Stream Stage Research Articles

Implications of anthropogenic river stage fluctuations on mass transport in a valley fill aquifer

In humid regions a strong coupling between surface water features and groundwater systems may exist. In these environments the exchange of water and solute depends primarily on the hydraulic gradient between the reservoirs. We hypothesize that daily changes in river stage associated with anthropogenic water releases (such as those from a hydroelectric dam) cause anomalous mixing in the near‐stream environment by creating large hydraulic head gradients between the stream and adjacent aquifer. We present field observations of hydraulic gradient reversals in a shallow aquifer. Important physical processes observed in the field are explicitly reproduced in a physically based two‐dimensional numerical model of groundwater flow coupled to a simplistic surface water boundary condition. Mass transport simulations of a conservative solute introduced into the surface water are performed and examined relative to a stream condition without stage fluctuations. Simulations of 20 d for both fluctuating river stage and fixed high river stage show that more mass is introduced into the aquifer from the stream in the oscillating case even though the net water flux is zero. Enhanced transport by mechanical dispersion leads to mass being driven away from the hydraulic zone of influence of the river. The modification of local hydraulic gradients is likely to be important for understanding dissolved mass transport in near‐stream aquifer environments and can influence exchange zone processes under conditions of high‐frequency stream stage changes.

Use of spatially distributed stream stage recorders to augment rain gages by identifying locations of thunderstorm precipitation and distinguishing rain from snow

Precipitation measurements in complex terrain are difficult to obtain, particularly during convective thunderstorm precipitation or mixed rain and snow. In such cases, stream stage recorders distributed across many small, headwater streams can bridge the gap between point measurements of precipitation and larger‐scale total basin discharge. We use case studies from two steep basins with shallow soils in the Sierra Nevada, California to illustrate how distributed stream sensors can help identify the location, timing, and intensity of spatially variable precipitation.

Seasonal and inter‐annual variability in hyporheic water quality revealed by continuous monitoring in a salmon spawning stream

AbstractOver a 3.5 year period, levels of dissolved oxygen (DO) saturation were continuously monitored in surface waters and at depths of 150 and 300 mm in the hyporheic zone of a riffle in a montane stream where Atlantic salmon spawn. Throughout this period, DO in surface waters remained close to 100% saturation, but exhibited daily variations related to CO2 cycling driven by diurnal patterns of respiration and photosynthesis. However, in the hyporheic zone, variations were much more dynamic over storm event, seasonal and inter‐annual timescales. At 300 mm, DO saturation was generally close to 100% during summer low flows, though levels occasionally fell during warm periods which appeared to be related to diffusion gradients caused by benthic respiration. Such DO decreases at low flows were much more common and marked at 150 mm. During wetter conditions, DO saturation at 300 mm fell to zero for prolonged periods; this is consistent with increased fluxes of groundwater discharging through the hyporheic zone. During the wettest periods this also affects DO saturation at 150 mm. However, during hydrological events, hyporheic water quality is ‘re‐set’ as head reversals cause streamwater ingress which results in transient periods of re‐oxygenation, which end during the hydrograph recession. This is consistent with stream‐ward hydraulic gradients being re‐established in riparian ground water as the stream stage falls. The connectivity between groundwater and streamwater through the hyporheic zone is driven by climatic conditions and is reflected in marked inter‐annual variability in water quality characteristics. In some cases, this variability may have implications for the ecology of the hyporheic environment—including the survival of salmon eggs—particularly if oxygen levels are affected. Copyright © 2009 John Wiley & Sons, Ltd.

