Putting the wood back into our rivers: an experiment in river rehabilitation

This paper presents an overview of a project established to assess the effectiveness of woody debris (WD) reintroduction as a river rehabilitation tool. An outline of an experiment is presented that aims to develop and assess the effectiveness of engineered log jams (ELJs) under Australian conditions, and to demonstrate the potential for using a range of ELJs to stabilise a previously de-snagged, high energy gravel-bed channel. Furthermore, the experiment will test the effectiveness of a reach based rehabilitation strategy to increase geomorphic variability and hence habitat diversity. While primarily focusing on the geomorphic and engineering aspects of the rehabilitation strategy, fish and freshwater mussel populations are also being monitored. The project is located within an 1100m reach of the Williams River, NSW. Twenty separate ELJ structures were constructed, incorporating a total of 430 logs placed without any artificial anchoring (e.g., no cabling or imported ballast). A geomorphic control reach was established 3.1 km upstream of the project reach. In the 6 months since the structures were built the study site has experienced 6 flows that have overtopped most structures, 3 of the flows were in excess of the mean annual flood, inundating 19 of the ELJs by 2 - 3 m, and one by 0.5 m. Early results indicate that with the exception of LS4 and LS5, all structures are performing as intended and that the geomorphic variability of the reach has substantially increased

Strategies in the 2D numerical modelling of wood transport in rivers

In recent years the improvements in computational capacity and the advances in numerical modelling techniques have produced a significant increase in the type of river processes that can be studied with the support of numerical models. Water quality and sediment transport are some of these processes, and it also applies to the case of wood transport. In the last five years several publications have proven the utility of numerical modelling of wood transport for predicting and better understanding wood dynamics, analyzing the influence of wood on flow conditions, and the interactions with infrastructures, and for including this phenomenon in the flood risk assessment. Besides these studies, numerical modelling of wood in rivers is still challenging, and different strategies can be used. We present and discuss some details of numerical strategies used in the simulation of wood transport within a 2D hydrodynamic model based on the finite volume method.Peer ReviewedPostprint (published version

Economic assessment of acquiring water for environmental flows in the Murray Basin *

This article is an economic analysis of reallocating River Murray Basin water from agriculture to the environment with and without the possibility of interregional water trade. Acquiring environmental flows as an equal percentage of water allocations from all irrigation regions in the Basin is estimated to reduce returns to irrigation. When the same volume of water is taken from selected low-value regions only, the net revenue reduction is less. In all scenarios considered, net revenue gains from freeing trade are estimated to outweigh the negative revenue effects of reallocating water for environmental flows. The model accounts for how stochastic weather affects market water demand, supply and requirements for environmental flows. Net irrigation revenue is estimated to be 75 million less than the baseline level for a scenario involving reallocating a constant volume of water for the environment in both wet and dry years. For a more realistic scenario involving more water for the environment in wet and less in dry years, estimated net revenue loss is reduced by 48 per cent to 39 million. Finally, the external salinity-related costs of water trading are estimated at around 1 million per annum, a quite modest amount compared to the direct irrigation benefits of trade. Copyright 2007 The Authors Journal compilation 2007 Australian Agricultural and Resource Economics Society Inc. and Blackwell Publishing Ltd .