Summary

A total of 436 logs were used to create 20 engineered log jams in a 1.1 km reach of the Williams River, a gravel-bed river that has been desnagged and had most of its riparian vegetation removed over the last 200 years.

The experiment described in this paper was designed to test the effectiveness of reintroducing woody debris as a means of improving channel stability and recreating habitat biodiversity in NSW rivers. This study assessed geomorphic and ecological responses to introducing woody habitat by comparing paired test and control sections of the river. Channel characteristics (e.g., bedforms, bars, texture) within test and control reaches were assessed before and after wood placement to quantify the morphological variability induced by the artificial log jams in the test reach. Since construction in September 2000, the log jams have been subjected to five overtopping flows, three of which were larger than the mean annual flood. A high-resolution, three-dimensional survey was completed after major flows. Cumulative changes induced by consecutive floods were also assessed.

After 12 months, there were major geomorphologic changes in the test reach compared to the control reach. Fish assemblages in the test reach showed an increase in species richness and abundance, and reduced temporal variability compared to the control reach, suggesting that the changes in physical habitat were beneficial to fish.