Assessment of erosion processes in the South Pine River in close proximity to Energex infrastructure. Final Report August 2010.

Abstract

This report details an assessment of a specified reach of the South Pine River (SPR) adjacent to an existing electricity supply network owned and operated by Energex Ltd. The reach in question has undergone channel planform changes in response to several significant flooding events over the past 18-24 months. The reach is located approximately 4km upstream of the confluence of the North and South Pine Rivers and encompasses a large meander loop with cleared paddocks used for grazing purposes on the majority of adjacent land, (Figure 2.1) Energex have an existing electricity supply line traversing the meander loop in a north to south axis and it is proposed that this supply is duplicated within the current easement approx 20m east of the existing line. The meander loop has been cut off from the main flow of the river and now only flushes through tidal movement of water with minimal inflow from the upstream catchment. The existing supply line and associated towers are currently inaccessible as a consequence of the meander loop cut off and advice is sought on a preferred access point for the maintenance of existing and proposed electricity supply infrastructure. An interim report using field assessments and the analysis of historical aerial photographs was presented in June 2010 (Appendix 1) and the findings of this earlier work are discussed in the main body of this report. In addition to the assessment of appropriate access, this report was commissioned by Energex Ltd to investigate the rates of channel migration along specific reaches of the lower SPR and whether lateral migration of the channel will affect adjacent infrastructure. Two approaches have been adopted:  The use of historical data to determine past migration rates for the study reach of the SPR, and  Hydraulic modelling of the channel to identify sites of high erosion potential. The results of these investigations are provided to assist in the decision making process regarding the placement of new infrastructure and access points. They also illustrate the potential benefits of bank revegetation.