Soil moisture states,lateral flow,and streamflow generation in a semi‐arid,snowmelt‐driven catchment

Hydraulic connectivity on hillslopes and the existence of preferred soil moisture states in a catchment have important controls on runoff generation. In this study we investigate the relationships between soil moisture patterns, lateral hillslope flow, and streamflow generation in a semi‐arid, snowmelt‐driven catchment. We identify five soil moisture conditions that occur during a year and present a conceptual model based on field studies and computer simulations of how streamflow is generated with respect to the soil moisture conditions. The five soil moisture conditions are (1) a summer dry period, (2) a transitional fall wetting period, (3) a winter wet, low‐flux period, (4) a spring wet, high‐flux period, and (5) a transitional late‐spring drying period. Transitions between the periods are driven by changes in the water balance between rain, snow, snowmelt and evapotranspiration. Low rates of water input to the soil during the winter allow dry soil regions to persist at the soil–bedrock interface, which act as barriers to lateral flow. Once the dry‐soil flow barriers are wetted, whole‐slope hydraulic connectivity is established, lateral flow can occur, and upland soils are in direct connection with the near‐stream soil moisture. This whole‐slope connectivity can alter near‐stream hydraulics and modify the delivery of water, pressure, and solutes to the stream. Copyright © 2005 John Wiley & Sons, Ltd.     

Review of Laboratory Scale Models of Karst Aquifers: Approaches,Similitude, and Requirements

This review focuses on investigations of groundwater flow and solute transport in karst aquifers through laboratory scale models (LSMs). In particular, LSMs have been used to generate new data under different hydraulic and contaminant transport conditions, testing of new approaches for site characterization, and providing new insights into flow and transport processes through complex karst aquifers. Due to the increasing need for LSMs to investigate a wide range of issues, associated with flow and solute migration karst aquifers this review attempts to classify, and introduce a framework for constructing a karst aquifer physical model that is more representative of field conditions. The LSMs are categorized into four groups: sand box, rock block, pipe/fracture network, and pipe-matrix coupling. These groups are compared and their advantages and disadvantages highlighted. The capabilities of such models have been extensively improved by new developments in experimental methods and measurement devices. Newer technologies such as 3D printing, computed tomography scanning, X-rays, nuclear magnetic resonance, novel geophysical techniques, and use of nanomaterials allow for greater flexibilities in conducting experiments. In order for LSMs to be representative of karst aquifers, a few requirements are introduced: (1) the ability to simulate heterogeneous distributions of karst hydraulic parameters, (2) establish Darcian and non-Darcian flow regimes and exchange between the matrix and conduits, (3) placement of adequate sampling points and intervals, and (4) achieving some degree of geometric, kinematic, and dynamic similitude to represent field conditions.     

Biofilm growth in porous media: Experiments,computational modeling at the porescale,and upscaling

Biofilm growth changes many physical properties of porous media such as porosity, permeability and mass transport parameters. The growth depends on various environmental conditions, and in particular, on flow rates. Modeling the evolution of such properties is difficult both at the porescale where the phase morphology can be distinguished, as well as during upscaling to the corescale effective properties. Experimental data on biofilm growth is also limited because its collection can interfere with the growth, while imaging itself presents challenges.In this paper we combine insight from imaging, experiments, and numerical simulations and visualization. The experimental dataset is based on glass beads domain inoculated by biomass which is subjected to various flow conditions promoting the growth of biomass and the appearance of a biofilm phase. The domain is imaged and the imaging data is used directly by a computational model for flow and transport. The results of the computational flow model are upscaled to produce conductivities which compare well with the experimentally obtained hydraulic properties of the medium. The flow model is also coupled to a newly developed biomass–nutrient growth model, and the model reproduces morphologies qualitatively similar to those observed in the experiment.     

