Complex groundwater flow paths in a small Taupo hillslope

Abstract

The Waihora research site is a small (0.7 ha) pastoral hillslope that drains into the headwaters of the Tutaeuaua Stream on the northern shores of Lake Taupo. To understand how the strong vertical redox stratification that has been observed at several well sites (Stenger, 2011) affect the groundwater system’s assimilative capacity for nitrate it is essential to elucidate the 3D groundwater flow paths. Early modelling studies assumed a sloping water table with linear flow following the land surface topography downhill towards the wetland/stream (Woodward et al., 2009). However, recent tracer studies in several wells have found the principal direction of tracer movement to be quite unexpected, with diagonal transport across the hillslope.