Perched and leaky layers in complex surface-subsurface flow environments: the Kawerau shallow groundwater aquifer, New Zealand

Headnote

Abstract

Perched and leaky geological layers can play an important role in hydrological systems by redirecting land surface recharge and reducing total recharge volume to regional aquifers. The extent of continuity and permeability of perched layers can be key physical parameters in surface and subsurface flow connection to regional groundwater systems. A semi-permeable perched layer with discontinuities, heterogeneity, fractures and faults will inevitably increase the spatial complexity of local recharge in an otherwise simple system. Relatively little is known about how perched and leaky layers might control linkages between surface flow, shallow groundwater flow, and regional groundwater. We describe one such system in the Kawerau shallow groundwater aquifer (New Zealand), where a thin, semi-permeable and fractured layer alternates between leaky and perching behaviour. A numerical groundwater model indicates the perching layer plays a critical role in controlling the volume and spatial pattern of water exchange between surface water and local and regional groundwater systems.

Keywords

perched and leaky, shallow aquifer, surface water groundwater interaction, Kawerau, Rotoiti, Matahina, semi-permeable

(ProQuest: ... denotes formulae omitted.)

Introduction

Perched water tables have long been classified as aquifers (Fetter and Fetter, 2001; Freeze and Cherry, 1979). In addition, surface-subsurface flow interaction has been the subject of many recent research projects (Bayani Cardenas, 2008; Cloke et al., 2006; Ebel et al., 2007; Gauthier et al., 2009; Lemieux et al., 2008; Li and Duffy, 2011; Maxwell and Kollet, 2008; Meyerhoff and Maxwell, 2011; Shokri and Bardsley, 2016; Smerdon et al., 2008). However, the importance of perched aquifers on surface and subsurface flow integration has seldom been investigated in detail.

Perched aquifers can effectively redirect land surface recharge along horizontal impermeable layers to springs, streams, wetlands, and lakes (Amit et al., 2002; Driese et al., 2001; O'Driscoll and Parizek, 2003; Rabbo, 2000; Von der Heyden and New, 2003), consequently decreasing the volume of vertical recharge to deeper aquifers (Bagtzoglou et al., 2000). Furthermore, the extent of continuity and permeability of perched layers plays an important role in connections between surface-subsurface flow and the regional groundwater system. Where perched layers are fully continuous and impermeable, surface and subsurface flow becomes isolated from the regional groundwater system (Golden etal., 2014; Pirkle and Brooks, 1959). However, a semi-permeable perched layer with internal discontinuity, fractures, and...