Mid-Mataura Groundwater Model : final report / Phreatos Limited.

Includes bibliographical references (p. 43).

The mid-Mataura catchment has experienced a considerable increase in groundwater abstraction over the past five years. Between 2000 and 2005 groundwater demand in Southland increased eight-fold, driven primarily by the expansion of pasture irrigation in northern Southland. Demand for additional water supplies for irrigation continues to grow - particularly in the Riversdale area. The shallow, productive alluvial aquifers of the mid-Mataura catchment are hydraulically connected with rivers and springs - groundwater and surface water are fundamentally a ♯single resourceα. This characteristic of the groundwater system has led to considerable focus being directed at the cumulative effects of groundwater abstractions on the surface water environment. Management of the cumulative depletion effects of groundwater abstractions is driven partly by the requirements of the Mataura River Water Conservation Order (1997). The Order stipulates that at any point, 95% of the natural flow in the Mataura River must remain. The sustainable management of groundwater allocation in the mid-Mataura catchment requires a reliable and scientifically robust understanding of the groundwater environment, and the dynamics of its interaction with surface water systems. Groundwater allocation in the Riversdale Groundwater Management Zone is currently approaching the ♯first orderα allocation limit set by Environment Southland. At present the cumulative depletion effects of groundwater allocations is not fully understood. The stream flow depletion effects of individual takes are currently assessed by Environment Southland as part of the consenting process, but a more comprehensive examination of the cumulative effects is required. Environment Southland has therefore commissioned a groundwater modelling study from Phreatos Limited to assist in the evaluation and management of groundwater allocations in the mid-Mataura catchment.