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Journal of Hydrology 292 (2004) 210–228
www.elsevier.com/locate/jhydrol
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.
q 2004 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
* Corresponding author. Tel.: þ1-416-7362100x88620; fax: þ 1416-736-5988.
E-mail address: [email protected] (P.G.F. Vidon).
0022-1694/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jhydrol.2004.01.005
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 characteristics such as topography, stratigraphy and hydraulic properties of sediments that control hydrology.
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
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 denitrification 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
211
the river, the effect of stream water level on water
table dynamics in the riparian zone is negligible.
Although the importance of landscape hydrogeologic 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 hydrology, we need to conduct a comparative analysis of
riparian zones in landscapes that differ in hydrogeologic 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 2 6.7 8C and a mean July
212
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
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.
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, Ganatsekiagon 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
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
213
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.
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 (# 1026 cm s21)
restricting subsurface flow in the riparian zone
and adjacent upland, was determined using a combination 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
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P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
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. Equipotential lines for the vertical cross-sections were
determined by triangulation by hand. The anisotropy
ðKh =Kv Þ of 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 illustrations 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:
Q ¼ Ks ðdh=dlÞA
ð1Þ
where Q is the water flux (l day21); Ks is the saturated
hydraulic conductivity (m day21) and dh=dl is the
hydraulic gradient comprising the change in hydraulic
head ðhÞ between two adjacent equipotential lines with
distance ðlÞ along the direction of flow. Variations of
Ks in 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 A of 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 A on 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 Ks values 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 (Ks ¼ 1024 cm s21)
thins rapidly downslope where a 1 m thick humic peat
deposit with Ks values of 1025 cm s21 extends
towards the river (Fig. 3a). Beneath the gravel and
peat deposits, a clay till forms a confining layer
(Ks ¼ 1026 cm s21) 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 (Ks ¼ 1026 =1025 cm s21)
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) 210–228
215
Fig. 3. Vertical cross section along the main transect showing riparian lithology. Dots represent piezometer slot zones. (a) Eramosa site;
(b) Boyne; (c) Road 10; (d) Speed river site; (e) Maskinonge; (f) Ganatsekiagon; (g) Highway 27; (h) Vivian (SL, sandy loam; LS, loamy sand;
FS, fine sand; S, sand; CS, coarse sand; G, gravel).
within the riparian area (Fig. 3b). The peats overlie
fine sands and a layer of coarse sand and fine gravel
with Ks values of 1023 cm s21. The regional clay
underlies the sands and gravels at approximately 6 m
near the valley side and 2 m below the river channel.
The Road 10 site is a 30 m wide riparian zone with
a mainly flat topography located on the Alliston sand
plain. There is an initial drop of approximately 1 m in
elevation at the field edge and then a relatively flat
riparian area leading to the stream. Although this site
is underlain by the 9 – 12 m thick unconfined
Algonquin sand aquifer, the stream bottom is only
3 m below the sand plain surface. Subsurface flow
path data (Section 4.5) suggest that groundwater
deeper than 5 m below the riparian area (6 m below
the sand plain surface) does not significantly interact
with the stream and riparian zone. The soils at the
Road 10 site are mainly sands (Ks ¼ 1023 cm s21),
216
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
Table 1
Site physical characteristics
Topography
type
Eramosa River
(fourth order) SGTa
Boyne River
(fourth order) SP
Road 10 (first order) SP
Riparian
width (m)
Upland permeable
sediment depth (m)
220
9–10
204
30
Speed river (second
order) SGT
Maskinonge (second
order) T
Ganatsekiagon (first
order) T
66
Riparian
vegetation
Slope
gradient (%)
750
SW
15
1400
SW
6
200
H
200
H þ HW
23.6/ , 2,b
overall: 5.7
38.6/ , 2,
overall: 5.2
18.0/ , 1,
overall: 5.2
5.0/ , 1,
overall: 2.9
13.1/ , 1,
overall: 5.1
Overall: 13.2
2.8–3
Upland slope
length (m)
45
2
230
H þ HW
25
1.4
300
H
Highway 27 (first order) T
33
1.2
400
H þ HW
Vivian (second order) KM
37
0.9
250
H
20.1/1–2,
overall: 11.3
Overall: 1
HW, hardwood; SW, softwood; H, herbaceous.
