hillslope storage boussinesq model for subsurface flow and variable source areas along complex hillslopes 2 intercomparison with a three dimensional richards equation model 1 the boussinesq equation for subsurface flow in an idealized sloping aquifer of unit width has recently been extended to hillslopes of arbitrary geometry by incorporating the hillslope width function w x into the governing equation where x is the flow distance along the length of the hillslope troch et al 2003 introduction of a source sink term n allows simulation of storm interstorm sequences in addition to drainage processes while a function sc x representing the maximum subsurface water storage can be used to account for surface saturation response in variable source areas activated by the saturation excess mechanism of runoff generation the model can thus simulate subsurface flow and storage dynamics for nonidealized more realistic hillslope configurations in this paper we assess the behavior of this relatively simple one dimensional model in a series of intercomparison tests with a fully three dimensional richards equation model special attention is given to the discretization and setup of the boundary and initial conditions for seven representative hillslopes of uniform convergent and divergent plan shape drainage and recharge experiments are conducted on these hillslopes for both gentle 5 and steep 30 bedrock slope angles the treatment and influence of the drainable porosity parameter are also considered and for the uniform idealized hillslope case the impact of the unsaturated zone is examined by running simulations for different capillary fringe heights in general terms the intercomparison results show that the hillslope storage boussinesq model is able to capture the broad shapes of the storage and outflow profiles for all of the hillslope configurations in specific terms agreement with the richards equation results varies according to the scenario being simulated the best matches in outflow hydrographs were obtained for the drainage experiments suggesting a greater influence of the unsaturated zone under recharge conditions due to transmission of water throughout the hillslope in the spatiotemporal water table response a better match was observed for convergent than divergent hillslopes and the bedrock slope angle was not found to greatly influence the quality of the agreement between the two models on the basis of the intercomparison experiments we make some suggestions for further development and testing of the hillslope storage model

evaluation of a distributed catchment scale water balance model the validity of some of the simplifying assumptions in a conceptual water balance model is investigated by comparing simulation results from the conceptual model with simulation results from a three dimensional physically based numerical model and with field observations we examine in particular assumptions and simplifications related to water table dynamics vertical soil moisture and pressure head distributions and subsurface flow contributions to stream discharge the conceptual model relies on a topographic index to predict saturation excess runoff and on philip s infiltration equation to predict infiltration excess runoff the numerical model solves the three dimensional richards equation describing flow in variably saturated porous media and handles seepage face boundaries infiltration excess and saturation excess runoff production and soil driven and atmosphere driven surface fluxes the study catchments a 7 2 km2 catchment and a 0 64 km2 subcatchment are located in the north appalachian ridge and valley region of eastern pennsylvania hydrologic data collected during the machydro 90 field experiment are used to calibrate the models and to evaluate simulation results it is found that water table dynamics as predicted by the conceptual model are close to the observations in a shallow water well and therefore that a linear relationship between a topographic index and the local water table depth is found to be a reasonable assumption for catchment scale modeling however the hydraulic equilibrium assumption is not valid for the upper 100 cm layer of the unsaturated zone and a conceptual model that incorporates a root zone is suggested furthermore theoretical subsurface flow characteristics from the conceptual model are found to be different from field observations numerical simulation results and theoretical baseflow recession characteristics based on boussinesq s groundwater equation

little ice age aridity in the north american great plains a high resolution reconstruction of salinity fluctuations from devils lake north dakota usa the little ice age was an interval between about ad 1500 and 1850 characterized by advancing glaciers in mountainous regions of europe and western north america however it is unclear whether this cool moist period was truly global in extent or how it was manifested in other regions with different climatic controls a high resolution reconstruction of salinity fluctuations in devils lake north dakota based on fossil diatoms ostracode shell geochemistry and bulk carbonate geochemistry indicates that saline conditions prevailed throughout much of the recent past these results suggest an arid climate in the northern great plains throughout the little ice age and that during this interval climatic gradients between the great plains and regions to both the east and west may have been quite steep

radiocarbon ages on late pleistocene loess stratigraphy of nebraska and kansas central great plains u s a in the central great plains of the united states radiocarbon dating of loess and buried soils is clarifying the late quaternary loess chronology for the period 25 000 to 10 000 bp along harland lake nebraska a soil developed in the gilman canyon formation and overlain by peoria loess has radiocarbon ages on soil humates of 30 700 to 21 500 bp at one site two picea charcoal bands in the lower meter of peoria loess have radiocarbon ages of 21 250 and 19 730 bp therefore in the vicinity of harlan lake deposition of peoria loess apparently began around 21 000 bp peoria loess deposition appears to have been interrupted by an episode of river entrenchment prior to 12 600 bp spring activity shortly thereafter suggests that incision was coeval to an increase in effective moisture the termination of peoria loess deposition is marked by the brady soil which in the harlan lake area has radiocarbon ages on soil humates of 11 800 to 10 200 bp comparison of the harlan lake chronology with chronologies completed elsewhere in the central great plains reveals general synchrony among periods of pedogenesis and peoria loess deposition little is known however about vegetation conditions in the region when loess was accumulating charcoal has been noted chiefly in the basal peoria loess suggesting that some trees were present during initial peoria loess deposition the extent of this tree cover is unknown however charcoal is rare in the middle and upper peoria loess

analytical solutions to hillslope subsurface storm flow and saturation overland flow we present the analytical solutions to a hillslope based formulation of subsurface storm flow and saturation overland flow here a hillslope is defined as the area between two streamlines originating from two ends of a channel link or from the channel head and ending at the ridgelines the three dimensional soil mantle of a hillslope is reduced to a one dimensional profile along which the soil moisture and discharge are modeled continuity and a kinematic form of darcy s law lead to quasi linear wave equations solvable with the method of characteristics examples are given to illustrate the ability and limitations of the solutions in capturing the essential runoff behavior of different slope types

a low dimensional hillslope based catchment model for layered groundwater flow despite the strong interaction between surface and subsurface waters groundwater flow representation is often oversimplified in hydrological models for instance the interplay between local or shallow aquifers and deeper regional scale aquifers is typically neglected in this work a novel hillslope based catchment model for the simulation of combined shallow and deep groundwater flow is presented the model consists of the hillslope storage boussinesq hsb model representing shallow groundwater flow and an analytic element ae model representing deep regional groundwater flow the component models are iteratively coupled via a leakage term based on darcy s law representing delayed recharge to the regional aquifer through a low conductivity layer simulations on synthetic single hillslopes and on a two hillslope open book catchment are presented and the results are compared against a benchmark three dimensional richards equation model the impact of hydraulic conductivity hillslope plan geometry uniform convergent divergent and hillslope inclination 0 2 5 and 30 under drainage and recharge conditions are examined on the single hillslopes good matches for heads hydrographs and exchange fluxes are generally obtained with the most significant differences in outflows and heads observed for the 30 slope and for hillslopes with convergent geometry on the open book catchment cumulative outflows are overestimated by 1 4 heads in the confined and unconfined aquifers are adequately reproduced throughout the catchment whereas exchange fluxes are found to be very sensitive to the hillslope drainable porosity the new model is highly efficient computationally compared to the benchmark model the coupled hsb ae model represents an alternative to commonly used groundwater flow representations in hydrological models of particular appeal when surface subsurface exchanges local aquifer regional aquifer interactions and low flows play a key role in a watershed s dynamics copyright 2011 john wiley sons ltd

the variability of holocene climate change evidence from varved lake sediments varved sediments from a lake near the present forest prairie border in northwestern minnesota provide an annual record of climate change for the last 10 400 years climate sensitive mineral chemical and biological components show that the mid holocene dry interval between 8500 and 4000 years ago is asymmetrical and actually consists of two distinct drier pulses separated by a moister interval that lasted about 600 years cyclic fluctuations with periods of several hundred years were abrupt and persistent throughout the holocene and are most clearly recorded within the two drier pulses

