Surface Subsurface Water Research Articles

On the transferability of residence time distributions in two 10-km long river sections with similar hydromorphic units

Quantifying hydrologic exchange fluxes (HEFs) at the stream-groundwater interface and their residence time distributions (RTDs) in the subsurface are important for managing the water quality and ecosystem health in dynamic river corridors. However, field measurements and directly simulating high-spatial resolution HEFs and RTDs can be time-consuming, particularly at watershed-scale. Recent research has proposed the potential application of using hydromorphic units (HUs), which cluster the bathymetry and surface water hydrodynamics attributes, to aid in RTD estimation. However, more pioneering studies have demonstrated that underground structure and large-scale river channel geomorphology are the primary factors controlling the HEFs and RTDs. To address this contradiction, this work evaluates the HEFs and resulting HU-RTD relationships for two 10-km long river sections along the Columbia River, leveraging a one-way coupled three-dimensional transient surface–subsurface water transport modeling framework. Applying such a framework at the two river sections with similar HUs allows for quantitative comparisons of HEFs and RTDs using both statistical tests and machine learning classification models. The comparison reveals that the similarity and transferability of the HU-RTD relationship is very low for the two investigated river sections. This suggests that, creating a general algorithm to estimate RTDs in large-scale river reaches based solely on surface water hydrodynamics and short-distance bathymetry topography data may be nearly impossible.

Assessment of factors and mechanism contributing to groundwater depressurisation due to longwall mining

Assessment of mining impact on groundwater is one of critical considerations for longwall extension and sustainability, however usually constrained by limited data availability, hydrogeological variation, and the complex coupled hydro-mechanical behaviour. This paper aims to determine the factors and mechanism of groundwater depressurisation and identify knowledge gaps and methodological limitations for improving groundwater impact assessment. Analysis of dewatering cases in Australian, Chinese, and US coalfields demonstrates that piezometric drawdown can further lead to surface hydrology degradation, while the hydraulic responses vary with longwall parameters and geological conditions. Statistical interpretation of 422 height of fracturing datasets indicates that the groundwater impact positively correlates to panel geometry and depth of cover, and more pronounced in panel interaction and top coal caving cases. In situ stress, rock competency, clay mineral infillings, fault, valley topography, and surface–subsurface water interaction are geological and hydrogeological factors influencing groundwater hydraulics and long-term recovery. The dewatering mechanism involves permeability enhancement and extensive flow through fracture networks, where interconnected fractures provide steep hydraulic gradients and smooth flow pathways draining the overlying water to goaf of lower heads. Future research should improve fracture network identification and interconnectivity quantification, accompanied by description of fluid flow dynamics in the high fracture frequency and large fracture aperture context. The paper recommends a research framework to address the knowledge gaps with continuous data collection and field-scale numerical modelling as key technical support. The paper consolidates the understanding of longwall mining impacting mine hydrology and provides viewpoints that facilitate an improved assessment of groundwater depressurisation.

Drainage network dynamics in an agricultural headwater sub-basin

Headwaters provide many ecosystems services. Currently, these vulnerable systems are subject to threats related to human activities. This work aims to analyse the spatial pattern changes (expansion/contraction) in the drainage network (DN) of a headwater sub-basin under agriculture between 1966 and 2019 in the Argentine Pampas Region. We study and discuss the hydrometeorological and land use context to understand the spatial and temporal dynamics of the DN, and propose a conceptual model that synthesizes the complex interactions between the factors involved in that dynamics. A broad (1950–2019, at the Del Azul Creek basin) and a short (1996–2019, at the sub-basin of the Videla Creek -SVC-) temporal and spatial scale analysis of data were carried out. We studied rainfall, evapotranspiration, water table depth, streamflow and land use. Temporal and spatial changes in the DN of the SVC were analysed by aerial photos and historical satellite images. Four wet and three dry periods were identified, and close surface-subsurface water interactions typical of plains, were found. The area under agriculture showed a first gradual increase (1975–2012), which turned sharp from 2012 (30,908 ha year−1), with a leading role of soybeans' sown area. The area of the DN increased 1.4699*105 m2 between 1966 and 2010, both under dry conditions, which evidenced its expansion. The study of the flatlands' particular hydrology within the current land use and management trends provided key elements to understand DN area's changes. Complex interactions between processes associated with climatic forcing and the system's sensitivity (its state to receive and process the inputs), are involved in the spatial and temporal dynamics of the DN. Our work improves the understanding of the functioning of these vulnerable systems within agricultural areas, nowadays under productive pressures associated with increasing global food demand, and threats to changes in the hydrological dynamics by global change.

