A coupled model for simulating surface water and groundwater interactions in coastal wetlands

Coastal wetlands are characterized by strong, dynamic interactions between surface water and groundwater. This paper presents a coupled model that simulates interacting surface water and groundwater flow and solute transport processes in these wetlands. The coupled model is based on two existing (sub) models for surface water and groundwater, respectively: ELCIRC (a three‐dimensional (3‐D) finite‐volume/finite‐difference model for simulating shallow water flow and solute transport in rivers, estuaries and coastal seas) and SUTRA (a 3‐D finite‐element/finite‐difference model for simulating variably saturated, variable‐density fluid flow and solute transport in porous media). Both submodels, using compatible unstructured meshes, are coupled spatially at the common interface between the surface water and groundwater bodies. The surface water level and solute concentrations computed by the ELCIRC model are used to determine the boundary conditions of the SUTRA‐based groundwater model at the interface. In turn, the groundwater model provides water and solute fluxes as inputs for the continuity equations of surface water flow and solute transport to account for the mass exchange across the interface. Additionally, flux from the seepage face was routed instantaneously to the nearest surface water cell according to the local sediment surface slope. With an external coupling approach, these two submodels run in parallel using time steps of different sizes. The time step (Δt_g) for the groundwater model is set to be larger than that (Δt_s) used by the surface water model for computational efficiency: Δt_g = M × Δt_s where M is an integer greater than 1. Data exchange takes place between the two submodels through a common database at synchronized times (e.g. end of each Δt_g). The coupled model was validated against two previously reported experiments on surface water and groundwater interactions in coastal lagoons. The results suggest that the model represents well the interacting surface water and groundwater flow and solute transport processes in the lagoons. Copyright © 2011 John Wiley & Sons, Ltd.     

Stream and bed temperature variability in a coastal headwater catchment: influences of surface‐subsurface interactions and partial‐retention forest harvesting

Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10‐min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired‐catchment analysis revealed that partial‐retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post‐harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post‐harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre‐harvest regression models for shallow groundwater were not suitable for applying the paired‐catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre‐harvest year. Copyright © 2012 John Wiley & Sons, Ltd.     

Groundwater–surface‐water interactions in a braided river: a tracer‐based assessment

Natural tracers (alkalinity and silica) were used to infer groundwater–surface‐water exchanges in the main braided reach of the River Feshie, Cairngorms, Scotland. Stream‐water samples were collected upstream and downstream of the braided section at fortnightly intervals throughout the 2001–2002 hydrological year and subsequently at finer resolution over two rainfall events. The braided reach was found to exert a significant downstream buffering effect on the alkalinity of these waters, particularly at moderate flows (4–8 m³ s^?1/?Q_30–70). Extensive hydrochemical surveys were undertaken to characterize the different source waters feeding the braids. Shallow groundwater flow systems at the edge of the braided floodplain, recharged by effluent streams and hillslope drainage, appeared to be of particular significance. Deeper groundwater was identified closer to the main channel, upwelling through the hyporheic zone. Both sources contributed to the significant groundwater–surface‐water interactions that promote the buffering effect observed through the braided reach. Their impact was less significant at higher flows (>15 m³ s^?1/>Q₁₀) when acidic storm runoff from the peat‐covered catchment headwaters dominated, as well as under baseflow conditions (<4 m³ s^?1/<Q₇₀), when upstream alkalinity was already buffered owing to headwater groundwater sources assuming dominance. The significant temporally and spatially dynamic influence of these groundwater–surface‐water interactions was therefore seen to have important implications for both catchment functioning and instream ecology. Copyright © 2004 John Wiley & Sons, Ltd.     

3D surface‐wave estimation and separation using a closed‐loop approach

Surface waves in seismic data are often dominant in a land or shallow‐water environment. Separating them from primaries is of great importance either for removing them as noise for reservoir imaging and characterization or for extracting them as signal for near‐surface characterization. However, their complex properties make the surface‐wave separation significantly challenging in seismic processing. To address the challenges, we propose a method of three‐dimensional surface‐wave estimation and separation using an iterative closed‐loop approach. The closed loop contains a relatively simple forward model of surface waves and adaptive subtraction of the forward‐modelled surface waves from the observed surface waves, making it possible to evaluate the residual between them. In this approach, the surface‐wave model is parameterized by the frequency‐dependent slowness and source properties for each surface‐wave mode. The optimal parameters are estimated in such a way that the residual is minimized and, consequently, this approach solves the inverse problem. Through real data examples, we demonstrate that the proposed method successfully estimates the surface waves and separates them out from the seismic data. In addition, it is demonstrated that our method can also be applied to undersampled, irregularly sampled, and blended seismic data.     