Use of heat to estimate streambed fluxes during extreme hydrologic events

Using heat as a tracer, quantitative estimates of streambed fluxes and the critical stage for flow reversal were calculated for high‐flow events that occurred on the Bogue Phalia (a tributary of the Mississippi River) following the 2005 Hurricanes Katrina and Rita. In June 2005, piezometers were installed in the Bogue Phalia upstream from the stream gage near Leland, Mississippi, to monitor temperature. Even with the hurricanes, precipitation in the Bogue Phalia Basin for the months of June to October 2005 was below normal, and consequently, streamflow was below the long‐term average. Temperature profiles from the piezometers indicate that the Bogue Phalia was a gaining stream during most of this time, but relatively static streambed temperatures suggested long‐term data was warranted for heat‐based estimates of flux. However, the hurricanes caused a pair of sharp rises in stream stage over short periods of time, increasing the potential for rapid heat‐based modeling and for identification of the critical stage for flow reversal into the streambed. Heat‐based modeling fits of simulated‐to‐measured sediment temperatures show that once a critical stage was surpassed, flow direction reversed into the streambed. Results of this study demonstrate the ability to constrain estimates of streambed water flux and the critical stage of flow reversal, with little available groundwater head data, by using heat as a tracer during extreme stage events.

Characterizing Storm Hydrograph Rise and Fall Dynamics With Stream Stage Data1

Abstract: Storm‐flow transients (i.e., hydrograph rise and fall dynamics) may represent an important aspect of understanding streamflow dynamics. However, little is known about how temporal resolution of transient data and climate variability may color these potential indicators of hydrologic pattern or condition. Warm‐season stream stage and rainfall were monitored continuously (5 min) during the 2002 water year in eight tributaries of the Little Miami River (Ohio), which drain 17‐58 km2 catchments. Rise rates generated using 5‐min data were different than those generated with mean daily data [calculated with the Indicators of Hydrologic Alteration (IHA) software], though fall rates were similar for fine and coarse temporal data. This result suggests that data with low temporal resolution may not be adequate to fully represent the dynamics of storm rise rates. Conversely, fall rates based on daily stage data (via IHA) were similar to those based on the 5‐min data, and so daily mean data may be appropriate for characterizing fall rates. We next analyzed the possible correlations between rainfall variability and storm‐flow stage dynamics. We derived rise and recession rates from storm stage hydrographs by assuming exponential rise and decay of a runoff peak. We found that raw rise rates (Rraw) were correlated with both the maximum rainfall rate and the time to the centroid of a rain event. We subsequently removed the trend based on these rainfall characteristics, which yielded new representations of rise rates abbreviated as Rrate and Rtcent, respectively, and that had lower variability than the uncorrected (raw) data. Fall rates were found to be independent of rainfall characteristics. Due to the predominant influence of stream hydrology upon aquatic biota and nutrient fluxes, our work suggests that these stage data analysis protocols can refine or otherwise reduce variability in these indices by accounting for relevant factors such as rainfall forcing. These protocols for derivation of transient indices should be tested for their potential to improve correlations between stream hydrology and temporally aligned biotic data and dissolved nutrient fluxes in streams.

Quantifying Bank Storage of Variably Saturated Aquifers

Numerical simulations were conducted to quantify bank storage in a variably saturated, homogenous, and anisotropic aquifer abutting a stream during rising stream stage. Seepage faces and bank slopes ranging from 1/3 to 100/3 were simulated. The initial conditions were assumed steady-state flow with water draining toward the stream. Then, the stream level rose at a constant rate to the specified elevation of the water table given by the landward boundary condition and stayed there until the system reached a new steady state. This represents a highly simplified version of a real world hydrograph. For the specific examples considered, the following conclusions can be made. The volume of surface water entering the bank increased with the rate of stream level rise, became negligible when the rate of rise was slow, and approached a positive constant when the rate was large. Also, the volume decreased with the dimensionless parameter M (the product of the anisotropy ratio and the square of the domain's aspect ratio). When M was large (>10), bank storage was small because most pore space was initially saturated with ground water due to the presence of a significant seepage face. When M was small, the seepage face became insignificant and capillarity began to play a role. The weaker the capillary effect, the easier for surface water to enter the bank. The effect of the capillary forces on the volume of surface water entering the bank was significant and could not be neglected.

Does Learned Shape Selectivity in Inferior Temporal Cortex Automatically Generalize Across Retinal Position?

