The Demand, Use, and Efficient Allocation of Groundwater in Martinborough, Wairarapa, New Zealand

Abstract

Over the last ten years the rapid expansion of viticulture in Martinborough has resulted in increased groundwater use. Viticulture in this area would not be possible without irrigation because the area lacks precipitation during the summer months. The aim of this research is to quantify water allocation, demand and need for the Eastern Martinborough Terrace Groundwater Zone. From this information suggestions to improve the allocation regime are made. The theoretical need for water by viticulture was determined using climate data from Martinborough. Actual water use by the vineyards was quantified by the frequent reading of their water meters during the 2004/05 and 2005/06 irrigation seasons. This actual water use data was supplemented by secondary data. During the irrigation season the computed evapotranspiration demand of grapes (554mm) is much greater than the dependable rainfall (186mm). Therefore, it is estimated that 369mm of water needs to be supplied by irrigation to enable grapes to grow without water stress. Allocating water on the basis of the estimated irrigation requirements (ED) would reduce current water allocations by 62%. Actual water use of the nine consent holders using groundwater over four irrigation seasons (2002 to 2006) was only 22% of their allocated volume. That is substantially less then their maximum allocated amount and less then the estimated ED values. Once vine density and the actual irrigated area were taken into account, the smaller vineyards were found to use larger amounts of water per hectare and per vine. Annual water use per hectare and per vine of the vineyards using bore water and those using town supply were not significantly different. Hence, if allocations were reduced to the ED values current use would not have to be reduced. As demand for water resources increases, revised water allocation guidelines, which are based on crop water requirements, soil hydraulic characteristics, and climatic conditions can help efficient and effective allocation and irrigation practices to be achieved. The results from this research could enhance the management of the region's scarce water resources.