Saltwater intrusion estimation in a karstified coastal system using density-dependent modelling and comparison with the sharp-interface approach

Abstract

Saltwater intrusion is a naturally occurring phenomenon that is exacerbated significantly by excessive groundwater exploitation in coastal aquifers. In order to determine the extent of saltwater intrusion in a karstified coastal aquifer in Crete, Greece, a three-dimensional, density-dependent groundwater flow and transport model was developed and compared to the more traditional sharp-interface approach. The karstified medium was modelled using a combination of the equivalent porous medium approach (for lower-order fractures) and a discrete fracture approach (for the main fractures/faults). The model takes into consideration the geomorphologic characteristics of the karstic system, such as the depth and orientation of the fault network, and the diffusion phenomena associated with the variable densities of freshwater and saltwater—parameters that create a complex system, inducing uncertainty in the model. The model results showed that the orientation of the fractures, the pumping activity and the fluid density effects drive the seawater intrusion front asymmetrically inland.

Editor Z.W. Kundzewicz

Citation Dokou, Z. and Karatzas, G.P., 2012. Saltwater intrusion estimation in a karstified coastal system using density-dependent modelling and comparison with the sharp-interface approach. Hydrological Sciences Journal, 57 (5), 985–999.     

Estimating groundwater recharge for an arid karst system using a combined approach of time‐lapse camera monitoring and water balance modelling

Groundwater is the principal water resource in semi‐arid and arid environments. Therefore, quantitative estimates of its replenishment rate are important for managing groundwater systems. In dry regions, karst outcrops often show enhanced recharge rates compared with other surface and sub‐surface conditions. Areas with exposed karst features like sinkholes or open shafts allow point recharge, even from single rainfall events. Using the example of the As Sulb plateau in Saudi Arabia, this study introduces a cost‐effective and robust method for recharge monitoring and modelling in karst outcrops. The measurement of discharge of a representative small catchment (4.0 · 10⁴ m²) into a sinkhole, and hence the direct recharge into the aquifer, was carried out with a time‐lapse camera. During the monitoring period of two rainy seasons (autumn 2012 to spring 2014), four recharge events were recorded. Afterwards, recharge data as well as proxy data about the drying of the sediment cover are used to set up a conceptual water balance model. The model was run for 17 years (1971 to 1986 and 2012 to 2014). Simulation results show highly variable seasonal recharge–precipitation ratios between 0 and 0.27. In addition to the amount of seasonal precipitation, this ratio is influenced by the interannual distribution of rainfall events. Overall, an average annual groundwater recharge for the doline (sinkhole) catchment on As Sulb plateau of 5.1 mm has estimated for the simulation period. Copyright © 2015 John Wiley & Sons, Ltd.     

On the testing of fully integrated surface–subsurface hydrological models

Studies employing integrated surface–subsurface hydrological models (ISSHMs) have utilized a variety of test cases to demonstrate model accuracy and consistency between codes. Here, we review the current state of ISSHM testing and evaluate the most popular ISSHM test cases by comparing the hydrodynamic processes simulated in each case to the processes found in well‐characterized, real‐world catchments and by comparing their general attributes to those of successful benchmark problems from other fields of hydrogeology. The review reveals that (1) ISSHM testing and intercode comparison have not adopted specific test cases consistently; (2) despite the wide range of ISSHM metrics available for model testing, only two model performance diagnostics are typically adopted: the catchment outflow hydrograph and the catchment water balance; (3) in intercode comparisons, model performance is usually judged by evaluating only one performance diagnostic: the catchment outflow hydrograph; and (4) ISSHM test cases evaluate a small number of hydrodynamic processes that are largely uniform across the model domain, representing a limited selection of the processes of interest in well‐characterized, real‐world catchments. ISSHM testing would benefit from more intercode comparisons using a consistent set of test cases, aimed at evaluating more catchment processes (e.g. flooding) and using a wider range of simulation diagnostics (e.g. pressure head distributions). To achieve this, a suite of test case variations is required to capture the relevant catchment processes. Finally, there is a need for additional ISSHM test problems that compare model predictions with hydrological observations from intensively monitored field sites and controlled laboratory experiments. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis and integrated modelling of groundwater infiltration to sewer networks