Groundwater temperature evolution in the subsurface urban heat island of Cologne,Germany

Long‐term heating of shallow urban aquifers is observed worldwide. Our measurements in the city of Cologne, Germany revealed that the groundwater temperatures found in the city centre are more than 5 K higher than the undisturbed background. To explore the role of groundwater flow for the development of subsurface urban heat islands, a numerical flow and heat transport model is set up, which describes the hydraulic conditions of Cologne and simulates the transient evolution of thermal anomalies in the urban ground. A main focus is on the influence of horizontal groundwater flow, groundwater recharge and trends in local ground warming. To examine heat transport in groundwater, a scenario consisting of a local hot spot with a length of 1 km of long‐term ground heating was set up in the centre of the city. Groundwater temperature‐depth profiles at upstream, central and downstream locations of this hot spot are inspected. The simulation results indicate that the main thermal transport mechanisms are long‐term vertical conductive heat input, horizontal advection and transverse dispersion. Groundwater recharge rates in the city are low (<100 mm a^?1) and thus do not significantly contribute to heat transport into the urban aquifer. With groundwater flow, local vertical temperature profiles become very complex and are hard to interpret, if local flow conditions and heat sources are not thoroughly known. Copyright © 2014 John Wiley & Sons, Ltd.     

Flow based oversampling technique for multiscale finite element methods

Oversampling techniques are often used in porous media simulations to achieve high accuracy in multiscale simulations. These methods reduce the effect of artificial boundary conditions that are imposed in computing local quantities, such as upscaled permeabilities or basis functions. In the problems without scale separation and strong non-local effects, the oversampling region is taken to be the entire domain. The basis functions are computed using single-phase flow solutions which are further used in dynamic two-phase simulations. The standard oversampling approaches employ generic global boundary conditions which are not associated with actual flow boundary conditions. In this paper, we propose a flow based oversampling method where the actual two-phase flow boundary conditions are used in constructing oversampling auxiliary functions. Our numerical results show that the flow based oversampling approach is several times more accurate than the standard oversampling method. We provide partial theoretical explanation for these numerical observations.     

Analysing the relation between rainfall characteristics and lahar activity at Mount Pinatubo,Philippines

The eruption of Mount Pinatubo in June 1991 altered the conditions of the surrounding river catchments. Pyroclastic flows and tephra fall were deposited over extensive areas, stripping off the forest cover and burying drainage divides. These recent deposits are very loosely consolidated and generally consist of sand‐sized particles, which commonly mobilize into lahars in response to rainfall of a certain magnitude. Several devastating lahar occurrences have buried settlements covering tens to several hundred square kilometres in a single event. Correlation of storm rainfall intensities and durations with lahar activity as recorded by acoustic flow monitors is used to investigate trends in the initiation conditions for lahar activity. This research confirms that the relationships of rainfall intensity and duration with lahar initiation threshold values are not linear but rather approximate a power relation. Different relations were found for lahar initiation in different years, from 1991 to 1997, as a result of the dynamic changes in hydrologic and geomorphic conditions of the affected catchments. Data from acoustic flow monitors are used to distinguish debris flow and hyperconcentrated flow activity from that of muddy water. Copyright © 2005 John Wiley & Sons, Ltd.     

Simultaneous identification of parameter,initial condition,and boundary condition in groundwater modelling

In this paper, we perform an inverse method to simultaneously estimate aquifer parameters, initial condition, and boundary conditions in groundwater modelling. The parameter estimation is extended to a complete inverse problem that makes the calibrated groundwater flow model more realistic. The adjoint state method, the gradient search method, and the least square error algorithm are combined to build the optimization procedure. Horizontal two‐dimensional groundwater flow in a confined aquifer is exemplified to demonstrate the correlation between unknowns, the contribution of observation, as well as the suitability of applying the inverse method. The correlation analysis shows the connection between storage coefficient and initial condition. Besides, transmissivity and boundary conditions are also highly correlated. More observations at different location and time are necessary to provide sufficient information. A time series of unsteady head is requested for estimation of storage coefficient and initial condition. Observation near boundary is very effective for boundary condition estimation. The observation at pumping well mostly contributes to the estimation of transmissivity. According to all observations, it is possible to identify parameters, initial condition, and boundary condition simultaneously. Furthermore, the results not only illustrate the traditional assumption of known boundary condition but also initial condition, which may cause an incorrect estimation. Copyright © 2009 John Wiley & Sons, Ltd.     

