CHAPTER 3
RIVER -GROUNDWATER
INTERACTION – AN OVERVIEW
CHAPTER 3
RIVER - GROUNDWATER INTERACTION – AN OVERVIEW
3.0. INTRODUCTION
The interconnection between groundwater and river systems remain poorly understood in
many catchments throughout the world, and yet are fundamental for effectively managing
water resources. In order to comprehend the importance of groundwater-river interactions
on water resource sustainability, knowledge of the basic principles guiding groundwater
and river water interactions are required. This chapter provides an overview of different
types of river water-groundwater interactions and the factors that govern groundwater-river
water interactions. The ecological significance of river-groundwater interactions and
human impacts on the interconnection between the river and groundwater are also
presented in this Chapter.
3.1. PHYSICAL INTERACTION
The physical interaction existing between the surface water and groundwater was
recognized early in hydrological history. Meinzer (1923) recognized that the rivers and
groundwater interact in three basic ways 1) The rivers gain water from the zone of
saturation where the upper surface of the river stands lower than the water table or the
piezometric surface of the aquifer 2) The rivers lose water to the zone of saturation where
the upper surface of the river stand higher than the water table or the piezometric surface
of the aquifer and 3) The rivers gain water in some reaches and lose water in other reaches,
or gain and lose in the same river reach at different times.
58
Meinzer (1923) used the term ‘effluent’ or ‘gaining’ to describe those streams or stretch of
streams which receive water from the zone of saturation (Fig. 3.1.a) and ‘influent’ or
‘losing’ to those streams which contributes water to the zone of saturation. He also
recognized that an influent stream can be separated from the underlying groundwater by a
zone of aeration and used the term ‘perched stream’ to describe those streams. In the more
recent literature (Winter et al., 1998; Osman and Bruen 2002; Sophocleous 2002; Fox and
Durnford 2003; Treese et al. 2009), the term ‘disconnected’ is used instead of ‘perched
stream’ to describe the losing streams separated from the underlying groundwater by an
zone of aeration (3.1.b) and the term ‘connected’ to describe those influent streams losing
water to the saturated zone (Fig. 3.1.c)
Disconnected streams occur where certain hydraulic conditions combine to restrict the
movement of water down from the river into the saturation zone of an aquifer (Brown bill
et al., 2011). Brownbill et al., (2011) highlighted that in a disconnected system, the surface
water body and the groundwater are disconnected only in the sense that the changes in
groundwater level do not affect the infiltration rate. However, the infiltration rates of the
disconnected systems are higher than those under the connected flow regime. The water
table in a disconnected stream may have a discernible mound below the stream if the rate
of recharge through the streambed and unsaturated zone is greater than the rate of lateral
ground-water flow away from the water-table mound (Winter et al., 1998).
Based on the belief that the exchange flux is zero or constant in disconnected systems,
Australian National Water Commission (2009) suggested that joint management of surface
water and groundwater is only required for connected regimes. Braaten and Gates (2003)
and Ivkovic (2009) documented that pumping under a disconnected stream is unlikely to
59
affect stream flow, giving further support to the notion that they can be managed
separately.
However, Fox and Durnford (2003) demonstrated that pumping adjacent to a disconnected
river will increase the length of river that is disconnected, and thus may affect the flow
rates of the river. According to Brunner et al., (2011), the infiltration rate of a disconnected
stream is dependent on the depth and width of the surface water body. Therefore, surface
water management will affect the groundwater system, independent of the state of
connection. This suggests that surface water and groundwater should be managed
conjunctively, irrespective of the connection status.
Winter et al., (1998) also documented yet another type of physical interaction termed
‘Bank storage’ (Fig.3.2). It is a particular type of interaction that occurs when a rapid rise
in river stage causes water to move from the river into the stream bank. This process is
usually associated with intense rainfall events, rapid snowmelt, or a release of water from a
dam. Most of the water in the stream bank returns to the river within a few days or weeks.
