Water Table Response Research Articles

Experimental and Modeling Investigation of Shallow Water Table Fluctuations in Relation to Reverse Wieringermeer Effect

Soil column experiments and modeling investigations were performed to study the behavior of shallow water table in response to various recharge events. Hence, shallow water table fluctuations inside sandy (Toyoura sand) and clayey (Chiba light clay) soil columns in response to surface and sub-surface recharge events were investigated under laboratory conditions. Experimental results showed that small application of water could raise the shallow water table level more than 100 times in depth in the case of Toyoura sand and more than 50 times in the case of Chiba LiC, reflecting a reverse Wieringermeer effect (RWE) response type of groundwater. This rise was associated with a prompt change of pressure head values which exhibited instantaneous fluctuations of centimeters due to the addition of millimeters of water. The recharge volumes leading to such disproportionate water table rise were successfully estimated using a simple analytical model based on the moisture retention curve of the soil and considering the hysteresis effect on soil water dynamics within the capillary fringe zone.

Shallow Water Table Response to Seasonal and Interannual Climate Variability

Headwater seepage wetlands occur near the base of slopes and bluffs, typically at the outer edge of a floodplain or stream corridor, and may serve important roles in local and regional biodiversity, water quality, and biogeochemical cycling. The features are surface expressions of the water table aquifer that flows from adjacent upslope land. The water table is the primary source of streamflow, especially baseflow, in many Coastal Plain streams, so changes in precipitation patterns and land use may impact local habitat and downstream water supply. This article reports on some of the trends and dynamics of the water table in headwater seepage areas on the South Carolina Coastal Plain at seasonal and interannual time scales. The two study sites are in the Four Hole Swamp and Halfway Swamp Creek watersheds. Shallow monitoring wells were installed in mid-2005 in four seepages along with continuous water level loggers. There was significant interannual variability in water table depth during the 5.5-year study interval. The pattern was similar between wells at the same site but not between sites, suggesting that local geomorphology and soils influence the groundwater travel time of precipitation to the seepage discharge. Diurnal water table dynamics also show similarity between wells at the same site but not between sites. At Four Hole Swamp there were significant seasonal differences but not at the Halfway Swamp Creek site. Site morphology, soils, and vegetation are hypothesized as key factors in these observations. These results suggest that the water table aquifer is a resource that requires explicit protection in the context of increased human development and uncertain trends in future precipitation.

A new analytical solution of water table response to tidal fluctuations and its application to estimate aquifer properties at the Niijima Island, Japan

地下水面の潮汐応答データを用いて原位置における沿岸不圧帯水層の物性評価を行うため、主要四分潮から成る潮位変動の境界条件の下でBoussinesq方程式の摂動解を導いた。得られた摂動解を用いて、伊豆諸島新島の白ママ層中の不圧帯水層の地下水面変動の時系列観測データに対するパラメータフィッティングを行い、帯水層物性評価を試みた。その結果、透水量係数が0.12∼1.7m2/sであると推定された。この結果は、地下水面変動の振幅・位相のどちらからも同様な値が求められおり、さらにDupuit-Ghyben-Herzbergモデルを用いた解析の結果とも矛盾しておらず、適切に評価されたと考えられる。

Heterogeneous water table response to climate revealed by 60 years of ground water data

Recent findings suggest that climate change will lead to modifications in the timing and nature of precipitation, giving rise to an altered hydrologic cycle. The response of subsurface hydrology to decadal climate and longer‐term climate change to date has been investigated via site specific analyses, modeling studies, and proxy analysis. Here we present the first instrumental long‐term regional compilation and analysis of the water table response to the last 60 years of climate in New England. Ground water trends are calculated as normalized anomalies and analyzed with respect to regional compiled precipitation, temperature, and streamflow. The time‐series display decadal patterns with ground water levels being more variable and lagging that of precipitation and streamflow pointing to site specific and non‐linear response to changes in climate. Recent trends (i.e., last 10 years) suggest statistically significant increasing water tables, which could lead to a higher risk for flooding in New England.

