Journal of Hydrology 520 (2015) 123–133

Contents lists available at ScienceDirect

Journal of Hydrology
journal homepage: www.elsevier.com/locate/jhydrol

Water ﬂow and nitrate transport through a lakeshore with different
revetment materials
Yong Li a,b,⇑, Jirka Šimůnek c,⇑, Zhentin Zhang b, Manli Huang b, Lixiao Ni b, Liang Zhu b, Jianlan Hua d,Yong Chen daMinistry of Education Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Hohai University, Nanjing 210098, China
College of Environment, Hohai University, Nanjing 210098, China
Department of Environmental Sciences, University of California Riverside, Riverside, CA 92521, USAdNanjing Water Planning and Designing Institute Co. Ltd, Nanjing 210006, Chinabca r t i c l e

i n f oArticle history:
Received 6 June 2014
Received in revised form 10 November 2014
Accepted 15 November 2014
Available online 22 November 2014
This manuscript was handled by Corrado
Corradini, Editor-in-Chief, with theassistance of Stephen Worthington,
Associate Editor
Keywords:
Lakeshore
Groundwater
Flow regime
NitrateSlope revetment material
Hydrus-2D

s u m m a r y
As an important part of a transition zone surrounding a lake, lakeshore plays a critical role in connectinghydrology and biochemistry between surface water and groundwater. The shape, slope, subsurface
features, and seepage face of a lakeside slope have been reported to affect water and nutrient exchange
and consequently the water quality of near-shore lake water. Soil tank experiments and Hydrus-2Dmodel simulations were conducted to improve our understanding of the inﬂuence of slope revetment
materials (SRMs) on water ﬂow and solute transport in a lakeshore zone. The low hydraulic conductivityof SRMs affected ﬂow patterns in the lakeshore zone and resulted in a local increase of the groundwatertable near the slope face. Water and solute ﬂux distributions on the slope face under bare-slope conditions followed an exponential function. Fluxes were concentrated within a narrow portion of the slope
surface near the intersection point between the lake water level and the slope face. Surface pollutants(for example from ﬁshponds and paddy ﬁelds surrounding a lake) were transported into the lake along
shallow groundwater through both unsaturated and saturated zones. The SRMs on the slope face affected
the ratio of water and solute ﬂuxes in the unsaturated zone, increasing along with the decline of thehydraulic conductivity of SRMs. Furthermore, as the hydraulic conductivity of SRMs decreased, the retention time and the potential for oxygen reduction correspondingly increased, which affected the nitrogentransport and transformations in the lakeshore zone. Simulated and experimental results indicate that if
concrete along the shoreline of Lake Taihu is replaced with a relatively high-conductivity lime or theslope is left bare, water ﬂuxes will increase less than solute ﬂuxes, which will rise signiﬁcantly, in particular in the unsaturated zone and along the seepage face. On the other hand, the largest water and solute
ﬂuxes along the shoreline for the bare and lime-slope conditions will be located higher at the slope thanfor the concrete-slope conditions. Hydrus-2D provided a good description of complicated hydrodynamic
and solute transport/transformation conditions in the lakeshore zone.
Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction
Lakeshore is an important component of the transitional zone
surrounding a lake and plays a critical role in connecting hydrological and biogeochemical cycles of near- and off-shore regions(Ostendorp, 2004). Lake water, groundwater, and soil water mutually interact in the lakeshore zone, while pollutants are subject toconcurrent transport and transformation processes under these⇑ Corresponding authors at: Ministry of Education Key Laboratory of Integrated
Regulation and Resource Development on Shallow Lakes, Hohai University, Nanjing
210098, China (Y. Li).
E-mail addresses: liyonghh@hhu.edu.cn (Y. Li), Jiri.Simunek@ucr.edu (J. Šimůnek).
http://dx.doi.org/10.1016/j.jhydrol.2014.11.045
0022-1694/Ó 2014 Elsevier B.V. All rights reserved.

complex hydrological conditions. The lakeshore zone is often considered an effective buffer region that retards pollution from surrounding land areas before it enters into lake water (Howarth
et al., 2011). Recently, increasing attention has been given to theimportance of a riparian zone (including a lakeshore) and attenuation of nitrates and other pollutants in this region (Ostendorp,
2004; Burgin and Groffman, 2012). A large number of studies havebeen carried out evaluating the effects of the slope, width, andshape of a lakeshore on hydrological and solute cycles in this zone
(Cey et al., 1998; Genereux and Bandopadhyay, 2001; Li et al., 2007;
Zhu et al., 2012). However, the effects of different slope revetment
materials (SRMs) used on a lakeshore slope on hydrological andbiogeochemical processes still have not been thoroughly studied.