The initials indicate the landform information. SGT, spillways and gravel terraces; SP, sand plain; T, till; KM, Kame moraine.
b
The first value indicates the gradient of the steepest section of the riparian zone at the upland/riparian boundary and the second indicates the
slope gradient of the remaining part of the riparian zone.
a
however, a loamy-sand layer with lower Ks values of
1025 cm s21 extends across the riparian zone at
depths 1 –3 m (Fig. 3c).
The terrain at Speed River is gently sloping and the
riparian zone and adjacent upland are underlain by a
3 m thick coarse gravel and cobble deposit with
hydraulic conductivities of 1024 cm s21 (Fig. 3d).
Beneath this layer, substrates with low Ks values of
1026 cm s21 form a confining layer for groundwater
flow. The lengths of upslope areas contributing
subsurface flow to Road 10 and Speed sites were
approximately 200 m.
The Maskinonge and Highway 27 riparian zones
have a concave topography with moderate to steep
slopes at the upland perimeter and level terrain near the
streams. Soils at the riparian perimeter and in the
adjacent upland at the Maskinonge site are loamysands that extend to a depth of 2 m and have Ks values
of 1024 cm s21. At greater depths, a dense stony silty
sand till (Ks ¼ 1027 cm s21) restricts subsurface flow.
Within the riparian zone, peat increases in thickness
from 0.4 m, near the perimeter, to a maximum of 2.7 m,
15 m from the river (Fig. 3e). Hydraulic conductivities
decline from 10 25 cm s 21 in the upper 50 to
10 26 cm s 21 at greater depths in the peat.
The Highway 27 site is developed on a dense sandy
loam till (Ks ¼ 1027 cm s21) that forms a confining
layer at a depth of 1.2 m at the field –riparian zone
margin. The soil above the confining layer is a sandy
loam on the slope changing to a loamy-sand
(Ks ¼ 1024 cm s21) near the stream. The lengths of
the contributing areas at the Maskinonge and Highway
27 sites were 230 and 400 m, respectively.
The Ganatsekiagon site receives runoff from a
300 m long upland. The riparian zone is 27 m wide
with a slightly convex topography and an average slope
of 13.2% that extends to the stream (Fig. 3f). The soil
profile is composed of a coarse sandy ablation till with
thin layers of gravel (Ks ¼ 1023 cm s21) between 50
and 100 cm. A dense sandy loam basal till with Ks
values of 1026 cm s21 restricts subsurface flow to
depths , 1.4 m in both the riparian zone and the
adjacent upland. The topography at the Vivian site is
flat (slope 1%) and outwash silt with Ks values of
1026 – 1027 cm s21 forms an aquitard that varies in
depth from 0.9 m at the riparian perimeter to
1.4– 1.5 m near the stream (Fig. 3h). The sediment
profile above this confining layer in the riparian area is
a sandy-loam (Ks ¼ 1025 cm s21) between 0 and
50 cm and a loamy-sand mixed with gravel between
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
50 and 90 cm (Ks ¼ 1024 cm s21). The length of the
upland area recharging the Vivian site was estimated to
be approximately 250 m.
4.2. Upland –riparian zone linkage
Fig. 4 shows the duration of the upland – riparian
zone subsurface hydrologic connection for the eight
riparian sites. The period where the riparian zone is
hydrologically connected to its upland aquifer is
defined as the time interval during which the water
table at the field – riparian zone boundary is above the
confining layer.
Five of the riparian sites had a permanent
hydrologic connection to the adjacent upland throughout the study. Depths of permeable upland sediments
which maintain this linkage ranged from 2 to 15 m.
In contrast, permeable sediment depths overlying an
aquitard were , 2 m in upland areas at the Highway
27, Ganatsekiagon and Vivian riparian sites where an
intermittent hydrological linkage was found (Fig. 4).
Upland slope lengths at these three riparian sites were
similar to the slope lengths at Speed and Maskinonge
sites that maintained a permanent hydrologic link.
The duration of the upland –riparian zone connection
and the dates of disconnection from the upland aquifer
varied among sites and from year to year.
