models for recession flows in the upper blue nile river stream flow recessions are commonly characterized by the exponential equation or in the alternative power form equation of a single linear reservoir the most common measure of recession is the recession constant k which relates to the power function form of the recession equation for a linear reservoir however in reality it can be seen that the groundwater dynamics of even the simplest of aquifers may behave in a non linear fashion in this study three different storage outflow algorithms single linear non linear and multiple linear reservoir were considered to model the stream flow recession of the upper blue nile the recession parameters for the linear and non linear models were derived by the use of least squares regression procedures whereas for the multiple linear reservoir model a second order autoregressive ar 2 model was applied first in order to determine the parameters by the least squares method the modelling of the upper blue nile recession flow performed shortly after the wet season when interflow and bank storage may be contributing considerably to the river flow showed that the non linear reservoir model simulates well with the observed counterparts the variation related to preceding flow on a recession parameter of the non linear reservoir remains significant which was obtained by stratification of the recession curves although a similar stratification did not show any systematic variation on the recession parameters for the linear and multiple linear reservoir models copyright 2004 john wiley sons ltd

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

a distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

effect of catchment scale subsurface mixing on stream isotopic response a 3 8 ha watershed on the west coast of new zealand was instrumented with suction lysimeters and automatic water samplers to determine the relationship between subsurface isotopic and chemical concentrations to those of rainfall and resulting streamflow a t test showed that 2 represented a significant difference between successive sample deuterium values eleven rainfall episodes were subdivided into two categories 1 two events where stream isotopic composition did not deflect 2 from prestorm values and 2 four events which demonstrated new water flushing detailed analysis of one 47 mm rainfall 9 8 mm runoff event showed that old water dominated stream water exiting the watershed by 90 using a standard two component hydrograph separation for deuterium corroborated by cl and electrical conductivity three component hydrograph separation indicated that 12 16 was in the form of soil water with 5 as on channel precipitation and 80 groundwater analysis of over 1000 water samples revealed systematic trends in soil water and groundwater isotopic composition both in a downslope and downprofile direction between storm suction lysimeter deuterium data showed a systematic dampened response to temporally variable rainfall deuterium concentrations multivariate cluster analysis revealed three distinct soil water groundwater groupings with respect to soil depth and geographic position within the watershed within storm suction lysimeter sampling preserved similar groupings indicating that the subsurface reservoir is poorly mixed on short time scales understanding subsurface mixing response to rainfall should greatly improve models of episodic stream response and partitioning of storm flow into waters of different age

numerical analyses of subsurface flow in a steep hillslope under rainfall the role of the spatial heterogeneity of the formation hydraulic properties 1 the paper aims at analyzing subsurface flow and streamflow generation in steep hillslopes after rainfall the principal scope of the work is to assess the role played by the spatial variability of the hydraulic properties on the subsurface flow patterns and hillslope discharge we try to address this task through a three dimensional numerical model which solves the richards equation under prescribed initial and boundary conditions along an established practice the relevant hydraulic parameters are modeled as random space functions with given statistical properties realistic features of the spatially variable formation parameters and the precipitation data are incorporated into the simulation model it is found that spatial heterogeneity has a significant impact on the movement of water in the hillslope and the streamflow generation in particular the heterogeneous systems are more sensitive to rain input and display an increase of both the water table and saturation which is faster than the homogeneous case the same is for water velocity which is everywhere larger when heterogeneity is considered as a consequence the dynamics of subsurface stormflow recognized as the leading mechanism for streamflow generation in the simulations and the outflow discharge produced by the hillslope after a rain event are enhanced by heterogeneity despite of the possible lack of generality of the numerical experiments they provide useful insight into the complex dynamics occurring in hillslope systems the simulations show the importance of including realistic spatial heterogeneity in hillslope hydrology studies

an integrated approach to modelling hydrology and water quality in glacierized catchments the results are summarized of an integrated investigation of glacier geometry ablation patterns water balance meltwater routing hydrochemistry and suspended sediment yield the ultimate objective is to evaluate the assumptions of lumped two component mixing models as descriptors of glacier hydrology and to develop a semi distributed physically based model as an alternative the results of the study demonstrate that a reconstruction of probable subglacial drainage alignments can be achieved through a combination of terrain modelling based on estimated potential surface and dye tracing experiments recession curve analysis evidence of the seasonal instability of the englacial and subglacial electrical conductivities assumed in a mixing model evidence of the non conservative behaviour of water chemistry in the presence of suspended sediment and evidence of the seasonal evolution of the subglacial drainage system based on dye tracing all indicate that an alternative to a lumped static model of the hydrology is necessary the alternative presented in this paper is based on the combination of an energy balance model for surface melt which operates on an hourly time step and accounts for the changing spatial distribution of melt through the day as shading patterns change and routing procedures that transfer surface melt to moulins on the basis of glacier surface gradients then route water through reconstructed conduit systems using a hydraulic sewer flow routing procedure

recession curve estimation for storm event separations an accurate recession curve model is important for separating individual flow events which is especially difficult over catchments in regions with a maritime climate where frequent rainfall events cause the flows to rise before they reach the baseflow level the traditional recession curve equations are based on static linear and nonlinear reservoir models these models work quite well for ground water dominated recession curves but not so well when the direct runoff is significant in the recession part in this study a new modelling methodology is explored based on self adaptive parameters in the linear and nonlinear reservoir models it has been found that the adaptive forms performed better than the static ones especially when a window for the adaptive parameter estimation is properly selected while the nonlinear adaptive model had better accuracy over the linear one it could become unstable if its window is too narrow indicating that more research work is needed to find an useful pattern for the window size a comparison between the recession curve models and pdm model a rainfall runoff model has shown that they agreed quite well in most winter events but less so in the summer

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

drainage system development in consecutive melt seasons at a polythermal arctic glacier evaluated by flow recession analysis and linear reservoir simulation 1 the drainage systems of polythermal glaciers play an important role in high latitude hydrology and are determinants of ice flow rate flow recession analysis and linear reservoir simulation of runoff time series are here used to evaluate seasonal and inter annual variability in the drainage system of the polythermal finsterwalderbreen svalbard in 1999 and 2000 linear flow recessions are pervasive with mean coefficients of a fast reservoir varying from 16 1999 to 41 h 2000 and mean coefficients of an intermittent slow reservoir varying from 54 1999 to 114 h 2000 drainage system efficiency is greater overall in the first of the two seasons the simplest explanation of which is more rapid depletion of the snow cover reservoir coefficients generally decline during each season at 0 22 h d 1 in 1999 and 0 52 h d 1 in 2000 denoting an increase in drainage efficiency however coefficients do not exhibit a consistent relationship with discharge finsterwalderbreen therefore appears to behave as an intermediate case between temperate glaciers and other polythermal glaciers with smaller proportions of temperate ice linear reservoir runoff simulations exhibit limited sensitivity to a relatively wide range of reservoir coefficients although the use of fixed coefficients in a spatially lumped model can generate significant subseasonal error at finsterwalderbreen an ice marginal channel with the characteristics of a fast reservoir and a subglacial upwelling with the characteristics of a slow reservoir both route meltwater to the terminus this suggests that drainage system components of significantly contrasting efficiencies can coexist spatially and temporally at polythermal glaciers

