Water Journal : Water Journal April 2012
catchment management technical features 102 APRIL 2012 water Indices such as these can be used to scenario-test how changes in catchment characteristics may impact water quality. This is illustrated in Figure 3 using the information from the study to predict water quality in a recently completed asset, Wyaralong Dam. Non-urban diffuse source pollutant loads have been identified in South-East Queensland to be a major contributor to poor water quality and aquatic ecosystem health in the region's catchments, and are a significant issue for water treatment (HWL 2007). Seqwater and its research partners have developed a strategic research program to address a number of key knowledge gaps to better understand and manage non-urban diffuse source pollutant loads, including: • What are the pathways of sediment and nutrient transport through catchments? • What is the relationship between sediment and nutrient transport and rainfall events, and how is the transport of these pollutants impacted by land use and land management practices? • How effective are remnant riparian vegetation and certain rehabilitation actions on reducing sediment and nutrient export to waterways? • How do we monitor and measure the success of any management interventions to inform future investment in natural assets and adaptive management? This project will use sediment- tracing techniques, hillslope-scale plots of rainfall and run-off in grazing lands, assessment of remote sensing, aerial and LiDAR imagery, and water quality and rainfall data to answer the above questions. The project will also research, develop and design appropriate monitoring programs to evaluate the effectiveness of management interventions. The project has been split into two sub-projects, the first of which focuses on sediment transport and nutrient pathways in catchments: sources, processes and their relationship with land management. The second focuses on land and stream management interventions: methods, implementation and the monitoring and evaluation of their success. Initial findings of this project have already delivered some key information around catchment processes. Effective management of sediment delivery in water supply catchments depends in part on the identification of the primary erosion process generating the sediment. At the local level, it is common for either hillslope or channel erosion to clearly be the dominant erosion process, which in turn relates to different management strategies to mitigate the impact. Channel erosion is best managed by preventing stock access to streams, protecting vegetation cover in areas prone to channel erosion, revegetating bare banks, and reducing sub-surface seepage in areas with erodible sub-soils. Hillslope erosion is best managed by promoting groundcover, maintaining soil structure, and promoting deposition of eroded sediment before it reaches the stream. Table 1. Probability index (0 to 1) that the 137Cs concentration on the river sediment sample belongs to either the hillslope or channel distribution (A = rising limb, B = mid-hydrograph, C and D = falling limb). Sample Sequence Probability Hillslope Channel Catchment A AB 0.05 0.95 Catchment A C 0.04 0.96 Catchment B A 0.68 0.32 Catchment B BC 0.04 0.96 Catchment C AB 0.05 0.95 Catchment C C 0.74 0.26 Catchment C D 0.66 0.34 Catchment D A 0 1 Catchment D B 0.47 0.53 Catchment D C 0.04 0.96 Catchment E AB 0.01 0.99 Catchment F A 0 1 Catchment F B 0.02 0.98 Catchment G A 0 1 Catchment G B 0.06 0.94 Catchment G C 0.07 0.93 Vulnerability Index 0.2 0.4 0.6 0.8 1.0 Decreased grazing cover (-10%) 0.2 0.4 0.6 0.8 Increased grazing cover (+10%) Coo LN EwManHin LH MacKurBarMarWyaBor NPMooSom Wiv 0.2 0.4 0.6 0.8 1.0 Wyaralong under current grazing cover (47%) One year after construction Wyaralong under current grazing cover (47%) 20 years after construction Decreased grazing cover (-10%) Coo LN Ew Hin LH Man MacBarKurMarNPBorWyaMooSomWiv Increased grazing cover (+10%) Figure 3. Vulnerability Index summary for 16 reservoirs in subtropical Queensland, at one, five, 20 and 100 years since the planned completion of Wyaralong dam wall in 2011, given: the current percentage of grazing land cover in Wyaralong catchment (top row); minus 10% (middle row); plus 10% (bottom row). Unbroken arrows show the change in the level of among-reservoir vulnerability between grazing cover scenarios. Broken arrows show the change in among-reservoir vulnerability through time with varying grazing scenarios (Leigh et al., 2010).
Water Journal May 2012
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