Introduction
This report has been commissioned as a result of a two-year project conducted by Ministry of Agriculture & Forestry and the Ministry for the Environment, to encourage and ensure efficient and effective water allocation in New Zealand. One of the outcomes of that project was the identification of issues in groundwater management, as a result of a survey of regional councils and consultation with the Regional Groundwater Forum of council groundwater scientists. These issues include:
- Knowledge about an aquifer often follows demand on the groundwater resource;
- Allocation decisions, with potential long-term effects, must be made on the basis of information that is perceived to be insufficient;
- The amount of information about an aquifer may increase with time, but may never have included the state of zero demand
- An adaptive management approach was suggested for optimal decision-making when both demand and information are increasing with time.
This report presents an approach to groundwater assessment and allocation that enables the application of relatively simple analytical methods that are appropriate to the availability of data. This approach is derived from the same mathematical theory as groundwater modelling software, such as MODFLOW, so that compatibility with these methods is intended where there are sufficient data for more refined analyses.
The groundwater allocation issues that are addressed in this report are based on a whole-aquifer point of view that accounts for time-varying environmental effects such as changes to the low-flow regime of streams. There are of course other effects such as stream depletion and salt water intrusion, which may be caused primarily by short-term local groundwater demand. There are established analytical methods for assessing these latter effects, and the interface between these methods and the new approach will be discussed.
The report is presented in two parts. Section A describes a Best Practice Guideline for groundwater management, which is intended to be a general framework for analysing and resolving issues of groundwater allocation. Section B provides a detailed description of one method of analysing a groundwater resource for the purpose of supporting the adaptive management approach proposed in Section A.
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