a shifting hydrological regime a field investigation of snowmelt runoff processes and their connection to summer base flow sunshine coast british columbia the annual hydrographs of british columbian rivers are either characterized by glacial nival pluvial or hybrid both pluvial and nival sources of runoff climate change scenarios for the 2050s indicate that snow water equivalent swe could diminish by 50 to 80 in lower snowfeddominated basins in the south coastal region of b c compared to historical values this could trigger a shift from a hybrid to a pluvial regime for many creeks originating in the coastal mountains including streams used as primary water supply such as chapman creek on the sunshine coast it has been suggested in previous studies that this change in runoff regime will negatively impact summer low flows due to an earlier onset of snowmelt and a prolonged summer recession period however the connection between groundwater recharge during snowmelt and late summer water yield remains unclear a local headwater catchment stephen s creek was instrumented and monitored from the fall of 2008 to the fall of 2009 a two and a threecomponent isotopic hydrograph separation 2 3 ihs method was developed by adapting the runoff corrected model runce to a semi distributed environment in order to account for spatial variability in snowmelt and in isotopic release from the snowpack ihss results show that event water snowmelt and soil water composed most of the streamflow both at the headwater site 66 19 and at the mouth 62 23 during the peak of the freshet while the contribution of event water to streamflow was significantly different in july 34 11 at the headwater site vs 7 4 at the mouth hydrometric isotopic and geochemical data suggest that saturated throughflow was the predominant flow path taken by melt water during freshet preliminary streamflow recession analysis revealed that the snowmelt recharged headwater catchment can support a steadier summer baseflow than robert s creek a much larger but rainfed dominated watershed it is concluded that the large input of melt water during the spring was sufficient to over turn the shallow subsurface reservoir of the headwater catchment and recharge deeper flow paths at a rate that can not be matched by rainfed dominated systems the results are of interest to water resource planning in the south coastal region

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

an estimate of average lower mantle conductivity by wavelet analysis of geomagnetic jerks it has recently been proposed that geomagnetic jerks observed at the earth s surface could be viewed as singularities in the time behavior of the geomagnetic field with a regularity of about 1 5 when wavelet analyzed such a signal should have suffered some distortion when diffusing from the core mantle boundary cmb through the conducting mantle assuming that the upper mantle is an insulator and given the electromagnetic time constant of the mantle we compute the distortion that a pure singularity introduced at the cmb suffers as it traverses the mantle we compute this distortion through its effects on the so called ridge functions extracted from the wavelet transform of the signal this distortion is very similar to the small but significant one that we observe in real data we therefore speculate that jerks must have been pure singularities at the base of the mantle and infer an average estimate for the mantle electromagnetic time constant from the way the signal is distorted by fitting the synthetic ridge functions to the experimental ones assuming for example a thickness of 2000 km for a uniform lower conducting mantle we find an electrical conductivity smaller than 10 s m 1 this value is in reasonable agreement with values derived from high pressure experiments for a silicate mantle

a physics based function for modeling transient groundwater discharge at the watershed scale in the majority of lumped water balance models of river basins groundwater is represented by a single reservoir and groundwater discharge is described by a single valued function of storage in the reservoir it is demonstrated that single valued storage discharge functions are often incapable of representing the actual storage discharge characteristics of a river basin an alternative discharge function is proposed which is derived from a solution to the one dimensional saturated flow equation for an idealized hillslope with spatially varying physical properties the saturated flow in the whole river basin is however generally better described by a two dimensional flow equation therefore in order to apply the new discharge function to a whole basin it is first necessary to show that the two dimensional flow of groundwater can in some way be encapsulated in a conceptual model which can be represented by the one dimensional flow equation two different methods for deriving such a conceptual model are developed and tested on an example river basin the new discharge function based on one of these conceptual models successfully reproduces the discharge simulated by solving the two dimensional flow equation

hydrology and hydrochemistry of a deglaciating high arctic catchment svalbard summary the impact of deglaciation on contemporary hydrological and biogeochemical functioning in the rieperbreen foxfonna catchment in western svalbard was observed in 2007 2008 an overall negative mass balance was observed during 2007 mass loss was high below the equilibrium line altitude ela but spatially patchy mass increases due to superimposed ice and firn were evident above the ela runoff from above the ela was almost exclusively routed through low gradient hydraulically inefficient supraglacial flowpaths which fed steeper highly efficient supraglacial and englacial subglacial channels downstream as interaction with debris rich environments subglacial and proglacial was minimal and transit times were rapid below the ela runoff from supraglacial sources had a low solute content in addition two further parallel hydrological pathways existed snowmelt fed springs emerging from the glacier s contemporary marginal moraines and multiple shallow intermittent streams within recent moraines throughout the glacier forefield and along its northern moraine flank runoff from these additional pathways flowed through highly reactive sediments composed of shale carbonate and sandstones their intense chemical and physical weathering meant moraines were important sources of solute contribution to the catchment s bulk runoff chemistry ecological succession at the glacier margin is therefore highly likely to be dependent upon nutrient acquisition by hydrological processes within moraines as the catchment undergoes deglaciation

earth s core internal dynamics 1840 2010 imaged by inverse geodynamo modelling inverse geodynamo modelling seeks to estimate the dynamic state of earth s core from geo magnetic data and the statistical information brought by a prior self consistent 3 d numerical model of the geodynamo the method rests on the use of least squares inversions under constraints and estimates hidden quantities by taking advantage of linear relations and long range statistical correlations with the magnetic observations the data together with their error statistics are provided by geomagnetic field models cov obs gufm sat q3 and cm4 covering epochs 1840 2010 the prior numerical model is the recently published coupled earth dynamo the output of which presents a high degree of morphological semblance to the geomagnetic field while reproducing the main features of its secular variation an analysis of the inversion misfits to the data shows that the prior model generally accounts well for the main field and secular variation data within their specified errors throughout the investigated time period inverted core flows are confirmed to be mainly organized in columns parallel to the earth s rotation axis a previously observed giant eccentric columnar gyre of westward drifting flow is found to be present from epoch 1870 onwards and its structure is shown to slowly rotate westwards at a rate up to 0 1 yr 1 confirming an earlier prediction based on direct numerical modelling temporal variations in the axisymmetric part of the gyre accurately account for observed variations of the length of the day in recent epochs inverted magnetic structures support a mechanism of azimuthal flux expulsion by convective columns to explain the origin of low latitude magnetic flux patches existing beneath the atlantic the 1840 2010 time average of the inverted density anomaly field has a longitudinal hemispheric structure with most of the buoyancy in the eastern hemisphere consistent with rapid surges of convective columns imaged in this hemisphere with earlier proposals of a faster inner core freezing there and with a possible east to west convective translation of the solid inner core the typical timescales of flow variation observed in the inversions are two to three times shorter than those naturally produced by a direct simulation of the prior model underlining its limits in fully rendering the earth s core short timescale dynamics

conceptualization and scale in hydrology abstract it is argued that the levels of scale at which a meaningful conceptualization of physical processes is possible are not arbitrary and their range is not continuous formulations appropriate at a given level usually are not applicable at the immediately adjoining levels this is seen as one of the important reasons for the slow progress of hydrological science on basin scale since it is dominated by different effects than those observed at the immediately lower level of channel reaches and hillslopes which represent the focus of current hydrological research the search for an appropriate level of conceptualization can proceed either upward or downward along the hierarchy of scales both possibilities are discussed and an example of the downward route is given