applicability of effective parameters for unsteady flow in nonuniform aquifers as a rule a groundwater aquifer consists of materials whose characteristics vary in space on account of the uncertainty in determining these characteristics and their variation in the field and also for the sake of parsimony it is often desirable to assume that the aquifer may be considered homogeneous and uniform in other words the prototype is modeled by an equivalent homogeneous and uniform aquifer with a set of effective parameters which displays the same flow characteristics to study the applicability of this concept a monte carlo technique was used in the simulation of unsteady gravity drainage from a large unconfined aquifer for given criteria of hydraulic equivalence applied to the outflow rate effective parameters hydraulic conductivity and drainable porosity were obtained hose variation was studied it was found that only under certain conditions is it possible to define a single set of effective parameters to reproduce the median outflow hydrograph the effective parameters were found to depend on both the distribution of the hydraulic conductivity and its spatial correlation

sudden drawdown and drainage of a horizontal aquifer drainage of a saturated horizontal aquifer following a sudden drawdown is reanalyzed using the boussinesq equation the effect of the finite length of the aquifer is considered in detail an analytical approximation based on a superposition principle yields a very good estimate of the outflow when compared to accurate numerical solutions an illustration of the new analytical approach to analyze basin scale field data is used to demonstrate possible field applications of the new solution

hillslope subsurface flow similarity real world tests of the hillslope peclet number 1 similarity analysis offers the ability to model hydrological response using quantifiable landscape descriptors it is possible to develop similarity indices based on analytical solutions to the governing dynamic equations brutsaert 2005 berne et al 2005 provide derivation of such a similarity index the hillslope peclet number of subsurface flow and saturation for hillslopes with exponential width functions they showed that the hillslope peclet number depends only on geometric properties of the hillslope their work was validated using laboratory experiments conducted on constructed hillslopes with homogeneous soil structure and varying bedrock slope angle this study applies the similarity analysis of berne et al 2005 to two data sets 1 the trench hillslope study at the maimai research catchment conducted by woods and rowe 1996 and 2 the isolated hillslope study near troy idaho united states conducted by brooks et al 2004 the maimai trench study was selected because it provides subsurface flow data from hillslopes with different planform geometries the troy hillslope study was selected because the experimental results of brooks et al 2004 provide an estimate of hydraulic conductivity consistent with the support scale of the hillslope we estimated the hillslope peclet number of the hillslopes on the basis of elevation data and reported values of average soil depth this hillslope peclet number quantifies the geomorphological control on how water moves through these hillslopes and creates a basis for comparison independent of hydraulic properties we then estimated the first and second moments of the characteristic subsurface response function of each hillslope on the basis of subsurface flow data to compare the empirical and theoretical moments the hydraulic properties saturated hydraulic conductivity and drainable porosity of the hillslopes were related using a base flow recession analysis then we were able to derive the dimensionless moments of the hillslopes observed characteristic response function using hydraulic conductivities reported in the literature the agreement between the observed and theoretical moments shows the promise of implementing the hillslope peclet number as a similarity parameter to describe first order hydrological response in humid environments

a hillslope scale experiment to measure lateral saturated hydraulic conductivity 1 one of the most challenging parameters in hillslope and watershed scale distributed hydrologic models is the lateral saturated hydraulic conductivity ks in this paper we present a methodology to determine the hillslope scale lateral ks above a moderately deep sloping restrictive layer in an 18 35 m hillslope plot using perched water level measurements and drain tile outflow data the hillslope scale lateral ks was compared to small scale ks measured with small soil cores and the guelph permeameter our results show that small scale ks measurements underestimate the actual hillslope scale ks the hillslope scale ks measurements were 13 7 4 1 and 3 2 larger than small soil core measurements in the a b and e horizons respectively we argue that the gap between small scale and hillslope scale ks within the same porous medium is foremost a measurement problem data analysis provided the ks distribution with depth showing a sharp decrease in ks within the first 0 1 m of the soil and an exponential decline in ks below 0 1 m the distribution of ks with depth was best described by a double exponential relationship overall results indicate the importance of macroporosity perhaps of biological origin in determining ks at a hillslope scale

storage dependent drainable porosity for complex hillslopes 1 in hydraulic groundwater theory the parameter drainable porosity f a storage coefficient that accounts for the effect of the unsaturated zone on water table dynamics is usually treated as a constant for shallow unconfined aquifers the value of this parameter however depends on the depth to the water table and the water retention characteristics of the soil in this study an analytical expression for f as a function of water table depth is derived under the assumption of quasi steady state hydraulic equilibrium in this way accounting in part for the effects of the unsaturated zone on groundwater dynamics the derived expression is implemented in the nonlinear hillslope storage boussinesq hsb model troch et al 2003 to simulate the drainage response of complex hillslopes the model s behavior is analyzed by comparison to 1 the hsb model with a constant value for f and 2 measurements of water tables and outflow hydrographs on a 6 0 2 5 0 5 m laboratory hillslope experiment the comparison is conducted for a pure drainage case on two different hillslope shapes linearly convergent and divergent and for three different slope inclinations 5 10 and 15 comparison 1 is run in an uncalibrated and a fully calibrated mode and it enables us to evaluate the effect of a dynamic state dependent value for f on model output comparison 2 allows us to test the hsb model on several hillslope configurations and to analyze whether the concept of a storage dependent f enhances the model performance the comparison of the hsb models to the measurements from the laboratory hillslopes shows that it is possible to capture the general features of the outflow hydrograph during a drainage experiment using either one of the hsb models overall the original constant f hsb model with one fitting parameter more than the revised hsb model shows a slightly better fit on the hydrographs when compared to the revised variable f hsb model however the peak outflow values the first few minutes after initiation of the experiments are better captured by the revised hsb model the revised hsb model s performance in simulating water table movements is much more accurate than that of the original hsb model the improved match of the revised hsb model to piezometric measurements is worth stressing because the ability to model water tables is a key attribute of the model making it possible to investigate phenomena such as saturation excess runoff also noteworthy is the good match between the revised hsb model and the outflow measurements without any calibration for the divergent slopes the changing values of the calibrated drainable porosity parameter for the original hsb model as different configurations are simulated slope angle plan shape initial conditions together with the ability of the revised hsb model to more accurately simulate water table dynamics clearly demonstrates the importance of regarding drainable porosity as a dynamic storage dependent parameter

comment on base flow recession from unsaturated saturated porous media considering lateral unsaturated discharge and aquifer compressibility by liang x h zhan y k zhang and k schilling 2017

spatial and temporal patterns of late quaternary eolian deposition eastern colorado u s a abstract eolian sediment covers about 60 of colorado east of the rocky mountains about 30 of the sediment is sand and 70 is loess initially flood plains were the principal sources of eolian sediment but during the holocene dunes formed from older eolian sand and alluvium on uplands since latest pleistocene time dominant dune forming winds have been northwesterly in the northern part of the region and southwesterly in the southern part at present sand sheets and dunes mainly parabolic types are stable and covered with vegetation in dunes sand is commonly 20 30 m thick but elsewhere averages

eolian landscape evolution and soil formation in the chaco dune field southern colorado plateau new mexico abstract eolian deposits of the chaco dune field cover a broad expanse of the southeastern colorado plateau in new mexico and comprise a large part of the late quaternary sedimentary record in this region the primary eolian landforms include sand sheets parabolic and modified parabolic dunes barchan barchanoid dune complexes and ridge dunes many of the eolian landforms in the chaco dune field have remained stable over a sufficiently long time to permit soil development weakly to moderately developed calcic soils which formed in eolian deposits of mid holocene and latest pleistocene age possess clay enriched weak argillic b horizons these soils have been buried progressively by younger eolian sediments forming regionally correlative bounding surfaces over the chaco dune field and recording relict latest pleistocene and middle holocene eolian landscapes soil geomorphic relations and radiocarbon dated material within the eolian deposits have been useful in 1 delineating three regionally correlative soil stratigraphic units and their associated landforms and 2 studying the types and rates of landscape evolution and climatic changes within this portion of the colorado plateau the most significant period of eolian landform construction is inferred to have occurred during the latest pleistocene glacial to interglacial climatic change forming widespread sand sheets and modified parabolic dunes eolian deposition during the middle and late holocene were dramatically influenced by the presence of previously developed latest pleistocene to early holocene buried soils which may have enhanced sand sheet and parabolic dune development due to the binding effect of the soils middle holocene eolian deposition may be related primarily to neoglacial climatic changes which enhanced ground surface moisture and promoted sand sheet and parabolic dune formation the youngest period of wolian deposition occurred after 1 5 ka and resulted in the formation of the most diverse suite of eolian landforms and deposition of volumetrically more eolian sediments than the mid holocene event in contrast to earlier interpretations the classic mid holocene or altithermal event apparently did not play a major role in the formation of eolian landscapes in the chaco dune field

