The impact of urban groundwater upon surface water - eTheses ...

REVIEW
features of groundwater/surface water interactions in five general types of terrain:
mountainous, riverine, coastal, glacial and dune, and karst.
2.1.2 The groundwater/surface water interface
Interactions between groundwater and surface water occur across a transition zone within the
beds of lakes, rivers, or seas (Henry, 2002). In the case of a river, a ‘hyporheic zone’ develops
where mixing between groundwater and surface water occurs (Biksey et al., 2001). This is an
ecological term that refers to an ecotone where both groundwater and surface water are
present within a stream bed along with a specific set of biota (Conant, 2000). The flow of
river water over variations in the surface of the riverbed may cause localised variations in
pressure that induce flow through the riverbed, causing groundwater/surface water mixing
(Figure 2.2). The extent of this mixing zone may range from centimetres to hundreds of
meters if surface water flows through the flood plain sediments are considered (Woessner,
2000, Wroblicky et al., 1998). The zone is heterogeneous, dynamic and dependent on the
surface water and groundwater head distribution, river flow, riverbed hydrogeology and
bedform (Fraser et al., 1998).
Large gradients in concentration and environmental conditions often exist across the transition
zone (Boulton et al., 1998). These affect the spatial and temporal distribution of aerobic and
anaerobic microbial processes as well as the chemical form and concentration of nutrients,
trace metals and contaminants. Microbial and biological activity may lead to biodegradation
of organic contaminants, reducing levels by several orders of magnitude within this zone
(Conant, 2000). The hyporheic zone is important ecologically because it may store nutrients
(and potentially contaminants), transform compounds biologically and chemically, and
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