Estimation of Surface-Subsurface Water Balance in Lower Tapi River Basin Using Gridded Data and Station-Based Observed Data

ABSTRACT Water is an essential resource. An understanding of catchment water balance is crucial to ensure water availability in the region. Hydrological models are credible tools for water balance assessment of a region. These models are data intensive. The traditional hydrological modeling approach relies on station-based observed data. The availability of sufficient long-term consistent observed data is often limited. On the other hand, climate reanalysis data for a long timeperiod is available from multiple data sources. This study estimates runoff characteristics for Lower Tapi River Basin in western India, with the help of a Soil Conservation Service Curve Number method. The catchment water balance in terms of runoff, baseflow, and recharge at sub-basin scale is worked out with the help of station-based and climate reanalysis datasets. The model output are calibrated against observed river gauging data. A reasonable fit between model-simulated and observed runoff is obtained in terms of duration and magnitude of runoff peak. Tested model is applied to future climate scenarios. The simulations show an increase in surface runoff, recharge, baseflow and total runoff for future time period. Results reveal that climate changes have significant impact on hydrology of the basin.

Advancing measurements and representations of subsurface heterogeneity and dynamic processes: towards 4D hydrogeology

Abstract. Essentially all hydrogeological processes are strongly influenced by the subsurface spatial heterogeneity and the temporal variation of environmental conditions, hydraulic properties, and solute concentrations. This spatial and temporal variability generally leads to effective behaviors and emerging phenomena that cannot be predicted from conventional approaches based on homogeneous assumptions and models. However, it is not always clear when, why, how, and at what scale the 4D (3D + time) nature of the subsurface needs to be considered in hydrogeological monitoring, modeling, and applications. In this paper, we discuss the interest and potential for the monitoring and characterization of spatial and temporal variability, including 4D imaging, in a series of hydrogeological processes: (1) groundwater fluxes, (2) solute transport and reaction, (3) vadose zone dynamics, and (4) surface–subsurface water interactions. We first identify the main challenges related to the coupling of spatial and temporal fluctuations for these processes. We then highlight recent innovations that have led to significant breakthroughs in high-resolution space–time imaging and modeling the characterization, monitoring, and modeling of these spatial and temporal fluctuations. We finally propose a classification of processes and applications at different scales according to their need and potential for high-resolution space–time imaging. We thus advocate a more systematic characterization of the dynamic and 3D nature of the subsurface for a series of critical processes and emerging applications. This calls for the validation of 4D imaging techniques at highly instrumented observatories and the harmonization of open databases to share hydrogeological data sets in their 4D components.

Well hydraulics in dual-zone heterogeneous wedge-shaped aquifers under an ambient flow from stream-wise varying boundary heads

• Closed-form analytical solution for flow net considering non-uniform ambient flow. • Generality of solution in choosing hydrological input parameters. • A framework for assessment of mass balance at aquifer and sub-aquifer scales. • Uncertainty analysis to quantify model response to randomness in input parameters. A steady-state analytical solution based on the method of Green’s function is presented for the analysis of hydraulic interference between pumping wells and ambient flow in a heterogeneous wedge-shaped aquifer. Two intersecting streams with spatially variable head form the boundaries of the wedge and establish non-uniform distribution of ambient flow across it. The dual-zone aquifer consists of two porous media of constant but contrasting transmissivities and refraction conditions are exactly satisfied along their common interface. The method of Green’s function affords an integral representation of boundary heads which is readily evaluated in terms of Lerch transcendent function. Integration of Cauchy-Riemann equations gives the associated stream function in closed-form which in turn completes analytical description of the flow net. A systematic way for the assessment of mass balance at both aquifer and sub-aquifer (well capture zone) scales is discussed which also helps identifying whether a certain reach of the boundary stream is losing or gaining water to or from the adjoining aquifer. The solution is general in the sense that the wedge angle, location and discharge of the wells, dual-zone transmissivities and slopes of boundary head variation can be arbitrary chosen. The solution encompasses the case of stream-barrier wedge as a subset. Hypothetical examples demonstrate the complex interaction between surface–subsurface waters showing formation of stagnation point on the capture zone envelopes. In each case, head profiles are in excellent agreement with numerical counterparts from adaptive finite element method. Finally, uncertainty analysis quantifies the extent to which stochastic nature of dual-zone transmissivities and boundary head slopes (model inputs) affects hydraulic head at specific observation points (model output).