the determination of permafrost thawing trends from long term streamflow measurements with an application in eastern siberia 1 permafrost has been reported to be degrading at increasing rates over wide areas in northern regions of eurasia and north america the evidence has come mainly from in situ observations in the soil profile which have limited spatial and invariably limited temporal coverage herein three methods are proposed to relate low river flows or base flows during the open water season with the rate of change of the active groundwater layer thickness resulting from permafrost thawing at the scale of the upstream river basin as an example the methods are tested with data from four gaging stations within the lena river basin in eastern siberia one in the upper lena basin and three in two of its tributaries namely the olyokma and the aldan basins the different results are mutually consistent and suggest that over the 1950 2008 period the active layer thickness has been increasing at average rates roughly of the order of 0 3 to 1 cm a 1 in the areas with discontinuous permafrost and at average rates about half as large in colder more eastern areas with continuous permafrost these rates have not been steady but have been increasing thus it appears that in the earlier years over the period 1950 1970 some large regions have not been undergoing active layer thickness increases and perhaps even decreases whereas from the 1990s onward vast areas have experienced larger average layer thickness increases especially those with continuous permafrost

dune dammed paleovalleys of the nebraska sand hills intrinsic versus climatic controls on the accumulation of lake and marsh sediments although running water is the dominant geomorphic agent on earth eolian processes can gain ascendancy in regions where the climate is arid vegetation is sparse and abundant sand is available for transport with climate change the boundaries between fluvial dominated and eolian dominated areas may shift although there have been few reports in the north american literature of river systems blocked by dune sand our work in the nebraska sand hills provides evidence of multiple episodes of such blockage events during prolonged arid intervals in latest pleistocene and middle holocene time eolian dune sand blocked two large valley systems in western nebraska these blockages raised the water table of the high plains aquifer as much as 25 m over an area of 7000 km2 and created over one thousand lakes wetlands far removed from the discharge points of the buried paleovalley system are strongly alkaline exceeding 250 000 mg l total dissolved solids tds relatively fresh 280 mg l tds flow through lakes are present at the distal end of the system where the gradient of the water table is steep and the cross section of the buried valley is large anomalously thick marsh and lake sediments accumulated in deep paleovalleys upstream of dune dams near the southern margin of the sand hills our cores and radiocarbon dates from blue and crescent lakes reveal their histories to be quite distinct from adjacent swan lake these differences are best explained by multiple blockage events our work explains why lakes are most abundant in the driest part of the sand hills it also provides another line of evidence for major dune activity in the sand hills region during holocene time and shows that factors other than regional climate specifically location height and hydraulic conductivity of dune dams can control the rise and fall of the ground water table and the chemistry of lakes

pollen diagram from the nebraska sandhills and the age of the dunes abstract radiocarbon dates of organic alluvium beneath as much as 40 m of dune sand along the dismal river have led to the suggestion that the nebraska sandhills date from the holocene rather than the last glacial period on the other hand the basal layers of lake and marsh deposits in interdune depressions at three localities date in the range of 9000 to 12 000 yr b p implying a pre holocene age for the sand dunes a pollen diagram for one of these sites swan lake indicates prairie vegetation throughout the last 9000 yr with no suggestion that the landscape was barren enough to permit the shaping of the massive dunes characterizing the area sand was not transported across the site during the holocene either during the marsh phase which lasted until 3700 yr b p or during the subsequent lake phase the sand that buries the alluvium along the dismal river may represent only local eolian activity or it may indicate that the younger of the two main dune series identified by h t u smith 1965 journal of geology 73 557 578 is holocene in age and the older one late wisconsin in age

analytical approximation for the recession of a sloping aquifer an approximation is obtained for the recession of a sloping aquifer the analytical approximation can provide a useful tool to analyze data and obtain physical properties of the aquifer in contrast to the case of a horizontal aquifer when plotting the time derivative of the flux versus the flux on a log scale the result shows that the flux derivative reaches a minimum value and that the curve can have a slope of unity as often observed illustration of the application of the analytical results to the mahantango creek data is also discussed

radiocarbon ages of soils and charcoal in late wisconsinan loess south central nebraska abstract the farmdale soil occurs below late wisconsinan loess throughout the u s midwest at the la sena site in the central great plains humates in the farmdale interstadial soil have a corrected age of 21 000 yr b p humates in a buried bt horizon and a bulk sample of overlying loess 2 5 m above the farmdale interstadial soil have ages of 17 000 and 19 000 yr b p respectively in the republican river valley picea spruce charcoal is common in the lower meter of peoria loess near bloomington nebraska humates from burned organic matter only 60 cm above the base of peoria loess have a corrected age of ca 19 000 yr b p

on the use of the boussinesq equation for interpreting recession hydrographs from sloping aquifers 1 the method of recession analysis proposed by brutsaert and nieber 1977 remains one of the few analytical tools for estimating aquifer hydraulic parameters at the field scale and beyond in the method the recession hydrograph is examined as dq dt f q where q is aquifer discharge and f is an arbitrary function the observed function f is parameterized through analytical solutions to the one dimensional boussinesq equation for unconfined flow in a homogeneous and horizontal aquifer while attractive in its simplicity as originally presented it is not applicable to settings where slope is an important driver of flow or where hydraulic parameters vary greatly with depth we compare analytical solutions to the linearized one dimensional boussinesq equation for a sloping aquifer to numerical solutions of the full nonlinear equation the behavior of the nonlinear boussinesq equation is also assessed when the aquifer is heterogeneous wherein the lateral saturated hydraulic conductivity k varies as a power law with height z above the impermeable layer k zn n constant 0 all of the analytical solutions differ in key aspects from the nonlinear solution when plotted as dq dt f q and thus are inappropriate for a brutsaert and nieber type analysis however new analytical solutions for a sloping aquifer are derived empirically from the numerical simulations that are applicable during the late period of recession when the recession curve converges to dq dt aqb where b 2n 1 n 1 and a is a function of the dimensions and hydraulic properties of the aquifer

analytical solution of the linearized hillslope storage boussinesq equation for exponential hillslope width functions 1 this technical note presents an analytical solution to the linearized hillslope storage boussinesq equation for subsurface flow along complex hillslopes with exponential width functions and discusses the application of analytical solutions to storage based subsurface flow equations in catchment studies

a similarity framework to assess controls on shallow subsurface flow dynamics in hillslopes 1 an understanding of the dominant controls on water fluxes through landscapes at scales smaller than the resolution of a hydrologic model is useful for choosing appropriate parameterizations and for developing a classification system for landscape hydrology the links between these controls and the parameters in hillslope scale models of subsurface lateral saturated flow have been treated implicitly in both physical e g characteristic response function and empirical formulations such as power law storage discharge relations in particular the controls exerted by the boundary condition at the toe of the hilslope and the temporal variability of the recharge have not been integrated with the understanding of the controls of topography and soil properties in this work we develop a dimensionless similarity framework for assessing these controls on the subsurface flow dynamics based on the boussinesq equation in an idealized hillslope system using this framework we demonstrate the relationship between 1 the exponents of the storage discharge relations 2 the boundary conditions and 3 the characteristic storage thickness used in the characteristic response function parameterization we use the concept of hydrologic regimes to incorporate information about the population of recharge events that drive the system and set up the initial condition of saturated storage for each storm event the analysis demonstrates that for planar hillslopes with uniform soil properties exponents range between 0 when the flow through the hillslope is dominated by the topographic gradients and is in the early stages of draining and 2 when the flow is driven by water table gradients and the thickness of the aquifer at the seepage face is small compared to the average thickness the similarity framework can be used to make first order predictions of these exponents and classify hillslopes using a simple typology of subsurface flows based on two components of the behavior the relative dominance of the topographic and water table gradients and the responsiveness of the hillslope discharge to temporal variability of the recharge inputs