Refractive Flow and Treatment Systems: Conceptual, Analytical, and Numerical Modeling

Refractive flow and treatment (RFT) systems are designed for passive or low-maintenance in situ ground water remediation for rock or soil of low to moderate permeability. An RFT system captures and refracts contaminated ground water and conveys it to an in situ permeable treatment zone without the need for pumping. Flow to the treatment zone is through one or more high-permeability collection cells, and flow from the treatment zone back into the adjacent native media is through one or more high-permeability dispersal cells.
Conceptual, analytical, and numerical modeling demonstrates the potential for RFT systems to be successful. Analytical modeling shows that the most important factor for this success is that RFT system components be engineered to have comparatively high hydraulic conductivities. A numerical model, capable of representing site-specific conditions, is required for actual RFT system design.     

Eruption rate, area, and length relationships for some Hawaiian lava flows

Volcanic geomorphologists have investigated various relationships between eruption rate and morphologic parameters of lava flows, particularly with regard to preferred statistical correlations and the conditions under which they are valid. Here we employ two simple models for lava flow heat loss by Stefan-Boltzmann radiation to derive eruption rate versus planimetric area relationships. Both of these models predict a linear relationship between eruption rate and planimetric area, modulated by distinct prefactors potentially sensitive to compositional and temperature differences among different flows. Regardless of any theoretical considerations, we show that eruption rate is highly correlated with planimetric area for the Hawaiian basaltic flows analyzed in this work. Moreover, this observed correlation is superior to those from other obvious combinations of eruption rate and flow dimensions. On the basis of the theoretical models for lava flow heat loss, the correlations obtained here suggest that the surfaces of Hawaiian flows radiate at an effective temperature much less than the inner parts of the flowing lava in agreement with numerous field observations. This work also indicates that eruption rate versus planimetric area correlations can be markedly degraded when data from different vents, volcanoes and epochs are combined. These previously unrecognized sensitivities identified by the thermal loss modeling may have contributed to past unresolved debates on relationships between eruption rates and morphologic dimensions.     

Hydrometric and hydrochemicai evidence for fast flowpaths at La Cuenca, Western Amazonia

A hydrological reconnaissance study in a first-order tropical rainforest catchment in western Amazonia implicated overland flow as an important hydrological pathway. A complementary hydrometric and hydrochemical approach that involved the recording of overland flow hydrographs and the determination of streamflow, overland flow, groundwater, soil water, and throughfall chemical signatures, was essential to establish unambiguously the importance of this pathway. Largely uncontrolled by topography, overland flow does occur in any season, regardless of antecedent moisture conditions, which only influence the volumes generated. The latter effect is also reflected in a close approximation of stormflow and overland flow chemical signatures, as expressed in the K/SiO ratio. We conclude that, despite its greater logistical demands, a complementary hydrometric/hydrochemical approach is essential to understand a catchment's hydrological behaviour, especially where fast pathways are at work; such pathways are apparently common in more forest ecosystems than has been previously assumed.     