Water table response to an experimental alley farming trial: dissecting the spatial and temporal structure of the data

Clearing vegetation for traditional agriculture diminishes native habitat and reduces plant transpiration, leading to increased groundwater recharge and onset of dryland salinization due to rising groundwater and mobilization of salt stores in the soil profile. This change in hydrology and salinity can also negatively affect biodiversity in many semiarid regions. Alternating native perennial tree belts with mono-species agriculture within the tree belt alleys is one possible system that can provide recharge control and recover some of the ecosystem services of degraded agricultural landscapes. To assess the effect of this agroforestry technique on groundwater levels, an alley farming trial was established in 1995, incorporating different combinations of belt width, alley width, and revegetation density. Transects of piezometers within each design have been monitored from October 1995 to January 2008. The data set consisted of 70 piezometers monitored on 39 dates. Two trends were observed within the raw data: An increase in water table depth with time and an increase in the range of depths monitored at the site were clearly discernible. However, simple hydrograph analysis of the data has proved unsuccessful at distinguishing the effect of the tree belts on the water table morphology. The statistical techniques employed in this paper to show the effect of the experiment on the water table were variation partitioning, principal coordinates of neighbor matrices (PCNM), and canonical redundancy analysis (RDA). The environmental variables (alley farming design, distance of piezometer from the tree belt, and percentage vegetation cover including edge effect) explained 20-30% of the variation of the transformed and detrended data for the entire site. The spatial PCNM variables explained a further 20-30% of the variation. Partitioning of the site into a northern and southern block increased the proportion of explained variation for the plots in the northern block. The spatial PCNM variables and vegetation cover remained the most significant variables. The PCNM analysis revealed no spatial pattern that could be attributed to the trial. The high proportion of unexplained variation may be due to site variables that have not been considered in this study.

Water-table response to tidal forcing at sloping beaches

The groundwater response to tidal forcing is described by Laplace’s equation for the hydraulic head subject to appropriate boundary conditions. A previous solution to this problem based on long-wave and shallow-aquifer approximations is extended to higher-order and a general solution scheme, automated in Mathematica, is described. The solution can, in principle, be extended to arbitrary order, but is restricted to a detailed study of the properties of the solution when truncated to sixth-order. These results show that the mean water table height increases throughout the aquifer to a steady inland height elevated above mean sea level. The phase shift of the fluctuations and the asymmetry of the pore drainage process are investigated using Fourier analysis.

Water table response to a tidal agitation in a coastal aquifer: The Meyer–Polubarinova-Kochina theory revisited

The linear potential model of Meyer and Polubarinova-Kochina (MPK) solves Laplace’s equation in a quadrant, the vertical face of which is subject to a harmonic variation of hydraulic head induced by a tide. On the horizontal face of the quadrant a linear combination of the partial derivatives of the head with respect to time and with respect to the vertical Cartesian coordinate are linearly related. The fields of pore pressure (head) and Darcian velocity, trajectories of marked particles, the oscillating phreatic surface and its upper envelope are obtained. Hydrograph in a piezometer located 60 m from the shore line in a thick unconfined coastal aquifer (Oman) is interpreted by the analytical results of the model using the detected groundwater amplitude attenuated as compared with the tide amplitude. MPK method provides a potentially superior description to the Dupuit–Forchheimer method for tidally driven phreatic systems.

Combining unsaturated and saturated hydraulic observations to understand and estimate groundwater recharge through glacial till

