vidon2004

Landscape controls on the hydrology of stream riparian zones
Philippe G.F. Vidon*, Alan R. Hill
Department of Geography, York University, 4700 Keele Street, Toronto, Ont. Canada M3J 1P3
Received 10 December 2002; revised 15 December 2003; accepted 8 January 2004
Abstract
Increased knowledge of hydrology is essential to an understanding of the water quality function of stream riparian zones.
We examined the effect of upland surficial aquifer size, topography and riparian sediment lithology on the subsurface hydrology
of eight riparian sites on glacial till and outwash landscapes in southern Ontario, Canada. Riparian sites had a permanent
subsurface hydrologic connection to the adjacent upland in landscapes where upland permeable sediment depths were 2 –15 m.
In contrast, a hydrologic connection was absent in summer and autumn at riparian sites with ,2 m of permeable sediments
overlying an aquitard. Riparian zones linked to thicker and more extensive upland aquifers had large relatively constant
groundwater inputs that maintained a stable riparian water table. Sites that were seasonally disconnected from uplands had large
annual water table drawdowns that dried out the riparian area unless the water table was sustained by the stream. Peats with low
hydraulic conductivity and a thinning of highly permeable sediment layers occurred in some riparian zones producing upward
groundwater flow that created seeps and surface rivulets. Subsurface flow data indicated a consistent downslope flow path in
areas of the riparian zone where the slope gradient was .5%. Where the riparian zone was level to gently sloping (,5%),
subsurface flow directions were influenced by stream water level. Riparian subsurface flows at these sites often shifted from a
hillslope to stream pattern to a down valley and even a stream to hillslope direction during summers. A conceptual framework
of riparian hydrologic types based on hydrogeologic setting is developed to generalize the hydrology of riparian zones at the
landscape scale.
q2004 Elsevier B.V. All rights reserved.
Keywords: Riparian zone; Groundwater hydrology; Soil lithology; Topography; Water table; Hydrogeology
1. Introduction
During the past 20 years, the fate of agricultural
contaminants in stream riparian zones has been
extensively studied (Peterjohn and Correll, 1984;
Lowrance, 1992; Haycock and Pinay, 1993; Jordan
et al., 1993; Gilliam, 1994; Hill, 1996). These studies
have shown that in order to understand and predict the
fate of contaminants in riparian zones, we first need to
understand riparian zone hydrology. The hydrology of
stream riparian zones is strongly influenced by
the landscape hydrogeologic setting (Winter 1992;
Brinson, 1993; Lowrance et al., 1997; Baker et al.,
2001). This encompasses the location of the riparian
zone in the catchment in relation to surface and
groundwater flows as well as the geological charac-
teristics such as topography, stratigraphy and hydrau-
lic properties of sediments that control hydrology.
Journal of Hydrology 292 (2004) 210–228
www.elsevier.com/locate/jhydrol
0022-1694/$ - see front matter q2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jhydrol.2004.01.005
*Corresponding author. Tel.: þ1-416-7362100x88620; fax: þ1-
416-736-5988.
E-mail address: [email protected] (P.G.F. Vidon).

The size of upland aquifers controls the magnitude
and seasonality of subsurface flow and elements
inputs to riparian areas (Hill, 2000). The threshold
between riparian zones that are seasonally and
permanently connected to uplands may be the result
of small differences in average depth of upland
storage in some landscapes (Devito et al., 1996).
The size and seasonality of upland hydrologic
connection also influences riparian zone water table
fluctuations and the extent of surface saturation with
consequent effects on soil microbial redox reactions
and water chemistry (Roulet, 1990; Hill and Devito,
1996; Devito and Hill, 1997).
The depth and permeability of saturated sediments
overlying a confining layer in riparian zones can
influence riparian hydrologic flowpaths, water
residence times and renewal rates (Schnabel et al.,
1994; Correll et al., 1997). A confining layer at a
shallow depth increases the interaction of subsurface
flow with vegetation root systems and surface soils
and enhances the potential of the riparian zone for
nitrate removal (Hill, 1996). In riparian zones where a
confining layer is absent, groundwater flow at depth
may bypass the riparian zone and discharge directly to
the stream channel (Bohlke and Denver, 1995).
