Revegetation Of Water Supply Catchments Following Bushfire

Author :
Publisher :
ISBN 13 :
Total Pages : 18 pages
Book Rating : 4.:/5 (747 download)

DOWNLOAD NOW!

Download or read book Impacts on Water Quality by Sediments and Nutrients Released During Extreme Bushfires written by and published by . This book was released on 2007 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes the final stage of a collaborative research project between CSIRO and the Sydney Catchment Authority (SCA) on the potential impacts on water quality of extreme bushfires in the Sydney water supply catchments. The project has investigated the transfer of sediments and nutrients between different components of the Nattai River catchment slopes to Lake Burragorang reservoir continuum, following extensive wildfire in the Nattai River catchment in December 2001, to develop an understanding of the impacts of fire induced erosion on water quality. The fire burnt 225,000 ha mainly in the Nattai River catchment, and over a large proportion of this area the fire was previously found to be of high to extreme severity as measured by remote sensing and ground inspections. Phase one of the research reviewed available data and process understanding of the impact of forest fires on erosion rates. Phase two of the research demonstrated extensive redistribution of surface soil and nutrients on a burnt hillslope in the Nattai River catchment, with some storage in foot-slope locations. Phase three of the research found that sediment delivery to the river network from burnt areas in 2002 was approximately six times the mean-annual pre-fire rate, and was dominated by surface sources high in phosphorus, in contrast to predominantly sub-surface sources pre-fire. In 2002-2003, the yields of suspended sediment and phosphorus for individual runoff events were up to two orders of magnitude greater than those pre-fire due to their greatly increased availability for transport. The fourth and final phase of the research focussed on the downstream impacts of post-fire sediment and nutrient yield to Lake Burragorang. Radionuclide and geochemistry tracers were used to investigate the long term contribution of fire to reservoir sedimentation relative to non-fire causes of catchment erosion. The results show that sediment yield to Lake Burragorang in the 13 months following the 2001 fires was below the long-term annual average rate since the reservoir was completed in 1960. This low sediment yield was unexpected given the visibility of post-fire erosion. However, 2002 was drier than average, with the annual discharge from the Nattai River being 34% of mean-annual discharge, and subsequent years were similarly dry. The dry conditions limited the post-fire erosion from the much higher rates that could have occurred in wetter conditions. Sediment delivery to the river network, and delivery through the river network to the reservoir were also limited by the below-average post-fire rainfall and low river discharge. The actual annual post-fire sediment yields to Lake Burragorang from the Nattai River were several times higher than what would have occurred without fire in the dry post-fire conditions. If post-fire rainfall had been higher, the post-fire delivery of sediment to the reservoir may have had a larger impact on reservoir water quality, including the possibility of algal blooms.