The loss of stream water to bank storage and return of this water to the stream in a period
of days or weeks tends to reduce flood peaks and later supplement stream flows. However,
when the rise in stream stage is sufficient to overtop the banks and flood large areas of the
land surface, widespread recharge to the water table takes place throughout the flooded
area. In this case, the time it takes for the recharged floodwater to return to the stream by
ground-water flow may be weeks, months, or years because the lengths of the groundwater
flow paths are much longer than those resulting from local bank storage. Depending on the
frequency, magnitude, and intensity of storms and on the related magnitude of increases in
stream stage, some streams and adjacent shallow aquifers will be in a continuous
60
readjustment from interactions related to bank storage and overbank flooding (Winter et
al., 1998).
Woessner (2000) identified two other conditions of physical interaction between the stream
and groundwater in the fluvial plains namely the 1) Parallel flow condition (Fig.3.3.a) and
2) flow through condition (Fig.3.3.b). According to Woessner (2000), a flow through
channel forms when the channel stage is less than groundwater head on one bank and
greater than the head at the opposite bank. The parallel flow channel occurs when the
channel stage and groundwater head are equal. Woessner (2000) also documented that
even though the parallel flow channel were previously termed as ‘zero exchange channel’,
on a smaller scale some limited exchange between the stream and its bed may occur.
In addition to the different ways of physical interaction distinguished on the basis of the
position of the river with respect to the groundwater, White (1993) distinguished three
cross sectional types of potential surface water groundwater interaction depending on the
volume of sediment deposition over which the stream flows and are 1) Surface water
flowing over an impermeable stratum without any surficial sub terranean exchange
process. 2) The channel consists of a more or less extended sediment layer over an
impermeable layer and is influenced only by advected surface water maintaining a
hyporheic zone 3) A large sediment deposition with a groundwater zone which is in
contact with the surface water mediated by a hyporheic zone.
61
(a)
(b)
(c)
Fig. 3.1.Schematic diagram representing the physical interaction between stream
and aquifer
(a) Effluent condition
(b) Influent condition (disconnected)
(c) Influent condition (connected) (Figures based on Winter et al., 1998;
Brunner et al., 2011)
62
Fig.3.2. Storage of excess water in neighboring river banks (Bank storage)
(after Winter et al., 1998)
(a)
(b)
Fig.3.3. Interaction of groundwater and surface water in fluvial plains
(a) Parallel flow condition (b) Flow through condition
(modified from Woessner, 2000)
63
3.2. CHEMICAL INTERACTION
Winter et al., (1998) recognized that even though groundwater and river water is having
distinct chemical characteristics, the river water and groundwater chemistry cannot be dealt
separately in areas where the river and the groundwater systems interact.
Groundwater generally contains more dissolved chemical elements than river water, and is
largely governed by the rocks through which it flows. The lower concentration of chemical
elements in river water under natural conditions is due to shorter duration of its contact
with the rocks over which it flows. Compared with the groundwater, the river water is
vulnerable to pollution processes and very quickly disperses the polluting element by
dilution, chemical or biological processes (Winter et al., 1998).
Triska et al. (1993) recognized that the exchange of water between the river and
groundwater at the hyporheic zone, a porous area connecting the stream water and
groundwater, is characterized by steep physico-chemical gradients. Research has shown
that significant chemical and biological processes occur at the hyporheic zone that affect
both surface water and groundwater chemistry. They also documented that variation in
local exchange of flows between the stream and groundwater at hyporheic zone produces
temporal shifting in the concentration gradients of dissolved oxygen, nitrate, and
ammonium in the subsurface, and that biological activity played a significant role in the
chemical transformations. Dahm et al. (1991) found that anaerobic carbon cycling was an
important process in the hyporheic zone of several mountain streams in New Mexico. Ford
and Nairnan (1989) identified that biologically related oxidative processes in the hyporheic
64
zone of a headwaters stream in Ontario were responsible for removing dissolved organic
carbon from inflowing groundwater.
The need to determine the extent of the chemical interaction has become widespread
because of the concern that the contaminated river water will contaminate shallow ground
water. Water chemistry and the related determinants of conductivity and total dissolved
load are therefore most likely to be diagnostic of groundwater dominance closest to the
point of entry to the channel, and will be characterized by relatively high concentrations of
aquifer geochemicals and stability of thermal regime (Smith, 1981).