Although there has been much previous research into various aspects of the flow mechanisms through glacial till, an integrated analysis of the flow system from the ground surface to the aquifer is lacking. This paper describes such an approach with reference to a detailed field study of the hydraulic processes controlling groundwater recharge through lodgement till in Shropshire, UK. A fieldsite was instrumented with tensiometers and piezometers at a range of depths through the profile, and the geology investigated in detail through field and laboratory testing. The median matrix hydraulic conductivity of the 6 m thick till is found to be around 2 × 10−10 m/s on the basis of laboratory measurements. Using the barometric efficiency of the till derived from on-site pressure responses, the specific storage for the till is found to be in the range 2 × 10−6–6 × 10−6 m−1 and approximately 3 × 10−6 m−1 for the underlying Permo-Triassic sandstone, the regional aquifer. The hydraulic data indicate that till water table responses to rainfall occur during the summer period even when large tensions are present higher in the profile. This is thought to be due to preferential flow through hydraulically active fractures in the till, which were observed in a test pit dug on-site. The field evidence indicates that the fractures are usually infilled with a variety of materials derived and transported from clasts within the till. The bulk hydraulic conductivity of the till seems to be greatly enhanced by these features and it is shown on the basis of hydraulic testing and numerical modelling that the bulk hydraulic conductivity of the till is orders of magnitude greater than that of the till matrix and reduces with depth below ground surface. The paper furthers understanding of the hydraulic processes contributing to recharge through till and makes the link between the detail of these processes and simplified models of recharge estimation, which may be needed for larger scale water resource studies. The results are relevant also to contaminant migration studies and aquifer vulnerability assessments.

Piezometric response in zones of a watershed with lateral preferential flow as a first‐order control on subsurface flow

AbstractCharacterizing zones of a watershed based on the water table is used to understand and predict internal watershed processes. In watersheds dominated by lateral preferential flow, the water table response typically shows a distinct hydraulically limited pattern. This response is characterized by a capping of the rising water table when the lateral preferential flow features are activated and subsurface flow still increases. We expected that this response would be related to the contributing area since nearby hillslope excavations showed that the development of preferential flow network was positively correlated with the contributing area. The watershed was stratified into three predetermined zones and installed 25 piezometers to measure the water table dynamics. The objectives were (1) to characterize the water table–runoff relationship, (2) to prove preferential flow by observable characteristics and (3) to test the feasibility of identifying areas within a watershed that are dominated by lateral preferential flow. Watershed zones were not well defined and there was no strong relationship between the hydraulically limited response and observable watershed characteristics. Although zones might still be useful for grouping the hillslope processes, the piezometric response may not be an appropriate indicator for mapping the watershed into areas with runoff dominated by lateral preferential flow. Copyright © 2010 John Wiley & Sons, Ltd.

Water balance modelling in a tropical watershed under deciduous forest (Mule Hole, India): Regolith matric storage buffers the groundwater recharge process

Accurate estimations of water balance are needed in semi-arid and sub-humid tropical regions, where water resources are scarce compared to water demand. Evapotranspiration plays a major role in this context, and the difficulty to quantify it precisely leads to major uncertainties in the groundwater recharge assessment, especially in forested catchments. In this paper, we propose to assess the importance of deep unsaturated regolith and water uptake by deep tree roots on the groundwater recharge process by using a lumped conceptual model (COMFORT). The model is calibrated using a 5 year hydrological monitoring of an experimental watershed under dry deciduous forest in South India (Mule Hole watershed). The model was able to simulate the stream discharge as well as the contrasted behaviour of groundwater table along the hillslope. Water balance simulated for a 32 year climatic time series displayed a large year-to-year variability, with alternance of dry and wet phases with a time period of approximately 14 years. On an average, input by the rainfall was 1090 mm year(-1) and the evapotranspiration was about 900 mm year(-1) out of which 100 mm year(-1) was uptake from the deep saprolite horizons. The stream flow was 100 mm year(-1) while the groundwater underflow was 80 mm year(-1). The simulation results suggest that (i) deciduous trees can uptake a significant amount of water from the deep regolith, (ii) this uptake, combined with the spatial variability of regolith depth, can account for the variable lag time between drainage events and groundwater rise observed for the different piezometers and (iii) water table response to recharge is buffered due to the long vertical travel time through the deep vadose zone, which constitutes a major water reservoir. This study stresses the importance of long term observations for the understanding of hydrological processes in tropical forested ecosystems. (C) 2009 Elsevier B.V. All rights reserved.