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In essence, SRMs used on the waterside slope affect local
hydraulic conductivities (Mohamed, 2006) and consequently theﬂow direction and ﬂuxes, ﬂow pathways, retention times, and eventhe soil reduction–oxidation potential (Lee, 2000; Lassabatere
et al., 2004; Bouazza et al., 2006). The hydraulic conductivity of
the near shore region signiﬁcantly affects inﬂow/outﬂow hydrodynamics of a shoreline (Lee, 2000). Genereux and Bandopadhyay(2001) reported for inﬂow lakes that adding low-conductivity lake
sediments, and decreasing their conductivity, produced a shift ofgroundwater seepage further offshore. Increasing the anisotropyof the surrounding porous medium had the same effect.
SRMs used in China mainly include concrete (with an extremely
low conductivity), but also other materials such as ecological concrete (with a medium–high conductivity), lime with geotextiles(with a relatively low conductivity), and other materials (Wangand Luo, 2006; Yao and Yue, 2012). The present shoreline of Lake
Taihu, the third largest freshwater lake in China, is almost entirely
covered by a concrete material on the waterside slope in order toprotect people and agricultural crops against ﬂoods (Hu et al.,2011). During the past several decades, the importance of the concrete lake shoreline to prevent erosion due to ﬂoods and wind
waves could not been questioned. Nevertheless, as public preference for natural landscaping increased in importance and thenear-shore lake water quality decreased, detrimental functions of
the concrete lakeshore started to be discussed and questioned.
Some researchers have suggested that the concrete shoreline
should be replaced with materials that are more natural in orderto rebuild the connection between near-shore and off-shore zones.
Some have suggested that the lake shoreline should be returned tonatural conditions (namely natural soils with grass) (Yang et al.,2005; Shaw et al., 2011). Others have insisted that the ﬂood control
function of the lake shoreline should be preserved by using a low
conductivity material with embedded geotextiles (Nahlawi et al.,2007; Lamy et al., 2013). However, it is not well understood how
such changes would alter hydrological and biogeochemical
processes in the lakeshore zone. Hydraulic coupling between Lake
Taihu and groundwater is difﬁcult to assess through in-situ observations because of the presence of the concrete material at the lakeshoreline. Therefore, before making any engineering decisions, preliminary studies have to be carried out to evaluate the effects ofdifferent SRMs on hydrological and biochemical processes in thelakeshore zone. More research is also deﬁnitely needed to evaluate
the effects of the lake water level on shoreline groundwater
processes (Schneider et al., 2005).
The exchange of water and solutes between groundwater andlakes is a complex process, and it is still a challenge to understandits temporal and spatial variability (Kidmose et al., 2011). Models
are useful tools for identifying various hydrological factors that
affect groundwater and solute discharge ﬂuxes into sensitive surface water bodies such as lakes and wetlands (Lee, 2000; Simpson
et al., 2003). The Hydrus-2D model, which has been used widelyin similar research studies (e.g., Lee, 2000), was therefore used tosimulate these processes in order to improve our understandingof water ﬂow and nitrate transport processes in the lakeshore zone.
To improve our understanding of environments of lakeshore
zones, we have conducted both laboratory soil tank experiments
and corresponding numerical simulations using the Hydrus-2Dmodel. Obtained data were analyzed to reveal general characteristics of water and nitrogen regimes in the lakeshore zone covered
using three different SRMs. The effects of SRMs on distributionsof water and solute ﬂuxes on the slope face were studied in particular. Furthermore, relative fractions of water and solute ﬂuxes
passing through seepage face and submerged zones on the slope
face were compared for the three SRM-cover conditions in order
to better understand the transport pathways from land surface pollutant sources (for example from ﬁsh ponds or paddy ﬁelds).

2. Material and methods
2.1. Soil tank experiment2.1.1. Design and set-up
A large soil tank (Fig. 1a) was used to simulate water ﬂow andsolute transport in the lakeshore zone. The tank was ﬁlled with soil
layer by layer; each evenly compacted using a heavy object. The
lakeside slope (a) was set at about 35°. Two thin PVC (Polyvinyl
chloride) panels vertically divided the tank into three sections withdifferent surface covers (Fig. 1b). Namely, one section was covered
with a concrete material (with a low hydraulic conductivity),
another section with a lime material (with a moderate conductivity), and the center section remained bare (additional soil wasadded to have the same embankment thickness). The SRMs (limeor concrete) only covered the upper section of the slope, while
the lower section of the slope (beneath 30 cm) was ﬁlled withrocks. The groundwater table (GWT) was constant upstream (theHP boundary in Fig. 1a), supplied by two submerged pumps with
ﬂow meters. The lake water level (LWL, the AO boundary in
Fig. 1a) was kept constant as well, controlled using overﬂow
troughs with ﬂow meters. The ﬁshpond was set up on the land
surface 95 cm away from the upstream boundary and its leachingﬂux (10 cm day1) with pollutants was controlled by one micro
pump. Before the experiments, steady-state water ﬂow conditionsin the soil tank were established by maintaining constant waterlevels upstream (GWT) and downstream (LWL) for about one
month. Selected soil physical and chemical properties are listed
in Table 1.
Multiple experiments were concurrently carried out in three
sub soil tanks, in order to better understand the effects of different
SRMs on ﬂow patterns and solute transport in the lakeshore zone.
Based on ﬁeld observations carried out in the lakeshore zone ofLake Taihu, average groundwater gradients were set at three typical values of 0.063, 0.043, and 0.022 m m1, corresponding to thedry (a LWL was 30 cm), normal (40 cm), and wet (50 cm) seasons,respectively (Fig. 1c). The GWT at the upstream boundary (line HP
in Fig. 1a) was kept constant (60 cm) in all experiments. The ratiod/D represents the ratio between the relative distance from point O
to the entire length of the slope face (D). Variables d30, d40, and d50
represent the distances on the slope face from point O to the intersection points B, C, and D of LWLs with the slope face, respectively(Fig. 1c).
Solutes were mixed into the assumed ﬁshpond (or a paddyﬁeld) after a steady state water ﬂow was reached. A solution of
NaNO3 and NaCl was mixed into the ﬁshpond along with pumped
water. The concentrations of chloride and nitrate were 10.0 mg L1.
The experiment representing dry-season conditions was
conducted ﬁrst. After the experiment was ﬁnished, the soil tank
was slowly ﬂushed for about one month until solute concentrations at all observation points stabilized. Then, the experiment
representing the normal season was carried out, followed by theexperiment representing the wet season.