3.3. FACTORS CONTROLLING RIVER- GROUNDWATER INTERACTION
Woessner et al., (2000) documented that the large-scale hydrologic exchange of
groundwater and surface water in a landscape is controlled by 1) the distribution and
magnitude of hydraulic conductivities, both within the channel and the associated fluvial
plain sediments (Woods, 1980; Holmes et al., 1994; Dahm et al., 1998; Winter et al., 1998)
(2) the relation of stream stage to the adjacent groundwater level and (3) the geometry and
position of the stream channel within the alluvial plain.
The direction of the exchange processes varies with hydraulic head, which in turn is
subject to influence by precipitation events and seasonal patterns, whereas water flow
depends on the contrasts in the hydraulic conductivities of soils and rocks at different parts
of the system, as well as the connectivity of the referential-flow-network (Faybishenko,
2000). Streams receive discharge from ground water where the hydraulic head of the
stream is lower than heads in the contiguous groundwater system. Conversely, streams lose
65
water to groundwater where the hydraulic head of the stream is higher than heads in the
contiguous groundwater system (Woessner 2000).
Natural catchment characteristics, such as geology, geomorphology, and soils also exert
important influence on river-groundwater interactions and serve as the template upon
which other important factors, such as land use, are superimposed (Farvolden, 1963;
Vivoni et al., 2008; Bloomfield et al., 2009).
In geologic formations that have high hydraulic conductivity, the gradients between the
stream and the groundwater system generally are not large, but the quantity of water
exchanged between the two water compartments can be substantial. Conversely, in
geologic formations that have low hydraulic conductivity, the gradients between the stream
and the groundwater system generally are large, but the quantity of water exchanged
between the two water compartments usually is small (Winter, 2007). He documented that
a stream originating in an extensive, highly permeable aquifer commonly will have a
relatively stable supply of water in its headwater area and large recession indexes. This is
because most precipitation infiltrates to recharge groundwater, which is then slowly
released to the stream, resulting in slowly diminishing stream flow between precipitation
events. He also noticed that the streams that originate in terrain having low permeability
generally have highly variable flow, resulting in unreliable supplies of water not only to
the headwater area, but also to downstream reaches. Such streams also tend to have small
recession indexes because most precipitation runs off rather than recharging ground water,
resulting in minimal release of ground water to the stream.
66
Within a context of consistent bedrock type, topography may exert substantial influence on
river-groundwater interaction particularly in areas of pronounced relief (McGuire et al.,
2005, Vivoni et al., 2008; Tetzlaff et al., 2009). Spatial variability in evapotranspiration
and precipitation may result from differences in topographic characteristics such as aspect
and elevation among watersheds (Kovner, 1956). Furthermore, topographic slope and
channel network development influence transmission rates of water (Vivoni et al., 2008;
Tetzlaff et al., 2009). Climatic and topographic variability additionally influence the
storage reservoir itself, through their effects on bedrock weathering and soil development.
The effects of land use change on baseflow timing and quantity may be mitigated or
amplified by basin topography, and there may be situations in which topographic
conditions exert such strong control on baseflow that drastic changes in land use are
required to induce detectible changes in low flows (Konrad and Booth, 2002).
Geomorphologic factors such as relief, slope, drainage density, and watershed shape,
which all influence the ability of water to flow to the channel network and out of the
watershed, significantly relate to stream low flow (Vogel and Kroll, 1992; Schumn et al.,
1995; Woods et al., 1997; Zecharias and Brutsaert, 1988; Sear et al., 1999).
On a smaller scale, water flow into and out of the streambed may be induced by pressure
variations on the streambed caused by geomorphological features such as pool-riffle
sequences, discontinuities in slope, or obstacles on the streambed (Thibodeaux and Boyle,
1987; Hutchinson and Webster, 1998). Also, a relocation of sediment grains on the
streambed may lead to a trapping of stream water in the sediment interstices and a release
of interstitial water to the stream (Elliott and Brooks, 1997).
67
3.4. ECOLOGICAL SIGNIFICANCE
Earlier studies on the ecological significance of hyporheic zone suggest that it is a region
of intensified biogeochemical activity (Grimm and Fisher 1984; Duff and Triska 1990;
Triska et al. 1993; Dahm et al. 1998) and valuable habitat for microorganisms, macro
invertibrate species and faunal populations (Creuze des Chatelliers and Reygrobellet 1990;
Brunke and Gonser, 1997; Gibert et al., 1997). The hyporheic zone also exerts a major
influence on thermal heterogeneity along the vertical, lateral, and longitudinal dimensions
of riverine landscapes (White et al., 1987; Brunke and Gonser, 1997).