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

geomagnetic jerks as chaotic fluctuations of the earth s magnetic field 1 the geomagnetic field is chaotic and can be characterized by a mean exponential time scale after which it is no longer predictable it is also ergodic so time analyses can substitute the more difficult phase space analyses taking advantage of these two properties of the earth s magnetic field a scheme of processing global geomagnetic models in time is presented to estimate fluctuations of the time scale here considering that the capability to predict the geomagnetic field is reduced over periods of geomagnetic jerks we propose a method to detect these events over a long time span this approach considers that epochs characterized by relative minima of fluctuations in time scale i e those periods when a geomagnetic field is less predictable are possible jerk occurrence dates we analyze the last 400 years of the geomagnetic field covered by the gufm1 model to detect minima of fluctuations i e epochs characterized by low values of the time scale most of the well known jerks are confirmed through this method and a few others have been suggested finally we also identify some short periods when the field is less chaotic more predictable than usual naming these periods as steady state geomagnetic regime to underline their opposite behavior with respect to jerks

on the generation of delayed peaks in stream discharge abstract where deep permeable soils overlie impermeable bedrock and where steep hillslopes border a narrow floodplain subsurface stormflow dominates the hydrograph in such cases delayed peaks in stream discharge may occur several days after rainfall providing the major volumetric response and possibly also the highest peak discharge the general occurrence of such delayed peaks is considered making reference to field data from two small drainage basins in southwest england and to the results of computer simulations using a distributed hillslope model the importance of soil water convergence into hillslope hollows is stressed the relative roles of rainfall and antecedent soil moisture in controlling the size and timing of the delayed peak is discussed the implications of the results for hillslope runoff modelling are briefly considered

subglacial drainage system changes of the gulkana glacier alaska discharge and sediment load observations and modelling hydrological characteristics of englacial and subglacial drainage systems in gulkana glacier alaska were examined by analysing temporal variations of discharge and sediment load in the proglacial phelan creek in 2001 from data plots on semi log paper it appeared appropriate to separate both discharge and sediment load into fast and slow components the two components were possibly produced by two different drainage systems an englacial and subglacial channellized system in the ablation zone and a subglacial distributed system in the accumulation zone the data indicate the occurrence of an event during which part of the distributed drainage system changed into the channellized drainage system the daily time series of discharge and sediment load were represented using a tank model in the model the drainage from an additional tank was added supposing that a subglacial reservoir full of water and sediment collapsed slowly when the subglacial drainage system changed from distributed to channellized the simulation with the collapsed tank gave much more reasonable results than those with no collapsed tank the contribution of the collapsed tank to total sediment load is 24 which is much larger than 9 to total discharge copyright 2006 john wiley sons ltd

hydrological discharges and motion of fels and black rapids glaciers alaska u s a implications for the structure of their drainage systems characteristics of the hydrology and motion of black rapids and fels glaciers alaska were observed from 1986 to 1989 hydrological measurements included stage electrical conductivity and suspended sediment concentration in the discharge stream of each glacier and were made at 0 5 1 h intervals continuously through most of the melt seasons variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time lapse photography 1 d time resolution strain meters 0 5 1 h resolution and seismometers set up to count acoustic emissions both glaciers show similar seasonal diurnal and short term event changes in hydrological discharges and ice speed the hydrological behavior is analyzed in terms of a fast sub system composed of surface streams moulins and large tunnels with discharge that responds rapidly and a slow sub system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day the timing and amplitude of water discharge in the diurnal cycle indicate that roughly 10 40 of the water is routed directly into the fast system the remaining 90 60 of the water enters the slow system dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related a small time lag from discharge maximum minimum to solute minimum maximum suggests that the fast system is confined to roughly the lowermost 30 40 of the full glacier length the residence time of water in the fast system is short compared to 1 d the slow system contains both short and long residence time passages characteristics of the diurnal cycles are somewhat variable through the melt season but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur which suggests parallel evolution of the variables that control the response of the fast system events were characterized by contemporaneous increases in suspended sediment concentration in the discharge water and distinct changes in straining on the glaciers events caused by increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water the correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products hydrological differences between black rapids and fels glaciers can be explained by differences in the size of the glaciers if there is a difference in bed structure that explains the difference in dynamics surge black rapids glacier versus non surge fels glacier it does not affect the hydrological parameters that were observed

grimm the gfz reference internal magnetic model based on vector satellite and observatory data summary in this paper the new gfz reference internal magnetic model grimm is presented the model has been derived from nearly 6 yr of champ satellite data and 5 yr of observatory hourly means at high latitudes full vector satellite data are used at all local times which allows a separation between on one hand the fields generated by ionosphere and field aligned currents and on the other hand the fields generated in the earth s core and lithosphere this selection technique leads to a data set without gaps during the polar summers resulting in a core field model that has an unprecedented time resolution the modelled static core field secular variation and lithospheric field are all in good agreement with previously published magnetic field models order five b splines are used to model the variation in time of the core field the energy in the secular acceleration has therefore a smooth behaviour in time and increases continuously from 2003 5 mapping the field acceleration from 2001 5 to 2005 5 reveals its rapid and complex evolution over this time period at the earth s surface due to the applied regularization technique the acceleration energy in spherical harmonics 6 11 is significantly larger than for other models and we show that such a spectrum is acceptable

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 conceptual linear reservoir runoff model to investigate melt season changes in cirque glacier hydrology abstract this paper presents a conceptual linear reservoir runoff model and applies it to a small glacierized cirque basin in the french pyrenees over the 1995 melt season a series of modelling experiments are undertaken i to explore the response of diurnal hydrograph form to seasonal changes in surface meltwater recharge and glacier storage and routing processes and ii to investigate the possible structure of the hydrological system of this remnant glacier high resolution spatially and temporally distributed observations of snow and ice melt and precipitation records are used to estimate bulk meltwater inputs which feed into a lumped meltwater drainage model empirical hydrograph recession limb analysis provides a basis to identify the most likely structure of the glacier s hydrological system this structure is then represented in the model by two fast and slow linear reservoirs although fast reservoir storage coefficients show only a moderate decline 13 00 5 25 h the proportion of bulk meltwater entering this reservoir increases as the glacier snowline retreats and the slow reservoir storage coefficient decreases 45 00 17 75 h consequently modelled hydrographs become increasingly peaked over the ablation season later in the melt season the drainage system is mathematically best represented as a single reservoir with a storage coefficient of 6 00 8 25 h due to meltwater production occurring mainly in the lower mid ablation zone reduction in the extent capacity of the slower storage areas and or integration of the slow and fast pathways in terms of glacier hydrology the modelling experiments suggest that the fast reservoir represents ice melt draining into a semi distributed system beneath the lower glacier and the slow reservoir represents a snowpack fed distributed system below the upper glacier the nature of storage and routing within the hydrological system and the degree to which these processes are significant in determining outflow from this vestigial glacier compared with larger glaciers raises some interesting scale related issues the paper also demonstrates the utility of simple conceptual modelling approaches for investigating glacier hydrological systems in addition to their more traditional application in runoff forecasting

the geomagnetic jerk of 2003 5 characterisation with regional observatory secular variation data abstract the 2003 5 geomagnetic jerk was identified in geomagnetic records from satellite data and a matching feature reported in variations in length of day lod but detailed study has been hampered by lack of geomagnetic observatory data where it appears strongest here we examine secular variation annual differences of monthly means based on a new resource of 43 chinese observatory records for 1998 until the present focusing on 10 series of particularly high quality and consistency to obtain a clean series we calculate the covariance matrix of residuals between measurements and a state of the art field model chaos 6 and use eigenvalue analysis to remove noisy contributions from the uncorrected data the magnitude of the most significant eigenvector correlates well with dcx corrected extended dst suggesting the noise originates from unmodelled external magnetic field removal of this noise eliminates much coherent misfit around 2003 2005 nevertheless the 2003 5 jerk is seen clearly in the first time derivative of the east component in chinese data and is also seen in the first time derivative of the vertical component in european data estimates of the jerk time are centred on 2003 5 but with some spatial variation this variation can be eliminated if we allow a discontinuity in the secular variation as well as its temporal gradient both regions also provide evidence for a jerk around 2014 although less clearly than 2003 5 we create a new field model based on new data and chaos 6 to further examine the regional signals the new model is close to chaos 6 but better fits chinese data although modelling also identifies some data features as unphysical