Infiltration of groundwater to sewer systems is a problem for the capacity of the system as well as for treatment processes at waste water treatment plants. This paper quantifies the infiltration of groundwater to a sewer system in Frederikshavn Municipality, Denmark, by measurements of sewer flow and novel model set‐up, which simulates the interaction between groundwater and sewer flow. The study area has a separate waste water sewer system, but the discharged volumes from the system are approximately twice the volumes from a tight system without infiltration. The model set‐up makes use of two commercial models: mike she for simulation of groundwater transport and mike urban (mouse ) [DHI, Hørsholm, Denmark] for simulation of sewer flow. By simulating the groundwater level and calibrating infiltration coefficients against sewer flow measurements, it has been possible to estimate the average infiltration to the sewer system with satisfying results. The infiltration processes are indeed complicated and to a large degree heterogeneous throughout the sewer system. The paper shows contribution from both saturated and unsaturated groundwater zones, which makes the modelling process complex. Copyright © 2016 John Wiley & Sons, Ltd.     

Modelling surface‐water depression storage in a Prairie Pothole Region

In this study, the Precipitation‐Runoff Modelling System (PRMS) was used to simulate changes in surface‐water depression storage in the 1,126‐km² Upper Pipestem Creek basin located within the Prairie Pothole Region of North Dakota, USA. The Prairie Pothole Region is characterized by millions of small water bodies (or surface‐water depressions) that provide numerous ecosystem services and are considered an important contribution to the hydrologic cycle. The Upper Pipestem PRMS model was extracted from the U.S. Geological Survey's (USGS) National Hydrologic Model (NHM), developed to support consistent hydrologic modelling across the conterminous United States. The Geospatial Fabric database, created for the USGS NHM, contains hydrologic model parameter values derived from datasets that characterize the physical features of the entire conterminous United States for 109,951 hydrologic response units. Each hydrologic response unit in the Geospatial Fabric was parameterized using aggregated surface‐water depression area derived from the National Hydrography Dataset Plus, an integrated suite of application‐ready geospatial datasets. This paper presents a calibration strategy for the Upper Pipestem PRMS model that uses normalized lake elevation measurements to calibrate the parameters influencing simulated fractional surface‐water depression storage. Results indicate that inclusion of measurements that give an indication of the change in surface‐water depression storage in the calibration procedure resulted in accurate changes in surface‐water depression storage in the water balance. Regionalized parameterization of the USGS NHM will require a proxy for change in surface‐storage to accurately parameterize surface‐water depression storage within the USGS NHM.     

Modelling a cohesive‐frictional debris flow: an experimental,theoretical, and field‐based study

The rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders, in addition to water. Few studies have addressed debris flow rheology from observational, experimental, and theoretical viewpoints in conjunction. We present a coupled rheological‐numerical model to characterize the debris flows in which cohesive and frictional materials are both present. As a first step, we consider small‐scale artificial debris flows in a flume with variable percentages of clay versus sand, and measure separately the rheological properties of sand–clay mixtures. A comparison with the predictions of a modified version of the numerical model BING shows a reasonable agreement between measurements and simulations. As application to a field case, we analyse a recent debris flow that occurred in Fjærland (Western Norway) for which much information is now available. The event was caused by a glacial lake outburst flood (GLOF) originating from the failure of a moraine ridge. In a previous contribution (Breien et al., Landslides, 2008 , 5: 271–280) we focused on the hydrological and geomorphological aspects. In particular we documented the marked erosion and reported the change in sediment transport during the event. In contrast to the laboratory debris flows, the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud‐to–clast supported material. We present simulations with a modified BING model with the new cohesive‐frictional rheology. To account for the severe erosion operated by the debris flow on the colluvial deposits of Fjærland, we also suggest a simple model for erosion and bulking along the slope path. Numerical simulations suggest that a self‐sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain.     