Biological visual systems have the remarkable ability to recognize objects despite confounding factors such as object position, size, pose, and lighting. In primates, this ability likely results from neuronal responses at the highest stage of the ventral visual stream [inferior temporal cortex (IT)] that signal object identity while tolerating these factors. However, for even the apparently simplest IT tolerance ("invariance"), tolerance to object position on the retina, little is known about how this feat is achieved. One possibility is that IT position tolerance is innate in that discriminatory power for newly learned objects automatically generalizes across position. Alternatively, visual experience plays a role in developing position tolerance. To test these ideas, we trained adult monkeys in a difficult object discrimination task in which their visual experience with novel objects was restricted to a single retinal position. After training, we recorded the spiking activity of an unbiased population of IT neurons and found that it contained significantly greater selectivity among the newly learned objects at the experienced position compared with a carefully matched, non-experienced position. Interleaved testing with other objects shows that this difference cannot be attributed to a bias in spatial attention or neuronal sampling. We conclude from these results that, at least under some conditions, full transfer of IT neuronal selectivity across retinal position is not automatic. This finding raises the possibility that visual experience plays a role in building neuronal tolerance in the ventral visual stream and the recognition abilities it supports.

Effect of freshets on the flux of groundwater nitrate through streambed sediments

The passage of a flood wave over sandy stream sediments can cause changes in the discharge of groundwater to the stream that range from a transient reduction in the discharge rate to a reversal of flow and temporary storage of stream water in the stream sediments. These phenomena were examined in laboratory studies with an intact core and by numerical modeling to assess the effect of both physical and biological processes on the nitrate flux from nitrate‐contaminated groundwater to a stream. The balance between the rates of groundwater flow through organic‐rich sediments and of denitrification ultimately determines the efflux of nitrate to the stream. The transient impact on nitrate loading suggested by results from the numerical model indicates that high flood stage and low‐sediment hydraulic diffusivity can result in excess nitrate loading to surface water following storm events, whereas large‐sediment hydraulic diffusivity, regardless of the size of stream stage changes, facilitates greater removal of NO3− by denitrification by allowing for a longer residence time of water in the subsurface.

FTABLE Generation Method Effects on Instream Fecal Bacteria Concentrations Simulated With HSPF1

Abstract: Computer simulation models are used extensively for the development of total maximum daily loads (TMDLs). Specifically, the Hydrological Simulation Program‐FORTRAN (HSPF) is used in Virginia for the development of TMDLs for bacteria impairments. HSPF estimates discharge from a reach using function tables (FTABLES). The FTABLE relates stream stage, surface area, and volume to discharge from a reach. In this study, five FTABLE estimation methods were assessed by comparing their effect on various simulation outputs. Four “field‐based” methods used detailed cross‐sectional data collected via site surveys. A fifth “digital‐based” method used digital elevation data in combination with the Natural Resources Conservation Service Regional Hydraulic Geometry Curves. Sets of FTABLEs created using each method were used in simulations of instream bacteria concentration for a Virginia watershed. Several statistics relating to instream bacteria including long‐term average concentration, die‐off, and the violation rate of Virginia’s bacteria criterion were compared. The pair‐wise Student’s t‐test was used for the comparison. The HSPF simulations that used FTABLES estimated from digitally based data consistently produced significantly higher long‐term average instream fecal bacteria concentrations, significantly lower instream fecal bacteria die‐off, which is related to differences in residence time in the streams, and significantly higher water quality criterion violation rates.

On diurnal riparian zone groundwater-level and streamflow fluctuations

Summary Gribovszki et al. (Gribovszki, Z., Kalicz, P., Szilagyi, J., Kucsara, M., 2008. Riparian zone evapotranspiration estimation from diurnal groundwater-level fluctuations. J. Hydrol.) recently reported a peculiar phase-shift in diurnal streamflow and riparian zone groundwater-level fluctuations during streamflow recession for a small forested watershed. Employing high-frequency (10 min) groundwater-level and streamflow measurements in a wooded riparian zone of a gaining stream they demonstrated that groundwater-level changes lagged behind that of streamflow changes by about 1–1.5 h. To check the validity of their claim, a 2D finite element numerical model of the coupled system of vadose and saturated zones was employed with diurnal fluctuations in evapotranspiration. The model successfully reproduced the reported phase-shift and produced diurnal groundwater and streamflow fluctuations similar in their characteristics to what was reported. This finding demonstrates that by observing a similar phase-shift in diurnal fluctuations between high-frequency streamflow rate (or stream stage) and groundwater-level measurements during recession flow conditions, does not, in itself, indicate that the stream section is a losing one.