2.1.2. Measurements and analysis
Inﬂow ﬂuxes through the upstream boundary (the HP line in
Fig. 1a) were recorded using ﬂowmeters connected with pumps.
Groundwater table data were observed from scales connecting
stainless steel tubes in the soil tank. The tubes were installed
beneath the groundwater table 100, 200, 290, 420 and 465 cm
away from the upstream boundary (Fig. 1a). Soil solutions werecollected every ten days using porous ceramic suction cups at
S1–S11 (Fig. 1a). The residual solution in the suction cups wascleansed using an injector each time before sampling. The cups
were then evacuated to about 80 kPa by a vacuum pump with a

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Fig. 1. Schematic of the experimental set-up (a), slope revetment materials (b), and the detail of the slope face (c). All units are in cm.

Table 1
Physical and chemical properties of soil materials used in the soil tank experiments.
Layer

Lakeshore
Lime

Soil particle size distribution (%)
Sand (>0.05 mm)

Silt (0.002–0.05 mm)

Clay (<0.002 mm)

87.4
58.9

10.2
31.4

2.4
9.7

tensiometer. The concentrations of chloride and nitrate were analyzed using a continuous ﬂow auto-analyzer.
2.2. Hydrus-2D model
2.2.1. Model description
The Hydrus-2D model (Šimůnek et al., 2008) was concurrently
used to simulate the laboratory tank experiments to improve ourunderstanding of the ﬂow and transport patterns in the lakeshore
zone. Considering the two-dimensional isothermal uniform Darcian
water ﬂow in a variably-saturated rigid porous medium, andassuming that the air phase plays an insigniﬁcant role in the liquid
ﬂow process, the governing water ﬂow and solute transport equations are given by the Richards and convection–dispersion equations, respectively. Both governing equations are numericallysolved in Hydrus-2D using the method of ﬁnite elements. An
appropriate spatial discretization is crucial to avoid numerical

Bulk density (g cm3)

Organic matter (%)

pH (H2O)

1.43
1.59

0.18
0.10

6.9
7.4

oscillations and to achieve acceptable mass balance errors(Šimůnek et al., 2008). The total number of triangular ﬁnite elements (FE) was 18,167 in all simulations. At the slope surface andnear the ﬁshpond (areas with large pressure head gradients), thesize of FE was approximately 1 cm, while in other parts of the transport domain it was approximately 1–6 cm. Time steps were automatically controlled by the Hydrus-2D model within the initially
speciﬁed range of 107 and 0.1 day. As suggested in the manual of
the Hydrus-2D model for minimizing or eliminating numericaloscillations, the Peclet (Pe) and Courant (Cr) numbers were controlled by a stability condition ‘‘Pe  Cr 6 2’’ (Šimůnek et al., 2012).
2.2.2. Input parameters
The Hydrus-2D input parameters are required to characterize
two main sets of processes: the soil hydraulic parameters for waterﬂow and solute transport and reaction parameters for solutetransport. The initial estimates of the van Genuchten (1980) soil