lumped hysteretic model for subsurface stormflow developed using downward approach the terms downward and upward synonymous with top down and bottom up respectively are sometimes used when describing methods for developing hydrological models a downward approach is used here to develop a lumped catchment scale model for subsurface stormflow at the 0 94 km2 slapton wood catchment during the development as few assumptions as possible are made about the behaviour of subsurface stormflow at the catchment scale and no assumptions are made about its behaviour at smaller scales in an upward approach in contrast the modelling would be based on assumptions about and data for the behaviour at smaller scales such as the hillslope plot and point scales the model has a single store with a relatively simple relationship between discharge and storage based on equations describing hysteretic patterns seen in a graph of discharge against storage double peaked hydrographs have been observed at the catchment outlet rainfall on the channel and infiltration excess and saturation excess runoff give a rapid response and shallow subsurface stormflow gives a delayed response hydrographs are successfully simulated for the large delayed responses observed in 1971 1980 and 1989 1991 then a lumped model for the rapid response is coupled to the lumped hysteretic model and some double peaked hydrographs simulated a physical interpretation is developed for the lumped hysteretic model making use of information on patterns of perched saturation observed in 1982 on a hillslope at the slapton wood catchment downward and upward approaches are complementary and the most robust way to develop and improve lumped catchment models is to iterate between downward and upward steps possible next steps are described copyright 2006 john wiley sons ltd

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

characteristics of oxygen 18 and deuterium composition in waters from the pecos river in american southwest abstract the pecos river situated in eastern new mexico and western texas receives snowmelt from winter storms in the headwater region of the southern rocky mountains and runoff from warm season monsoonal rainfall in the lower valley the isotopic composition of the two water sources differs from each other due to their different geographical origins in the pacific north and the gulf of mexico to better assess the physical features of the pecos river oxygen and hydrogen isotopic compositions 18 o and d major ion concentrations and other physical variables e g water temperature and electrical conductivity were measured on water samples collected from the main stem and its selected tributaries during a growing season march may and july in 2005 the results of this work indicate that stream water from the pecos river contains a relatively large magnitude of variations in 18 o and d with 18 o ranging from 8 9 to 3 6 and d from 64 5 to 1 6 the average value of 18 o is around 3 which is significantly larger than that of the snowmelt but almost identical to that of the mexican monsoonal rainfall on the other hand the average value of d is around 30 which is significantly larger than that of the snowmelt but lower than that of the mexican monsoonal rainfall application of a dual isotope index deuterium excess d excess allows us to assess the relative contribution of various hydrologic components and processes that shape the stream hydrology of the pecos river the river water from the upper valley is characterized by relatively low values of 18 o and d and relatively high values of d excess d 10 documenting the isotopic fingerprint of the snowmelt the middle basin is topographically gentle and its water quality has been severely affected by anthropogenic disturbances e g water impoundments and diversions as a result chemical and isotopic composition of the water from the middle basin is highly variable depending on its time location and degree of disturbances both 18 o and d increase significantly from upstream to downstream and from cold to warm seasons because of evaporation induced isotopic enrichments the average 18 o value of the heavy isotope enriched waters from the middle basin is identical to that of the waters from the lower valley in contrast d excess of the waters from the middle basin usually is negative and substantially lower than that of the waters from the lower valley using a simple d excess based hydrologic model we estimated that there was up to 85 of stream flow which was derived from local freshwater sources mainly from the mexican monsoonal rainfall in the lower valley and that there was up to 33 of stream water which was lost through evaporation occurring in stream channels and fields of the middle basin additionally the correlation of d excess and electrical conductivity further highlights the role of evaporative enrichments in regulating stream chemistry and isotope hydrology this study demonstrates the usefulness of combined isotopic and geochemical data especially the applicability of d excess for watershed baseline assessments

derivation and use of core surface flows for forecasting secular variation improving forecasts of the temporal and spatial changes of the earth s main magnetic field over periods of less than 5 years has important scientific and economic benefits various methods for forecasting the rate of change or secular variation have been tried over the past few decades ranging from the extrapolation of trends in ground observatory measurements to computational geodynamo modeling with data assimilation from historical magnetic field models we examine the utility of an intermediate approach using temporally varying core surface flow models derived from relatively short periods of magnetic field data to produce by advection secular variation estimates valid for the earth s surface we describe a new method to compute a core flow changing linearly with time from magnetic secular variation and acceleration data we invert a combination of data from the champ satellite mission and ground observatories over the period 2001 0 to 2010 0 for a series of such models we assess their ability to forecast magnetic field changes by comparing them to chaos 4 a state of the art model using data from 1997 to 2014 5 we show that the magnetic field predictions tend to have a lower root mean square difference from chaos 4 than the international geomagnetic reference field or world magnetic map series of secular variation models

flow pathways in the slapton wood catchment using temperature as a tracer summary this study investigates the potential of temperature as a tracer to provide insights into flow pathways the approach couples fieldwork and modelling experiments for the eastergrounds hollow within the slapton wood catchment south devon uk measurements in the eastergrounds hollow were carried out for soil temperature spring temperature and the stream temperature and use was made of an existing 1989 1991 data set for the entire slapton wood catchment the predominant flow in this hollow is a result of subsurface stormflow and previous work has suggested that the water flows vertically down through the soil and then subsurface stormflow occurs at the soil bedrock interface where the water is deflected laterally the depth of the subsurface stormflow was previously thought to be around 2 2 m however analysis of the new spring stream and soil temperature data suggests a deeper pathway for the subsurface stormflow modelling of water flow and heat transport was carried out using shetran and this was calibrated to reproduce the water flow in the entire slapton wood catchment and soil temperatures in the eastergrounds hollow the model was tested for the entire eastergrounds hollow with two different soil depths a depth of 2 2 m based on previous knowledge was unable to reproduce the eastergrounds spring temperature a depth of 3 7 m produced an excellent comparison between measured and simulated stream and spring temperatures in the eastergrounds hollow this work suggests that the depth of the flow pathways that produce the subsurface stormflow are deeper than previously thought it also provides a demonstration on the use of temperature as a tracer to understand flow pathways

chandler wobble and geomagnetic jerks abstract some features of the polar motion may be due to core mantle coupling but no convincing quantitative mechanism has yet been proposed considering phase jumps in the chandler wobble and noticing their correlation with geomagnetic jerks j geophys res 103 b11 1998 27069 27089 we suggest that the instability of a layer at the top of the core and its downward propagation induce a step in the core mantle torque strong enough to explain phase jumps in the chandler wobble the surface magnetic signature of this instability is comparable with the typical evolution of the geomagnetic field during a jerk

magnetic flux expulsion from the core as a possible cause of the unusually large acceleration of the north magnetic pole during the 1990s 1 the north magnetic pole nmp has been drifting in a north northwesterly direction since the 19th century both local surveys and geomagnetic models derived from observatory and satellite data show that the nmp suddenly accelerated during the 1990s its speed increased from about 15 km yr in 1989 to about 60 km yr in 2002 after which it started to decrease slightly using a green s function we show that this acceleration is mainly caused by a large negative secular variation change in the radial magnetic field at the core surface under the new siberian islands this change occurs in a region of the core surface where there is a pair of secular variation patches of opposite polarities which we suggest could be the signature of a so called polar magnetic upwelling of the type observed in some recent numerical dynamo simulations indeed a local analysis of the radial secular variation and magnetic field gradient suggests that the secular variation change under the new siberian islands is likely to be accompanied by a significant amount of magnetic diffusion in agreement with such a mechanism we thus hypothesize that the negative secular variation change under the new siberian islands that produced the nmp acceleration could result from a slowdown of the polar magnetic upwelling during the 1990s we finally note that the nmp drift speed is determined by such a combination of factors that it is at present not possible to forecast its future evolution