Compound flood modeling framework for surface–subsurface water interactions

Abstract. Compound floods are an active area of research in which the complex interaction between pluvial, fluvial, coastal and groundwater flooding are analyzed. A number of studies have simulated the compound flooding impacts of precipitation, river discharge and storm surge variables with different numerical models and linking techniques. However, groundwater flooding is often neglected in flood risk assessments due to its sporadic frequency (as most regions have water tables sufficiently low that do not exacerbate flooding conditions), isolated impacts and considerably lower severity with respect to other types of flooding. This paper presents a physics-based, loosely coupled modeling framework using FLO-2D and MODFLOW-2005 that is capable of simulating surface–subsurface water interactions. FLO-2D, responsible for the surface hydrology and infiltration processes, transfers the infiltration volume as recharge to MODFLOW-2005 until the soil absorption capacity is exceeded, while MODFLOW-2005 returns exchange flow to the surface when the groundwater heads are higher than the surface depth. Three events characterized by short-duration intense precipitation, average tide levels and unusually high water table levels are used to assess the relevance of groundwater flooding in the Arch Creek Basin, a locality in North Miami particularly prone to flooding conditions. Due to limitations in water level observations, the model was calibrated based on properties that have experienced repetitive flooding losses and validated using image-based volunteer geographic information (VGI). Results suggest that groundwater-induced flooding is localized, and high groundwater heads influence pluvial flooding as the shallow water table undermines the soil infiltration capacity. Understanding groundwater flood risk is of particular interest to low-elevation coastal karst environments as the sudden emergence of the water table at ground surface can result in social disruption, adverse effects to essential services and damage to infrastructure. Further research should assess the exacerbated impacts of high tides and sea level rise on water tables under current and future climate projections.

Integrated surface-subsurface water and solute modeling of a reclaimed in-pit oil sands mine: Effects of ground freezing and thawing

Study regionAthabasca Oil Sands, Alberta, Canada. Study focusThe upland and wetlands substrate in reclaimed oil sands landforms will be constructed of post-mining materials with an objective of replicating the landscape and hydrology of the surrounding boreal systems. Porewater in these materials contain elevated levels of salts and other solutes. Water quality will govern the success and sustainability of the reclaimed landscape. Tightly coupled water and heat dynamics control water and solute movement in boreal systems. We used three-dimensional integrated surface-subsurface flow and chloride transport models with and without ground freezing-thawing to compare performance of an in-pit oil sands mine currently being reclaimed. New hydrological insights for the regionTransient simulations under wet/dry climate cycles suggest that the reclaimed landform will shed water only during wet years. Annual water balance with and without coupled heat dynamics is identical. However, the three-dimensional representation of ground freeze-thaw results in reduced snowmelt infiltration, summer groundwater table, and solute release during winter. The outcome is increased spring runoff, 20% decrease in chloride mass release over simulated eight-year wet climate cycle and relatively reduced summer runoff. The model results suggest that (1) coupled heat dynamics should be considered for detailed evaluation of reclaimed in-pit landforms at finer time scales, and (2) modeling reclaimed landforms without freeze-thaw provides conservative annual solute release estimates, which is appropriate for coarse site-wide models.

Seepage-evaporation controlled depletion of initially water-filled reservoirs on Earth and Mars: Analytic versus HYDRUS modeling

Analytical solutions are obtained for water extinction from an axisymmetric crater, filled at t < 0 and depleted by evaporation and transient infiltration into a Gardner or capillarity-free homogeneous soil during the time interval 0 ≤ t ≤ Te. The extinction time Te is found for crater beds, the shapes of which are shallow cones, spherical, spheroidal, and paraboloidal caps. An instantaneous seepage flow rate, Q(t), is approximated by truncated two-term formulae of Wooding for a zero-depth disk in Gardner's soil or Hunt for paraboloidal craters (soils with no capillarity). The instantaneous evaporation losses are the product of a constant A-pan evaporation rate and the shrinking area of a flat horizontal disk of the free water, which dwindles in the crater. In HYDRUS simulations of a van Genuchten soil, the Reservoir Boundary Condition is used for a falling water level in the ponded depressions. Cones and paraboloids are selected as craters, initially fully or partially filled with free water at t = 0, and infiltrating until extinction. The results are presented as drawdown curves and – for shallow craters - attest a good match between analytical approximations and HYDRUS numerical simulations. Experiments with the extinction of water from small axisymmetric ponds in dune sand are also carried out. They allow blitz-evaluation of hydraulic parameters of the subjacent sand. Hydrological implications for commingling surface-subsurface (pore) water entities in terrestrial and Martian environments are discussed.