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hydraulic parameters (hr, hS, a, and n: residual and saturated watercontents, and two shape parameters, respectively) were estimatedusing the RETC software by ﬁtting retention data, h(h), measured
using the pressure chamber apparatus. The pore connectivity
parameter (l) was assumed equal to an average value (0.5) for
many soils. The solute transport parameters were considered using
the following values: the molecular diffusion coefﬁcient in free2
1
water (Dw) for NO
, the initial longitudinal dis3 was 1.64 cm day
persivity (aL = 45 cm) was assumed to be one-tenth of the travel
distance, and the initial transverse dispersivity (aT = 4.5 cm) was
considered to be equal to one-tenth of the longitudinal dispersivity(Gelhar et al., 1985; Phogat et al., 2012). Denitriﬁcation rates were
initially assumed to be the same (namely Kdn = 0.02 day1) in all
soil materials and then adjusted to 0.015 day1 according tomeasured data.
2.2.3. Initial and boundary conditions
The initial distribution of the pressure head was set to decreaselinearly with a unit gradient (hydrostatic equilibrium) from thebottom to the top of the soil proﬁle. The initial chloride and nitratecontents in the soil were zero. The groundwater table at the
upstream boundary was assumed to be 60 cm above the bottomof the soil proﬁle. The groundwater table at the downstream
boundary reﬂected the water level in the lake (LWL). A potential
seepage face boundary condition was assigned to the part of theboundary above the LWL when there was no cover or when lime
was placed on the slope. The nodes with an active seepage facewere assigned a pressure head equal to zero. This part of theboundary was assigned a ‘‘no ﬂow’’ boundary condition when concrete was present on the slope. A constant ﬂux boundary condition(10 cm day1) was assigned to the boundary representing the ﬁshpond. Evaporation was neglected in order to investigate only theeffects of SRMs. A third-type boundary condition (a Cauchy boundary condition) was used at both upstream and downstream boundaries for solute transport.
2.3. Model evaluation
Simulated values of the groundwater table, total water ﬂuxes,
and chloride and NO
3 N concentrations in the soil were comparedwith the corresponding measured data from the soil tankexperiments. The correspondence between simulated andobserved data was evaluated using the coefﬁcient of determination(r2) at p = 0.05 and the root mean square error (RMSE). The RMSE
was calculated asrﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1 Xn
RMSE ¼
ðS  M i Þ2
1 inwhere Si and Mi are simulated and measured values, respectively,
and n is the number of compared values. Optimum values of r2
and RMSE are 1 and 0, respectively.
3. Results
3.1. Model calibration and validation
Observed GWTs and inﬂow ﬂuxes were used to further calibrate
the soil hydraulic parameters, obtained earlier from laboratory
retention data, using Hydrus-2D. Simulated GWTs showed a good
agreement with observed data (Fig. 2, RMSE = 0.39 cm, n = 54,
r2 = 0.97) for calibrated soil hydraulic parameters. Simulated
groundwater ﬂuxes into the lake were compared with total water
ﬂuxes, which included upstream inﬂow and ﬁshpond leakage(RMSE = 26.4 cm2 day1, n = 108, r2 = 0.96).

Fig. 2. Simulated and observed groundwater tables under bare-, lime-, andconcrete-slope conditions during the dry, normal, and wet seasons. The letter ‘‘O’’
indicates the end of the slope (see also Fig. 1c). The water level at the upstream
boundary was kept at 60 cm, while at the downstream boundary at 30 cm, 40 cm,
and 50 cm to represent the dry, normal, and wet seasons. The horizontal distance ismeasured from the upstream boundary (as seen in Fig. 1a).

Chloride and nitrate concentrations observed in soil tankexperiments with a bare slope face during the wet season wereused to calibrate the transport and reaction parameters inHydrus-2D. Selected calibration results for chloride and nitrateconcentrations at six observation points near the lakeshore zone,
namely S1–S3 and S5–S7, are displayed in Fig. 3. The calibrated longitudinal dispersivity (aL) and transverse dispersivity (aT) were
7.0 cm and 0.5 cm, respectively, which are far lower than theirrespective initial values (45 cm and 4.5 cm). The difference
between chloride and nitrate concentrations was used to calibrate
the denitriﬁcation rate. RMSEs for the calibrated model are about
0.14 mg L1 (n = 69, r2 = 0.97, Fig. 3a) for chloride and 0.16 mg L1(n = 70, r2 = 0.96, Fig. 3c) for nitrate. Corresponding observed concentrations (under bare-slope conditions) during the wet season
were then used to validate the solute transport and reaction
parameters. RMSEs for the validation run are 0.15 mg L1 (n = 72,
r2 = 0.94, Fig. 3b) for chloride and 0.18 mg L1 (n = 66, r2 = 0.93,
Fig. 3d) for nitrate. Simulated chloride and nitrate concentrations
matched the observed data very well. The overall good descriptionof observed groundwater tables and ﬂuxes, and chloride andnitrate concentrations, implies that the calibrated parameters(Table 2) used in Hydrus-2D are reasonable.
Fig. 3e and f additionally show a comparison of experimental
and simulated (with calibrated parameters) results during thewet season when the shoreline is covered with either lime or concrete, respectively. This comparison should validate the adequacyof applied boundary conditions at the downstream boundary, representing either an impermeable or partially permeable shoreline
cover. The observed and simulated nitrate concentrations agreed
well with a RMSE of 0.22 mg L1 (n = 68, r2 = 0.94; Fig. 3e) for a lime
cover and a RMSE of 0.21 mg L1 (n = 70, r2 = 0.93; Fig. 3f) for a concrete cover. Consequently, the downstream boundary conditions
for water ﬂow (a seepage face above LWLs and a constant pressure
head below LWLs) and solute transport are feasible.
Overall, Fig. 3 shows that chloride and nitrate had similar distributions (although at a different level due to nitriﬁcation, Fig. 3aand c) at all observation points. However, signiﬁcant changes exist
between the dry and wet seasons (Fig. 3a and b), which indicatesthat the LWL affected the solute transport into lake water. Additionally, as show in Fig. 3d–f (for the wet season), signiﬁcant differences can be found in nitrate concentrations at S1 and S2 between
bare-, lime-, and concrete-cover conditions. This implies that SRMs
on the lakeshore slope affected the nitrate transport into the lakeshore zone.