Relative impacts of key drivers on the response of the water table to a major alley farming experiment

Abstract. Widespread clearing of native vegetation in Southwest Western Australia has led to land degradation associated with rising groundwater, secondary salinisation and waterlogging. Re-establishing deep-rooted perennial vegetation across parts of the landscape is one technique for managing land degradation. Alley farming is an agroforestry practice where multiple perennial tree belts are planted in alternation with traditional agricultural crops. To identify the best configuration (belt width versus alley width) for controlling rising groundwater levels and providing viable economic returns, a large scale experiment was established in 1995. The experiment contains seven different alley farming designs, each with transects of piezometers running across tree belts into adjacent alleys to monitor changes in the groundwater level. Two control piezometers were also installed in an adjacent paddock. Groundwater at the site is shallow (<3 m) and of poor quality (pH 3–5, Ec 2.1–45.9 mS cm−1) so root water uptake from the saturated zone is limited. Simple hydrograph analysis could not separate treatment effects on the water table response. Subsequent statistical analysis revealed that 20–30% of the variability in the water table data over the 12 year study period was attributable to the alley farming experiment. To futher investigate the effect of the experiment on groundwater response, additional hydrograph analysis was conducted to compare the trends in the control piezometers in relation to those located within the belts. A difference of 0.9 m was observed between the mean groundwater levels in the control piezometers and the mean levels in the perennial belt piezometers. For a mean specific yield of 0.03 m3 m−3 (standard deviation of 0.03 m3 m−3) this equates to an additional average annual water use of 27 mm yr−1 (standard deviation of 33 mm yr−1) by the perennial agroforestry system. It is concluded that declining annual rainfall is the principal control on hydrograph response at the site, whilst perennial biomass development has a lesser impact on water table depth.

A model for flow in the chalk unsaturated zone incorporating progressive weathering

Summary Groundwater from unconfined chalk aquifers constitutes a major water resource in the UK. The unsaturated zone in such systems plays a crucial role in the hydrological cycle, determining the timing and magnitude of recharge, and the transport and fate of nutrients. However, despite more than three decades of study, our physical understanding of this system is incomplete. In this research, state of the art instrumentation provided high temporal resolution readings of soil moisture status, rainfall and actual evaporation from two sites in the Pang and Lambourn catchments (Berkshire, UK), for a continuous two year period (2004/5). A parsimonious, physically based model for the flow of water through the chalk unsaturated zone, including a novel representation of the soil and weathered chalk layers, was developed. The parameters were identified by inverse modelling using field measurements of water content and matric potential. The model was driven by rainfall and evaporation data, and simulated fluxes throughout the profile (including the discrete matrix and fracture components), down to the water table (but not the water table response). Results showed that the model was able to reproduce closely the observed changes in soil moisture status. Recharge was predominantly through the matrix, and the recharge response was strongly attenuated with depth. However, the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity. Relatively modest increases in rainfall led to dramatically different recharge patterns, with potentially important implications for groundwater flooding. The development and migration of zero flux planes with time and depth were simulated. The simulations also provided strong evidence that, for water table depths greater than 5 m, recharge fluxes persist throughout the entire year, even during drought conditions, with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models.

Time response of the water table and saltwater transition zone to a base level drop

This paper investigates the effect of a drainage base level drop on the groundwater system in its vicinity, using theoretical analysis, simulations, and field data. We present a simple and novel method for analyzing the effect of a base level drop by defining two characteristic times that describe the response of the water table and the transition zone between the fresh and saline water. The Dead Sea was chosen as a case study for this process because of the lake's rapid level drop rate. During a continuous lake level drop, the discharge attains a constant value and the hydraulic gradient remains constant. We describe this new dynamic equilibrium and support it by theoretical analysis, simulation, and field data. Using theoretical analysis and sensitivity tests, we demonstrate how different hydrological parameters control the response rate of the transition zone to the base level drop. In some cases, the response of the transition zone may be very rapid and in equilibrium with the water table or, alternatively, it can be much slower than the water table response, as is the case in the study area.

A Controlled Experiment to Determine the Water Table Response Using Ground Penetrating Radar

Ground penetrating radar (GPR) data were explored during a physical model experiment that utilized a polyethylene tank and an abiotic sand matrix to simulate water contamination in the vadose zone under fluctuating water table conditions. The main objective of this experiment was to determine the source of GPR reflections from a changing water table in a controlled experimental environment. During the experiment, the water table was varied by injecting water into the bottom of the tank and subsequently draining it. The experiment was conducted over a number of days, during which various conditions (unsaturated, saturated, residual saturation) were characterized using GPR measurements. As a result of this approach, a more comprehensive comparison was possible for each step and results were compared with mass balance information. Results of the study indicate that, under saturated conditions, the main reflector of GPR energy is indicative of the capillary fringe and not the actual water table. Well readings and estimates of the mass balance of water input into the system confirm this interpretation.