Midchannel islands in lowland river corridors and their impacts on flow structure and morphology:A numerical based conceptual analysis

Midchannel islands (MCIs) are influential geomorphic units in regulating morphological and ecological dynamics in sand-dominated rivers. The primary objectives of the study were to understand a) the relationship between morphometric characteristics of the basin and the occurrence location of the MCIs, b) the role of MCIs on the hydraulic gradient and the other hydraulic variables along the reach, and c) the influence of island growth process on hydrodynamics in the wake and contraction regions. Spatial distributions of MCIs depending on the morphometric features of the three characteristic basins were considered. While the basin-scale analysis was conducted using GIS-based data, the reach and individual scale analyses were performed based on a Reynolds-averaged Navier–Stokes (RANS) model. Uniform circular cylinder and island geometries were exposed to identical flow conditions. The expansion of these island geometries was mimicked both in rectangular and trapezoidal cross-sections. The variation of water surface slope and bottom shear stress variables, which greatly trigger the intensive bilateral interaction between hydrological-morphological-ecological elements in river corridors, depending on the growth of the island, was determined. The role of imposed island geometry on the secondary flow structure within the downstream cross-section of the island and streamwise velocity fluctuations in contraction regions were analyzed. The basin-scale analysis showed that with decreasing basin slopes, the family of islands emerged at a longer distance to the basin outlet. It was also seen that MCIs location is closer to the basin outlet forbasins with a lower aspect ratio. Besides, asymmetrical large-scale counter-rotating streamwise vortices were detected behind the MCIs based on numerical simulations. GIS-based data showed that this coherent flow structure brought about channel adjustments in downstream of the island. In addition to morphological consequences, it was hypothesized that this alteration in the flow structure due to MCI has potential impacts on riverine ecology. These impacts are increase in groundwater recharge, vertical exchange of surface–subsurface water, local heterogeneity in sediment characteristics (i.e., convenient fish spawning areas), and enlargement in the hyporheic zone.

Usage of long-term river discharge data in water balance model for assessment of trends in basin storages

Unsustainable utilization of the surface–subsurface water is responsible for the rapid depletion of the earth’s land–water storage. To assess the depletion rate, the water balance model is a universal approach, and suitable for any temporal and spatial scale. Through this study, we demonstrate the importance of river discharge data as a significant component of water balance model. In this regard, a water balance study is done to assess the depletion rate of basin water storage in the Ramganga river basin in India using the classified-archived river discharge data along with IMD rainfall and NTSG-Global ET dataset. The assessment has been done at three CWC hydro-meteorological sites: Moradabad, Bareilly, and Dabri. Trends and net change in basin water storages are estimated for the 1982–2013 period. The results suggest that long-term trends for basin water storages are declining continuously in the entire Ramganga river basin. The reasons for this decline appear to be anthropogenic activities, and resulting climate change.

Coupled model of surface runoff and surface-subsurface water movement

Surface runoff has been recognized as an important component in agricultural water management. Extensive studies have been developed to measure surface runoff, and numerical methods have been applied to simulate surface water dynamics. For simulations of surface runoff in agricultural systems, three processes should be considered: (1) the movement of water along the soil surface, i.e., surface runoff; (2) the accumulation of water in depressions; and (3) the water fluxes across the soil/atmosphere interface (i.e. infiltration, evaporation and exfiltration through seepage faces). The objective of this study is to develop a physical-based surface runoff model that includes all the three processes. Numerical implementation of the new runoff model was developed and incorporated within 2DSOIL, a simulation package for soil water, energy and solute movement. The new model describes the subsurface flow near the soil surface following a unified boundary condition, expressed with the Heaviside step function. This expression enables continuous and automatic changes of boundary conditions between infiltration and runoff. The surface water flow is simulated using Saint-Venant equations. The ponded water height on the soil surface and the infiltration rate are adjusted based on the runoff flux and topography. Numerical tests based on an experimental dataset are used to evaluate the accuracy of this model, and numerical examples of surface water flow along a variety of topography are used to demonstrate model performance. The simulations match the experimental results, and the surface water mass balance errors of the numerical examples are less than 1%. A practical example of using the surface runoff model to estimate the runoff efficiency in a ridge-furrow water harvesting is carried out. In conclusion, the newly developed surface runoff model can successfully simulate surface water dynamics. This model can further support the design and evaluation of agricultural water management strategies and field water budgets.