Changes in streambank erodibility and critical shear stress due to subaerial processes along a headwater stream, southwestern Virginia, USA

Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility ( k d) and critical shear stress ( τ c) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in k d and τ c from soil desiccation and freeze–thaw cycling. Soil erodibility and τ c were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted k d was 2.9 and 2.1 times higher ( p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in k d was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions ( r 2 = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.

A Numerical Modeling System of the Hydrological Cycle for Estimation of Water Fluxes in the Huaihe River Plain Region, China

Abstract To analyze the water budget under human influences in the Huaihe River plain region in China, the authors have developed a numerical modeling system that integrates water flux algorithms into a platform created by coupling a soil moisture model with the modular three-dimensional finite-difference groundwater flow model (MODFLOW). The modeling system is largely based on physical laws and employs a numerical method of the finite difference to simulate water movement and fluxes in a horizontally discretized watershed or field. The majority of model parameters carry physical significance and can be determined by field and laboratory measurements or derived from watershed characteristics contained in GIS and remote sensing data. Several other empirical parameters need to be estimated by model calibration. The numerical modeling system is calibrated in the Linhuanji catchment (2 560 km2) to estimate surface runoff, groundwater recharge, and groundwater loss for evapotranspiration and stream baseflow. Model validation is conducted at a small runoff experimental field (1.36 km2) in the Wuduogou Hydrological Experimental Station to test the model’s capability to simulate hydrological components and estimate water fluxes using observed stream stage and groundwater data, as well as lysimeter-measured precipitation recharge and groundwater loss. As proven by the promising results of model testing, this physically based and distributed-parameter model is a valuable contribution to the ever-advancing technology of hydrological modeling and water resources assessment.

Riparian hydroecology: A coupled model of the observed interactions between groundwater flow and meadow vegetation patterning

Stream incision is altering the hydroecology of riparian areas worldwide. In the Last Chance watershed in the northern Sierra Nevada, California, logging, overgrazing, and road/railroad construction have caused stream incision, which resulted in drainage of riparian meadow sediments and a succession from native wet meadow vegetation to sagebrush and dryland grasses. Restoration efforts have been initiated to reestablish the ecosystem function of these systems. Original field data including stream stage records, water table hydrographs, sediment hydraulic properties, topographic transects, and aerial imagery of vegetation patterning were used to develop a model of an archetype meadow. Hydrologic behavior was simulated with a finite element model of variably saturated groundwater flow. This model was coupled to an empirical, time‐dependent, vegetation threshold relationship between vegetation type and depth to the water table. This was a two‐way coupling requiring an iterative approach because water table depth is a determinant of vegetation type, yet the vegetation regime influences water table depth through evapotranspiration. The hydrology and vegetation patterns were analyzed under pristine, degraded (incised), and restored conditions. For the case of deep streambed incision, our hydroecological model predicts the observed shift from mesic (wetter) to xeric (drier) vegetation communities and reproduces their imaged longitudinal zonation. This patterning is explained as a response to groundwater drainage to the stream, which creates dry zones with xeric vegetation adjacent to the stream, while preserving sufficient moisture at the margins of the meadow to support holdout populations of mesic vegetation. The model further predicts the reestablishment of meadow vegetation when the incised channel is filled and a new shallow channel is restored. The coupling of a near‐surface hydrologic model to a vegetation response model may be used to design stream restoration projects by predicting vegetation patterning.

Discussion of “Stream Multiaquifer Well Interactions” by Govinda C. Mishra and Mohd Fahimuddin

