Thirty one wells in the area were selected for sampling. The location and well heights of each well were measured to a high degree of accuracy. Additionally, up and downstream sampling locations were determined on both the Hokitika River and Kokatahi River.
Water elevations were calculated from this data and then analysed to produce groundwater contours. These contours indicated that groundwater on the south end of the Kowhitirangi Plain is recharged by the Hokitika River from there, flows generally northward. Groundwater from this system enters the Hokitika River on the northwest side of the Plain. Some of this flow may also enter the Kokatahi River; however, the direction of groundwater flow along that River appears to flow generally parallel to it. Groundwater underlying the Kokatahi Plain flows to the northwest and enters the Hokitika River.
Results indicated that water quality around the Kowhitirangi and Kokatahi Plains was generally good and, with the exception of nitrate and sulphate, does not change significantly between dry and wet seasons. In contrast, groundwater nitrate and sulphate concentrations were higher during the wet season. Seasonal changes potentially reflect precipitation-facilitated downward migration of nitrate-nitrogen and sulphate from anthropogenic surface sources such as farming operations.
There were higher concentrations of nitrate in the centre of both Plains with lower concentrations along the river boundaries. In most cases results for nitrate-nitrogen were low (i.e., on the order of 1 mg/L or less).