The ecological importance of the hyporheic zone has also been recognized recently in
some parts of the world (Winter et al., 1998, Boulton, 2000). A primary reason for this
recognition is the realization of the significance of the surface water-groundwater in
maintaining water quality by biological filtration, supporting biodiversity and providing
buffers for floods. Physical, chemical, and biological conditions of the hyporheic zone
allow it to have a filtering effect on the water that travels through it (Vervier et al., 1992).
Review of the earlier studies shows that three filtration mechanisms can occur concurrently
or consecutively in most hyporheic zones. The most obvious is the physical mechanism,
where the sediment particles impede the flow of silt and particulate matter as water enters
and moves through the hyporheic zone (Vervier et al., 1992). Second, biological filtering
mechanism works in a manner similar to the trickle filters of sewage treatment plants
(Ward et al., 1998). Nutrients dissolved in either ground- or surface waters are taken up or
transformed by microbial biofilms coating the sediments (Vervier et al., 1992). The
efficiency of biological filtration is correlated to microbial activity (Marmonier, et al.,
1995). Subsurface invertebrates then feed upon the biofilms, and the nutrients enter the
68
food chain. A third filtering mechanism is provided primarily by the chemical conditions
prevalent within the hyporheic zone, which allow the precipitation of dissolved minerals
and metals (Wielinga et al., 1994, Harvey and Fuller 1998). The precipitate is then trapped
by the physical filter, where it may be degraded biologically (Gibert 1990). Therefore, by
increasing solute residence time and contact time with substrates in environments with
spatial gradients in dissolved oxygen and pH, the hyporheic zone influences the
biogeochemistry of stream ecosystems (Bencala 2000).
3.5. ANTHROPOGENIC IMPACTS ON RIVER- GROUNDWATER INTERACTION
The impact of river-groundwater interaction by human activities has been addressed by
several workers. The groundwater abstraction within the sub-surface drainage area affects
the level of phreatic surfaces and thereby the potential for groundwater re-emergence in
stream channels. The depletion of the groundwater table by the groundwater pumping near
the head of perennial river also leads to the induced recharge of the aquifer from the river
which in turn results in substantial environmental degradation of the river habitats, loss of
naturally sustained fisheries, reductions in the general amenity value of the river (Owen,
1991; Gustard et al., 1992, Bickerton et al., 1993, Clausen et al., 1994 and Fendekova and
Nemethy, 1994). Deforestation has also proved to affect the river-groundwater interaction.
The deforestation tends to decrease the recharge of groundwater and also the base flow of
streams (Winter et al., 1998; Bruijzeel, 2004). Irrigation and application of chemicals to
the cropland also effects the river-groundwater interaction.
Aside from direct manipulations, such as impoundments and water withdrawals from
streams and subsurface storage, human activity also influences river-groundwater
69
interaction by indirect mechanisms associated with changes in land use and land cover.
Conversion of native vegetation to other vegetative covers or artificial surfaces can
drastically alter evapotranspiration (Liu et al., 2008). Land use change also may alter
surface permeability characteristics, through soil compaction associated with human land
use and addition of impervious surface to watersheds (Rose and Peters, 2001; Gregory et
al., 2006) which in turn affects river- groundwater interaction.
The ecological integrity of groundwater and fluvial systems is also threatened by human
activities. The down welling river water is naturally filtered during its passage through the
hyporheic zone (Gibert 1990). However, in the case of river water contaminated with
persistent organic compounds, such as chloroform and inorganic pollutants, the natural
filtering taking place in the hyporheic zone has been observed to be inadequate and thereby
contaminating extensive areas of groundwater (Schwarzenbach et al. 1983; Santschi et al.
1987; Whittemore, et al. 2000).
Increased sewage disposal to rivers often leads to clogging by promoting the development
of dense algal mats, or by causing sedimentation of an organic layer on the river bed. The
clogging exerts severe impacts on the renewal of groundwater through river bank filtration
and the development and colonization of invertebrates and fish (Brunke and Gonser,
1997).
70