217
At Ganatsekiagon, the upland – riparian zone connection ceased between late July 2000 and late January
2001. In 2001, flow ceased in late July until late
October. In 2002, the riparian zone remained
connected to the upland aquifer until mid-June.
The Highway 27 riparian zone was disconnected
from the upland aquifer from mid-July 2000 to
February 2001. In 2001, flow ceased between late
June and late October. In 2002, the riparian zone
became disconnected from its upland aquifer in early
July. At Vivian creek, the upland –riparian zone
linkage ceased in early August 2000, re-connected
briefly in September, and ceased again until February
2001. In 2001, there was no hydrologic linkage
between late June and late December and in 2002, the
riparian zone remained connected to its upland aquifer
until mid-July.
4.3. Water inputs
Large, relatively stable water inputs were observed
at the Eramosa and Boyne sites which were connected
to large upland aquifers (Table 2). In contrast, at the
Speed and Maskinonge sites, where upland permeable
sediment depths were 2– 3 m, fluxes were lower and
more seasonally variable. Nevertheless, small inputs
during periods of maximum water table drawdown
Fig. 4. Duration of the upland– riparian zone hydrological connection versus upland permeable sediment depth for the riparian zones.
218
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
Table 2
Subsurface water inputs (L day21 m21 width) from adjacent upland
to the riparian zones during high, medium and low water table
periods
Eramosa
Boyne
Road 10
Speed
Maskinonge
Ganatsekiagon
Highway 27
Vivian
High water
table
Medium water
table
Low water
table
394
320
44
66
72
244
30
0.7
355
300
0
22
26
1.8
9
0.4
300
280
0
14
4
0
0
0
maintained a continuous upland riparian zone linkage.
Significant hillslope discharge at the Road 10 site only
occurred during high water table conditions in the
spring. The change in elevation between the field and
the riparian zone was only 1 m at this site and water
inputs from the field ceased as the hydraulic gradient
decreased to almost zero. Fluxes were very variable at
Ganatsekiagon, Highway 27 and Vivian sites,
where hillslope discharge ceased during summer and
early autumn.
Groundwater inputs to the riparian zones during
periods of intermediate water table elevation had a
significant positive correlation with upland permeable
sediment depth ðr 2 ¼ 0:77; p , 0:05Þ and upland
slope length ðr 2 ¼ 0:72; p , 0:05Þ: However, these
relationships were not significant for high water table
periods because of the large subsurface input at the
Ganatsekiagon site where the upland aquifer was
small. When this site was excluded from the analysis,
we found a significant positive correlation
between water input during high water table
conditions and both upland permeable sediment
depth ðr 2 ¼ 0:75; p , 0:05Þ and upland slope length
ðr 2 ¼ 0:65; p , 0:05Þ:
4.4. Water table fluctuations
Seasonal variations in riparian water table
fluctuations at the eight sites are shown in Fig. 5.
These water table elevations were averaged for wells
located between the perimeter and the mid-point of
each riparian area where the water table was influenced
Fig. 5. Mean water table depth below ground surface (BGS) for
(a) sites with a continuous upland–riparian hydrologic connection
and (b) sites with a discontinuous upland–riparian hydrologic
connection.
mainly by upland subsurface inputs rather than inflow
from the stream. The water table remained close to the
ground surface at the Eramosa and Boyne sites.
The minimum mean water table height at the Eramosa
site was only 13 cm. At the Boyne site, the minimum
elevations of 47 and 50 cm occurred for a few weeks in
the dry summers of 2001 and 2002, respectively.
Annual water table fluctuations at the Road 10, Speed
and Maskinonge sites were larger than at the Boyne
and Eramosa sites. Although the water table was often
near the surface at these sites in spring, it dropped to
112, 134 and 126 cm in the summers of 2000– 2002 at
the Road 10 site. Minimum mean water table heights at
the Speed and Maskinonge sites in the dry summer of
2001 were 137 and 62 cm, respectively (Fig. 5).