Flow,bed topography,grain size and sedimentary structure in open channel bends: A three-dimensional model

Bed topography and grain size are predicted for steady, uniform flow in circular bends by consideration of the balance of fluid, gravity and frictional forces acting on bed load particles. Uniform flow pattern is adequately described by conventional hydraulic equations, with bed shear defined as that effectively acting on bed load grains. This analysis is used as a basis to predict bed topography and grain size for steady, non-uniform flow in non-circular bends (represented by a ‘sine-generated’ curve). The non-uniform flow pattern is calculated using the method of Engelund (1974a). Equilibrium bed form, hence sedimentary structure, is found by comparison of existing flow conditions with one of the schemes describing the hydraulic stability limits of the various bed forms. The model was compared with bankfull flow observations from a channel bend on the River South Esk, Scotland. Theoretical bed topography and velocity distribution were very close to the observed data. However, bed shear stress showed only a broad agreement, probably because of the use a constant friction coefficient value. Mean grain size distribution showed good agreement, but theory did not account adequately for gravel sizes in the talweg region and on the upstream, inner part of the bar, possibly due to theoretical underestimation of effective bed shear. Bed form and sedimentary structure are predicted well using the familiar stream power-grain size scheme. The behaviour of the model under unsteady uniform flow conditions in circular bends was analyzed, and suggests that any variation of grain size and bed topography with stage is likely to be limited to deeper parts of the channel.     

Lateral flow thresholds for aspen forested hillslopes on the Western Boreal Plain,Alberta, Canada

To predict the long‐term sustainability of water resources on the Boreal Plain region of northern Alberta, it is critical to understand when hillslopes generate runoff and connect with surface waters. The sub‐humid climate (P ≤ ET) and deep glacial sediments of this region result in large available soil storage capacity relative to moisture surpluses or deficits, leading to threshold‐dependent rainfall‐runoff relationships. Rainfall simulation experiments were conducted using large magnitude and high intensity applications to examine the thresholds in precipitation and soil moisture that are necessary to generate lateral flow from hillslope runoff plots representative of Luvisolic soils and an aspen canopy. Two adjacent plots (areas of 2·95 and 3·4 m²) of contrasting antecedent moisture conditions were examined; one had tree root uptake excluded for two months to increase soil moisture content, while the second plot allowed tree uptake over the growing season resulting in drier soils. Vertical flow as drainage and soil moisture storage dominated the water balances of both plots. Greater lateral flow occurred from the plot with higher antecedent moisture content. Results indicate that a minimum of 15–20 mm of rainfall is required to generate lateral flow, and only after the soils have been wetted to a depth of 0·75 m (C‐horizon). The depth and intensity of rainfall events that generated runoff > 1 mm have return periods of 25 years or greater and, when combined with the need for wet antecendent conditions, indicate that lateral flow generation on these hillslopes will occur infrequently. Copyright © 2008 John Wiley & Sons, Ltd.     

Hortonian overland flow from Japanese forest plantations—an aberration,the real thing,or something in between?

There is a growing opinion that poorly managed plantation forests in Japan are contributing to increased storm runoff and erosion. Here we present evidence to the contrary from runoff plots at two scales (hillslope and 0·5 × 2 m plots) for several forest conditions in the Mie and Nariki catchments. Runoff coefficients from small plots in untended hinoki forests were variable but typically higher than from better managed or deciduous forests during small storms at Nariki; at Mie, runoff during small events was highly variable from all small plots but runoff coefficients were similar for hinoki plots with and without understory vegetation, while the deciduous plot had lower runoff coefficients. Storm runoff was less at the hillslope scale than the plot scale in Mie; these results were more evident at sites with better ground cover. During the largest storms at both sites, differences in runoff due to forest condition were not evident regardless of scale. Dynamic soil moisture tension measurements at Nariki indicated that during a large storm, flow in the upper organic‐rich and root‐permeated soil horizons was 3·2 times higher than measured overland runoff from a small hinoki plot with poor ground cover and 8·3 times higher than runoff from a deciduous forest plot. On the basis of field observations during storms, at least a portion of the monitored ‘Hortonian overland flow’ was actually occurring in this near‐surface ‘biomat’. Therefore our field measurements in both small and large plots potentially included biomat flow in addition to short‐lived Hortonian runoff. Because overland flow decreased with increasing scale, rill erosion did not occur on hillslopes. Additionally, runoff coefficients were not significantly different among cover conditions during large storms; thus, the ‘degraded’ forest conditions appear not to greatly enhance peak flows or erosion potential at larger scales, especially when biomat flow is significant. Copyright © 2007 John Wiley & Sons, Ltd.     

