Maintenance of Geomorphic Processes in Bowen Basin River Diversions

The project builds upon knowledge acquired from two past ACARP Projects, being:

• (C8030) Maintenance of Geomorphic Processes in Bowen Basin River Diversions
• (C9068) Monitoring Geomorphic Processes in Bowen Basin River Diversions

Location of the Investigation
The project is based on the streams within the Bowen Basin Coal Field of Central Queensland. More specifically, the investigation has comprised review of form and processes of streams of similar type to that encountered by mining operations within the Bowen Basin. The streams are largely within the Fitzroy River Basin. However, as the coal measure extends beyond the catchment of the Fitzroy River, a number of streams outside the Fitzroy basin have been included in the investigation. The region is shown in Figure 1.1.

Need for the Investigation
The need for this project arose from a deficiency in quantitative guidelines for diversion design and rehabilitation in the Bowen Basin. Based on the outcomes of the work completed to date, there is now a higher level of understanding of the key features of, and processes occurring in, rivers and diversions of the Bowen Basin. This understanding highlighted the need for targeted research to quantify the key parameters that affect and dictate the shape and form of the rivers and streams of the Bowen Basin. These parameters form the basis of criteria that can be applied to the design and rehabilitation of diversions in the semi-arid region of the Bowen Basin.

The design of river diversions in the Bowen Basin is currently based on knowledge gained from processes occurring in rivers and streams of North America, Europe and southeast Australia. Much of this knowledge has been gained from perennial streams within humid regions. Transferring design parameters developed for perennial streams to intermittent streams is problematic due to the considerable variability between the two environments.

The poor level of information available for design and rehabilitation of diversions increases the risk of under-design (on-going failures) and over-design (excess cost) of diversions. As no agreed basis for design exists, the level of design and confidence of results varies markedly between mine sites and diversions. This research project seeks to quantify key parameters that can be used to assist the design of new diversions and the rehabilitation of existing diversions in the Bowen Basin.

This report and the outcomes contained do not replace the need for detailed geomorphic assessment of stream systems as the basis for design of diversions and rehabilitation efforts. Indeed a thorough geomorphic investigation should form the basis for any stream diversion design and rehabilitation program. Adjoining reaches of stream form useful "templates" for design and rehabilitation of river diversions. However, diversion construction can change the nature of a stream channel. The diversion of the watercourse may result or have resulted in a stream with a regularly engaged floodplain being laterally confined with limited opportunity for floodplain engagement. Similarly, some diversions may change a confined stream into one with a constructed and regularly engaged floodplain. In these circumstances, adjoining reaches of the same stream may not provide useful templates for design. In the absence of "templates" for stream design, parameters developed from research in other regions of Australia and overseas are adopted. These parameters offer a limited basis for design as they have been developed for streams in other regions of the world with a range of different influences and characteristics.

The purpose of this investigation is to provide parameters for design in the Bowen Basin based on research on the stream shape and form from within the basin.

Objectives of the Project

• improved basis for diversion design and rehabilitation
• improved understanding of geomorphic processes and how they affect diversion design
• more efficient use of time and resources in effectively managing diversions
• increased probability of mines obtaining short term re-licensing for diversions
• increased understanding of requirements to achieve long term sign-off
• reduced risk to mine operations and personnel safety by improving diversion design
• improved environmental performance of diversions and mines

Analysis of Results
The data collected was compiled to identify the occurrence and range of three parameters, the velocities, shear stress and stream powers, in natural rivers and streams throughout the region. The information was used to develop an understanding of the link between these hydrologic and hydraulic parameters and the shape, size and occurrence of geomorphic units within the stream systems. These geomorphic units include but are not limited to: meanders, benches, terraces, low flow channels, active channels and high flow channels.