Author(s)

N. Norton, S. Dawson, B. Ellwood & L. Mead

Abstract

We have developed an innovative approach for predicting the environmental sustainability of proposed irrigation schemes on rivers. There are three key elements to this approach. First, the water resource potentially available to be taken for out-of-stream use must be defined by setting a river flow regime that sustains in-stream and other environmental values. Second, the capacity of the environment to support intensified land-use must be evaluated, by predicting effects on water quality and related values, and identifying ways to mitigate adverse effects. Third, the predictions must be integrated in a way that allows iterative adjustment of the proposal and assists decision-makers with the holistic evaluation of positive and negative effects. We trialled the approach for a proposed irrigation scheme that would divert 20 m3/s from the Waitaki River, Canterbury, New Zealand, to irrigate 40,000 ha of pasture. This river has a mean annual flow of 369 m3/s downstream of a large hydropower dam. Water is used for irrigation and environmental flows, as well as electricity generation. Under New Zealand legislation an assessment of environmental effects (AEE) is required for proposals to use natural resources. Our team of scientists, engineers and planners collaborated to prepare an AEE for the proposed irrigation scheme. Predictive models were coupled in novel ways to achieve integration between the technical disciplines. For the first time in New Zealand we were able to make quantitative predictions of key cumulative effects at the catchment scale, of both the water abstraction and the use of water for irrigation. The predictions were integrated and the proposal adjusted to achieve a balance between the needs of conflicting values. This approach should achieve better information about the true environmental costs of alternative future water use scenarios and thus lead to better decisions on the environmental sustainability of irrigation proposals. Keywords: environmental impact assessment, irrigation management, river flow regime, water quality, land use intensification.

Keywords

environmental impact assessment, irrigation management, river flow regime, water quality, land use intensification.