on subsurface stormflow predictions with simple kinematic theory for saturated and unsaturated flows this paper provides analytical solutions for some simple cases of subsurface stormflow the solutions are based on kinematic approximations in both unsaturated and saturated zones solutions for rising falling and partial equilibrium hydrographs are given the analytical model has been applied to data collected on a hillslope of the east twin brook catchment mendip united kingdom measured and predicted hillslope hydrographs were in good agreement

power law catchment scale recessions arising from heterogeneous linear small scale dynamics 1 power law recession behavior has typically been attributed to the hydraulics of subsurface flows in the landscape e g the boussinesq equation many catchments exhibit enormous heterogeneity in their characteristics such as the permeability of soils hillslope length and gradient and soil mantle thickness in the paper we demonstrate using a simple linear flow model that the between hillslope heterogeneity alone can give rise to observed apparently nonlinear recession slope curves the degree of nonlinearity represented by the exponent fitted to the recession slope curve is shown to increase with the degree of heterogeneity of catchment hydraulic properties in sufficiently heterogeneous catchments the recession is also sensitive to the history of recharge events tending to increase when the past events have built up a storage of water in the slow parts of the catchment the models based on the catchment heterogeneity were fitted to data from the panola mountain research watershed yielding a good fit and allowing us to infer how the heterogeneity in catchment properties varies with scale the range of exponents explained by this theory overlaps with the range explained by the hydraulics of subsurface flow which raises doubts about our ability to extract catchment hydraulic parameters on the basis of recession curves so long as the heterogeneity is not accounted for in general the results presented here have enabled us to show how the heterogeneity of landscape characteristics is upscaled and manifested in the apparent nonlinear relationship at the catchment scale

a low dimensional integrated subsurface hydrological model coupled with 2 d overland flow application to a restored fluvial hydrosystem upper rhine river france abstract an integrated hydrological model that couples a low dimensional 2 d subsurface model to 1 d river flow and 2 d overland flow is presented and applied to a real world system the 2 d subsurface equation stems from a careful integration a 3 d richards equation along a local direction normal to the bottom of the aquifer a normally integrated model nim is first compared with the integrated model cathy catchment hydrology in regard to a synthetic test case with complex geometry heterogeneous hydraulic conductivity field of the subsurface compartment and various interactions between the surface and the subsurface this exercise reveals the gain in computation time associated with the use of a low dimensional model by a factor of 6 nim is then applied to simulate the hydrodynamics of an actual restored hydrosystem namely rohrschollen island of the upper rhine river with the aim of assessing the ability to address highly transient hydrological conditions and the efficiency of the restoration strategy the calibration and validation steps associated with this exercise show that the coupled model describes the hydraulic head evolution and water mass balance induced by artificial injections of surface water in a channel dug for the purpose of reconnecting the rhine to an old and clogged channel the low dimensional coupled model of this study is simpler than the state of the art integrated models employing the solution of the 3 d richards equation it is however suited to investigate fine scale problems in relation to water resource management and hydraulic developments with reasonable computational costs and a physically based approach to model flow processes

the importance of hydraulic groundwater theory in catchment hydrology the legacy of wilfried brutsaert and jean yves parlange based on a literature overview this paper summarizes the impact and legacy of the contributions of wilfried brutsaert and jean yves parlange cornell university with respect to the current state of the art understanding in hydraulic groundwater theory forming the basis of many applications in catchment hydrology ranging from drought flow analysis to surface water groundwater interactions hydraulic groundwater theory simplifies the description of water flow in unconfined riparian and perched aquifers through assumptions attributed to dupuit and forchheimer boussinesq 1877 derived a general equation to study flow dynamics of unconfined aquifers in uniformly sloping hillslopes resulting in a remarkably accurate and applicable family of results though often challenging to solve due to its nonlinear form under certain conditions the boussinesq equation can be solved analytically allowing compact representation of soil and geomorphological controls on unconfined aquifer storage and release dynamics the boussinesq equation has been extended to account for flow divergence convergence as well as for nonuniform bedrock slope concave convex the extended boussinesq equation has been favorably compared to numerical solutions of the three dimensional richards equation confirming its validity under certain geometric conditions analytical solutions of the linearized original and extended boussinesq equations led to the formulation of similarity indices for baseflow recession analysis including scaling rules to predict the moments of baseflow response validation of theoretical recession parameters on real world streamflow data is complicated due to limited measurement accuracy changing boundary conditions and the strong coupling between the saturated aquifer with the overlying unsaturated zone however recent advances are shown to have mitigated several of these issues the extended boussinesq equation has been successfully applied to represent baseflow dynamics in catchment scale hydrological models and it is currently considered to represent lateral redistribution of groundwater in land surface schemes applied in global circulation models from the review it is clear that wilfried brutsaert and jean yves parlange stimulated a body of research that has led to several fundamental discoveries and practical applications with important contributions in hydrological modeling

analytical approximations of discharge recessions for steeply sloping aquifers in alpine catchments the validity and applicability of various methods to infer hydraulic properties of sloping aquifers in alpine settings using the power law relationship between the discharge recession and its first time derivative is explored for this purpose a synthetic spring catchment implemented in the numerical groundwater flow model modflow as well as the example of a relict rock glacier in an alpine setting is examined the various approaches are found to differ particularly in the late time domain whereas most of them agree fairly well in the early time domain and at the transition point between the two time domains as the early recession may be affected by uncertainties from inappropriate initial conditions it is proposed to use the transition point for estimating aquifer thickness and transmissivity using only prolonged winter recessions in the analysis of the field data from the relict rock glacier yields estimates of aquifer thickness and hydraulic conductivity consistent with results from a geophysical survey and tracer tests respectively in the other seasons the recession is frequently interrupted by minor recharge events and using the lower envelope of the entire data is found to yield estimates that are too high in the given case it is thus recommended to focus on the winter recession in the analysis of hydrograph data from alpine settings

geomorphological origin of recession curves 1 we identify a previously undetected link between the river network morphology and key recession curves properties through a conceptual physical model of the drainage process of the riparian unconfined aquifer we show that the power law exponent of dq dt vs q curves is related to the power law exponent of n l vs g l curves which we show to be connected to hack s law where l is the downstream distance from the channel heads n l is the number of channel reaches exactly located at a distance l from their channel head and g l is the total length of the network located at a distance greater or equal to l from channel heads using digital terrain models and daily discharge observations from 67 us basins we find that geomorphologic estimates match well the values obtained from recession curves analyses finally we argue that the link between recession flows and network morphology points to an important role of low flow discharges in shaping the channel network

slope runoff processes and flow generation in a subarctic subalpine catchment hillslope runoff was studied in a subarctic subalpine environment to improve understanding of runoff generation processes and the mechanisms whereby water moves from hillslopes to the stream runoff characteristics of four hillslopes were examined between 1997 and 1999 each with distinct soils frost topography and vegetation lateral fluxes were confined to hillslopes with porous organic soils overlying less permeable mineral substrates setting up a two layer flow system whereby most drainage occurs as quickflow in the porous organic layer as matrix flow and or as preferential flow in pipes rills and interconnected surface depressions during snowmelt meltwater infiltrated and percolated the porous frozen organic layers with little resistance percolation ceased at the organic mineral interface due to the impermeable nature of frozen mineral soils forming a perched saturated zone and initiating runoff snowmelt runoff was greater on slopes with greater snow water equivalent and reduced organic layer thickness in summer runoff was greatest on slopes where wet conditions were sustained by inflow stormflow hydrographs responded rapidly to rainfall while exhibiting extended recessions compared with temperate regions where sustained inflow occurred the recession limb showed two segments to reflect different source areas of stormflow production recession analysis was used to quantify contributing areas which were highly variable and controlled largely by hillslope wetness and organic layer properties results indicate that the concept of variable source area for runoff generation applies to subarctic subalpine catchments

a base flow separation algorithm based on the linearized boussinesq equation for complex hillslopes 1 the separation of base flow from discharge records is an important issue in hydrology the objective of this paper is to develop a base flow separation algorithm based on groundwater theory in which the shape of the aquifer is taken into account and for which the parameters can be estimated from river discharge measurements for this purpose an analytical solution to the linearized boussinesq equation for realistic aquifer shapes and temporally variable recharge rates is derived this solution is combined with a mass balance at the land surface in order to construct the base flow separation algorithm the parameters of the base flow filter are calculated on the basis of the same analytical solution comparison of the results of the new algorithm to existing base flow separation methods shows the need for a physical basis for base flow filters

