Groundwater management tools : analytical procedure and case studies

This report addresses an issue of groundwater management that was identified by regional council staff, as part of a project conducted by Ministry of Agriculture & Forestry and the Ministry for the Environment for encouraging and ensuring effective and efficient water allocation in New Zealand. The issue is how to manage groundwater allocation under conditions of increasing abstraction and imperfect, but developing, knowledge of the resource. The overall objective is to maintain sustainability of the groundwater resource in terms of acceptable environmental effects. The first part of this report is a draft Best Practice Guideline, which sets the context of the nature of the groundwater resource, quality and availability of data, and an appropriate resource management approach. A recommendation from the water allocation project was that an adaptive approach to groundwater management was required, and that there was a need for appropriate analytical tools to support this approach. A companion report addresses the origin and philosophy of adaptive management in water resources. The second part of the report is concerned with the development and demonstration of a suitable analytical method, and guidelines for its implementation, which supports the recommended adaptive management strategy. The "eigenmodel" method is concerned primarily with the amount of water stored in an aquifer, and how this responds to recharge and abstraction. The resulting information about groundwater levels can be related to environmental effects such as low flow in streams, for example. It is a "whole aquifer" approach and does not purport to be suitable for detailed investigation of local effects caused by abstraction stresses. These problems require other well established modelling techniques, and their compatibility with the eigenmodel method is discussed. The issue of sparse data is addressed by the simplicity of the analytical format, which enables identification of fundamental properties of aquifer storage, sometimes from only one observation well record. Implementation of the procedure is ideally suited to spreadsheet software. These simple models can also be expressed in a form that incorporates continual monitoring of groundwater levels for "real-time" forecasting as decision support for adaptive management. Several demonstrations with observed data from two aquifer systems are presented to illustrate the capabilities of the procedure