hydrograph separation using stable isotopes silica and electrical conductivity an alpine example abstract hydrograph separation of runoff events in two nested alpine subalpine basins in the coast mountains of british columbia was carried out using electrical conductivity specific concentration of silica and the stable isotopes oxygen 18 and deuterium as hydrological tracers the methods predicted consistent high pre storm water contribution for the subalpine site 60 90 but more variable contribution at the alpine basin outlet 25 90 the pre storm water contribution is much larger than had previously been expected precipitation is believed to run off as overland flow due to the steep slopes in combination with the hydrophobic soils until it can enter the subsurface environment the rapid influx of stored water is possibly caused by pressure propagation in the macropore system which could be enhanced by the heavily fractured bedrock and permeable landslide debris acting as efficient hydrological conduits the study suggests that alternative hydrological tracers such as electrical conductivity and silica concentration can be used under certain hydrological and lithological conditions these alternative tracers should however be verified against more conventional tracers before use as the behaviour depends on specific characteristics of each basin at the upper basin outlet both electrical conductivity ec and silica underestimated the pre storm contribution at the lower station silica and ec showed a similar pattern to deuterium and oxygen 18 tracers the calculated pre storm component using ec was however 10 20 lower than the calculated values from the other three tracers the advantage of using these alternative tracers is that hydrograph separation results can a priori be anticipated

the 2003 geomagnetic jerk and its relation to the core surface flows abstract in this paper we examine the core surface flow obtained by an inversion of a continuous model of the geomagnetic field and its temporal variation using the diffusion less induction equation the continuous chaos model is derived from satellite data up to spherical harmonic degree 14 and covers the period 1999 to 2006 the chaos secular variation when downward continued to the core surface shows stripe like features which can be attributed to spherical harmonic degree 12 and higher these contributions are removed by applying a tapering method and the resulting tapered model is then inverted for the core surface flow satellite based field models have a high spatial resolution however their temporal resolution is limited in order to enhance the temporal resolution of the flow we additionally constrain the flow to fit the secular variation from ground based observatory data a range of solutions subject to different constraints are computed two flow hypotheses being considered purely toroidal flow and tangentially geostrophic flow we show that both flow types provide similar results however the purely toroidal flow provides a better fit to the secular variation in the equatorial region than the tangentially geostrophic flow we then analyze the residuals between observed secular variation and its predictions from the flow we note larger residuals for the tangentially geostrophic flow where strong radial secular variation and a weak radial field are observed although diffusive effects cannot be ruled out as a potential source of the mismatch we attribute the larger residuals to be caused by a flawed estimation of the poloidal flow we also seek to relate temporal changes in the fluid flow to the geomagnetic jerk which occurred at the beginning of 2003 it is found that this geomagnetic jerk coincides with variations in the zonal flow components of both flow types suggesting a possible link to torsional oscillations however we argue that other flow components are important to obtain a detailed fit of the observed secular variation finally we compare observed changes in the length of day and the predictions from the flow solutions

observations and modeling of hillslope throughflow temperatures in a coastal forested catchment a growing body of research on stream thermal regimes has highlighted the importance of heat advection associated with surface water and groundwater interactions such as hyporheic exchange groundwater discharge and hillslope throughflow inputs existing catchment models that predict stream temperature use a variety of approaches to estimate throughflow temperatures but none has been evaluated against field measurements of throughflow temperature in this study throughflow temperatures were monitored over two winters at 50 locations adjacent to a headwater stream 11 ha catchment area located in the rain on snow zone of the pacific northwest existing approaches to estimate throughflow temperature under or overpredicted throughflow temperatures by up to 5 c or were unable to represent the influence of transient snow cover therefore a conceptual parametric model that is computationally efficient was developed that simulates hillslope hydrology and throughflow temperatures the model structure includes an upslope reservoir that drains into a downslope reservoir that in turn drains into the stream vertical and lateral energy and water fluxes are simulated using simplified process representations the model successfully predicts throughflow temperatures and highlights the dominant role of throughflow advection and the influence of snow cover on stream thermal regimes during high flow periods and rain on snow events

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

aquifer scale flow equations as generalized linear reservoir models for strip and circular aquifers links between the darcian and the aquifer scale 1 an analytical treatment of aquifer flow is presented to establish a link between runoff models and aquifer properties recently developed one dimensional analytical solutions for transient flows in homogeneous aquifers produce expressions for the flux between the aquifer and the surface water and the difference between the average hydraulic head in the aquifer and the surface water it is shown that the ratio between these large scale variables i e the aquifer scale hydraulic conductivity can assume one of three asymptotic values a non darcian aquifer scale flow equation is derived for the average head in the aquifer minus the surface water level this first order ordinary differential equation has nonconstant coefficients based in part on the aquifer scale conductivity the aquifer scale equation is a generalization of linear reservoir models when the aquifer scale conductivity is stationary its solution has an exponential term like a linear reservoir with a reservoir coefficient that depends on external factors and a constant term the solution applies to a wider range of problems than conventional linear reservoir models the aquifer s characteristic time derived from the solution shows that dense drainage networks can make aquifers behave like linear reservoirs most of the time while large systems never will when the asymptotic values are used before the time period for which they become valid i e shortly after a perturbation in the surface water level or recharge extraction the predicted fluxes can be very inaccurate and possibly have the wrong sign in such cases the full analytical solutions should be used

solute generation and transfer from a chemically reactive alpine glacial proglacial system the environs of the glacier de tsanfleuron switzerland was used as a study site to investigate the controls on the relative efficiency of solute generation and removal from glacial and proglacial environments here a 1500 m wide glacier forefield consists of a karstic limestone plateau flanked to the north by a till floored valley bedrocks and glacial debris are composed of chemically reactive pure and impure mesozoic and tertiary limestones with accessory pyrite spot sampling of ice snow and meltwaters in the late melt season was supplemented by systematic measurements of the main meltstream including during periods of rainfall and simple laboratory leaching and weathering experiments isotopic parameters were used to investigate water sources most meltwater and glacier ice samples lay close to a meteoric water line d 8 3 18o 14 defined by waters from small tributary streams heavy isotopic excursions of bulk meltwater chemistry were caused by rainfall events recovering within days to a 18o baseline around 12 permil no regular diurnal variations in 18 o were apparent the atmosphere is the source of cl and most na but the bulk of other solutes are generated in the environment ion loads of up to 1 meq l 1 are rapidly attained by calcite dissolution over periods of weeks to months pyrite oxidation generates sulphate and acidity that drives further calcite dissolution low water rock ratio weathering environments have characteristically high so42 mg2 sr2 and ratios of these species to calcium the characteristic cation ratios are influenced by non congruent calcite dissolution the ratio of sulphate to other species is highest where water rock contact times are highest although this relationship is complicated by spatial variations in pyrite abundance meltstream time series illustrate that 90 per cent of daily ion yields in fine weather are concentrated in the 12 h time period of higher discharge ion yields increase downstream mainly by a combination of dissolution of calcareous suspended sediment and input from tributaries and seepage from the till banks rainstorms lead to increased solute concentrations and resulting hourly fluxes can match daily fine weather ion fluxes excess nitrate appears to be largely sourced from the proglacial surface the capacity of the proglacial environment for yielding significant subsurface water as a result of the storm seems low unlike non glacial environments this implies that most of the excess solutes mobilized by storms comes from subglacial sources increased efficiency of yield of solutes from low water rock ratio subglacial weathering environments persists after the isotopic signature of the rainfall event has died away a simple conceptual model of the sources of water and solutes agrees with conclusions from attempts at hydrograph separation that mixing of water reservoirs of fixed solute composition cannot be used for quantitative descriptions of the system estimated annual solute yields 17 ton per km2 per m precipitation are high but cannot be readily expressed in purely areal terms because of likely significant losses to the underlying karstic system a tentative conclusion is that the proglacial environment is overall less efficient at producing solutes than the glacial environment but more information is required on processes in the early melt season to substantiate this statement copyright 1999 john wiley sons ltd

