Evidence for perched aquifer recharge from the Wairau River

Abstract

The Wairau River is the main source of the recharge for the highly productive Wairau Aquifer. Concurrent flow gaugings measured at low flow indicate that a 7 cumec loss occurs over a 10 km length of the river between Rock Ferry and Wratts Road. Approximately half of this loss occurs over a 4 km reach upstream of the SH6 bridge, although the nature of this loss is not well understood. Theoretically, the relationship between a river and groundwater can be considered as being hydraulically connected (gaining or losing), disconnected (perched), or transitional (Brunner et al. 2011). A disconnected river is distinguished from a hydraulically connected river by the presence of a partially saturated zone between the river bed and the aquifer. The aim of this study is to improve our conceptual understanding of how the flow losses occur, and to test a new hypothesis that much of the river may be perched above the aquifer.