Risk-Based Decision-Support Groundwater Modeling for the Lower San Antonio River Basin,Texas, USA

A numerical surface-water/groundwater model was developed for the lower San Antonio River Basin to evaluate the responses of low base flows and groundwater levels within the basin under conditions of reduced recharge and increased groundwater withdrawals. Batch data assimilation through history matching used a simulation of historical conditions (2006-2013); this process included history-matching to groundwater levels and base-flow estimates at several gages, and was completed in a high-dimensional (highly parameterized) framework. The model was developed in an uncertainty framework such that parameters, observations, and scenarios of interest are envisioned stochastically as distributions of potential values. Results indicate that groundwater contributions to surface water during periods of low flow may be reduced from 6% to 25% with a corresponding 25% reduction in recharge and a 25% increase in groundwater pumping over an 8-year planning period. Furthermore, results indicate groundwater-level reductions in some hydrostratigraphic units are more likely than in other hydrostratigraphic units over an 8-year period under drought conditions with the higher groundwater withdrawal scenario.     

Kinematics, structure and relationship to metamorphism of the east-west flow in the Sanbagawa Belt, southwest Japan

Abstract Deformation in the Sanbagawa Belt is characterized by ductile flow in an east-west direction sub-parallel to its length. The east-west flow (D₁) caused large-scale recumbent folding of the metamorphic sequence in central Shikoku, which can explain the inverted thermal structure of this region. Chemical zoning of metamorphic minerals associated with D₁ microstructures also suggest that the east-west flow developed under retrograde conditions. D₁ is therefore related to exhumation rather than subduction processes. A variety of kinematic indicators show that during the east-west flow, deformation was partitioned into structurally continuous domains with opposed senses of shear. This suggests that bulk deformation was not simple shear but included a component of flattening.     

Geometry,bed topography and drainage system structure of the haut glacier d'Arolla,Switzerland

As part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier. This structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio-echo sounding techniques. The two reconstructions simulate the drainage system structures expected for (a) closed channels, in which water is pressurized by the overlying ice, and (b) gravity-driven, open-channel flow. The closed-channel model provides the best fit to the observed structure, even though theoretical calculations suggest that, under summer discharge conditions, open-channel flow may be widespread beneath the glacier. Possible reasons for this apparent discrepancy are discussed.     

Influence of afforestation on water regime in Jizera Catchments,Czech Republic

This paper studies the influence of afforestation on the water regime in two catchments in the Jizera Mountains that are similar in size and altitude but have different afforestation pattern. In this paper a range of different modelling tools is used to establish whether the differences in catchment water regime can be quantified and attributed to differences in catchment characteristics. Frequency analysis of low and high flows and a number and duration of flows over a threshold value are used to look for the differences in flow regime in both catchments. Low flow conditions are modelled using the Wittenberg nonlinear store approach. A rainfall-runoff process is modelled using a Data Based Mechanistic approach. The results indicate that the differences in the catchment response to external climatic factors outweigh the influence of land use apart from the low flows, where the changes in the response might be attributed to afforestation.     

On inviscid stratified parallel flows varying in two directions

Abstract

A stratified parallel flow in a potential force field is investigated. The density, the velocity, and the potential field of the flow are allowed to vary in two directions. Three sufficient conditions are derived for guaranteed stability of the flow. Two are the classical stability conditions in their respective directions. The third, measured by a newly defined Richardson number, is a result of the shear interaction and the pressure balance condition for stability. Like the classical Richardson number which is always positive preceding stability, this new number acts as a constraint on the other two stability conditions. In addition to the above stability criteria, a semi-ellipse theorem is derived for the present flow.