The largest water table drawdowns were recorded for
the Ganatsekiagon, Highway 27 and Vivian sites,
which were hydrologically disconnected from the
adjacent upland in summer and autumn. The water
table declined below the confining layer at these sites in
2001 and 2002 to minimum elevations of . 150 cm
(Ganatsekiagon), . 200 cm (Highway 27) and
. 250 cm (Vivian).
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
4.5. Groundwater flow paths in the vertical plane
Groundwater flow patterns in a vertical cross-section
along the main piezometer transect for each site are
shown for two dates representative of periods of high
and low water table, respectively (Fig. 6). Except for
219
the Eramosa site where there was only one piezometer
transect, the second transect, which had fewer piezometer nests, showed groundwater flow patterns which
were similar to the main transect at each site.
At the Eramosa site, equipotential lines indicate
up-welling at the slope bottom between nests 105
Fig. 6. Hydraulic head contours (cm) for a vertical cross section along the main transect of each riparian zone for one date in spring 2001 (high
water table) and one date in summer 2001 (low water table). (a) Eramosa; (b) Boyne; (c) Road 10; (d) Speed; (e) Maskinonge; (f) Ganatsekiagon;
(g) Highway 27; (h) Vivian. Dashed line represents location of the water table. The small flow arrows only represent the general direction of
flow because the vertical exaggeration affects the angle with which the flow system crosses the equipotential lines.
220
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
Fig. 6 (continued )
and 103. Groundwater discharged to the surface in
seeps creating surface rivulets, which flowed across
the riparian zone from nests 105 to 102A in summer
and beyond nest 100 in the spring (Fig. 6a).
Equipotential lines also indicate that near surface
water recharged to deeper sediments, downslope from
nest 102A, especially during the driest months of the
year. The flow net indicates predominantly horizontal
flow from the riparian perimeter to the river
at the Boyne site (Fig. 6b). Springs were present
at the surface of the peat between nests 3 and 4
although the hydraulic heads did not indicate strong
vertical gradients within the peat. Small surface
rivulets produced by the springs extended to nests
6– 7 before recharging to the peat from March to May.
There was enough hillslope discharge to maintain a
hydraulic gradient from field to stream in the spring at
the Road 10 site (Fig. 6c). However, during summer,
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
hillslope discharge decreased and the hydraulic
gradient from field to stream declined to almost
zero by late summer. Equipotential lines indicate
up-welling of groundwater from the Alliston sand
aquifer beneath the riparian zone in spring.
This upward flow persisted near the stream during
the summer. At depths of . 5 m, groundwater flow was
predominantly horizontal beneath the riparian area
(Fig. 6c).
At the Speed site, hillslope subsurface inputs
maintained a field to riparian zone hydraulic
gradient in the upper part of the riparian zone (nests
5 –3) throughout the year (Fig. 6d). Nevertheless,
as the riparian zone dried out during the summer,
there was a decrease of the hydraulic gradient between
nests 5 and 3 and a reversal of the water table gradient
was observed in the lower part of the riparian zone
(nests 1– 2A).
The pattern of groundwater flow observed at the
Maskinonge site was similar to the Eramosa site
(Fig. 6e). Hydraulic head contours showed upward
gradients of water toward the surface adjacent to the
upland – riparian perimeter between nests 12 and 11B.
In spring, groundwater seeps produced surface
rivulets that recharged into the riparian zone soil
between nests 11A and 11. Although this riparian
zone is permanently connected to the upland aquifer,
hillslope discharge significantly decreased during the
summer. In the lower part of the riparian zone
(nests 11– 10), the hydraulic gradient was almost nil
during that period, indicating that groundwater
discharge to the stream was very limited during
summer months (Fig. 6e).
During periods of upland – riparian hydrologic
linkages, subsurface flow paths were parallel to the
slope surface and the shallow underlying confining
layer at the Highway 27, Ganatsekiagon and Vivian
sites (Fig. 6f – h). Hillslope discharge was very
intermittent at the Ganatsekiagon site and the water
table declined rapidly in early summer each year
(Fig. 6f). Flow reversal situations were never
observed at this site during the study period. When
the Highway 27 riparian zone was disconnected from
the upland in the summer and autumn, the upper part
of the riparian zone dried out and the hydraulic
gradient near the stream was almost zero (Fig. 6g).