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Fig. 3. Selected simulated and observed concentrations of chloride (Cl, a–b) and nitrate (NO
3 , c–f) near the lakeshore slope under bare (for dry and wet seasons), lime (wetseason), and concrete (wet season) slope cover (lines: simulated by Hydrus-2D; symbols: observed during the soil tank experiments). Results (for the dry season and the bareslope) displayed in (a) and (c) were used for model calibration and those (for the wet season and the bare slope) displayed in (b) and (d) for model validation. Results in (e)and (f) were used to test the validity of the downstream boundary condition. C0: the input solute concentration from the ﬁshpond/paddy ﬁeld.

Table 2
Optimized values of the residual water content, hr, the saturated water content, hs, van Genuchten’s shape parameters, a, and n, the saturated hydraulic conductivity, Ks, thelongitudinal dispersivity, aL, the transverse dispersivity, aT, and the denitriﬁcation rate, Kdn.
Material

Soil typehr (cm3 cm3)hs (cm3 cm3)a (cm1)n

Ks (cm day1)aL (cm)aT (cm)Kdn (day1)

Lakeshore
Lime

Loamy sandLoamy sand

0.055
0.090

0.40
0.35

0.121
0.061

2.16
1.45

338.9
30.2

7.0
7.0

0.5
0.5

0.015
0.015

3.2. Groundwater table gradients in the lakeshore zone
Both GWT and LWL control the hydrology of the lakeshore zone
as well as its transmissivity. In particular, compared to a relatively
stable GWT, the LWL is subjected to frequent ﬂuctuations in
response to rainfall and wind waves on the lake shoreline. Additionally, the LWL can, in general, gradually rise or fall during an entire
hydrological year. However, SRMs on the slope alter the hydrological cycle in the lakeshore zone and the associated transport andtransformation of solutes. Fig. 2 shows the position of the GWTcorresponding to three different LWLs. GWT gradients increased
with the decline of the LWL, providing that the GWT remained
stable off the lakeshore zone. During the dry season, the GWT underbare-slope conditions connected smoothly with lake water, with anaverage gradient of about 2.2%. On the other hand, under lime- or
concrete-slope conditions, the GWT gradients in the lakeshore zone
were smaller overall, but precipitously dropped near the slope face.
Lee (2000) has also observed a rapid, steep water table mounding in

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the near-shore region of Lake Barco (in Florida, USA). During thenormal and wet seasons, the gradients near the slope face wereaffected by SRMs. The gradients were smaller when the surface
was covered with concrete as compared to the lime cover. Thus, it
can be seen that SRMs affected the GWT gradients once the lakewater submerged a part of the SRM. Overall, based on simulated
results, there was a relatively small increase in the groundwatertable near the slope face when the shoreline was covered with concrete rather than with lime. Beneath the ﬁshpond (100 cm from an
upstream boundary), a barely visible mound of GWT occurred dueto the continuous vertical ﬂux from the ﬁshpond.
3.3. Water ﬂux distributions on the slope-face
The distribution of water ﬂuxes (per a unit width of the tankand per a unit length of the slope face) on the slope face was signiﬁcantly different for different SRMs during three seasons (Fig. 4left). Overall, the maximum ﬂuxes declined when the LWL
increased (from levels for the dry season to the wet season). For

the concrete-cover conditions (Fig. 4a–c), the distribution of water
ﬂuxes were similar for all three seasons (i.e., wet, normal, and dry)and occurred within the same spatial extent (OB, Fig. 1c). For the
bare- and lime-cover conditions, the spatial extent of water ﬂuxes
on the slope increased with an increase in the LWL. The majorwater ﬂuxes occurred in a narrow range of the slope face near
the water level in the lake (LWL). During the dry season, the maximum ﬂuxes for the bare-, lime-, and concrete-slope conditions
were 175.1, 102.3, and 286.2 cm day1, respectively, and they were
all located near point B (the bottom end of SRM, Fig. 4). When lime
was used as a cover material, two ﬂux peaks existed during bothnormal and wet seasons, reﬂecting the location of two materials(soil and lime) on the slope. One peak was located at point B (thebottom end of the lime cover), and another at point C or D (the corresponding intersect points of the LWL with the slope face during
the normal and wet seasons, respectively, Fig. 1b and c). Overall,water ﬂuxes near the slope bottom (point O) were very low, implying that only little water exchange occurred between groundwaterand lake water at this location.

