and evolve through erosion and enlargement. The evolution of these anabranches typically leads to the capture and eventual abandonment of the parent channel (in this case the Murray River itself). The development of these anabranches has the potential to considerably impact upon the social, economic and environmental values of the river system. The Parlour Reach is situated within the Lake Hume to Yarrawonga section of the River Murray system and contains a complex anabranch network on both sides of the floodplain. Named anabranches within the Parlour Reach include Chinamans, Chambers, Gulf, Parlour, Sawyers, Common, Doolans and Punt Creeks. Several anabranches within this network, including Parlour Creek and Common Creek form significantly straighter, shorter and hence steeper sections of stream in comparison to the adjacent section of the Murray River. As such, there is a risk these channel networks will further develop and capture an increasing proportion of flow from the Murray River. The Department of Water and Energy (DWE) is responsible for the management of the River Murray between Lake Hume to Yarrawonga. The DWE recently identified an opportunity to install timber snags within Common Creek in an attempt to manage anabranch development in this section of the stream network. Whilst challenging, the strategic placement of timber snags within Common Creek has the potential to delay the expected capture of the Murray River while providing overall benefits to the river system and neighbouring community. The present study has been undertaken to assess how the timber snags will affect the hydraulic conditions within Common Creek, Parlour Creek and the Murray River. The purpose of these assessments is to allow DWE to develop a comprehensive management strategy for the Parlour Reach, making use of available natural resources such as locally sourced timber, while also considering the dynamic nature of the river system itself. A coupled 1D-2D hydrodynamic modelling approach has been adopted for the hydraulic modelling. The entire Parlour Creek and Murray River system has been modelled dynamically in 1D using available cross-section surveys to define the existing hydraulic conditions in the system. A more detailed 2D model has been used for Common Creek and the adjoining sections of the Murray River and Parlour Creek where the local impacts of the timber placement are most critical. The development of these more detailed 2D models has been possible through the use of LIDAR survey for the Murray floodplain and continuous bathymetric survey within Common Creek. The detailed geometry and configuration of the proposed timber snag placement can be well represented in the 2D model. The results of the hydraulic modelling have been used to assess the distribution of timber snags along Common Creek and the potential impacts on both flow and the geomorphic development of the anabranch system. This paper investigates the geomorphic and hydraulic implications associated with the placement of timber snags within Common Creek.