Comparison of two modeling approaches for groundwater–surface water interactions

An assessment of interactions between groundwater and surface water was carried out by applying two different modeling approaches to a small‐scale study area in the municipality of Havelock, Quebec. The first approach involved a commonly used sequential procedure that consists in determining the daily recharge rate using a quasi 2D infiltration model (HELP), applied in the next step as an imposed flux to a 3D finite‐element groundwater flow model. The flow model was calibrated under steady‐state and transient conditions against measured water levels. The second approach was based on a recently developed physically based, 3D fully coupled groundwater–surface water flow model (CATHY) applied to the entire flow domain in an integrated manner. Implementation, calibration, and results of the simulations for both approaches are presented and discussed. For equal annual precipitation (1038 mm/y) and evapotranspiration (556 mm/y), the second approach computed a recharge rate of 233 mm/y (8.9% higher than the first approach) and a net upward flow from the fractured aquifer (the first approach predicted a net downward flow to the rock). The simulated annual discharge was similar for the two approaches (9.6% difference). Both approaches were found to be useful in understanding the interactions between groundwater and surface water, although limitations are apparent in the sequential procedure's inability to account for surface–subsurface feedbacks, for instance near stream reaches where groundwater discharge is prevalent. The decoupled, two‐model approach provides disaggregated surface, vadose, and aquifer flows, and a simple aperçu at the different components of total discharge. The fully coupled model accounts for continuous water exchanges between the land surface, subsurface, and stream channel in a more complex manner, and produces a better match against observed data. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling groundwater levels in an urban coastal aquifer using artificial neural networks

The prediction of groundwater levels in a basin is of immense importance for the management of groundwater resources, especially in coastal regions where the water table fluctuations are to be limited to avoid seawater intrusion. In this paper, an Artificial Neural Network (ANN) methodology is presented to predict groundwater levels in individual wells with one month lead. Groundwater levels were also predicted in neighboring wells using model parameters from the best network of a well. This methodology is applied to an urban coastal aquifer in Andhra Pradesh state, India. The results suggest that the feed forward neural network with Levenberg Marquardt (LM) algorithm is a good choice for predicting groundwater levels in individual wells. Bayesian Regularization (BR) model parameters of Balaji Nagar well are also used successfully to predict groundwater levels in the study area. It was observed that the ANN‐based algorithms were a better choice for the prediction of groundwater levels with limited hydrological parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

The impact of groundwater–surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern Germany

The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time‐variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM‐ETH‐I with the three‐dimensional finite‐difference‐based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km²), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km² catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain‐dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd.     

A tracer‐based simulation approach to quantify seasonal dynamics of surface‐groundwater interactions in the Pantanal wetland

The Pantanal wetland is one of the least explored regions of South America. It is characterized by an outstanding flora and fauna adapted to a seasonal flood pulse controlled by a dry and a wet season within each year. The resulting inundation covers in average an area of approximately 150 000 km² and is seen as the most important driver for ecological integrity. Evaporation from the large floodplain is supposed to influence the climate of the whole continent. The regional groundwater is connected to the surface water and plays an important role for the characteristic flooding regime by regulating the wetland's water table. The water balance assessment of the wetland and the internal water exchange between surface and groundwater is therefore of high relevance for the conservation of the Pantanal biodiversity. Despite of its importance, water balance studies including groundwater–surface water interactions based on field data are rarely undertaken. This is mainly due to the remoteness and difficulty in accessing this area, which results in lack of data. In our study, we developed a new tracer‐based model to simulate the spatio–temporal surface and subsurface fluxes for a range of water bodies. The model was able to simulate these fluxes considering a dynamic simulation of inflow and outflow using a newly collected 2‐year dataset of water levels, stable water isotopes and chloride collected from several water bodies in the northern Pantanal region. Quantitative differences between water bodies according to their location in the floodplain were determined by the flooding regime and connectivity as well as site‐specific characteristics, such as hydraulic conductivity and water depth. Our model simulated water balance fluxes with a Nash–Sutcliffe efficiency of 0.61, whereas it simulated stable water isotopic compositions better than chloride. We present the first study based on field data for the Pantanal, which is able to quantify water balances fluxes. Because their representation in global climate and land cover products is insufficient, our simulation results are valuable for validating large‐scale models. Copyright © 2016 John Wiley & Sons, Ltd.     