Influence of subhumid climate and water table depth on groundwater recharge in shallow outwash aquifers

Hypothetical one‐dimensional models of unsaturated flow were used to estimate the probability of groundwater recharge to shallow, glacial outwash aquifers. Simulations were supported by field data, previous three‐dimensional modeling, and cross‐sectional models of water table response to precipitation events for a research area in northern Alberta, Canada. Groundwater recharge rates were found to depend on the year‐to‐year climate variation, the depth to the water table, and were largely driven by annual snowmelt. Simulations indicate that in summer months, when transpiration and canopy interception were considered explicitly, groundwater recharge was negligible. For water table depths less than 6 m below ground surface, the occurrence of recharge depends on climatic conditions (water deficit or surplus) of the current and previous year, and can vary from 0 to 266 mm yr−1. For water table depths of 6 m or more, recharge will depend on climate conditions from the most recent decade, have less annual variability, and a mean annual rate of approximately 45 mm yr−1.

Hyporheic flow as a potential geomorphic agent in the evolution of channel morphology in a gravel-bed river

Abstract Morphologic and hydrologic properties of head-cut gullies formed in meandering bends of a gravel-bed river in northern Japan were examined to investigate their topographic development. head-cut gullies had incised to 2 m below the floodplain surface and had perennial seepage outflows. Because no surface runoff was observed across the meandering necks, we hypothesized that hyporheic flow erosion cutting into the down-river edge of the meandering necks is one factor for the development of head-cut gullies. Several topographic features caused by sapping and piping erosion were observed within the head-cut gullies. A tracer experiment and examination of the water table, water chemistry, and water table responses in wells on the floodplain and within the head-cut gully revealed that significant preferential hyporheic flow occurred between coarse cobble and fine sediment layers of the floodplain materials. During a storm event, water tables around the head-cut gully quickly responded to changes in the water table of the stream channel; this result also suggests that hyporheic flow occurred across the meandering bends. Hyporheic flow around the head-cut gullies had higher hydraulic conductivities and preferential flow paths that may relate to buried beds of paleochannels. An erosion model suggests that it is unlikely that hyporheic flow alone had enough energy to account for all the soil erosion. Thus, a combination of hyporheic flow (sapping erosion) and channel erosion (bank erosion) appeared to contribute to the formation of the head-cut gullies. Hyporheic flow is an important component in the geomorphic evolution of channels and the floodplain in a gravel-bed river.

Streamflow response and water-table dynamics in a sub-Mediterranean research catchment (Central Pyrenees)

Summary Rainfall–runoff relationships at the event scale were studied in a small sub-Mediterranean research catchment in the central Spanish Pyrenees (Arnas catchment, 2.84 km 2 in area). The strong non-linearity between these two variables evidenced the high variability in the hydrological response of the catchment, linked to seasonal dynamics of the water reserves. Both the magnitude of rainfall events and the baseflow at the start of each event had a pronounced influence on the hydrological response, while the rainfall intensity played a major role in terms of discharge increment. Water-table data suggested a strong topographic control on saturation patterns and showed high seasonal dynamics, with a dry period during summer and a wet period during winter. The transition between dry and wet periods was characterised by high spatial variability in the water-table pattern. An analysis of streamflow and water-table response during a series of four events revealed the complexity of the hydrological processes operating within the catchment. During dry conditions, infiltration excess over localised areas is likely to be the main runoff process, whereas during wet conditions both saturated excess runoff and subsurface flow are most likely to be the dominant runoff processes. During the wetting-up period, the hydrological response was variable, depending mainly on the depth of the water table before the event and rainfall depth and intensity. In these conditions, the interpretation of runoff processes is not straightforward and requires further research.