Hillslope discharge was also very intermittent at the
Vivian site. During summer, the water table first
221
declined parallel to the ground surface and then, as
hillslope discharge ceased, the stream became the
main source of water to the riparian zone and a steep
hydraulic gradient was established towards the slope
(Fig. 6h).
4.6. Subsurface flow patterns in the horizontal plane
The configuration of well and piezometer nests
provides a three-dimensional perspective of groundwater flow for all sites except Eramosa, where
transects did not extend across the entire riparian
area and where the three-dimensional flow pattern
was not established. Water table elevations measured
at monthly intervals revealed three different patterns
of groundwater flow. The first pattern was found at
Vivian Creek and Road 10 sites where large seasonal
changes in subsurface flow direction occurred across
the entire riparian zone. At Vivian Creek, groundwater flow was parallel to the main topographical
gradient (Fig. 2h) during high water table conditions
in spring resulting in a slightly oblique flow direction
across the riparian area (Fig. 7b). During summer and
early autumn, when there was no runoff from the
hillslope, the riparian water table was sustained by
stream inflow. During this period, we observed a large
shift in flow direction across the riparian zone with
water flowing in a stream-to-riparian zone direction
with a strong downstream component (Fig. 7d).
By December, when water table levels were similar
to those observed in the spring, the flow pattern
returned to a hillslope to stream orientation.
Similar changes in flow direction between spring,
summer and autumn were observed at the Vivian site
each year. However, changes in flow direction were
less severe in 2000, a year with high rainfall in May
and June. The groundwater flow pattern in October
2000 (Fig. 7a), during the period of maximum annual
water table drawdown, was similar to June 2001 and
did not show the large reversal of hydraulic gradient
observed in September 2001 (Fig. 7d).
At Road 10 site (data not shown), the direction of
groundwater flow was from field-to-stream in the
spring. However, during the summer, the field to
riparian zone water table gradient decreased to near
zero producing a change in flow pattern to a down
valley orientation parallel to the stream. In contrast to
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P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
Fig. 7. Water table contour maps for Vivian Creek riparian site. (a)
October 2000, (b) April, (c) June, (d) September, (e) November and
(f) December 2001. Water table contours are 20 cm intervals. Arrow
sizes are not proportional to magnitude of flow. The dashed line
indicates the field edge.
Vivian Creek, a flow reversal from the stream to
the slope was not observed at this site.
A second type of flow pattern was observed at the
Speed River site where hillslope discharge was large
enough to maintain a field-to-riparian zone gradient
throughout the year in the upper half of the riparian
zone (Fig. 8). However, in the lower part of the
riparian zone significant changes in flow direction
were observed. As the water table declined, the
downstream component of subsurface flow became
predominant. In September 2001, a flow reversal was
observed from the stream towards the centre of the
riparian zone (Fig. 8d). As the water table levels
increased in November and December, the groundwater flow direction returned to the spring pattern
(Fig. 8e and f). As previously noted for the Vivian
site, the strong reversal of hydraulic gradient near the
stream did not occur during the summer and autumn
of 2000 at the Speed site (Fig. 8a).
A third riparian groundwater flow pattern occurred
at the Boyne River, Maskinonge, Highway 27 and
Ganatsekiagon sites. Groundwater flowed in the
direction of the steepest slope and was perpendicular
Fig. 8. Water table contour maps for Speed River riparian site. (a) November 2000, (b) April, (c) June, (d) September, (e) November and (f)
December 2001. Water table contours are 20 cm intervals. Arrow sizes are not proportional to magnitude of flow. The dashed line indicates the
field edge.
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
Fig. 9. Water table contour maps for Maskinonge Creek riparian
site. (a) April, (b) June and (c) September. Water table contours are
25 cm intervals. Arrow sizes are not proportional to magnitude of
flow. The dashed line indicates the field edge.
to the stream at these sites. This pattern was constant
throughout the year at the Boyne and Maskinonge
sites and occurred during the period of upland
hydrologic connection at Highway 27 and Ganatsekiagon. The Maskinonge site is representative of this
pattern (Fig. 9). As hillslope discharge decreased
during the summer, the water table declined parallel to
the ground surface but the water table hydraulic
gradient remained relatively constant from
the hillslope toward the stream.
