Hydrology of the Kaputone Stream: a quantitative analysis

Abstract

The upper reaches of the Kaputone Stream in Christchurch have been running dry with greater frequency and for longer periods than usual in recent years, and local residents have raised their concerns about this with the local councils (Environment Canterbury and Christchurch City Council). There have been several new developments in the area in the past few years and it is thought that these (in particular the Northwood residential development) may have adversely affected the hydrology of the area and caused the problem with the flow of the Kaputone.

Data on the flow status of the Kaputone Stream, the water level of the Waimakariri River, the flow of the Styx and Avon Rivers, daily rainfall and evaporation in the area, and the depth to groundwater at several wells in the area has been provided by Environment Canterbury and Christchurch City Council. The data was analysed quantitatively, using non-parametric statistical tests (Mann-Whitney, Kruskal-Wallis, Tukey rank transformation tests, Mann-Kendall). The aim was to determine whether there has been any change in the hydrology of the area surrounding the Kaputone catchment in the years from 1998 to 2004, and also to identify any long-term trends in the data.

The conclusions were that there is no doubt that the flow of the upper reaches of the Kaputone Stream has decreased greatly in the past few years. Also that it seems unlikely from the data that the stream's loss of flow has occurred naturally, or has been caused solely by an area-wide lowering of water levels. From the results it is not possible to say conclusively whether the Northwood development did or did not cause the problems with the flow of the Upper Kaputone. However, based on the data supplied, it does appear very likely that the development has had some effect. Recommendations are given on a number of issues, which could be used to further investigate and mitigate the flow problems at the Kaputone, and to help prevent such a situation from arising in future.