drying front in a sloping aquifer nonlinear effects 1 the profiles for the water table height h x t in a shallow sloping aquifer are reexamined with a solution of the nonlinear boussinesq equation we demonstrate that the previous anomaly first reported by brutsaert 1994 that the point at which the water table h first becomes zero at x l at time t t c remains fixed at this point for all times t t c is actually a result of the linearization of the boussinesq equation and not as previously suggested brutsaert 1994 verhoest and troch 2000 a result of the dupuit assumption rather by examination of the nonlinear boussinesq equation the drying front i e the point x f at which h is zero for times t greater than or equal to t c actually recedes downslope as physically expected this points out that the linear boussinesq equation should be used carefully when a zero depth is obtained as the concept of an average depth loses meaning at that time

baseflow recession and recharge as nonlinear storage processes discharge in many rivers is often fed by outflow from a shallow groundwater reservoir it is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow q and storage s for which the equation s aqb was adopted values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0 5 which is in accordance with the findings of other studies and theoretical approaches yielding b 0 5 for unconfined aquifers and relating the coefficient a to catchment properties primarily area and shape of basin pore volume and transmissivity this non linear reservoir function is proposed as a more realistic alternative to the linear reservoir function the relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of old pre event water into the river bed as fissure and pore volumes communicate hydraulically it appears physically reasonable to model the system by one non linear reservoir for catchments or parts of them instead of applying independent parallel linear reservoirs the non linear reservoir algorithms are supported by an analytical derivation they are extended for the automatic separation of baseflow from a time series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing the time series obtained allow the identification and quantification of long term changes to the water balance relationships between computed groundwater storage and observed groundwater level can also be established copyright 1999 john wiley sons ltd

analytical methods for estimating saturated hydraulic conductivity in a tile drained field determination of field scale hydraulic properties is required for many hydrologic predictions four analytical methods for determining the saturated hydraulic conductivity k on the field scale for a field drained by a network of parallel drains are considered these methods all derived from the boussinesq equation relate 1 time rate of change of discharge to discharge 2 relative discharge to time 3 time rate of change of water table height to height and 4 relative water table height to time though all four methods eliminate the need to know precisely the beginning time of the recession curve which is in practice ambiguous methods 2 and 4 do not require taking time derivates of observations which introduces noise the mean field scale k based on several recession events on two 1 ha fields using all methods was 4 m d this is near the median k of 5 m d calculated from 40 soil cores taken at various depths within the same fields but five times less than the mean k of the soil cores 20 m d q 2003 elsevier b v all rights reserved

accurate approximate semi analytical solutions to the boussinesq groundwater flow equation for recharging and discharging of horizontal unconfined aquifers abstract the boussinesq equation is usually used to describe one dimensional unconfined groundwater movement solutions of this equation are important as they provide useful insights regarding the water table response to stream level variations and allow us to quantify the exchange flow between the stream and the aquifer due to the nonlinearity of the boussinesq equation the solutions are generally obtained using numerical methods however for certain classes of initial and boundary conditions there are both exact and approximate analytical solution techniques this work focuses on the latter approach a new mathematical technique for approximate solutions of the boussinesq equation describing flow in horizontal unconfined aquifers induced by sudden change in boundary head is presented the method applies to the problems of recharging and dewatering of an unconfined aquifer and approximate solutions to both problems are derived the solutions were obtained by introducing an empirical function with four parameters which might be obtained using a numerical fitting procedure results based on this technique were found to be easily calculated and to be in good agreement with those obtained using numerical calculation based on runge kutta approach a benchmark between the proposed solutions and five existing approximate analytical solutions shows that the present solutions are the most accurate approximate solutions among those tested applications of the solutions are presented in the context of estimating aquifer hydraulic parameters

drainage of a horizontal boussinesq aquifer with a power law hydraulic conductivity profile 1 solutions to the boussinesq equation describing drainage into a fully penetrating channel have been used for aquifer characterization two analytical solutions exist for early and late time drainage from a saturated homogeneous and horizontal aquifer following instantaneous drawdown the solutions for discharge q can be expressed as dq dt aq b where a is constant and b takes on the value 3 and 3 2 for early and late time respectively though many factors can contribute to departures from the two predictions we explore the effect of having permeability decrease with depth as it is known that many natural soils exhibit this characteristic we derive a new set of analytical solutions to the boussinesq equation for k oc z n where k is the saturated hydraulic conductivity z is the height above an impermeable base and n is a constant the solutions reveal that in early time b retains the value of 3 regardless of the value of n while in late time b ranges from 3 2 to 2 as n varies from 0 to oo similar to discharge water table height h in late time can be expressed as dh dt ch d where d 2 for constant k and d oo as n in theory inclusion of a power law k profile does not complicate aquifer parameter estimation because n can be solved for when fitting b to the late time data whereas previously b was assumed to be 3 2 however if either early or late time data are missing there is an additional unknown under appropriate conditions water table height measurements can be used to solve for an unknown parameter

middle and late holocene dune reactivation in the nebraska sand hills usa a combination of optical dating of aeolian sand and radiocarbon dating of palaeosols and interdune sediments has allowed some refinements to the chronostratigraphy of the nebraska sand hills our results directly confirm previous inferences that multiple phases of aeolian deposition including megabarchan dune reactivation occurred within the sand hills during the middle and late holocene optical dates on stratified aeolian barchan dune sediments from two localities provide ages ranging from c 6 ka to 300 years ago weakly developed palaeosols intercalated within the dune sediments and other forms of post depositional modification indicate periods of relative stability and reduced dune mobilization optical dates on the upper 12 15 m of two dune exposures indicate repeated possibly regionally correlative reactivations which occurred between c 400 500 and 200 300 years ago comparison of late holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reacti

baltica and gondwana derived sediments in the mid german crystalline rise central europe implications for the closure of the rheic ocean abstract combined u pb and lu hf isotope analysis of detrital zircons reveals that the mid german crystalline rise mgcr contains palaeozoic sediments of distinct provenance in close proximity zircons from a metapelite of the brotterode group were derived from a gondwanan source whereas zircons from the rogis quartzite of the ruhla group point to provenance from baltica brotterode zircons mostly yield ages of 500 720 ma and 2 0 2 1 ga and show an age gap between 1 0 and 1 7 ga which is characteristic of gondwana peri gondwanan detrital zircon populations combined u pb and hf isotope data suggest intense crustal recycling at 2 6 2 9 ga 1 8 2 1 ga and 570 720 ma as well as formation of juvenile crust during the latter two periods in contrast zircons of the rogis quartzite mostly yield ages between 0 9 and 1 8 ga which are typical of southwestern baltica minor age populations at 435 466 and 550 660 ma indicate that the quartzite is younger than late ordovician early silurian and that the baltica derived sediment is contaminated by minor peri gondwanan perhaps avalonia derived detritus minor age populations at 2 0 2 56 2 67 and 2 86 ga additionally point to a svecofennian and or karelian source u pb and hf isotope data imply that the baltica derived zircons were produced mainly through melting of juvenile palaeo to mesoproterozoic crust the data presented here indicate that the mgcr hosts the rheic suture between gondwana and balonia and that this suture zone was closed in a complex sequence of stages from the late silurian onwards

a subordinated kinematic wave equation for heavy tailed flow responses from heterogeneous hillslopes 1 analytical expressions of hillslope scale subsurface stormflow discharge are currently restricted to hillslopes with homogeneous or mildly heterogeneous conductivity fields in steep straight hillslopes with uniform recharge these exhibit a classical piston flow response which arises from an assemblage of impulses all moving at a constant velocity but with different starting locations heterogeneity within a hillslope soil creates variations in the downslope velocity of these impulses which may lead to nonpiston flow responses with either exponential or heavy power law tails the presence of heavy tails suggests that heterogeneity imparts a temporal memory on the motion of the impulses using this assumption a subordinated kinematic wave equation is proposed for moderately to highly heterogeneous hillslopes this equation convolves the piston response from a homogenous hillslope with a stable subordinator the stable subordinator randomizes the time that impulses spend in motion and produces nonpiston solutions with heavy tails through comparisons of synthetic data generated from numerical hillslope simulations with physically realistic parameters this equation faithfully reproduces both early and late time characteristics of heavy tailed flow responses from moderate to highly heterogenous hillslopes a systematic evaluation of hillslope responses under different degrees of heterogeneity revealed a quantitative link between the statistical properties of the heterogeneous random fields and the parameters of the subordination framework this suggests that the subordinator can be parameterized with the physical measurement of hillslope properties