Gravel layers in the soil profile beneath less
permeable sediments can be zones of preferential
subsurface flow across the riparian zone (Burt et al.,
1999). Conversely, sediments with low hydraulic
conductivities (e.g. peats, clays in oxbow channels)
can divert water upward or downward altering
subsurface flowpaths in the riparian zone (Hill,
1990; Brusch and Nilsson, 1993; Burt, 1997).
Research also indicates that topography affects the
hydrological functioning of riparian zones (Devito
et al., 2000a). The slope gradient, especially at the
riparian zone-upland margin, influences the hydraulic
gradient and the volume and velocity of water
entering the riparian zone. A concave riparian profile
typically favours interaction between subsurface
water and superficial soil horizons where denitrifica-
tion and root uptake are likely to occur, whereas
convex topography favours deeper water tables and
subsurface flowpaths. Burt et al. (2002) have shown
that when the riparian zone is flat, the stream water
level acts as a fixed point around which the water table
fluctuates, whereas when the slope directly borders
the river, the effect of stream water level on water
table dynamics in the riparian zone is negligible.
Although the importance of landscape hydrogeo-
logic setting is recognized, researchers have not
studied whether characteristics such as upland aquifer
thickness, topography and riparian lithology can be
used together to understand and predict the
hydrological functioning of riparian zones. In order
to develop a better understanding of how these
landscape characteristics control riparian zone hydrol-
ogy, we need to conduct a comparative analysis of
riparian zones in landscapes that differ in hydro-
geologic characteristics. With the exception of a
recent study of water table fluctuations in European
riparian zones by Burt et al. (2002), researchers have
examined single riparian sites.
In this study, we examine the effect of upland
aquifer size, topography and riparian sediment
lithology on the subsurface hydrology of eight
riparian sites located on glacial till and outwash
landscapes in southern Ontario, Canada. The riparian
zones were selected to provide a range of sediment
permeability, slope gradients and upland aquifer
depths. The comparison of the hydrology of
these riparian zones focuses on two main questions:
(1) what is the influence of increasing upland
aquifer size on the magnitude and duration of
upland–riparian hydrologic linkages? (2) how do
hillslope discharge, topography and riparian sediment
lithology interact to influence water table fluctuations,
riparian groundwater flow patterns and fluxes entering
the riparian zones? Our understanding of riparian
hydrology is used in the concluding section of the
paper to develop a conceptual framework of different
classes of riparian groundwater dynamics based on
hydrogeologic setting to generalize about riparian
zone hydrology at the landscape scale.
2. Study sites
The study sites are located in agricultural
catchments in southern Ontario near Toronto
(Fig. 1). The annual precipitation in the area is
800–900 mm/yr with 120 –240 mm falling as snow
between December and April (Singer et al., 1997).
The mean annual temperature is 7.2 8C with a mean
January temperature of 26.7 8C and a mean July
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228 211

temperature of 20.5 8C. There are frequent mid-winter
thaws but spring snowmelt in the March–April period
is the main runoff period. Lowest stream discharge
occurs in July–August when evapotranspiration is
highest. Considerable weather variations occurred
during the 2000–2002 study period. Rainfall in May
and June 2000 was more than two times higher than
the 30 year normal for these months. Snowfall in the
winter of 2000–2001 was 34% above the long-term
average and the snow cover duration of 104 days was
the longest ever recorded. Rainfall from June to
August 2001 was only 45% of normal for this period
and represents the driest summer recorded in the past
50 years. Winter precipitation in 2001–2002 was 22%
below normal and the mean temperature of 4.5 8C
above normal was the warmest recorded in the past
140 years in southern Ontario. Summer 2002 ranked
as the eighth driest summer of last 50 years with
15.4% less precipitation than normal.