5. Discussion
These data indicate that small differences in the
depth of permeable upland sediments capable of
serving as aquifers control the duration of the
hydrological connection between the riparian zone
and the adjacent upland. All riparian sites where the
depth of permeable sediments overlying a confining
layer was approximately 2 m or greater were permanently connected to their upland aquifer, whereas the
upland – riparian zone linkage was intermittent at all
sites with , 2 m of permeable upland sediments
(Fig. 4). In contrast, the length of upland slope
contributing subsurface flow to riparian zones with an
intermittent link was similar to several sites that had a
permanent hydrologic connection. The duration of the
upland – riparian zone linkage for the sites connected
to a thin aquifer is very strongly affected by periods of
low precipitation input. In November and December
2000, none of the sites in this category were
reconnected with their upland aquifer, whereas in
223
2001, hillslope discharge began by late October –
November. After a dry early autumn, precipitation in
late November and December 2000 occurred mainly
as snow, so there was almost no recharge during this
period. In contrast, although the summer of 2001 was
very dry, precipitation in September – November was
29% higher than the 30 year normal. Devito et al.
(1996) also showed that the upland – wetland linkage
in southern Ontario Canadian Shield catchments with
less than 2– 3 m of till overlying bedrock ceased
during the summer in response to variations in
precipitation. Our results and those of Devito et al.
(1996) suggest that approximately 2 m of permeable
sediments above a confining layer is a minimum depth
required for a permanent upland – riparian zone
linkage in the southern Ontario climatic regime.
The size of the upland aquifer influences the
magnitude and seasonality of fluxes entering the
riparian zone. However, the absolute values of these
groundwater inputs should be treated with caution
because of inherent measurement errors. The largest
and most constant water inputs were observed at the
Eramosa and Boyne sites where the upland slope
lengths were 750 and 1400 m, respectively, and
permeable sediment depths were 10 – 15 m.
The riparian zones connected to smaller upland
aquifers had lower and more seasonally variable
subsurface fluxes. Nevertheless, our correlation analysis for high water table periods only indicated a
significant positive relationship between riparian
water inputs and both upland permeable sediment
depth and slope length after exclusion of the
Ganatsekiagon site. The occurrence of large water
inputs at this site suggest that topography and soil
permeability are also important variables controlling
groundwater inputs to some riparian areas. At the
Ganatsekiagon site, despite a very thin upland aquifer
(, 1.4 m), the combination of steep topography and
highly permeable sediments produced fluxes that were
similar in magnitude to much thicker and more
extensive aquifers. However, because of the small
upland aquifer, these fluxes were limited to periods of
high water table during a few weeks in spring and
autumn whereas at a site like Boyne River, large
fluxes occurred throughout the year.
The results of this study also show that the
relationship between upland aquifer depth and the
maintenance of a hydrologic connection has
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P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
an important influence on riparian zone water table
fluctuations. Sites connected to a thick extensive
upland aquifer (Eramosa, Boyne) had small annual
water table fluctuations whereas sites that become
disconnected from uplands (Highway 27, Ganatsekiagon, Vivian) had annual water table drawdowns of
. 1 – 2 m which can result in the complete drying out
of the riparian area unless the water table is sustained
by the stream. Similar variability in the amplitude and
seasonal duration of water table elevation in relation
to upland hydrologic linkages has been reported for
small forested headwater wetlands (Devito et al.,
1996; Hill and Devito, 1996).
Sediment stratigraphy also influences water table
dynamics and subsurface flow paths in some riparian
sites. At the Eramosa site, the rapid decrease in
thickness of the gravel and cobble layer from 12 m at
the field edge to , 2 m overlying a low conductivity
clay till at the slope base produced groundwater
discharge to the riparian surface. This decrease in
aquifer thickness and continuous hillslope discharge
maintained a relatively stable water table
position within 15 cm of the surface even during
summer droughts.