confirmation of a short time expression for the hydrograph rising limb of an initially dry aquifer using laboratory hillslope outflow experiments the objective of this study is to assess the validity of a theoretical expression for the outflow from an initially dry aquifer subject to recharge this equation states that for small values of time this outflow is proportional to the square root of time here we report on experiments performed with two laboratory hillslopes in the wageningen rainfall simulator three different aquifer slopes were investigated with four replicates for each slope the relations between the measured outflows and the square root of time exhibited very high coefficients of determination all but one 0 9 the aquifer saturated hydraulic conductivity k and drainable porosity were determined using a base flow recession analysis with k being consistent with soil physical laboratory measurements the recharge rates obtained using the coefficient of the short time expression and the steady state discharge were consistent as well overall these results confirm the theoretical relationship between the aquifer outflow for the hydrograph rising limb and the square root of time

effects of unsaturated flow on hillslope recession characteristics recession flow analysis is usually conducted to infer hydraulic parameters of hillslope aquifers various boussinesq equation based models both linear and nonlinear have been used to analyze the recession curves for sloping aquifers with a focus on the long time recession behavior based on a modified boussinesq equation with capillarity incorporated we demonstrate the significant effect of unsaturated flow on the recession curve which result in three instead of two power law regimes with two transition points instead of one corresponding to the formation of a fully unsaturated zone at the adjacent area of the upslope boundary and across the whole domain respectively the results show that the power of the second and third recession regime is variable depending on the slope angles soil types and hillslope geometries the unsaturated flow effects also lead to the absence of drastic drop of formula presented at the transition between the first and second regime which was predicted by previous numerical models but has not been observed in the field or laboratory experiments these findings have important implications for recession flow analysis in studies of hillslope aquifers

investigating the linkage between streamflow recession rates and channel network contraction in a mesoscale catchment in new york state the rate of recession dq dt in a given time interval has long been plotted in log log space against the concurrent mean discharge qavg recent interpretations of these dq dt qavg plots have sought to look at curves for individual events instead of the data cloud from all the data points together these individual recession curves have been observed to have near constant slope but to have varying intercepts features hypothesized to possibly be explained by the nature of the contraction of the active channel network during recession for a steep 150 ha forested catchment in central new york state with an 8 8 km channel network changes in the active channel network were mapped between april and november 2013 streamflow recession occurred in a matter of days but changes in the active channel network occurred over a matter of weeks thus in this catchment it does not appear that channel contraction directly controls recession additionally field observations indicate that dry down did not occur in a spatially organized sequential way such that the upper end of higher order streams dried first instead the location of groundwater seeps in part controlled the active portion of the channel network consistent with the presence of different types of flow contributing zones the paper presents a conceptual model that consists of multiple parallel reservoirs of varying drainage rate and varying degrees of recharge at different times of the year this conceptual model is able to reproduce a slope of 2 and a seasonal shift in intercept typical of individual recession curves copyright 2015 john wiley sons ltd

spatially variable water table recharge and the hillslope hydrologic response analytical solutions to the linearized hillslope boussinesq equation 2014 american geophysical union all rights reserved the linearized hillslope boussinesq equation introduced by brutsaert 1994 describes the dynamics of saturated subsurface flow from hillslopes with shallow unconfined aquifers in this paper we use a new analytical technique to solve the linearized hillslope boussinesq equation to predict water table dynamics and hillslope discharge to channels the new solutions extend previous analytical treatments of the linearized hillslope boussinesq equation to account for the impact of spatiotemporal heterogeneity in water table recharge the results indicate that the spatial character of recharge may significantly alter both steady state subsurface storage characteristics and the transient hillslope hydrologic response depending strongly on similarity measures of controls on the subsurface flow dynamics additionally we derive new analytical solutions for the linearized hillslope storage boussinesq equation and explore the interaction effects of recharge structure and hillslope morphology on water storage and base flow recession characteristics a theoretical recession analysis for example demonstrates that decreasing the relative amount of downslope recharge has a similar effect as increasing hillslope convergence in general the theory suggests that recharge heterogeneity can serve to diminish or enhance the hydrologic impacts of hillslope morphology

some analytical solutions of the linearized boussinesq equation with recharge for a sloping aquifer subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the boussinesq equation several attempts have been made to solve this partial differential equation and exact solutions have been found for specific situations in the case of a sloping aquifer brutsaert 1994 suggested linearizing the equation to calculate the unit response of the hillslope in this paper we first apply the work of brutsaert by assuming a constant recharge to the groundwater table the solution describes the groundwater table levels and the outflow in function of time then an analytical expression is derived for the steady state solution by allowing time to approach infinity this steady state water table is used as an initial condition to derive another analytical solution of the boussinesq equation this can then be used in a quasi steady state approach to compute outflow under changing recharge conditions subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the boussinesq equation several attempts have been made to solve this partial differential equation and exact solutions have been found for specific situations in the case of a sloping aquifer brutsaert 1994 suggested linearizing the equation to calculate the unit response of the hillslope in this paper we first apply the work of brutsaert by assuming a constant recharge to the groundwater table the solution describes the groundwater table levels and the outflow in function of time then an analytical expression is derived for the steady state solution by allowing time to approach infinity this steady state water table is used as an initial condition to derive another analytical solution of the boussinesq equation this can then be used in a quasi steady state approach to compute outflow under changing recharge conditions

the unit response of groundwater outflow from a hillslope subsurface flow from a hillslope can be described by hydraulic groundwater theory as formulated by the boussinesq equation solution of its linear version brings out some of the essential features of this phenomenon arbitrary inputs can be accommodated by simple convolution of the sudden drawdown problem the relative magnitude of the driving mechanisms namely the streamwise pressure gradient resulting in diffusion and gravity i e slope resulting in advection can be determined by a simple dimensionless parameter

optical dating of young modern sediments using quartz results from a selection of depositional environments abstract equivalent dose ed evaluations for quartz grains extracted from a number of modern or young samples collected from a range of depositional environments are reported the signal used was optically stimulated luminescence osl with an argon ion laser tuned to 514 nm as a light source typical equivalent dose values were 0 05 0 3 gy for the given samples which is substantially less than equivalent doses expected for similar sediments by conventional thermoluminescence tl the non zero equivalent dose exhibited by the samples may be a product of relict osl from incompletely bleached traps sample pre treatment procedures or due to signal recuperation following bleaching during antiquity the potential significance of each are discussed a number of modifications to sample pre treatment and processing are also described

a hybrid 3d hillslope hydrological model for use in earth system models hillslope scale rainfall runoff processes leading to a fast catchment response are not explicitly included in land surface models lsms for use in earth system models esms due to computational constraints this study presents a hybrid 3d hillslope hydrological model h3d that couples a 1 d vertical soil column model with a lateral pseudo 2d saturated zone and overland flow model for use in esms by representing vertical and lateral responses separately at different spatial resolutions h3d is computationally efficient the h3d model was first tested for three different hillslope planforms uniform convergent and divergent we then compared h3d with single and multiple soil columns with a complex physically based 3 d model and a simple 1 d soil moisture model coupled with an unconfined aquifer as typically used in lsms it is found that simulations obtained by the simple 1 d model vary considerably from the complex 3 d model and are not able to represent hillslope scale variations in the lateral flow response in contrast the single soil column h3d model shows a much better performance and saves computational time by 2 3 orders of magnitude compared with the complex 3 d model when multiple vertical soil columns are implemented the resulting hydrological responses soil moisture water table depth and base flow along the hillslope from h3d are nearly identical to those predicted by the complex 3 d model but still saves computational time as such the computational efficiency of the h3d model provides a valuable and promising approach to incorporating hillslope scale hydrological processes into continental and global scale esms