can core surface flow models be used to improve the forecast of the earth s main magnetic field 1 geomagnetic main field models used for navigation are updated every 5 years and contain a forecast of the geomagnetic secular variation for the upcoming epoch forecasting secular variation is a difficult task the change of the main magnetic field is thought to be principally due to advection of the field by flow at the surface of the outer core on short timescales and when large length scales are considered with accurate secular variation sv and secular acceleration sa models now available from new satellite missions inverting for the flow and advecting it forward could lead to a more accurate prediction of the main field however this scheme faces two significant challenges the first arises from the truncation of the observable main field at spherical harmonic degree 13 this can however be handled if the true core flow is large scale and has a rapidly decaying energy spectrum the second is that even at a given single epoch the instantaneous sv and sa cannot simultaneously be explained by a steady flow nevertheless we find that it may be feasible to use flow models for an improved temporal extrapolation of the main field a medium term 10 years hindcast of the field using a steady flow model outperforms the usual extrapolation using the presently observed sv and sa on the other hand our accelerated toroidal flow model which explains a larger portion of the observed average sa over the 2000 2005 period fails to improve both the short term and medium term hindcasts of the field this somewhat paradoxical result is related to the occurrence of so called geomagnetic jerks the still poorly known dynamical nature of which remains the main obstacle to improved geomagnetic field forecasts

a distributed surface energy balance model for a small valley glacier i development and testing for haut glacier d arolla valais switzerland this paper describes the development and testing of a distributed surface energy balance model used to calculate rates of surface melting at haut glacier d arolla valais switzerland the model uses a digital elevation model dem of the glacier surface and surrounding topography together with meteorological data collected at a site in front of the glacier to determine hourly or daily totals of the energy balance components and hence of melting over the entire surface of the glacier with a spatial resolutio of 20 m the model can also be used to determine temporal and spatial variations in snow depth snow line position and glacier surface albedo calculations from the model are compared with observations made along the glacier centre line in 1990 and in general the model performs very well the correlation coefficients between calculated and measured snow line elevation albedo and ablation are 0 99 0 85 and 0 81 respectively the main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model

buoyancy frequency profiles and internal semidiurnal tide turning depths in the oceans 1 we examine the possible existence of internal gravity wave turning depths depths below which the local buoyancy frequency n z becomes smaller than the wave frequency at a turning depth incident gravity waves reflect rather than reaching the ocean bottom as is generally assumed here we consider internal gravity waves at the lunar semidiurnal m2 tidal frequency m2 profiles of n2 z the quantity in the equations of motion are computed using conductivity temperature and depth data obtained in the world ocean circulation experiment woce values for n2 z computed using gibbs seawater routines in two thermodynamically equivalent expressions for n2 z are found to yield values that are in excellent accord but differ significantly from n2 z computed from often used but inexact expressions that involve potential density uncertainties in n2 z are estimated using a monte carlo method where the data are averaged over a range in depth 80 200 m which is determined by minimizing a cost function our principal result reached from an analysis of all 18 000 woce casts is that turning depths are common for zonal east west propagating internal tides in the deep oceans inclusion of the full coriolis effect i e not making the so called traditional approximation leads to the conclusion that turning depths cannot occur for meridional and near meridional internal tides but the non traditional component has little impact on turning depths for internal tides that are near zonal i e propagating within about 30 of the east west direction at low and midlatitudes

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

jerks abound an analysis of geomagnetic observatory data from 1957 to 2008 we present a two step method for the removal of external field signals and the identification of geomagnetic jerks in magnetic observatory monthly mean data providing quantitative uncertainty estimates on jerk occurrence times and amplitudes with minimal a priori information we apply the method to the complete time series of x y and z components at up to 103 observatory locations in the period of 1957 2008 we find features fitting the definition of jerks in individual components to be frequent and not globally contemporaneous identified regional jerks have no consistent occurrence pattern and the most widespread in any given year is identified at 30 of observatories worldwide whilst we identify jerks throughout the period of study relative peaks in the global number of jerk occurrences are found in 1968 71 1973 74 1977 79 1983 85 1989 93 1995 98 and 2002 03 with the suggestion of further poorly sampled events in the early 1960s and late 2000s the mean uncertainties on individual jerk occurrence times and amplitudes are found to be 0 3 yrs and 2 1 nt yr2 respectively for all field components jerk amplitudes suggest possible periodic trends across europe and north america which may be related to the 6 yr periods detected independently in the secular variation and length of day

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

hydrograph separation using continuous open system isotope mixing we propose a new hydrograph separation method for runoff source modeling based on continuous open system isotope mixing using a variable source area and three isotopic reservoirs the three reservo

was the 1970 geomagnetic jerk of internal or external origin annual mean data from worldwide magnetic observatories show that there was a jerk1 step change in the second time derivative in the geomagnetic field which took place over an interval of 2 yr around 1970 if such a short lived phenomenon originated in the earth s core and were still detectable after passing through the mantle to the surface this would imply a much lower conductivity for the lower mantle than had been believed previously here we show by an objective test that most of the jerk has an internal origin

measurements and uncertainties of the occurrence time of the 1969 1978 1991 and 1999 geomagnetic jerks geomagnetic jerks are rapid time variations of the magnetic field at the earth s surface that are thought to be of primarily internal origin jerks are relevant for studies of the earth interior they likely give information on core dynamics and possibly on mantle electrical conductivity in such studies a precise determination of the jerk occurrence time and its error bar at each observatory is required we analyze the most well known global jerks 1969 1978 and 1991 and a possible local jerk in 1999 considering all three components of the magnetic field x y and z different data sets are investigated annual means 12 month running averages of observatory monthly means in rotated geomagnetic dipole coordinates and data representing the core field contribution synthesized from the cm4 time dependent field model the secular variation in each component of the field around the time of a jerk was modeled by two straight line segments using both least squares and 1 norm methods the 1969 1978 and 1991 jerks were globally detected while the 1999 event was only locally identified using this simple method enables us to calculate error bars in the jerk occurrence times and to quantify their nonsimultaneous behavior we find that our error bars are not in general symmetric about the mean occurrence time and that the mean errors on the x and z components of 1 7 years and 1 5 years are larger than that of 1 1 years on the y component generally the error bars were found to be larger in the southern hemisphere observatories our results are necessary prerequisites for further studies of the inverse problem that attempt to determine mantle electrical conductivity from variations in jerk occurrence times

