A region-wide pressure-state-impact model for freshwater flows — ASN Events

A region-wide pressure-state-impact model for freshwater flows (#191)

Doug Booker

The New Zealand government has adopted a pressure-state-impact framework for national environmental reporting. In this framework, pressures are indicators of human activities that influence the environment. States are indicators of the resulting conditions in the environment. Impacts are indicators of the implications for ecosystems health. Application of this framework to the freshwater environment requires estimates of how much water is being abstracted from rivers and the impacts of these takes on the freshwater environment, as well as the reliability of supply and potential for headroom in respect of water use. A pressure-state-impact model for freshwater flows has been devised that can provide these estimates on a daily basis across New Zealand using a national digital river network that comprises 570,000 segments. A national rainfall-runoff model is used to estimate naturalised flows (flows without any abstractions) for each segment. A database is used to collate information describing, for each abstraction, from where the water is being taken, the purpose of abstraction, total recorded water use, maximum allowable water use and any associated environmental flow rules. A model is applied to position each take on the river network, accumulate its downstream effects and therefore calculate total recorded water use and maximum allowable water use upstream of each river segment. Results will be shown for particular regions of New Zealand, including the Canterbury region. This region is important for agricultural and hydroelectricity production, but also contains many rivers with high environmental value such as large braided rivers.

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