The authors have attempted to analyze unsteady flow to a well taping two aquifers under the influence of an unsteady stream stage. The following points are raised: 1. Although it has been acknowledged that most streams only partially penetrate the upper aquifer, the study is based on a stream that fully penetrates the upper aquifer, thereby limiting its application. 2. The symbol K is used to denote unit step response function for rise in stream stage. This introduces some confusion as K is generally used to denote hydraulic conductivity. 3. Eq. 3 when used with s shows that the stream stage needs to be broken down into a number of time steps even for a constant rate of rise. Although theoretically, a single time step can be used for a constant rate of rise of stream stage, defining s thus increases the computations as the explicitly appearing t has been implicitly incorporated into s. Eq. 7 is a repetition of an earlier proposed equation equation below Eq. 3 . 4. The image well theory is generally applied for a constant stage of stream. The authors have applied the image well theory, assuming that the stream stage varies with time. This should have been explicity stated because such an application yields inconsistencies. 5. The authors have used two types of kernels for solving convolution equations. The kernels p1, p2, pi, and in are similar but different from the kernel s. This introduces inconsistency. Kernels defined on a similar basis should have been used. In view to keep uniformity of kernels, the s needs to be defined as was done by Singh 1994 . The following equation from Singh 1994, p. 19 is reproduced here

Groundwater head responses due to random stream stage fluctuations using basis splines

Stream‐aquifer interactions are becoming increasingly important processes in water resources and riparian management. The linearized Boussinesq equation describes the transient movement of a groundwater free surface in unconfined flow. Some standard solutions are those corresponding to an input, which is a delta function impulse, or to its integral, a unit step function in the time domain. For more complicated inputs, the response can be expressed as a convolution integral, which must be evaluated numerically. When the input is a time series of measured data, a spline function or piecewise polynomial can easily be fitted to the data. Any such spline function can be expressed in terms of a finite series of basis splines with numerical coefficients. The analytical groundwater response functions corresponding to these basis splines are presented, thus giving a direct and accurate way to calculate the groundwater response for a random time series input representing the stream stage. We use the technique to estimate responses due to a random stream stage time series and show that the predicted heads compare favorably to those obtained from numerical simulations using the Modular Three‐Dimensional Finite‐Difference Ground‐Water Flow Model (MODFLOW) simulations; we then demonstrate how to calculate residence times used for estimating riparian denitrification during bank storage.

Consideration for Unsaturated Flow beneath a Streambed during Alluvial Well Depletion

Unsaturated flow transforms streams from constant head boundaries to constant flux boundaries, impacting the quantity of stream recharge to groundwater. The objective of this research was to analyze the impact of unsaturated flow on stream/aquifer exchange by incorporating a three-regime, saturated/unsaturated flow, stream recharge model into MODFLOW, the most commonly used numerical flow model in ground water hydrology. This three-regime model extends prior research by accounting for a transition regime between fully saturated and gravity-driven unsaturated flow. Accounting for unsaturated flow between a stream and aquifer is necessary to adequately simulate stream depletion. Sensitivity analyses of steady stream recharge versus drawdown demonstrated that the transition regime became more important for cases with small stream stages, smaller streambed thicknesses, and larger entry pressure heads. Based on coarse sand and fine sand hypothetical scenarios, the transition regime in the proposed three-regime model could generally be neglected with minor error for most stream/aquifer scenarios. However, the transition regime became important when: (1) the drawdown stabilized near the range of drawdowns that represented the transition regime; and (2) there must be a significant difference (i.e., 0.2 m) in the entry and ultimate capillary pressure heads, which occurred with larger entry pressure heads (i.e., equal to or greater than 1.0 m) and a smaller pore size distribution index (i.e., approximately 1.0).

Response of sloping unconfined aquifer to stage changes in adjacent stream: II. Applications

Summary We convolve the system response functions of the linearised 1D equation of Boussinesq (extended for slope, Dupuit approximation) derived in the companion paper of Akylas and Koussis [Akylas, E., Koussis, A.D., (submitted for publication). Response of sloping unconfined aquifer to stage changes in adjacent stream: I. Theoretical analysis and derivation of system response functions, J. Hydrol] and develop solutions for the interaction of a fully penetrating stream with a sloping unconfined aquifer, taking also into account a low-conductivity streambed layer. These solutions give the aquifer stage and flow rate, the flow exchange rate at the stream–aquifer interface and the exchanged water volumes (bank storage/release). The solutions are analytical, when the flow-inducing stream stage variations are common functions; otherwise, the convolution integral is evaluated numerically. Responses are compared for aquifers on positive, negative and zero base slopes to a wave-like change in the stage of the stream. Analytical and numerical convolution-derived solutions are used to model the interaction of Cedar River and its adjacent unconfined aquifer near Cedar Rapids, Iowa. In the model, the aquifer base is taken to be horizontal or inclined and the streambed clogged by a low-conductivity sediment layer; the model is verified against data not used in the calibration and is found to perform very well.