Two of the riparian sites are located to the west of
the Niagara escarpment on the Eramosa and Speed
rivers, 4th and 2nd order streams respectively, that
flow in former glacial meltwater channels, bordered
by extensive gravel and cobble terraces (Fig. 1). The
Road 10 and Boyne river riparian sites are located on
the Alliston sand plain that forms an unconfined 9–
12 m thick aquifer underlain by a thick sequence of
silts and clays (Devito et al., 2000b). The Boyne River
is a fourth order stream draining into the Nottawasaga
River and the Road 10 site is adjacent to a first order
tributary of the Nottawasaga River. The other riparian
sites are located on glacial till (Maskinonge, Ganat-
sekiagon and Highway 27) or outwash silt (Vivian).
The Highway 27 site is located along an intermittent
first order tributary of the Nottawasaga River.
The Maskinonge and Vivian Creek sites border
second order streams in catchments that drain into
Lake Simcoe. The Ganatsekiagon site is on an
intermittent first order tributary of Duffin’s Creek,
that flows into Lake Ontario.
The Boyne and Eramosa riparian zones are forest
sites dominated mainly by white cedar
(Thuja occidentalis L.). The other riparian sites are
covered with an herbaceous plant community with
scattered shrubs and deciduous trees. All riparian sites
are located downslope from fertilized cropland.
3. Methods
An extensive network of wells and piezometer
nests was installed extending from the field-riparian
zone margin to the stream at each riparian site.
For most sites, two separate transects of wells and
piezometers were installed 20–80 m apart in order to
assess site variability and subsurface flow paths at the
riparian zone scale (Fig. 2). Each piezometer nest
consisted of piezometers constructed from 1.27 cm ID
PVC pipe with 20 cm long slotted ends installed at
depth between 0.5 and 5.5 m depending on sites.
Groundwater wells (ID 5.1 cm ABS pipe 1.5– 2 m
long) perforated throughout their length were installed
at most piezometer nests and at various other locations
within the riparian sites. When necessary, a bentonite
clay seal was used to prevent contamination by
surface water.
Riparian zone lithology was first determined from
visual inspection of cores collected by hand augering
during piezometer and well installation. Soil samples
Fig. 1. Location of study sites in relation to geomorphic regions.
(1) Glacial till, (2) sand plain, (3) clay plain, (4) spillways and
gravel terraces, (5) Kame moraine. The dashed line indicates the
Niagara escarpment. Letters identify riparian sites. E, Eramosa; B,
Boyne; R, Road 10; S, Speed; M, Maskinonge; G, Ganatsekiagon;
H, Highway 27; V, Vivian.
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228212

were later collected and the different fractions of sand
and the clay-silt fraction were separated by sieving
and then weighted to determine the soil texture.
Saturated hydraulic conductivities were measured in
piezometers and wells using the Hvorslev water
recovery method (Freeze and Cherry, 1979).
For each site, the confining layer defined as a horizon
with a low hydraulic conductivity (#10
26
cm s
21
)
restricting subsurface flow in the riparian zone
and adjacent upland, was determined using a combi-
nation of soil survey and hydraulic conductivity
distribution data. When the confining layer was
deeper than the deepest point surveyed in the field
(3– 5 m depending on sites), geology and water
resource reports were used to estimate the confining
layer depth (Deane, 1950; Sibul and Choo-Ying,
1971). Topographic maps were used to estimate the
length of the upslope contributing area to each
Fig. 2. Topography of the riparian zones showing the location of piezometer nests. The dashed line indicates the field edge. (a) Eramosa;
(b) Boyne; (c) Road 10; (d) Speed; (e) Maskinonge; (f) Ganatsekiagon; (g) Highway 27; (h) Vivian. Contour elevations are in meters above an
arbitrary datum.
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228 213

riparian zone. Both the depth of permeable sediments
and the slope length in the upland were used as
indicators of upland aquifer size.
Groundwater level and hydraulic heads were
measured at least once a month beginning in March
2000 (Maskinonge, Ganatsekiagon, and Vivian sites),
in May 2000 (Highway 27 site), in June 2000 (Boyne
and Eramosa sites) and July 2000 (Road 10 and
Speed sites) until September 2002 for all sites.