Spatial delineation of groundwater–surface water interactions through intensive in‐stream profiling

The dominance of ‘old’ pre‐event water in headwater storm runoff has been recorded in numerous upland catchment studies; however, the mechanisms by which this pre‐event water enters the stream channel are poorly understood. Understanding these processes is fundamental to determining the controls on surface water quality and associated impacts on stream ecology. Previous studies in the upland forested catchment of the Afon Hafren (River Severn) at Plynlimon, mid‐Wales, identified an active bedrock groundwater system that was discharging into the stream channel during storm response. Detailed analysis showed that these discharges were small and could not account for the majority of pre‐event storm water response identified at this site; pre‐event storm runoff had to be sourced predominantly from further upstream. An intensive stream survey was used to determine the spatial nature of groundwater–surface water (GW–SW) interactions in the Hafren Catchment. Detailed physico‐chemical in‐stream profiling identified a marked change in water quality indicating a significant discrete point of bedrock groundwater discharge upstream of the Hafren Transect study site. The in‐stream profiling showed the importance of high spatial resolution sampling as a key to understanding processes of GW–SW interaction and how quick and cost‐effective measurements of specific electrical conductance of stream waters could be used to highlight in‐stream heterogeneity. This approach is recommended for use in headwater catchments for initial characterisation of the stream channel in order to better locate instrumentation and to determine more effective targeted sampling protocols in upland catchment research. Copyright © 2012 John Wiley & Sons, Ltd.     

Groundwater–surface water interactions in a lowland watershed: source contribution to stream flow

The lower coastal plain of the Southeast USA is undergoing rapid urbanisation as a result of population growth. Land use change has been shown to affect watershed hydrology by altering stream flow and, ultimately, impairing water quality and ecologic health. However, because few long‐term studies have focused on groundwater–surface water interactions in lowland watersheds, it is difficult to establish what the effect of development might be in the coastal plain region. The objective of this study was to use an innovative improvement to end‐member mixing analysis (EMMA) to identify time sequences of hydrologic processes affecting storm flow. Hydrologic and major ion chemical data from groundwater, soil water, precipitation and stream sites were collected over a 2‐year period at a watershed located in USDA Forest Service's Santee Experimental Forest near Charleston, South Carolina, USA. Stream flow was ephemeral and highly dependent on evapotranspiration rates and rainfall amount and intensity. Hydrograph separation for a series of storm events using EMMA allowed us to identify precipitation, riparian groundwater and streambed groundwater as main sources to stream flow, although source contribution varied as a function of antecedent soil moisture condition. Precipitation, as runoff, dominated stream flow during all storm events while riparian and streambed groundwater contributions varied and were mainly dependent on antecedent soil moisture condition. Sensitivity analyses examined the influence of 10% and 50% increases in analyte concentration on EMMA calculations and found that contribution estimates were very sensitive to changes in chemistry. This study has implications on the type of methodology used in traditional forms of EMMA research, particularly in the recognition and use of median end‐member water chemistry in hydrograph separation techniques. Potential effects of urban development on important hydrologic processes (groundwater recharge, interflow, runoff, etc.) that influence stream flow in these lowland watersheds were qualitatively examined. Copyright © 2011 John Wiley & Sons, Ltd.     

Modelling discharge from a coastal watershed in southeast Sweden using an integrated framework

The field hydrology model DRAINMOD integrated with Arc Hydro in geographical information system (GIS) framework (Arc Hydro–DRAINMOD) was used to simulate the hydrological response of a coastal watershed in southeast Sweden. Arc Hydro–DRAINMOD uses a distributed approach to route water from each field edge to the watershed outlet. In the framework the Arc Hydro data model was used to describe the stream network in the watershed and to connect the individual simulated DRAINMOD‐field outflow time series from each plot using Arc Hydro schema‐links features, which were summed at Arc Hydro schema‐nodes features along the stream network to generate the stream network flow. Hydrology data collected during six periods between 2003 and 2008 were used to test Arc Hydro–DRAINMOD and its performance was evaluated by considering uncertainties in model inputs using generalized likelihood uncertainty estimation (GLUE). The GLUE estimates obtained (uncertainty bands 5% and 95%) agreed satisfactorily with measured monthly discharges. The percentage of time in which the observed discharges were bracketed by the uncertainty bands was 88% in calibration periods and 75% in validation periods. Although monthly time step simulations showed good agreement with observed discharges during the two main discharge events in spring, the contradictory daily time step results indicate that the watershed response simulations on a daily basis need to be improved. The uncertainty analysis showed that in periods of higher discharge, such as spring periods, the uncertainty in prediction was higher. It is important to note that these uncertainty estimations using the GLUE procedure include the uncertainties in measured discharge values, model inputs, boundary conditions and model structures. It was estimated that stream baseflow represented 42% of the total watershed discharge, but further research is needed to confirm this. These results show that the new Arc Hydro–DRAINMOD framework is applicable for predicting discharge from artificially drained watersheds in southeast Sweden. Copyright © 2010 John Wiley & Sons, Ltd.     

