Water Journal : Water Journal April 2013
WATER APRIL 2013 84 Feature Article must be able to consider how to rank potential problems such as the risk of an onsite wastewater over ow against other issues such as the presence of cattle within the catchment. A repeatable and transparent way of assessing these scenarios is required so that recti cation efforts may be addressed in priority order based on likely improvements and cost effectiveness. The most important step in identifying catchment hazards is to accurately determine the boundary of the drinking water catchments, followed by mapping the current land use in as detailed a form as possible. Additional data such as map layers of soils, topography, vegetation cover and location of settlements then further contribute to the identi cation of possible pollution sources. A common issue that arises is the fact that data collected quickly becomes unmanageable. At this point in time, a model that weights and ranks geographical information is required. Hunter Water has used the Source Water Improvement Support System (SWISS) model for this purpose. The model graphically identi es the catchment areas that pose greatest risk from pathogens (disease-causing organisms), suspended solids and nutrients (nitrogen and phosphorus, Figure 3). While more complex quantitative models are available, the SWISS is relatively simple in structure, thus allowing for it to be built, run and analysed by catchment managers with a relatively small amount of additional specialist support. Figure 3. An example of a SWISS risk output map. Put simply, the model inputs various spatial geographical information system (GIS) data 'layers' that may be continuous (e.g. rainfall) or point source (e.g. intensive animal sheds). It then uses weightings (determined from expert panel workshops) to multiply the importance of each layer to determine the areas with greatest contribution to nutrient, turbidity and pathogen risk in approximately 1700km2 of surface water catchments. There are various inbuilt scripts to calculate parameters such as the number of pathogens from livestock and the like. The output is a ranking of activities and associated areas in the catchment that pose the greatest hazard to drinking water quality. Catchment risks may then be ranked according to a prioritisation process that factors in practical aspects such as the cost of reducing each hazard, the likely effectiveness of remediation works and the level of con dence in the data. Hunter Water found that while the process of applying a spatial model was a powerful tool for making investment decisions, it was not essential. The process of collecting and spatially representing raw data is, however, essential. Collection of reliable spatial catchment information forms the basis of making good decisions about catchment management, and if a more complex model follows it may help bring issues into focus. ELEMENT 2 -- HAVE EFFECTIVE LEGISLATION The quality and quantity of source water is largely dependent upon the land-based activities that occur in the catchment. Poor development choices in drinking water catchments can have detrimental impacts on drinking water quality (Hurlimann, 2010) (Figure 4). Land use planning legislation that ensures developments consider the quality and quantity of water is essential to maintain or improve raw drinking water quality. Although not a consent authority, Hunter Water has adequate legislative controls in drinking water catchments to be a recognised stakeholder when developments are determined. Wherever possible, the catchment manager should seek legal advice about the scope of powers so they can be clear with the community and stakeholders about their responsibilities. Effective legislation refers not only to the strength and clarity of the law governing catchment land use, but also their integration into local planning instruments. Hunter Water has found that consent authorities (such as local councils and the NSW Department of Planning and Infrastructure), and those that are charged with anti-pollution duties (such as the Environment Protection Authority), are consistently supportive of recommendations made for the bene t of drinking water catchments, given good reasons. However, while legislation may be in place, it is Hunter Water's experience that staff turnover and shifting priorities within the consent authority often mean that components of catchment legislation can be overlooked. Regular stakeholder contact is, therefore, pivotal for catchment authorities in the implementation of successful catchment management. Figure 2. The eight elements of effective catchment management, showing that each element is dependent on the strength of others.
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