Fig. 4. Distributions of water (left) and nitrate (right) ﬂuxes along the slope under bare-, lime-, and concrete-slope conditions at 120 day during the dry (a, d), normal (b, e),and wet (c, f) seasons. See Fig. 1c for the deﬁnition of letters A, B, C, D, and O.

Y. Li et al. / Journal of Hydrology 520 (2015) 123–133

3.4. Solute concentration and ﬂux distributions on the slope-face
While nitrate ﬂux distributions (per a unit width of the tank anda unit length of the slope face) along the lakeshore slope are displayed in Fig. 4 (right), the solute concentration distributions (forboth chloride and nitrate) along the lakeshore slope are shown in
Fig. 5. In general, solute ﬂuxes closely resemble water ﬂuxes(Fig. 4 left). Also, chloride and nitrate concentration distributions
along the slope face are very similar (Fig. 5). While both chloride
and nitrate are not retarded, nitrate concentrations are reduced
due to denitriﬁcation. Positions (d/D) of peak values of chloride
concentrations were slightly higher than those of nitrate during
the three seasons under the bare-, lime-, and concrete-slope conditions. Differences in solute concentrations in the three seasons
mainly resulted from different ratios of the water ﬂux from theﬁshpond (which was constant) to the groundwater ﬂux (which
decreased with an increase in the LWL). As the water level in thelake increased, the solute concentrations on the slope also gradually increased (due to the higher ratio of the ﬁshpond ﬂux to the129

groundwater ﬂux). On the other hand, as the overall thickness ofthe groundwater increased, water and solute ﬂuxes decreased,
resulting in more vertical solute dispersion (Figs. 5 and 6). A common phenomenon was that all peak values were located in the
SRM zone (namely above point B, Fig. 1c and Fig. 4 right), even during the dry season (when the LWL was at point B).
When SRMs were partly submerged in lake water during thenormal and wet seasons, the solute distributions on the slope facewere affected by the SRMs (Fig. 5b and c). Although solute concentrations along the slope were more broadly distributed than water
ﬂuxes, solute ﬂuxes closely reﬂected water ﬂuxes, being concentrated in a narrow portion of the slope (Fig. 4 right). Major nitratetransport occurred through a narrow zone at the upper slope-face.
Except for the concrete-slope (assumed no-ﬂow) conditions, asmall portion of solute transport occurred through the seepage face
above the LWL (Fig. 6).
Fig. 5 shows that solute ﬂux distributions on the slope face aredifferent from water ﬂux distributions. Water ﬂuxes displayed two
peaks during the normal and wet seasons when two surface

Fig. 5. Distributions of chloride (left) and nitrate (right) concentrations on the slope under bare-, lime-, and concrete-slope conditions at 120 day during the dry (a, d), normal(b, e), and wet (c, f) seasons. See Fig. 1c for the deﬁnition of letters A, B, C, D, and O. The vertical green dashed lines indicate the extent of saturated and unsaturated zones. C0:
the input solute concentration from the ﬁshpond/paddy ﬁeld.

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1.000

0.700

0.500

0.300

0.250

0.200

0.150

0.100

0.050

0.025

0.000

C/C0:

Fig. 6. Relative concentration (C/C0) proﬁles of nitrate at 120 day under bare-, lime-, and concrete-slope conditions during the dry, normal, and wet seasons. The dashed line
indicates the groundwater table. C0: the input nitrate concentration from the ﬁshpond/paddy ﬁeld.

materials (i.e., lime and soil, or concrete and soil) were used on theslope face. Fig. 6 also shows that in the lakeshore zone, peaks ofnitrate concentrations during the dry and normal seasons occurred
above those of the GWT, while during the wet season they werenear the GWT. As the LWLs increased, nitrate concentration
plumes became more extended in both horizontal and verticaldirections. Higher LWLs thus shortened the water and nitratetransport pathways. Additionally, as the hydraulic conductivity of
the cover material decreased (for example from bare, to lime,
and to concrete), more nitrate was transported through the slope
face at the bottom of the slope (at point O). Particularly for the concrete cover, the SRM signiﬁcantly altered both the water andnitrate ﬂow paths (Fig. 6).

3.5. Water and solute transport through the seepage face
Due to the presence of a seepage face on the slope above the LWL,
water and solutes ﬂowed into the lake through both the seepage face
and the submerged zone (Fig. 6). The water ﬂux (per a unit width of
the tank) decreased with the decline in the hydraulic permeability of
SRMs from bare conditions, to lime, and to concrete (Fig. 7a). Differences in the total ﬂux became more signiﬁcant during the normal
and wet seasons when a part of the SRMs were submerged. During
the dry season, the fraction of the total ﬂux due to the ﬂux throughthe seepage face declined from 8.5% for a bare soil, to 2.2% for a lime
cover, and to zero for a concrete cover. During the normal and wet

