Assessing unmonitored water use in semi-rural environments: An investigation into the Okana and Okuti River catchments, Little River, Canterbury

Abstract

Lake Forsyth/Wairewa, on the southern side of Banks Peninsula in Canterbury is a shallow eutrophic lake with a history of degraded water quality. The two primary surface water inputs flowing into the lake are the Okuti and Okana Rivers. In order to better understand and address the underlying causes of degradation in the lake’s water quality, research is currently underway to create hydrological, sediment and nutrient budgets for the lake’s catchment. Currently water take from the Okuti and Okana Rivers and their tributaries is a permitted activity, so no consent is required, and no record is kept of how much water is being used. This study investigated water use in households in the Okuti and Okana River catchments, as the basis for a model that could estimate catchment-wide water use, for this and potentially other semi-rural catchments. The information obtained from this model could also be used to gain a better understanding of how water is moving through the catchments and the effect that present or predicted water use could have on the lake. Local households in the Okuti and Okana catchments were interviewed to obtain data on household water use. Contrary to the general perception, the majority of households in the two river catchments had an abundance of water, and water shortages were of little concern. Average domestic water use in the study area appeared to be high, at just over 580 l/person/day, compared to the New Zealand average of 160-260 l/person/day. This may reflect the hot summer weather in which the survey was undertaken and/or difficulties measuring actual water usage in some households. The water use of farming operations was investigated in the survey, so that a complete model of water use in the catchments could be constructed. The latest research on household and animal water use elsewhere was also incorporated into a model to estimate catchment-wide water use. The model calculated total water requirements for this semi-rural environment as just over 400,000 L/day, with a probable error of ± 35%. More accurate data for farming operations (e.g., stock type and number) would reduce this error considerably. The limitations of this research and recommendations for further research are discussed.