Multiple-methods investigation of recharge at a humid-region fractured rock site, Pennsylvania, USA

Lysimeter-percolate and well-hydrograph analyses were combined to evaluate recharge for the Masser Recharge Site (central Pennsylvania, USA). In humid regions, aquifer recharge through an unconfined low-porosity fractured-rock aquifer can cause large magnitude water-table fluctuations over short time scales. The unsaturated hydraulic characteristics of the subsurface porous media control the magnitude and timing of these fluctuations. Data from multiple sets of lysimeters at the site show a highly seasonal pattern of percolate and exhibit variability due to both installation factors and hydraulic property heterogeneity. Individual event analysis of well hydrograph data reveals the primary influences on water-table response, namely rainfall depth, rainfall intensity, and initial water-table depth. Spatial and seasonal variability in well response is also evident. A new approach for calculating recharge from continuous water-table elevation records using a master recession curve (MRC) is demonstrated. The recharge estimated by the MRC approach when assuming a constant specific yield is seasonal to a lesser degree than the recharge estimate resulting from the lysimeter analysis. Partial reconciliation of the two recharge estimates is achieved by considering a conceptual model of flow processes in the highly-heterogeneous underlying fractured porous medium.

Impact of change in vegetation cover on groundwater recharge to a phreatic aquifer in Western Australia: assessment of several recharge estimation techniques

Groundwater levels in a deep phreatic aquifer in the northern Perth Basin, Western Australia have risen between 10 and 55 cm/y over the last three decades due to the replacement of deep-rooted native vegetation with pasture and annual crops. This has sparked debate over increasing groundwater allocation limits to meet growing demand. Estimates of recent and historical rates of groundwater recharge are needed to manage the resource effectively. The Parmelia Formation, composed predominantly of sandstone, supplies domestic, stock and production bores for rural towns. Groundwater recharge was estimated using several recharge estimation techniques including the water-table fluctuation method and tracer techniques; groundwater chloride, chlorofluorocarbons (CFCs) and C-14. Vertical fluxes of soilwater under pasture and native vegetation were determined using chloride as a tracer. Apparent groundwater ages determined using CFCs and carbon-14 are generally younger than 40 years in piezometers that are screened within a few metres of the water-table from recharge under pasture, while groundwater is older than several thousand years in bores that are screened well below the water-table, and mixed waters occur at discharge areas. Recharge-rate estimates obtained under native vegetation are mainly <12 mm/y, whereas after replacement with pasture and annual crops, recharge rates are generally 20 – 50 mm/y. The presence of thick clay lenses in some areas may be responsible for observed delays of approximately one decade in the water-table response to land-use change. The study highlighted the fact that several recharge estimation techniques are required for better understanding of recharge processes and evaluation of recharge.

Analysis of water-level response to rainfall and implications for recharge pathways in the Chalk aquifer, SE England

Summary Water table response to rainfall was investigated at six sites in the Upper, Middle and Lower Chalk of southern England. Daily time series of rainfall and borehole water level were cross-correlated to investigate seasonal variations in groundwater-level response times, based on periods of 3-month duration. The time lags (in days) yielding significant correlations were compared with the average unsaturated zone thickness during each 3-month period. In general, for cases when the unsaturated zone was greater than 18 m thick, the time lag for a significant water-level response increased rapidly once the depth to the water table exceeded a critical value, which varied from site to site. For shallower water tables, a linear relationship between the depth to the water table and the water-level response time was evident. The observed variations in response time can only be partially accounted for using a diffusive model for propagation through the unsaturated matrix, suggesting that some fissure flow was occurring. The majority of rapid responses were observed during the winter/spring recharge period, when the unsaturated zone is thinnest and the unsaturated zone moisture content is highest, and were more likely to occur when the rainfall intensity exceeded 5 mm/day. At some sites, a very rapid response within 24 h of rainfall was observed in addition to the longer term responses even when the unsaturated zone was up to 64 m thick. This response was generally associated with the autumn period. The results of the cross-correlation analysis provide statistical support for the presence of fissure flow and for the contribution of multiple pathways through the unsaturated zone to groundwater recharge.