Fluctuation of groundwater in an urban coastal city of India: a GIS‐based approach

Groundwater is the most important and valuable natural resources especially in coastal urban environment where surface water is insufficient to satisfy the water requirement. Puri city is located on the east coast of India where groundwater is the only source available to meet city water supply. As the city is situated on the sandy aquifer, quality of groundwater is deteriorating because of anthropogenic activities, lack of sewerage system, etc. The objective of the study was to assess the groundwater fluctuation during post‐monsoon and summer with respect to hydrogeological conditions, topography, and groundwater consumption pattern of the city. For this assessment and analysis, Geographic Information System (GIS) was used to visualize topography of the area through digital elevation model (DEM) and distribution of groundwater contours spatially and temporally. The probable areas prone to contamination were identified based on aquifer property and depths to water table below ground. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterizing seasonal groundwater storage in alpine catchments using time-lapse gravimetry,water stable isotopes and water balance methods

Alpine areas play a major role in water supply in downstream valleys by releasing water during warm and dry periods. However, the hydrogeology of alpine catchments, which are particularly exposed to the effects of climate change, is currently not well understood. Increasing our knowledge of alpine hydrogeological processes is thus of considerable importance for any forward-looking hydrological investigations in alpine areas. The objectives of this study are to quantify seasonal groundwater storage variations in a small Swiss alpine catchment and to evaluate the capabilities of time-lapse gravimetry in the identification of zones of high groundwater storage fluctuations. Time-lapse gravimetric measurements enable rapid localisation of zones of dynamic groundwater storage changes and help to highlight aquifers with a higher storage decrease. Temperature sensors enable measurement of the temporal trend in stream and spring drying in the post-snowmelt period. Stable isotope measurements allow us to identify the origin of surface water exiting the catchment. The results improve our comprehension of a conceptual schema highlighting two different hydrogeological systems: (a) a shallow, rapidly depleted one fed directly by snowmelt and (b) a deeper one, with a slower recession, fed by main recharge during peak snowmelt and emerging at the lower part of the catchment below the talus and moraine of the catchment where bedrock is exposed. These dynamics confirm the high variability of storage in the talus and moraine aquifers and highlight the dominant role of Quaternary deposits and their connectivity to store water over seasonal and multi-year time-scales. The mechanisms explaining the importance of Quaternary deposits are the combination of moraine and talus with different permeabilities allowing the storage of sufficient quantities of water permitting continuous release during drier periods of the year.     

Continuous monitoring of stream δ18O and δ2H and stormflow hydrograph separation using laser spectrometry in an agricultural catchment

A portable Wavelength Scanned‐Cavity Ring‐Down Spectrometer (Picarro L2120) fitted with a diffusion sampler (DS‐CRDS) was used for the first time to continuously measure δ¹⁸O and δ²H of stream water. The experiment took place during a storm event in a wet tropical agricultural catchment in north‐eastern Australia. At a temporal resolution of one minute, the DS‐CRDS measured 2160 δ¹⁸O and δ²H values continuously over a period of 36 h with a precision of ±0.08 and 0.5‰ for δ¹⁸O and δ²H, respectively. Four main advantages in using high temporal resolution stream δ¹⁸O and δ²H data during a storm event are highlighted from this study. First, they enabled us to separate components of the hydrograph, which was not possible using high temporal resolution electrical conductivity data that represented changes in solute transfers during the storm event rather than physical hydrological processes. The results from the hydrograph separation confirm fast groundwater contribution to the stream, with the first 5 h of increases in stream discharge comprising over 70% pre‐event water. Second, the high temporal resolution stream δ¹⁸O and δ²H data allowed us to detect a short‐lived reversal in stream isotopic values (δ¹⁸O increase by 0.4‰ over 9 min), which was observed immediately after the heavy rainfall period. Third, δ¹⁸O values were used to calculate a time lag of 20 min between the physical and chemical stream responses during the storm event. Finally, the hydrograph separation highlights the role of event waters in the runoff transfers of herbicides and nutrients from this heavily cultivated catchment to the Great Barrier Reef. Copyright © 2015 John Wiley & Sons, Ltd.