seasons, these fractions dropped from 9.1% to 4.3%, and to zero,and from 6.7% to 2.9%, and to zero, respectively.
A fraction of solutes transported through the unsaturated zone
and the seepage face was in general larger than a corresponding
fraction of water. For the conservative solute chloride, the quantity
traveling through the submerged zone on the slope face was almost
the same for all conditions (Fig. 7b). On the other hand, the quantities of chloride traveling through the seepage face were signiﬁcantly different, and decreased with the decline in the hydraulicconductivity of SRMs. The difference in the chloride ﬂux (per a unit
width of the tank) between different scenarios mostly resulted fromthe solute ﬂux through the seepage face. On the other hand, thechloride ﬂuxes through the seepage face declined with the increaseof the LWL for all SRM conditions.
The nitrate ﬂuxes (per a unit width of the tank) through boththe seepage face and the submerged zone are markedly lower thanthe chloride ﬂuxes due to denitriﬁcation. During the dry season,
the nitrate ﬂuxes through the submerged zone were almost thesame for different SRM conditions (Fig. 7c), while through theseepage face they decreased from 242.5 mg cm1 day1 for baresoil, to 138.0 mg cm1 day1 for a lime cover, and to zero for a concrete cover. However, during the normal and wet seasons, thenitrate ﬂuxes through both the seepage face and the submergedzone decreased with a decline in the hydraulic conductivity of
SRMs. A decline in the total solute ﬂuxes through the seepage face
was much more signiﬁcant than through the submerged zone. During the dry, normal, and wet seasons, the ratios of the solute ﬂux

Y. Li et al. / Journal of Hydrology 520 (2015) 123–133

131

Fig. 7. Fluxes of water (a), chloride (b), and nitrate (c) through the seepage face and the submerged zone of the slope face under bare-, lime-, and concrete-covered conditionsat 120 day during the dry, normal, and wet seasons.

through seepage face to the total solute ﬂux decreased from 22.4%
for bare soil, to 14.2% for a lime cover, and to zero for a concrete
cover, from 20.2% (bare), to 11.1% (lime), to zero (concrete), andfrom 11.4% (bare), to 7.6% (lime), to zero (concrete), respectively.

4. Discussion
4.1. Flux distributions on the slope-facePrevious studies have reported that the ﬂux distribution along aslope-face follows an exponential function, increasing with the distance from the lake bottom (McBride and Pfannkuch, 1975;
Winter, 1978; Shaw et al., 1990). Namely, the ﬂux gradually
increases with d/D and rapidly ascends near the LWL on the slope
face. Shaw et al. (1990) found, based on ﬁeld observations using
seepage meters in Narrow Lake (Alberta), that the average seepage
ﬂux decreased with the distance from the shore. Genereux andBandopadhyay (2001) reported, using MODFLOW simulations, that
seepage rates on a lakebed could be ﬁtted well with an exponentialfunction. Li and Wang (2007) also reported that the seepage ﬂux
along a lakeshore could be well ﬁtted with an exponential function,and that the largest ﬂuxes occurred within a narrow portion of theslope near the LWL. Our simulations (Fig. 4) conﬁrm these results
when the hydraulic conductivity of the slope face is uniform, suchas under bare-slope conditions. For three LWLs, half of all water
enters the lake within 0.18D, 0.24D, and 0.31D from point O underbare-slope conditions, and within 0.23D, 0.31D, and 0.38D underlime-slope conditions, respectively. Very similar results were previously reported in the literature. For example, Lee (2000) reported
for hypothetical steady-state conditions that all predicted groundwater inﬂow into Lake Barco occurred within 5 m off the shore inwater less than 0.4 m deep, and the majority of inﬂow occurred
within 3 m off the shore in water less than 0.3 m deep. Wilson
and Gardner (2006) also found that, at all stages of the tide, thelargest velocities of groundwater ﬂow developed just below theintersection of the tide at the river bank, and most ﬂow occurred
within 15 m of the river.
However, some ﬁeld studies have shown non-exponential relationships of the seepage ﬂux on the slope face (Cherkauer andNader, 1989; Shaw and Prepas, 1990; Schneider et al., 2005). Thisis because hydraulic properties (such as the hydraulic conductivity)
were unevenly distributed along the slope face in most ﬁeld studies.
Kishel and Gerla (2002) found a high degree of seepage heterogeneity across a 170-m2 area near the lakeshore of the Shingobee Lake
(USA). Likewise, Guyonnet (1991) showed how small-scale sediment variations in relatively thin, either high- or low-permeability
layers can have a signiﬁcant effect on the seepage distribution.
Genereux and Bandopadhyay (2001) reported that low-permeability
lakebed sediments could have a major effect on the spatial distribution of the lake-bed seepage in both inﬂow or ﬂow-through lakes,
even when the sediments are of a constant thickness over the entire
lake bed. The lower the permeability of lake-bed sediments, themore even the distribution of seepage ﬂuxes. In a small area examined, the discharge ﬂux irregularly decreased with the distance into
the lake, indicating that sediment heterogeneity plays an importantrole in the distribution of groundwater discharge (Kishel and Gerla,2002). In addition to these factors, the regional hydrogeology significantly affects the seepage distribution on the slope face. Our simulated results also show that when different types of materials
cover the slope face, the ﬂux distribution does not follow the exponential distribution (Fig. 4). These conﬂicting results suggest that
underlying processes controlling the lakeshore seepage need additional clariﬁcation (Schneider et al., 2005).
The well-ﬁtted exponential distributions were usually derived
for hypothetical or theoretical conditions using mostly model simulations, rather than collected experimental data. Additionally, thevertical hydraulic conductivity signiﬁcantly affected the seepage
ﬂux distributions. Genereux and Bandopadhyay (2001) found that
seepage rates along the lake bed simulated using the 2D MODFLOW model were signiﬁcantly different from those simulatedusing the 3D model.

