Abstract
The Future Farm Industries CRC (FFI CRC) is focused on increasing the perenniality of land- use within catchments to improve natural resource management outcomes, while increasing profitability. A potential negative consequence of increasing perenniality is a decrease in catchment water yield. This paper considers the impact of some key FFI CRC land-use change strategies on catchment water yield. These strategies are plantation forestry and increasing perenniality of pasture based on EverGraze principles (www.evergraze.com.au). The study area for this project was the Glenelg Hopkins Region, South West Victoria, Australia; specifically the Wannon River catchment (345,477 ha). Plantation forestry was in the form of blue gums to be converted to wood pulp. The strategy to change pasture perenniality was based on EverGraze principles to ensure that CATPlus model outputs informed EverGraze activities and reinforced EverGraze outputs. EverGraze researchers along with other local farming experts helped this project focus its modeling research question to be relevant to their needs. Their questions required land-use changes at a farm scale, which reflected position in landscape (driven by whether the land was crest, slope or valley) and assess any potential impacts of increased perenniality on the filling of farm dams and wetlands within the catchment. Consideration of farm dams and wetlands was from the perspective of stock water supply and maintaining wetland health during extended dry periods, hence the modeling solution required greater spatial resolution than comparable dam models like TEDI whose primary design focus is the impact of farm dams on subsequent stream flow. From an agricultural perspective, reliable stock water supply via farm dams underpins the livestock grazing industry. In areas with saline groundwater, like the northern Wannon region, farm dams form the sole source of available stock water. This reliance on farm dams created concern with the expert working group that farm dams would not fill as frequently in a perennial dominated landscape. Some of the key results were that CATPlus was able to provide an adequate stream flow prediction over time (monthly CoE >0.8). Improvement in prediction over this period was achieved through accounting for gaining and losing water stores along a stream reach including dams and wetlands. The decrease in catchment water yield by tree plantations was 1.5 times that of EverGraze. In addition, a notable increase in the period when farm dams are dry only occurs in the Wannon catchment at higher levels of perennial adoption. This paper has shown the ability of CATPlus to predict the potential impacts of increasing catchment perenniality on stream flow and water bodies such as farm dams and wetlands. Due to the hydrological complexity of landscapes, the impact on streamflow of future increased perenniality will vary across the landscape. CATPlus presents a valuable tool for investigating these potential impacts.
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