storage outflow modelling of streamflow recessions with application to a shallow soil forested catchment abstract the objectives of this study were to introduce an alternative to the matching strip correlation and parameter averaging methods for deriving master recession characteristics from a set of recession segments and to apply the method to streamflow recession segments for a small forested catchment in which baseflow is provided by drainage of the saturated zone in the shallow permeable soil the method involves fitting conceptual storage outflow models using an iterative algorithm diagnostic plots revealed that the recessions were non linear and that the recessions did not follow a common single valued storage outflow relation a model involving two linear reservoirs provided substantially better fit than three single reservoir models indicating that the form of the recession curve probably depends not just on the volume of subsurface storage but also on its initial distribution amongst reservoirs

numerical simulation of unsaturated flow along preferential pathways implications for the use of mass balance calculations for isotope storm hydrograph separation an objective common to many watershed studies is to separate storm hydrographs into two components water that was present in the watershed prior to a storm event soil moisture and groundwater and water which fell on the watershed during the storm to use this approach a number of assumptions must be made including that the composition of water in the soil moisture and groundwater reservoirs are constant and known the objective of this paper is to show that in settings where flow and transport are dominated by preferential pathways for flow steady state mass balance calculations for quantitative hydrograph separation may be in error we present field data from a site where flow and transport are dominated by preferential pathways relict fractures in saprolite of sedimentary rocks which indicate that the 18o content of the water in the unsaturated and shallow saturated zones is not constant over the course of a storm event we use a numerical model to further explore the interactions between the fractures and surrounding matrix both the field data and modeling results indicate that the 18o of the previous storm event s has a strong influence on water in the fractures on the time scale of a storm event only the water in the matrix immediately surrounding the fracture mixes with water in the fracture while the bulk of the matrix is isolated from fracture flow the spatial and temporal heterogeneity of the 18o in the subsurface and the isolation of the most of the matrix water from flow in fractures make the measurement of a singular 18o value for subsurface reservoirs problematic and the assumption of a constant value doubtful since most near surface geologic materials have preferential flow paths we suggest that quantitative hydrograph separation using mass balance techniques is not possible in most situations future field and modeling investigations using the approach outlined here could be designed to explore the important temporal and spatial scales of variability in watersheds and lead to a more quantitative approach to storm hydrograph separation

a hydrological approach to estimating daily glacier ablation reduced meltwater discharge owing to glacier retreat can have severe impacts on downstream water users to assess these impacts it is essential to differentiate between water from glacier melt and other sources we propose a method for doing this on a daily time scale by applying a mixing law to electrical conductivity and proglacial discharge measurements daily ablation is then estimated by applying a recession law to the glacier melt component testing this method on summer hydrology and meteorology measurements from the baounet glacier france taken over six consecutive years 2008 2013 allowed us to reconstruct daily ablation during the ablation period mean ablation rates ranged from 20 to 30 mm day 1 air temperature measurements showed that periods of low ablation during the summer were linked to cooler days and snowfall periods comparisons for three consecutive summers showed that the ablation rates obtained by summing calculated daily ablation were statistically similar to the rates recorded

shallow subsurface storm flow in a forested headwater catchment observations and modeling using a modified topmodel transient perched water tables in the shallow subsurface are observed at the south fork brokenback run catchment in shenandoah national park virginia crest piezometers installed along a hillslope transect show that the development of saturated conditions in the upper 1 5 m of the subsurface is controlled by total precipitation and antecedent conditions not precipitation intensity although soil heterogeneities strongly influence local response the macroporous subsurface storm flow zone provides a hydrological pathway for rapid runoff generation apart from the underlying groundwater zone a conceptualization supported by the two storage system exhibited by hydrograph recession analysis a modified version of topmodel is used to simulate the observed catchment dynamics in this model generalized topographic index theory is applied to the subsurface storm flow zone to account for logarithmic storm flow recessions indicative of linearly decreasing transmissivity with depth vertical drainage to the groundwater zone is required and both subsurface reservoirs are considered to contribute to surface saturation

geomagnetic jerks in the polar regions 1 the occurrence of geomagnetic jerks over the arctic and antarctic regions is here investigated maps of geomagnetic secular acceleration over the polar regions are produced from the cm4 and chaos models and the occurrence of geomagnetic jerks is associated with jumps in secular acceleration the obtained results confirm that in antarctica geomagnetic jerks systematically follow geomagnetic jerks in the arctic region with a time delay from one to three years evidence is found of an abrupt change in secular acceleration in both polar regions around 1985 suggesting that the 1985 local jerk could actually be a worldwide event combining our results with the results previously obtained on the occurrence of a geomagnetic jerk at low mid latitudes around 2003 we support the hypothesis of a global extension of an event occurred at the beginning of the 21st century

temporal variations of strength and location of the south atlantic anomaly as measured by rxte abstract the evolution of the particle background at an altitude of 540 km during the time interval between 1996 and 2007 is studied using the particle monitor of the high energy x ray timing experiment on board nasa s rossi x ray timing explorer a special emphasis of this study is the location and strength of the south atlantic anomaly saa the size and strength of the saa are anti correlated with the 10 7 cm radio flux of the sun which leads the saa strength by 1 year reflecting variations in solar heating of the upper atmosphere the location of the saa is also found to drift westwards with an average drift rate of about 0 3 yr following the drift of the geomagnetic field configuration superimposed to this drift rate are irregularities where the saa suddenly moves eastwards and where furthermore the speed of the drift changes the most prominent of these irregularities is found in the second quarter of 2003 and another event took place in 1999 we suggest that these events are previously unrecognized manifestations of the geomagnetic jerks of the earth s magnetic field

rapidly changing flows in the earth s core variations in the earth s magnetic field over a span of a few months can be resolved despite the potential filtering effects of the electrically conducting mantle and are indicative of rapid flow in the earth s outer core

combining virtual observatory and equivalent source dipole approaches to describe the geomagnetic field with swarm measurements abstract a detailed description of the main geomagnetic field and of its temporal variations i e the secular variation or sv is crucial to understanding the geodynamo although the sv is known with high accuracy at ground magnetic observatory locations the globally uneven distribution of the observatories hampers the determination of a detailed global pattern of the sv over the past two decades satellites have provided global surveys of the geomagnetic field which have been used to derive global spherical harmonic sh models through some strict data selection schemes to minimise external field contributions however discrepancies remain between ground measurements and field predictions by these models indeed the global models do not reproduce small spatial scales of the field temporal variations to overcome this problem we propose to directly extract time series of the field and its temporal variation from satellite measurements as it is done at observatory locations we follow a virtual observatory vo approach and define a global mesh of vos at satellite altitude for each vo and each given time interval we apply an equivalent source dipole esd technique to reduce all measurements to a unique location synthetic data are first used to validate the new vo esd approach then we apply our scheme to data from the first two years of the swarm mission for the first time a 2 5 resolution global mesh of vo time series is built the vo esd derived time series are locally compared to ground observations as well as to satellite based model predictions our approach is able to describe detailed temporal variations of the field at local scales the vo esd time series are then used to derive global spherical harmonic models for a simple sh parametrization the model describes well the secular trend of the magnetic field both at satellite altitude and at the surface as more data will be made available longer vo esd time series can be derived and consequently used to study sharp temporal variation features such as geomagnetic jerks

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

a new approach to directly determine the secular variation from magnetic satellite observations 1 observatory monthly means provide an excellent opportunity to study the temporal changes of the geomagnetic field at a given location unfortunately determination of the global pattern of changes using observatory data is hampered by their uneven distribution satellite data provide excellent global coverage but the spacecraft movement makes direct comparisons of satellite and observatory data difficult to investigate short period secular variation in observatory and satellite data we developed an approach to extract satellite monthly means for virtual observatories at 400 km altitude using champ magnetic measurements comparison of these virtual observatory monthly means with the corresponding ground values shows a remarkably well correlated signal at time scales of months to years which is beyond the temporal resolution limit of recent global models here we describe this newly developed approach its validation and discuss how it can be used to understand short period changes of the recent geomagnetic field