Dynamic surface-water alterations during sapropel S1 preserved in high-resolution shallow-water sediments of Taranto Gulf, central Mediterranean

The high sedimentation rate and shallow-water depositional depth of the sediments at site DP 30 in the Gulf of Taranto (central Mediterranean) provide unique biogenic signals that are usually not preserved in deeper records. This permits the reconstruction of long and short-term surface water modifications across the sapropel S1 period (10–6.5 ka), including calcareous nannofossil data at centennial-scale resolution.The peculiar patterns of key taxa allowed the recognition of distinct long to short-term surface water changes that provide valuable evidence on climate conditions leading to sapropel deposition. As a long-term pattern, S1 is marked by a distinct increase of Helicosphaera carteri, thought to reflect increased detrital input/land-derived nutrients in the surface water, related to a higher influence of the Western Adriatic Current. A concomitant pattern of increased black organic particles in the sediments supports a connection between organic matter preservation at the seafloor and nutrient availability in the surface water. Decreased salinity in the surface water, testified by an increase of Braurudosphaera bigelowii, develops from 9.2 up to 6.5 ka.At higher frequencies, additional changes occurred in surface-subsurface waters during the formation of S1 at shallow depths. Starting from 11 ka, the relative abundance pattern of Florisphaera profunda indicates a gradual nutrient enrichment in the subsurface waters and the development of a deep chlorophyll maximum (DCM), which becomes well established at the onset of sapropel S1, between 10 and 9 ka. A further change in the plankton ecosystem occurs between 9 and 8.2 ka, when reduced coccolithophore production is concomitant with diatom occurrence and enhanced Br/Ti level, implying a productivity increase. From 8 to 6.5 ka, coccolithophore productivity is re-established in relation to a reduction both in surface-water stratification and turbidity/nutrient availability, characterizing the final phase of sapropel formation. The turbidity in the surface waters was briefly reduced at 8.2 and 7.3 ka, when also oxygen conditions at the seafloor improved. A centennial variability in turbidity/low light conditions in surface waters is evident across S1 and is illustrated by the abundance patterns of H. carteri and Gladiolithus flabellatus. The occurrence of ascidian spicules also represents a distinct biotic signal across the S1 layer, indicating an increase of shallow-water biogenic carbonate or an aragonitic near-coastal source. Surface-water modifications at longer and shorter time scales, accompanying the deposition of sapropel S1 in the Gulf of Taranto, occurred nearly simultaneously and with a magnitude that is comparable to changes observed in S1 deposits in the central and eastern Mediterranean basin and slope settings.

Estimating Soil Hydraulic Parameters Characterizing Rainwater Infiltration and Runoff Properties of Dryland Floodplains

The two-layered (0 - 50 and 50 - 250 mm) surface horizon hydraulic parameters of three dryland floodplain soil-types under aquafer water management in Postmasburg, Northern Cape Province of South Africa were estimated with HYDRUS-1D model. Time dependent water infiltration measurements at 30 and 230 mm depths from simulated rainfalls on undisturbed 1 m2 small plots with intensities of 1.61 (high), 0.52 (medium) and 0.27 (low) mm·min-1, were minimised using a two-step inversion. Firstly, separate optimisation of the van Genuchten-Mualem model parameters for the two surface-horizon layers and secondly, simultaneous optimisation for the joint two-layered horizon with first step optimal parameters entered as initial values. The model reproduced transient water-infiltration data very well with the Nash-Sutcliffe model efficiency coefficient (NSE) of 0.99 and overestimated runoff (NSE; 0.27 to 0.98). The upper surface horizon had highly optimised and variable parameters especially θs and Ks. Optimal Ks values from higher soil surface bulk-density (≥1.69 g·cm-3) were lower by at least one order of magnitude to double ring infiltrometers and water infiltration properties were different (P < 0.05) for the high rainstorm due to raindrop impact and surface crusting. Optimal α and n parameter values corresponded well with texture of the Addo (Greysols), Augrabies (Ferralsols) and Brandvlei (Cambisols) soil types. However, θs and Ksshowed greater sensitivity to model output and exerted greater influence on dryland floodplain water-infiltration and runoff characteristics. Increasing rainfall simulation period to attain near-surface saturated conditions and inclusion of surface ponding data in the inverse problem could considerable improve model prediction of hydro-physical parameters controlling surface-subsurface water distribution in fluvial environments.