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

effects of hydraulic conductivity variability on hillslope scale shallow subsurface flow response and storage discharge relations 1 an important problem in scientific hydrology is accounting for the effect of small scale heterogeneity in lumped representations of flow through landscapes in this work we investigate the effect of lateral variations in hydraulic conductivity on saturated subsurface lateral flow through hillslopes using an idealized model based on the boussinesq equation the model simulates flow over an impervious planar base through heterogeneous conductivity fields in response to simple recharge inputs and periodic recharge events the results indicate that the hillslope scale response depends on the relative importance of topographic and water table potential gradients driving flow the relative magnitude of these drivers is related to a dimensionless variable where water table gradients dominate a network of flow paths channel flow through the hillslope toward high conductivity areas and the response is primarily dependent on the boundary condition at the toe of the hillslope where the topographic gradients dominate the flow is delayed by low conductivity areas producing a power law like response suggesting that high exponents in observed storage discharge relations may be traced to the presence of heterogeneity in the landscape these observations suggest that the nature of the lumped hillslope scale hydrologic models depends on the emergent behaviors that arise at that scale as a result of the interactions between hillslope properties including their variability in space the relationship between the hillslopes and their surrounding landscape elements through the boundary conditions and the temporal variability of the recharge that enters the system

late holocene alluvial chronology and climate change in the central great plains abstract alluvium in one reach of the republican river valley south central nebraska dates to the holocene radiocarbon dating of fills underlying the two terraces in the valley reveals that entrenchment between 4500 and 3700 yr b p formed the high terrace subsequently alternating aggradation and stability occurred until sometime between 1800 and 1100 yr b p following another period of alluviation channel incision formed the low terrace general synchrony between this chronology and other late holocene fluvial chronologies of the central great plains suggests climatic control of fluvial activity the episodes of incision are tentatively correlated with different climate regimes illustrating the difficulty of attributing a given fluvial response to a particular direction of climatic change

the hillslope storage boussinesq model for non constant bedrock slope in this study the recently introduced hillslope storage boussinesq hsb model is cast in a generalized formulation enabling the model to handle non constant bedrock slopes i e bedrock profile curvature this generalization extends the analysis of hydrological behavior to hillslopes of arbitrary geometrical shape including hillslopes having curved profile shapes the generalized hsb model performance for a free drainage scenario is evaluated by comparison to a full three dimensional richards equation re based model the model results are presented in the form of dimensionless storage profiles and dimensionless outflow hydrographs in addition comparison of both models to a storage based kinematic wave kw model enables us to assess the relative importance of diffusion processes for different hillslope shapes and to analyze the influence of profile curvature on storage and flow patterns specifically the comparison setup consists of a set of nine gentle 5 bedrock slope and nine steep 30 bedrock slope hillslopes of varying plan shape and profile curvature interpretation of the results shows that for highly conductive soils the simulated storage profiles and outflow hydrographs of the generalized hsb model and re model match remarkably for 5 bedrock slope and for all plan and profile curvatures the match is slightly poorer on average for 30 bedrock slope in particular on divergently shaped hillslopes in the assessment of the influence of hydraulic diffusion we find good agreement in simulation results for the kw model compared to results from the generalized hsb model and the re model for steep divergent and uniform hillslopes due to a relatively low ratio between water table gradient and bedrock slope compared to convergent or gentle hillslopes overall we demonstrate that in addition to bedrock slope hillslope shape as represented by plan and profile curvature is an important control on subsurface flow response

examination of the seepage face boundary condition in subsurface and coupled surface subsurface hydrological models a seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions water table fluctuations and flow patterns its handling in hydrological models especially under complex conditions such as heterogeneity and coupled surface subsurface flow has not been extensively studied in this paper we compare the treatment of the seepage face as a static dirichlet versus dynamic boundary condition we assess its resolution under conditions of layered heterogeneity we examine its interaction with a catchment outlet boundary and we investigate the effects of surface subsurface exchanges on seepage faces forming at the land surface the analyses are carried out with an integrated catchment hydrological model numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the landscape evolution observatory the results show that the static boundary condition is not always an adequate stand in for a dynamic seepage face boundary condition especially under conditions of high rainfall steep slope or heterogeneity that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role and that seepage faces at the land surface are not always controlled by subsurface flow the paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way is applicable to unstructured grids and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

hillslope storage boussinesq model for subsurface flow and variable source areas along complex hillslopes 1 formulation and characteristic response 1 hillslope response to rainfall remains one of the central problems of catchment hydrology flow processes in a one dimensional sloping aquifer can be described by boussinesq s hydraulic groundwater theory most hillslopes however have complex three dimensional shapes that are characterized by their plan shape profile curvature of surface and bedrock and the soil depth field studies and numerical simulation have shown that these attributes are the most significant topographic controls on subsurface flow and saturation along hillslopes in this paper the boussinesq equation is reformulated in terms of soil water storage rather than water table height the continuity and darcy equations formulated in terms of storage along the hillslope lead to the hillslope storage boussinesq hsb equation for subsurface flow solutions of the hsb equation account explicitly for plan shape of the hillslope by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function we investigate the behavior of the hsb model for different hillslope types uniform convergent and divergent and different slope angles under free drainage conditions after partial initial saturation drainage scenario and under constant rainfall recharge conditions recharge scenario the hsb equation is solved by means of numerical integration of the partial differential equation we find that convergent hillslopes drain much more slowly compared to divergent hillslopes the accumulation of moisture storage near the outlet of convergent hillslopes results in bell shaped hydrographs in contrast the fast draining divergent hillslopes produce highly peaked hydrographs in order to investigate the relative importance of the different terms in the hsb equation several simplified nonlinear and linearized versions are derived for instance by recognizing that the width function of a hillslope generally shows smooth transition along the flow direction or by introducing a fitting parameter to account for average storage along the hillslope the dynamic response of these reduced versions of the hsb equation under free drainage conditions depend strongly on hillslope shape and bedrock slope angle for flat slopes of the order of 5 only the simplified nonlinear hsb equation is able to capture the dynamics of subsurface flow along complex hillslopes in contrast for steep slopes of the order of 30 we see that all the reduced versions show very similar results compared to the full version it can be concluded that the complex derivative terms of width with respect to flow distance play a less dominant role with increasing slope angle comparison with the hillslope storage kinematic wave model of troch et al 2002 shows that the diffusive drainage terms of the hsb model become less important for the fast draining divergent hillslopes these results have important implications for the use of simplified versions of the hsb equation in landscapes and for the development of appropriate analytical solutions for subsurface flow along complex hillslopes

a metahillslope model based on an analytical solution to a linearized boussinesq equation for temporally variable recharge rates 1 in hydrology the slow subsurface component of the discharge is usually referred to as base flow one method to model base flow is the conceptual approach in which the complex physical reality is simplified using hypotheses and assumptions and the various physical processes are described mathematically the purpose of this paper is to develop and validate a conceptual method based on hydraulic theory to calculate the base flow of a catchment under observed precipitation rates the governing groundwater equation the boussinesq equation valid for a unit width sloping aquifer is linearized and solved for a temporally variable recharge rate the solution allows the calculation of the transient water table profile in and the outflow from an aquifer under temporally variable recharge rates when a catchment is considered a metahillslope the solution can be used when coupled to a routing model to calculate the catchment base flow the model is applied to the zwalm catchment and four subcatchments in belgium the results suggest that it is possible to model base flow at the catchment scale using a boussinesq based metahillslope model the results further indicate that it is sufficient to use a relatively simple formulation of the infiltration overland flow and base flow processes to obtain reasonable estimates of the total catchment discharge

a note on groundwater flow along a hillslope 1 particular cases of groundwater flow along a hillslope are studied using the groundwater hydraulic theory e g dupuit approximation described by the boussinesq equation analytical solutions are found as simple transformations of known similarity solutions in particular the expressions for phreatic surface level and volume flux and the corresponding loop rating curve for the flow of a groundwater mound as well as the travelling wave solutions of the boussinesq equation are described in detail