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

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

extending comprehensive models of the earth s magnetic field with orsted and champ data summary a new model of the quiet time near earth magnetic field has been derived using a comprehensive approach which includes not only pogo and magsat satellite data but also data from the orsted and champ satellites the resulting model shows great improvement over its predecessors in terms of completeness of sources time span and noise reduction in parameters with its well separated fields and extended time domain of 1960 to mid 2002 the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997 because all sources are coestimated in a comprehensive approach intriguing north south features typically filtered out with other methods are being discovered in the lithospheric representation of the model such as the s atlantic spreading ridge and andean subduction zone lineations in addition this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection the f region currents through which the satellites pass are now treated as lying within meridional planes as opposed to being purely radial results are consistent with those found previously for magsat but an analysis at orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite besides the model a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset this has proven very useful in diagnosing the cause of peculiar artefacts in the magsat vector data which seem to suggest the presence of a small misalignment bias in the vector magnetometer

investigation of a secular variation impulse using satellite data the 2003 geomagnetic jerk abstract observatory monthly means provide an excellent opportunity to study the temporal changes of the magnetic field at a given location unfortunately the uneven distribution of the present observatory network makes it difficult to determine the global field change pattern recently we have developed an approach to extract satellite monthly means at a regular network of virtual observatories at 400 km altitude based on champ magnetic measurements using monthly means for 2001 2005 from those virtual observatories we investigate the space time structure of the short period variation of the earth s magnetic field by means of a spherical harmonic expansion followed by a separation into external magnetospheric and internal part this allows for the first time to study the secular variation globally and directly from satellite magnetic data analyzing the time series of the magnetic field at the virtual observatories as well as those of the spherical harmonic expansion coefficients we detect a secular variation impulse an abrupt jump in the second time derivative of the magnetic field in the champ satellite data during the first months of the year 2003 the jerk occurred simultaneously in the northern and southern hemispheres in a rather limited area near 90 e with maximum jerk strength at about 30 latitude a region also characterized by a strong secular acceleration second time derivative of the magnetic field we show that the 2003 geomagnetic jerk is not worldwide in occurrence and that there is an evidence for this event in the length of day variation

a geomagnetic jerk for the end of the 20th century abstract the series of magnetic measurements at some european observatories give some hint of a new geomagnetic jerk around 1999 the geomagnetic impulses would present the remarkable and intriguing property to occur with a frequency of one per decade in the last third of the 20th century the geomagnetic jerks have been proposed to be indicators which anticipate the changes in the earth s rotation rate if this statement is of general validity the 1992 jerk should be followed by an acceleration of the earth rotation which would take place now and along the same lines we might predict a new deceleration in less than 10 yr

recharge sources and hydrochemical evolution of an urban karst aquifer sete lagoas mg brazil the current water supply for the city of sete lagoas brazil is almost entirely groundwater from the sete lagoas karst aquifer with a small contribution from a fractured basement rock aquifer characterizing the hydrogeologic processes is important for proper water resource management avoiding contamination and other future issues the main goal of this study is to identify active hydrogeological processes such as possible surface ground water interactions sources of recharge and the hydrochemical evolution of groundwater through the use of stable isotopes 18o and 2h and major ion data the groundwater samples were collected from the karst aquifer central urban area and from the fractured aquifer southern part of the city surface water samples were collected from the seven main lakes and rainwater was sampled over a period of one year the stable isotope results indicated the groundwater origin is directly from local precipitation having a limited recharge period and locally receiving surface water contributions groundwater quality in the central urban area may be influenced by surface water infiltration where the karst aquifer is in contact with overlying unconsolidated sediments some samples with nitrate concentration of 10 mg l or higher indicates the natural composition of the groundwater has been altered by urban sewage contamination the highest concentrations of major ions were found in the central region where the most karstified area from the sete lagoas formation is located these data suggest a longer residence time for this water indicating more mineralization in accordance with the geological information

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

baseflow separation based on analytical solutions of the boussinesq equation a technique for baseflow separation is presented based on similarity solutions of the boussinesq equation the method makes use of the simplifying assumptions that a horizontal impermeable layer underlies a dupuit aquifer which is drained by a fully penetrating stream the value of the baseflow maximum as well as the baseflow recession hydrograph can be estimated by fitting the analytical solutions of the boussinesq equation to the observed discharge values for individual flood events for the rising limb of the baseflow hydrograph a linear function is assumed for simplicity the method is first demonstrated on three watersheds for a total of five flood events and extensively applied over a three year period for the mahantango creek pennsylvania watershed the proposed method reduces some of the subjective aspects long associated with baseflow separation techniques

signal from noise in geomagnetic field modelling denoising data for secular variation studies summary we analyse the residuals between a continuous geomagnetic field model of the internal field c3fm and observed secular variation a large part of the residual variations correlate closely with the dst index suggesting an origin from unmodelled external field variations removal of this signal enhances the resolution of fine scale detail in secular variation this is useful in considering the phenomenology of geomagnetic jerks the residual variations between different observatories show even better correlation suggesting the possibility of the construction of a proxy for the dst index notable cross correlation is also seen between the residuals and dst index with a lag of about 55 months

effects of a beaver pond on runoff processes comparison of two headwater catchments abstract natural variations in concentrations of 18 o d and h 4 sio 4 in two tributary catchments of woods lake in the west central adirondack mountains of new york were measured during 1989 1991 to examine runoff processes and their implications for the neutralization of acidic precipitation by calcium carbonate treatment the two catchments are similar except that one contained a 1 3 ha beaver pond evaporation from the beaver pond caused a seasonal decrease in the slope of the meteoric water line in stream water from the catchment with a beaver pond wo2 no corresponding change in slope of the meteoric water line was evident in stream water from the other catchment wo4 nor in ground water nor soil water from either catchment indicating that evaporative fractionation was not significant application of a best fit sine curve to 18 o data indicated that base flow in both catchments had a residence time of about 100 days ground water from a well finished in thick till had the longest residence time 160 days soil water from the o horizon and b horizon had residence times of 63 and 80 days respectively water previously stored within each catchment pre event water was the predominant component of streamflow during spring snowmelt and during spring and autumn rainfall events but the proportion of streamflow that consisted of pre event water differed significantly in the two catchments the proportion of event water rain and snowmelt in wo2 was smaller than at wo4 early in the spring snowmelt of march 13 17 1990 but the proportions of source water components for the two catchments were almost indistinguishable by the peak flow on the third day of the melt the event water was further separated into surface water and subsurface water components by utilizing measured changes in h 4 sio 4 concentrations in stream water during the snowmelt results indicated that subsurface flow was the dominant pathway by which event water reached the stream except during the peak flow of a rain on snow event on the last day of the melt streamflow from a spring rain storm with dry antecendent conditions two months later may 16 18 1990 was less than 5 event water at peak flow in wo2 and 26 in wo4 this change from the runoff pattern in march is attributed to retention of event water in the beaver pond favored by relatively low pre event storage and isothermal nonstratified conditions in the pond that allowed mixing streamflow during several autumn storms was about 15 25 event water at peak flow in wo4 the highest values for event water were associated with wet antecedent moisture conditions these results indicate that a beaver pond can significantly affect the downstream delivery of event water through evaporation and mixing but provides minimal retention during large runoff events such as snowmelt beaver ponds are expected to provide greater opportunity for neutralization of acidic waters during most of the year in catchments treated with calcium carbonate but little neutralization effect during snowmelt

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