Understanding the water balance paradox in the Athabasca River Basin, Canada

AbstractThis study demonstrates the importance of the including and appropriately parameterizing peatlands and forestlands for basin‐scale integrated surface–subsurface models in the northern boreal forest, with particular emphasis on the Athabasca River Basin (ARB). With a long‐term water balance approach to the ARB, we investigate reasons why downstream mean annual stream flow rates are consistently higher than upstream, despite the subhumid water deficit conditions in the downstream regimes. A high‐resolution 3D variably saturated subsurface and surface water flow and evapotranspiration model of the ARB is constructed based on the bedrock and surficial geology and the spatial distribution of peatlands and their corresponding eco‐regions. Historical climate data were used to drive the model for calibration against 40‐year long‐term average surface flow and groundwater observations during the historic instrumental period. The simulation results demonstrate that at the basin‐scale, peatlands and forestlands can have a strong influence on the surface–subsurface hydrologic systems. In particular, peatlands in the midstream and downstream regimes of the ARB increase the water availability to the surface–subsurface water systems by reducing water loss through evapotranspiration. Based on the comparison of forestland evapotranspiration between observation and simulation, the overall spatial average evapotranspiration in downstream forestlands is larger than that in peatlands and thus the water contribution to the stream flow in downstream areas is relatively minor. Therefore, appropriate representation of peatlands and forestlands within the basin‐scale hydrologic model is critical to reproduce the water balance of the ARB.

Insights on stream temperature processes through development of a coupled hydrologic and stream temperature model for forested coastal headwater catchments

AbstractStream temperature controls a number of biological, chemical, and physical processes occurring in aquatic environments. Transient snow cover and advection associated with lateral throughflow inputs can have a dominant influence on stream thermal regimes for headwater catchments in the rain‐on‐snow zone. Most existing stream temperature models lack the ability to properly simulate these processes. We developed and evaluated a conceptual‐parametric catchment‐scale stream temperature model that includes the role of transient snow cover and lateral advection associated with throughflow. The model consists of routines for simulating canopy interception, snow accumulation and melt, hillslope throughflow runoff and temperature, and stream channel energy exchange processes. The model was used to predict discharge and stream temperature for a small forested headwater catchment near Vancouver, Canada, using long‐term (1963–2013) weather data to compute model forcing variables. The model was evaluated against 4 years of observed stream temperature. The model generally predicted daily mean stream temperature accurately (annual RMSE between 0.57 and 1.24 °C) although it overpredicted daily summer stream temperatures by up to 3 °C during extended low streamflow conditions. Model development and testing provided insights on the roles of advection associated with lateral throughflow, channel interception of snow, and surface–subsurface water interactions on stream thermal regimes. This study shows that a relatively simple but process‐based model can provide reasonable stream temperature predictions for forested headwater catchments located in the rain‐on‐snow zone.

Engineering and enviro-management value of radius of influence estimate from mining excavation

In mining operations carried out below the water table, mine area could potentially affect the surrounding. With further deepening of the mine and quarry, the drawdown can impact on water supply wells and base flow. The variation in radius of influence under confined and unconfined aquifer condition is assessed using a hypothetical case study with three operational quarry sites. Average pit-wise radius of influence (R0) for the pit mine, under unconfined and confined aquifer conditions is 963 m and 61 km, respectively, whereas effective radius (Re) for total (cumulative) excavated mine area is 1.7 and 146 km, respectively. It means that the maximum and minimum value of overall impact/influence for the unconfined aquifer lies in-between 963 m and 1.7 km. Similarly that the maximum and minimum value of overall impact/influence for the confined aquifer lies in-between 61 and 146 km. Meanwhile, Re or effective radius for total (cumulative) excavated area seems more appropriate from evaluation viewpoint due to the overlapping (superposition) concentric mining quarries. Thus, assessment of quarry-wise and total radius of influence is of importance to fulfil targeted production, economically with minimum interruptions as part of the mine planning. Moreover, it helps us to assess, monitor and regulate the impact of a mine-dewatering program in the area. Also, the pumping test is often used to estimate radius of influence; it can trigger the inflow or radius of influence. Estimate of the radius of influence using analytical equation mainly independent of discharge/abstraction from the aquifer stands as a preferred choice for the prediction of radius of influence at the quarry/mine pit. There is a strong rationale that policies should be informed by such analytical assessment because it helps us to prevent or minimize negative impacts as part of regulation and pit-mining management and are useful tools for practitioners to design economically efficient and cost-effective in situ groundwater remediation systems, to contain contaminant plumes, to evaluate the surface–subsurface water interaction and to verify numerical models.

