Implications of Irrigation and Land Use Changes in a High Country Valley - The Hakataramea Valley

Abstract

There have been major changes to the farming practices across Canterbury in the past 50 years, with the biggest changes seen in the previous two decades. These changes in farming practices, namely dairy farming and irrigation, have lead to declining water quality in the region. The changes that have been experienced on the Canterbury plains are now being seen in the hill and high country settings, such as the Hakataramea Valley. This study found that the waterways in the Hakataramea Valley are susceptible to nutrient enrichment following a rainfall event that caused soil runoff. Wind erosion also occurrs in the valley and was believed to be the major source of nutrient transport in the waterways, however, this was proven to be not as significant as soil runoff. The valley showed a range in water quality, with the river generally being of a higher quality than the tributaries. One tributary in particular stood out as being lower in quality than the others, this was Rocky Point stream. It was identified that the tributary catchments that had extensive farming systems and no irrigation present (Grampians Stream and Rocky Point Stream) were of a lower quality than the tributary that had irrigation (Padkins Stream). This was due to the fact that waterways in this catchment were fenced, and on farm stockwater systems were in place, stopping stock from accessing the waterway. The OVERSEER modelling of the future scenarios presented showed that if the agriculture in the valley was to continue to develop and intensify, the water quality would decline. If the valley became completely irrigated this decline could potentially be large enough to result in a level that would become unsafe for recreational use and human and animal consumption. The future of the Hakataramea Valley and its waterways depends on improved management processes that focus on specific areas of the catchment and the catchment as a whole.