base flow recession from unsaturated saturated porous media considering lateral unsaturated discharge and aquifer compressibility unsaturated flow is an important process in baseflow recessions and its effect is rarely investigated a mathematical model for a coupled unsaturated saturated flow in a horizontally unconfined aquifer with time dependent infiltrations is presented the effects of the lateral discharge of the unsaturated zone and aquifer compressibility are specifically taken into consideration semi analytical solutions for hydraulic heads and discharges are derived using laplace transform and cosine transform the solutions are compared with solutions of the linearized boussinesq equation lb solution and the linearized laplace equation ll solution respectively a larger dimensionless constitutive exponent d a smaller retention capacity of the unsaturated zone leads to a smaller discharge during the infiltration period and a larger discharge after the infiltration the lateral discharge of the unsaturated zone is significant when d 1 and becomes negligible when d d 100 the compressibility of the aquifer has a non negligible impact on the discharge at early times for late times the power index b of the recession curve dq dt aqb is 1 and independent of d where q is the baseflow and a is a constant lumped aquifer parameter for early times b is approximately equal to 3 but it approaches infinity when t 0 the present solution is applied to synthetic and field cases the present solution matched the synthetic data better than both the ll and lb solutions with a minimum relative error of 16 for estimate of hydraulic conductivity the present solution was applied to the observed streamflow discharge in iowa and the estimated values of the aquifer parameters were reasonable

estimation of aquifer lower layer hydraulic conductivity values through base flow hydrograph rising limb analysis 1 the estimation of catchment averaged aquifer hydraulic conductivity values is usually performed through a base flow recession analysis relationships between the first time derivatives of the base flow and the base flow values themselves derived for small and large values of time are used for this purpose however in the derivation of the short time equations an initially fully saturated aquifer without recharge with sudden drawdown is assumed which occurs very rarely in reality it is demonstrated that this approach leads to a nonnegligible error in the parameter estimates a new relationship is derived valid for the rising limb of a base flow hydrograph succeeding a long rainless period application of this equation leads to accurate estimates of the aquifer lower layer saturated hydraulic conductivity further it has been shown analytically that if base flow is modeled using the linearized boussinesq equation the base flow depends on the effective aquifer depth and the ratio of the saturated hydraulic conductivity to the drainable porosity not on these three parameters separately the results of the new short time expression are consistent with this finding as opposed to the use of a traditional base flow recession analysis when base flow is modeled using the nonlinear boussinesq equation the new expression can be used without a second equation for large values of time to estimate the aquifer lower layer hydraulic conductivity overall the results in this paper suggest that the new methodology outperforms a traditional recession analysis for the estimation of catchment averaged aquifer hydraulic conductivities

geomorphic signatures on brutsaert base flow recession analysis this paper addresses the signatures of catchment geomorphology on base ow recessioncurves its relevance relates to the implied predictability of base ow features which arecentral to catchment scale transport processes and to ecohydrological function movingfrom the classical recession curve analysis method originally applied in the finger lakesregion of new york a large set of recession curves has been analyzed from swissstream ow data for these catchments digital elevation models have been preciselyanalyzed and a method aimed at the geomorphic origins of recession curves has beenapplied to the swiss data set the method links river network morphology epitomized bytime varying distribution of contributing channel sites with the classic parameterization ofrecession events this is done by assimilating two scaling exponents and b

improvement of the hillslope storage boussinesq model by considering lateral flow in the unsaturated zone unsaturated flow is an important factor that affects groundwater motion among various drainage models the nonlinear hillslope storage boussinesq hsb model has been commonly used to predict water flux along a slope in this study we improved this model by considering lateral flow in the unsaturated zone using modified van genuchten functions we analytically expressed the concept of equivalent propagation thickness in the vadose zone this analytical expression was then incorporated into the hsb model to reflect two different stages of the drainage process and to simulate the hillslope drainage process more accurately the model results indicated that lateral flow has significant effects in the unsaturated zone during the hillslope drainage process even in sandy aquifers the amount of water contributed by the unsaturated zone is a key factor that enables a decrease in the water table during the middle and late stages of the process a comparison between the measured and simulated results based on both convergent type and divergent type hillslope drainage processes revealed that the thickness of the saturated zone decreases as the unsaturated flow increases this study emphasizes the necessity of considering unsaturated flow in the hsb model to improve the accuracy of predicting groundwater outflow rates and develop more accurate hydrographs the concept of equivalent propagation thickness also provides a criterion for assessing the importance of unsaturated lateral flow for future drainage research

low dimensional modeling of hillslope subsurface flow relationship between rainfall recharge and unsaturated storage dynamics 1 we present a coupling between the one dimensional richards equation for vertical unsaturated flow and the one dimensional hillslope storage boussinesq equation hsb for lateral saturated flow along complex hillslopes here the capillary fringe is included in the flow domain as an integral part of the boussinesq aquifer the coupling allows quantitative investigation of the role of unsaturated storage in the relationship between rainfall and recharge the coupled model hsb coupled is compared to the original hsb model hsb original and a three dimensional richards equation re based model taken to be the benchmark on a set of seven synthetic hillslopes ranging from convergent to divergent using hsb original the water tables are overestimated and the outflow rates are generally underestimated and there is no delay between rainfall and recharge the coupled model however shows a remarkably good match with the re model in terms of outflow rates and the delay between rainfall and recharge is captured well we also see a clear improvement in the match to the water tables even though the values are still overestimated for some hillslope shapes in particular the convergent slopes we show that for the hillslope configurations and scenarios examined in this paper it is possible to reproduce hydrographs and water table dynamics with a good degree of accuracy using a low dimensional hydrological model

straight thinking about groundwater recession while in catchment and hillslope hydrology a more nuanced approach is now taken to streamflow recession analysis in the context of major aquifers it is commonly still assumed that the groundwater head recession rate will take exponential form an idea originally proposed in the 19th century however it is shown here that in early times the groundwater head recession in a major aquifer should take an almost straight line form with a rate approximately equal to the long term recharge rate divided by the aquifer storage coefficient the length of this phase can be estimated from an analytical expression derived in the paper which depends on the aquifer diffusivity length scale and the position of the monitoring point a transitional phase then leads to an exponential phase after some critical time which is independent of the position of the monitoring point major aquifers in a state of periodic quasi steady state are expected to have rates of groundwater flux recession which deviate little from the average rate of groundwater recharge where quasi exponential groundwater declines are observed in nature their form may be diagnostic of particular types of aquifer properties and or boundary effects such as proximity to drainage boundaries variations in transmissivity with hydraulic head storage changes due to pumping nonequilibrium flow at a range of spatial and temporal scales and variations in specific yield with depth recession analysis has applicability to a range of groundwater problems and is powerful way of gaining insight into the hydrologic functioning of an aquifer

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

holocene alluvial fills in the south loup valley nebraska abstract four holocene alluvial fills are present in nebraska s south loup river valley fill iv the oldest and thickest was deposited between 10 200 and 4800 14c yr b p fill iii has an age of about 3000 14c yr b p fill ii is younger than 2100 and older than 900 14c yr b p and fill i is younger than 900 14c yr b p regional contemporaneity of valley alluviation in the eastcentral great plains suggests that climate has controlled long term sediment storage in the south loup river valley

similarity analysis of subsurface flow response of hillslopes with complex geometry the matter of the efficient and parsimonious parameterization of hillslope subsurface flow remains an important issue in catchment hydrological studies brutsaert 1995 insights into the influence of the shape and hydraulic characteristics of hillslopes is required to further our understanding and our ability to model catchment hydrological processes recently troch et al 2003 introduced the hillslope storage boussinesq hsb equation to describe subsurface flow and saturation along geometrically complex hillslopes the hsb equation can be linearized and further reduced to an advection diffusion equation for subsurface flow in hillslopes with constant bedrock slopes and exponential width functions this paper presents a dimensional analysis of the latter equation in order to study the moments of the characteristic response function crf corresponding to the free drainage of this type of hillslope these moments in a dimensionless form can be expressed as functions of a similarity parameter hereafter called the hillslope peclet number and a group of dimensionless numbers accounting for the effects of the boundary and initial conditions the analytical expressions for the first four central crf moments are derived for two types of initial conditions the analysis of their respective influences shows that the hillslope peclet number is an efficient similarity parameter to describe the hillslope subsurface flow response moreover comparison between the crf moments predicted by means of our similarity analysis and empirical moments derived from outflow measurements for different types of laboratory hillslopes shows good agreement