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Numerical Modelling in Motueka

The Upper Motueka catchment is a 887km2 area of fertile river terraces suitable for irrigated agriculture, located on the Northwest part of the South Island in New Zealand. Similar to many regions in New Zealand, the Upper Motueka aquifer is strongly connected to the associated surface water system.

The regional authority in charge of water allocation are concerned that an increase in groundwater abstraction for irrigation may affect stream baseflow during summer.

GNS Science have developed a FEFLOW 3-D finite-element groundwater-river interaction model to guide utilisation of groundwater resources, while ensuring acceptable amounts of stream flow during low flow periods.

Finite element structure looking at Motupiko and Motueka rivers confluences.

Finite element structure looking at Motupiko and Motueka rivers confluences.

River networks within the catchment were identified as main recharge source for the Upper Motueka aquifer. Modifications of the current water allocation will affect river flow differently over the study area.

Further development of a dynamic river interaction model incorporating a river flow model developed in Mike11 is currently being undertaken to simulate the dynamic exchanges of water between the shallow aquifer and stream, and to evaluate the effects of different hydrological conditions and changes land use pattern.

Acknowledgements

This study was conducted in a cooperative project between GNS Science, Landcare Research and the Tasman District Council (TDC) as a component of the Integrated Catchment Management (ICM) project led by Landcare Research.