Permanent hillslope discharge at the Boyne site
associated with a decrease in thickness of the sand
aquifer beneath the riparian area and the presence of
low conductivity peats, was also linked to limited
water table fluctuations and the occurrence of surface
saturation within 70 –80 m of the riparian perimeter
for most of the year. Hinton et al. (1993) have reported
similar effects of decreasing sediment thickness along
flow paths on groundwater discharge and surface
saturation in a Canadian Shield glacial till catchment.
At the Maskinonge site, upward flow due to the
damming effect produced by low conductivity peats
maintained surface saturation for considerable periods
of the year. As a result, water table variations were
lower here than at sites such as Speed River which
have a larger upslope depth of permeable sediments,
but where riparian subsurface flow is not restricted by
low conductivity sediments. Brusch and Nilsson
(1993) also observed that groundwater flow from a
sand aquifer in Denmark was forced to the surface at
the perimeter of a riparian zone by a low permeability
organic deposit. Surface groundwater seeps
produced surface rivulets at the Eramosa, Boyne and
Maskinonge sites. This flowpath reduces residence
times and contact with riparian sediments which
can limit nitrate removal (Warwick and Hill, 1988;
Gold et al., 2001).
Landscape topography has a considerable
influence on riparian subsurface flow pattern.
Our data suggest that subsurface water tends to flow
downslope in areas of the riparian zone where the
slope gradient is steeper than 5%. The Road 10 site,
which has a slope gradient of 18% at the upland
perimeter, is an exception to this pattern. However,
the drop in elevation at the perimeter is only 1 m and
this is not enough to influence the water table
gradient. The sites with a steep concave topography
(Boyne, Eramosa) that we studied are connected to
thick extensive upland aquifers. The combination of
large, continuous hillslope discharge with a steep
topography (. 15%) at the field edge, maintained a
field to stream water table gradient throughout the
year even on the flat areas of the riparian zone.
The Speed and Vivian riparian zones occur in
landscapes with level to gentle slopes (, 5%) where
a low hydraulic gradient between uplands, riparian
areas and the stream increase the probability that the
water table in the riparian zone may fall below
the stream water level resulting in flow reversals
(Figs. 7 and 8). Burt et al. (2002) also indicate that
when the topography is flat, stream water level
can strongly influence water table dynamics in the
riparian zone.
6. Conclusions and conceptual model
The eight riparian sites examined in this study
represent a large portion of the range of hydrologic
behaviour typical of glacial till and outwash landscapes in southern Ontario where local groundwater
flow systems connect uplands to adjacent riparian
areas. A conceptual model of stream riparian
hydrology in these landscapes is presented in Fig. 10.
This model emphasizes the importance of upland
permeable sediment depth as an indicator of aquifer
size and topography of the riparian zone and adjacent
upland for the identification of different hydrologic
categories of riparian zones.
The first hydrologic type occurs on areas of level to
sloping topography underlain by clay soils behaving
as aquitards that extend almost to the surface.
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
225
Fig. 10. Conceptual framework identifying riparian hydrologic types.
Although this landscape setting was not included in
the present study, we suggest that subsurface flux will
be very small because of low soil permeability and
that runoff will occur mainly as overland flow during
snowmelt and rain events allowing contaminated
water to bypass the riparian soil.
A second category of riparian zone hydrologic
functioning occurs in landscapes with a thin upland
aquifer (1 – 2 m) and level to gently sloping topography (, 5%). The upland –riparian zone linkage is
generally very intermittent and hillslope discharge is
seasonally variable and precipitation dependent.
Water table drawdowns between 1 and 1.5 m are
common in normal years but can exceed 2 m in
especially dry years. Consequently, these sites have a
limited role in regulating subsurface contaminant
flows between uplands and streams. Large changes in
subsurface flow direction are likely to be observed in
this riparian hydrologic type, with water flowing in a
field-to-stream direction in the spring and then in the
direction of the valley gradient or even in a stream-tofield direction during the summer.
A third type is represented by riparian zones linked
to thin upland aquifers on steeper topography (. 5%).
These sites have water table dynamics and seasonality
of hillslope discharge that is similar to the second
riparian type. However, during periods of high water
table, sites with steeper slopes in combination with
highly conductive surficial sediments may produce
large subsurface fluxes of water and contaminants that
can exceed the buffering capacity of the riparian zone.