The topography of the riparian zone and the adjacent
upland was determined using a total station. Equipo-
tential lines for the vertical cross-sections were
determined by triangulation by hand. The anisotropy
ðKh=KvÞof sand and gravel is often approximately 10
(Barwell and Lee, 1981) and would be higher for finer
texture sediments and range from 0 to 1000 for peats
(Chason and Siegel, 1986). The vertical exaggerations
on the riparian cross-sections (Figs. 3 and 6) vary
between 3 and 14 depending on sites and are
therefore, approximately equivalent to the
transformed isotopic section for an overall anisotropy
of 10–100 (Freeze and Cherry, 1979). Topographical
and water table contour maps for plan view illus-
trations of riparian sites were determined using Surfer
7 mapping software (Golden Software, 1999). Water
fluxes entering each riparian zone at the perimeter
were calculated using Darcy’s Law:
Q¼Ksðdh=dlÞAð1Þ
where Qis the water flux (l day
21
); Ksis the saturated
hydraulic conductivity (m day
21
) and dh=dlis the
hydraulic gradient comprising the change in hydraulic
head ðhÞbetween two adjacent equipotential lines with
distance ðlÞalong the direction of flow. Variations of
Ksin relation to lithology in piezometer nests adjacent
to the riparian perimeter were used to calculate fluxes
for each layer of the soil profile. The hydraulic heads
used to calculate the hydraulic gradient were based on
the initial several nests along transects near the
riparian perimeter. Temporary shallow piezometers
were also installed in the field at the Maskinonge,
Vivian, Ganatsekiagon and Highway 27 sites to better
estimate the hydraulic gradient. For the riparian zones
where equipotentials were approximately vertical, the
groundwater flow was calculated for each soil layer
extending from the water table for that date to the top
of the confining layer. The area Aof each of these
layers parallel to equipotential lines was estimated as
the product of the vertical depth times a width of 1 m.
Fluxes for each of the layers were added to provide an
estimate of the groundwater flux entering each riparian
zone. Subsurface water flows with an upward
component at the riparian perimeter of the Eramosa
and Maskinonge sites. For these sites, groundwater
flow was calculated as the sum of fluxes for several
flow cells of area Aon a section of the riparian zone
parallel to equipotential lines using piezometers from
adjacent nests extending downslope in the zone of
upward flow.
4. Results
4.1. Site hydrogeomorphic characteristics
The key hydrogeomorphic features of the eight
riparian sites are summarized in Table 1. The range of
hydraulic conductivity expressed as an order of
magnitude using Ksvalues from several piezometers
is indicated for the main lithologic units in each of the
riparian sites. The Eramosa site is a 220 m wide
riparian zone with a concave topography connected to
an approximately 750 m long upslope aquifer.
The upland–riparian zone boundary has a steep
slope gradient of 24% that declines rapidly to ,2%
towards the river (Fig. 2a). The upland is underlain by
coarse gravel and cobble sediments which are 9– 10 m
thick at the field edge. At the slope base, 2.5 m of
loamy-sand and coarse gravel (Ks¼1024cm s
21
)
thins rapidly downslope where a 1 m thick humic peat
deposit with Ksvalues of 10
25
cm s
21
extends
towards the river (Fig. 3a). Beneath the gravel and
peat deposits, a clay till forms a confining layer
(Ks¼1026cm s
21
) throughout the riparian zone.
The Boyne river site is located in a valley incised
approximately 10–12 m below the adjacent upland
sand plain surface and connected to the Lake
Algonquin sand aquifer. The length of the aquifer
recharging the Boyne site is approximately 1400 m.
The topography at this site is concave with a very
steep slope at the field –riparian zone boundary of
38.6% and a flat, 180 m wide riparian zone extending
to the river channel which is incised 3 m below the
floodplain (Fig. 2b). The lithology at this site consists
of humic peat deposits (Ks¼1026=1025cm s
21
)
which thicken from 0.5 m at the valley side to 3 m
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228214