Response of sloping unconfined aquifer to stage changes in adjacent stream. I. Theoretical analysis and derivation of system response functions

We study the interaction of a stream with a sloping unconfined aquifer that the stream is assumed to fully penetrate. The analysis applies to flow in a vertical section, considers the existence of a low-conductivity streambed layer and the flow in the aquifer to be induced by variations of the stream stage. Invoking the Dupuit assumption yields the 1-D Boussinesq equation, extended for a sloping base. The Boussinesq equation is linearised, the derived flow model is critiqued and an objective procedure for determining the linearisation level is developed. We solve the linear governing equation by the method of Laplace transform, with analytical inversion; the horizontal-aquifer case is treated in the zero-slope limit. The system response function is derived for the general case (sloping aquifer, sediment bed layer) and for several specific cases, and solutions are verified against known analytical results. Responses are contrasted for aquifers on positive, negative and zero slopes to step changes in the stage of streams with and without a sediment bed layer. The solutions give the aquifer stage and flow rate, the flow exchange rate at the stream-aquifer interface and the exchanged water volumes (bank storage/release).

Evaluation of the streambed leakage concept in analytical models using data from three pumping tests

Two-dimensional analytical models of pumping induced drawdown and stream depletion account for the streambed properties and stream geometry. Using data from three pumping tests performed under various hydrologic conditions, the following hypotheses were tested: (1) a partially penetrating stream at a certain distance from the pumping well can be represented by the streambed leakage term in the analytical models; (2) in the streambed leakage term, the streambed conductance coefficient λ=(WK′)/m′ accounts for the average stream width W, the streambed thickness m′, and hydraulic conductivity K′. The first hypothesis was tested by comparing results from tests under flow and no-flow stream conditions. The second hypothesis was tested by comparing results from two tests under low and high streamflow conditions. Similar estimates of the hydraulic conductivity and storativity for all tests indicate the validity of the streambed leakage term. The drawdown data of the test under low- and high-flow conditions (varying W) do not follow the predictions of the analytical models, which results in inconsistent λ estimates. Thus, for different hydrologic conditions, λ cannot be scaled solely by the stream width W. One possible explanation for this result is streambed dynamics caused by the changes in the stream stage.

Measuring streambank erosion due to ground water seepage: correlation to bank pore water pressure, precipitation and stream stage

AbstractLimited information exists on one of the mechanisms governing sediment input to streams: streambank erosion by ground water seepage. The objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow/erosion with precipitation, stream stage and soil pore water pressure. The streambank site was located in Northern Mississippi in the Goodwin Creek watershed. Soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity (Ks) with depth, but differences between lateral Ks of a concretion layer and the vertical Ks of the underlying layers contributed to the propensity for lateral flow. Goodwin Creek seeps were not similar to other seeps reported in the literature, in that eroded sediment originated from layers underneath the primary seepage layer. Subsurface flow and sediment load, quantified using 50 cm wide collection pans, were dependent on the type of seep: intermittent low‐flow (LF) seeps (flow rates typically less than 0·05 L min−1), persistent high‐flow (HF) seeps (average flow rate of 0·39 L min−1) and buried seeps, which eroded unconsolidated bank material from previous bank failures. The timing of LF seeps correlated to river stage and precipitation. The HF seeps at Goodwin Creek began after rainfall events resulted in the adjacent streambank reaching near saturation (i.e. soil pore water pressures greater than −5 kPa). Seep discharge from HF seeps reached a maximum of 1·0 L min−1 and sediment concentrations commonly approached 100 g L−1. Buried seeps were intermittent but exhibited the most significant erosion rates (738 g min−1) and sediment concentrations (989 g L−1). In cases where perched water table conditions exist and persistent HF seeps occur, seepage erosion and bank collapse of streambank sediment may be significant. Copyright © 2007 John Wiley &amp; Sons, Ltd.