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Y. Li et al. / Journal of Hydrology 520 (2015) 123–133

Furthermore, we can see that the exchange of water and solutes
at the slope bottom (near point O) was signiﬁcantly smaller compared to those at points B, C, and D during three seasons (Fig. 6).
This implies that solutes accumulate near point O. Many studies(i.e. Fischer et al., 2005; Boulton et al., 2010; Stelzer et al., 2011)
reported that nutrients or pollutants are prone to accumulate at
the bottom of the hyporheic zone.
4.2. Seepage face
A portion of water ﬂowing through a seepage face is an important characteristic of the exchange between ground water and surface water. Many simulated and observed results have reported theexistence of a seepage face and its effects on water ﬂow and solutetransport (Vachaud et al., 1973; Simpson et al., 2003; Rushton,
2006; Chenaf and Chapuis, 2007). For example, in a sand box
experiment involving radial ﬂow and transport, Simpson et al.
(2003) found that the ﬂow velocity through the seepage face wasabout 30% higher than at the base of the aquifer, while the solutetransport patterns were strongly inﬂuenced by the ﬂow characteristics of the system. Yakirevich et al. (2010) also reported that a
seepage face might be responsible for causing the early arrival ofsolutes and the overall shape of the BTCs. Yuan et al. (2011)
reported that if the solute originates from the near shore surface
land, such as wetlands, the solute ﬂux from the seepage face provides an important source of solute for surface water.
Our simulated results show that when the source of surface pollution is on the land surface near the lake, both water and pollutants ﬂow into the lake partly through the seepage face (Figs. 6
and 7). Moreover, the ratios of water and solute ﬂuxes throughthe seepage face to the total ﬂuxes through the entire slope faceﬂuctuate with the LWL. They accounted for about 6.7–9.1% of thetotal discharge under bare-slope conditions, while they were only
about 2.2–4.3% under lime-slope conditions. The seepage facelength on the slope face is easily inﬂuenced by the surface waterlevel, which is further affected by wind waves and precipitation.
However, we could not conﬁrm that the seepage face has an accelerating effect on the solute transport due to different ﬂow paths tothe slope face. The distribution of hydraulic conductivity on theslope face also affects the seepage face length.
Additionally, the seepage face is also a connecting interface
between groundwater and atmosphere. Groundwater ﬂows throughthe soil towards an open boundary where the environmental factors, which may affect various reaction rates such as nitriﬁcationand denitriﬁcation, are very different. Burgin and Groffman (2012)
reported that soil O2 was consistently lower in the area closest to
the stream and increased further from the stream. In this case, thenitriﬁcation rate increases and the denitriﬁcation rate decreases
rapidly near the seepage face (Burgin and Groffman, 2012).
5. Conclusions
Lakeshore is an important transition zone connecting lakewater and surrounding groundwater. The hydrological connectivity signiﬁcantly affects the exchange of water and solutes between
surface waters and groundwater and the ﬂux distribution of waterand solutes on the slope face. Slope revetment materials artiﬁciallychange the local hydrological connectivity by altering the hydraulic conductivity of the slope face and consequently change thehydrological dynamics and nutrient discharge into lake water.
Based on the soil tank experiments and Hydrus-2D simulations,the distributions of water and solute ﬂuxes and solute concentrations on the shoreline face depend largely on the distribution of
the soil hydraulic conductivity of the slope face. Uneven distributionof the hydraulic conductivity results in a non-exponential distribution of water and solute ﬂuxes. Most water and solute discharge into

the lake within a narrow zone near the intersection point of the lakewater level and the slope face. Relatively low-conductivity slope
revetment materials change the seepage ﬂow path, increase theseepage face length, and increase the ratio of water and solutes
transported through the unsaturated zone. These changes may
affect denitriﬁcation processes in the near-shore region, by changing local water contents in the lakeshore zone. Relatively low
exchange of water and solutes at the lakeshore bottom may leadto the accumulation of pollutants at the bottom of the hyporheic
zone. The Hydrus-2D model proved to be a useful tool for analyzing
the hydrodynamics and solute transport in a lakeshore zone and forproviding better understanding of associated factors and processes.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No: 51079048), the Ministry of Education Key Laboratory of Integrated Regulation and Resource Development on
Shallow Lakes (No: 2008KJ003), the Water Conservancy Scienceand Technology Project of Jiangsu Province (No: 2013071), andthe China Scholarship Council.
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