Because of the steeper topography, subsurface water
flows in the direction of the steepest slope gradient
whenever these sites are hydrologically active. It is
important to note that a slope extending to the
stream decreases the buffer role of the riparian zone.
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P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
This could apply to several of the riparian types
presented here when moderate to steep slopes are
connected directly to the stream.
Another hydrologic type is represented by riparian
zones linked to upland aquifers with intermediate
thickness (2 – 6 m) and level to gently sloping
topography. These sites have considerable seasonal
variations in groundwater input but maintain a
continuous upland – riparian zone hydrological
connection. Water table drawdowns between 0.3 and
1.2 m in normal years and up to 1.5 m in especially
dry years are likely to be observed. These sites have
seasonal changes in subsurface flow direction with the
magnitude of the changes being directly related to the
balance between water level at the field edge and
stream water level dynamics. Subsurface flows may
shift from a field –riparian to a down valley gradient
in most summers, however, flow reversal situations
generally occur only in exceptionally dry years.
In contrast, subsurface flow paths in riparian zones
linked to intermediate aquifers on steeper topography
(. 5%) are generally in the direction of the steepest
slope except very close to the stream.
Riparian zones linked to thick aquifers (. 6 m)
may be located on level to gently sloping topography,
where the stream channel is incised only a few meters
below the landscape surface. As a result of the low
hydraulic gradient, groundwater interaction with the
riparian zone is restricted to the upper few meters of
the aquifer. Water table fluctuations and changes in
subsurface flow direction in this category of riparian
zone are similar to sites linked to intermediate
aquifers (2 – 6 m) on level to gently sloping
topography.
Our conceptual model identifies a final riparian
hydrologic type which is linked to a thick upland
aquifer and has a steep concave topography (locally
. 15%) as a result of valley incision. These riparian
zones have large seasonally constant groundwater
inputs, which maintain stable water tables. The initial
steep slope associated with a large and permanent
hillslope discharge generally maintains a stable field to
stream subsurface flow path across the entire riparian
zone. In some of these riparian zones, the water table
intersects the ground surface at the slope bottom
producing seeps and surface rivulets. In sites with
conductive sediments at depth, groundwater may
bypass the riparian area and discharge upward to
the stream channel. These flow paths may limit
the effectiveness of this riparian type as a water quality
buffer.
It may be possible to use widely available maps of
topography, soils and surficial geology to identify
these different riparian hydrologic types at the
landscape scale. Variations in riparian stratigraphy
and sediment permeability can also locally modify
water residence times and subsurface flow paths.
These site-specific characteristics may be difficult to
evaluate without individual site studies.
This conceptual model of riparian zone
hydrological functioning complements and extends
previous research on landscape setting and riparian
hydrology (Devito et al., 1996; Hill, 2000; Baker et al.,
2001; Burt et al., 2002). Our study is the first to use
data from a wide range of riparian sites to examine in
detail the interacting effect of upland aquifer size,
topography and lithology on riparian hydrology.
Our classification of riparian hydrologic types can
probably be used with minimum modifications in
most glacial till and outwash landscapes. However,
this conceptual framework may require modification
in other landscape and climatic settings. For example,
the critical depth of permeable sediments required to
maintain a continuous upland –riparian hydrologic
link may vary depending on seasonal patterns
of precipitation and evapotranspiration in different
climatic regimes.
It is important that future research emphasises the
development
of
process-based
conceptual
frameworks that link differences in riparian hydrology
to key landscape hydrogeologic characteristics.
These conceptual models provide an essential template for understanding and predicting similarities and
differences in the water quality function of riparian
zones at the catchment and landscape scales.
Acknowledgements
We thank Alan Michalsky for preparing the
piezometers and wells, Graham Carlyle, Robert
McDonald and Tim Duval for assistance in the field,
and Shan Sanmugadas and Jackson Langat for
laboratory assistance. Thanks are also due to
landowners for access to the riparian sites. We thank
Kevin Devito and Tim Burt for comments on
P.G.F. Vidon, A.R. Hill / Journal of Hydrology 292 (2004) 210–228
the manuscript. The research was supported by grants
from the Natural Sciences and Engineering Research
Council of Canada to A.R. Hill.
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