Coupled surface and subsurface flow modeling of natural hillslopes in the Aburrá Valley (Medellín, Colombia)

Numerical results are presented of surface-subsurface water modeling of a natural hillslope located in the Aburra Valley, in the city of Medellin (Antioquia, Colombia). The integrated finite-element hydrogeological simulator HydroGeoSphere is used to conduct transient variably saturated simulations. The objective is to analyze pore-water pressure and saturation variation at shallow depths, as well as volumes of water infiltrated in the porous medium. These aspects are important in the region of study, which is highly affected by soil movements, especially during the high-rain seasons that occur twice a year. The modeling exercise considers rainfall events that occurred between October and December 2014 and a hillslope that is currently monitored because of soil instability problems. Simulation results show that rainfall temporal variability, mesh resolution, coupling length, and the conceptual model chosen to represent the heterogeneous soil, have a noticeable influence on results, particularly for high rainfall intensities. Results also indicate that surface-subsurface coupled modeling is required to avoid unrealistic increase in hydraulic heads when high rainfall intensities cause top-down saturation of soil. This work is a first effort towards fostering hydrogeological modeling expertise that may support the development of monitoring systems and early landslide warning in a country where the rainy season is often the cause of hydrogeological tragedies associated with landslides, mud flow or debris flow.

Variability of tracer breakthrough curves in mountain streams: Implications for streamflow measurement by slug injection

Tracer dilution methods are commonly used to measure discharge in steep mountain streams. This research addressed knowledge gaps associated with dilution methods using original field data collected on nine streams in southwest British Columbia and discharge measurements conducted by Northwest Hydraulic Consultants Ltd. Minimum mixing lengths ranged between 2.4 and 24.5 stream wetted widths, but determining the mixing length can be confounded by surface-subsurface water fluxes. Probes need to be placed on opposite sides of the stream to verify adequate mixing, because probes located at different locations on the same of the stream sometimes suggested complete mixing had occurred when it in fact had not. For probes located downstream of complete mixing, breakthrough curves (BTCs) for probes located in the main current differed significantly from probes in zones with recirculating flow, even though they yielded discharge values within ± 10%. The peak of the BTC is a function of the mass of tracer injected, reach length, channel cross-sectional area, and the integral of a non-dimensional BTC, A*. The distribution of A* derived from analysis of 175 BTCs can be used, in conjunction with estimates of channel geometry and desired increases in electrical conductivity, to estimate dosing requirements to avoid under- or over-dosing a stream reach.

Capture Zone of a Multi-Well System in Bounded Rectangular-Shaped Aquifers: Modeling and Application

The capture zone equations of a multi-well system in bounded confined and unconfined aquifers are derived. The aquifer is rectangular-shaped in plan view and bounded along all four sides. The boundaries could be in-flow (constant head) or no-flow (barrier) or a combination of both, and hence, six boundary configurations are formed. Using the method of images, the flow field in bounded aquifers is first transformed to its equivalent in extensive aquifers, and then, the complex velocity potential theory is applied for the generation of stream function delineating the capture envelope. We show that the derived solution is general, and it may be easily reformulated for some existing solutions of well capture zone. Our solution is flexible in terms of well number, well location, well type, extraction/injection rate, uniform regional flow rate and direction, and number of boundaries. The derived equations are presented in the form of capture type curves that may be used for the remediation of contaminated groundwater project design, containment of contaminant plumes, the evaluation of surface–subsurface water interaction, and the verification of numerical models. Drawdown equations for the above six boundary configurations are also derived.