bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions between groundwater and surface water in a virginia coastal plain watershed. 2. Acid—base chemistry
Authors: Kuebler O'Brien Anne , Eshleman Keith N. , Pollard John S.
Published: February 2007

An intensive study was conducted on the biogeochemical processes controlling the acid‐base chemistry of Reedy Creek, a wetland‐influenced coastal plain stream located near Ashland, Virginia. In the context of the hydrological processes determined by Eshleman et al., the present research sought to: (1) identify the sources and sinks of anthropogenic and organic acidity within the watershed, (2) determine the seasonal and spatial variability in the stream base flow chemistry, (3) determine the episodic variability in stream stormflow chemistry and (4) quantify a watershed sulphate budget for the 1990 water year. Sulphate is the primary acidic anion in groundwater and surface water at the Reedy Creek watershed. Dissolved organic carbon (DOC) and anion deficit data suggest that organic acids are less important than sulphate in contributing acidity to the stream. In groundwater sampled from wells installed along two transects perpendicular to the stream, sulphate concentrations were higher and alkalinity lower in the groundwater in the hill‐slope than in the stream. Sulphate concentrations and alkalinity observed in groundwater in the wetland were usually between those of the hillslope and stream. These data suggest that the wetland is a sink for sulphate and acidity; sulphate reduction may be an important mechanism for generating alkalinity in the wetland. The DOC concentrations were higher in the stream and wetland groundwater than in hillslope groundwater. No consistent spatial patterns in sulphate concentrations were observed in surface water chemistry under base flow conditions. Anion deficit, DOC and the sum of base cation concentrations were usually higher at upstream sites than downstream sites. At all sites, sulphate concentrations were higher and alkalinity lower in winter and spring than during summer and autumn. Calculated anion deficits were lower in winter and spring than during summer and autumn, reflecting an increase in the contribution of organic acidity during the growing season. Seasonality was not observed in DOC concentrations. Stream discharge was found to be positively correlated with base flow sulphate concentrations and inversely correlated with alkalinity. A sulphate mass balance indicated that approximately 30% of the estimated 24.9kg SO2−2/ha yr wet atmospheric input was exported from the watershed as sulphate in stream runoff in the water year 1990.
Dissolved organic carbon dynamics in two streams draining forested catchments at loch ard, Scotland
Authors: Grieve Ian C.
Published: February 2007

Dissolved organic carbon (DOC) was measured at four or eight hour intervals between mid‐1989 and mid‐1991 in two catchments in west central Scotland. The experimental catchment had been recently clear‐felled and the control remained under forest. The amount of DOC varied during individual storm events following the stream hydro‐graph. Maximum variations were found in the summer half‐year and in the clear‐felled catchment. There was also evidence of the exhaustion of DOC in the later events of a sequence. Differences between the catchments were related to catchment characteristics and to land‐use change. The reduced magnitude of variation in DOC with discharge in the control stream was due to the influence of a wetland area through which the stream flowed. The mean DOC concentrations were similar in the two streams and annual exports were 15 g m−2 from the control and 16g m−2 from the felled catchment. The stream draining the clear‐felled catchment had greater high flow DOC concentrations in the summer half‐year, probably due to the effect of greater mean summer temperatures on DOC release and of the greater supply of organic debris in the stream channel.
Major ion variation and efflux related to discharge in a mafic piedmont province watershed
Authors: Rose Seth
Published: February 2007

Major‐ion variability related to discharge was analysed in a forested 187 km2 mafic Piedmont Province watershed using statistical (both parametric and non‐parametric), graphical (box‐plots) and curve‐fitting (log concentration‐log discharge) techniques. Baseflow alkalinity and base cation concentrations show systematic temporal variations as a result of the influx of additional water that occurs during the late autumn to early spring. Regression analyses indicate that storm‐related discharge and baseflow generated during periods of water surplus are characterized by similar dilution slopes. Mass balance estimates indicate that the additional water, which comprises storm/recession discharge and base‐flow from late autumn to early spring, is between about 30 and 80% as concentrated as summer low‐flow.

The thick clay‐rich soil mantle represents a key control on solute concentrations in that it stores water for periods of time sufficient for a high degree of water‐mineral interaction to occur. Hence solute‐discharge relationships (C = aQb, where b is typically < 0) are characterized by relatively low slope values and there is ample acid neutralizing capacity throughout the range of discharge. Owing to the predominance of amphibolite, solute efflux related to rock weathering from the Falling Creek watershed is much greater than other more felsic locations within the region. Statistical analyses (Mest and the non‐parametric Mann‐Whitney‐Wilcoxon test), along with accompanying box‐plot representations, provide a useful method of describing systematic annual hydrochemical variation within streamflow. These methods are particularly effective for those instances in which a long‐term data set exists, but is limited to relatively few sampling periods per year.
Evaluation of the method of collecting suspended sediment from large rivers by discharge‐weighted pumping and separation by continuous‐flow centrifugation
Authors: Moody John A. , Meade Robert H.
Published: February 2007

A method for collecting suspended sediment samples has been developed that pumps a discharge‐weighted volume of water from fixed depths at four to 40 locations across a river and separates the suspended sediment in the sample using a continuous‐flow centrifuge. The efficacy of the method is evaluated by comparing the particle size distributions of sediment collected by the discharge‐weighted pumping method with the particle size distributions of sediment collected by depth integration and separated by gravitational settling. The pumping method was found to undersample the suspended sand sized particles (> 63 μm) but to collect a representative sample of the suspended silt and clay sized particles (< 63 μm). The centrifuge separated the silt and clay sized particles (< 63 μm) into three fractions. Based on the average results of processing 17 samples from the Mississippi River and several of its large tributaries in 1990, about 10% of the silt and clay sized material was trapped in a centrifuge bowl‐bottom sealing unit containing the nozzle and consisted of mostly medium and coarse silt from 16 to 63 μm. About 74% was retained on a Teflon liner in the centrifuge bowl and consisted of sizes from 0–1 to 63 μm. About 9% was discharged from the centrifuge in the effluent and was finer than 0–1 μm. About 7% was lost during the processes of removing the wet sediment fractions from the centrifuge, drying and weighing.

The success of the discharge‐weighted pumping method depends on how homogeneously the silt and clay sized particles (< 63 μm) are distributed in the vertical direction in the river. The degree of homogeneity depends on the composition and degree of aggregation of the suspended sediment particles.
Mountain hydrology of Canada and China: A case study in comparative hydrology
Authors: Woo Ming‐Ko , Liu Changming
Published: February 2007

Comparative hydrology attempts to identify regions with similar environmental attributes and then compares the hydrological activities in these regions to facilitate the transfer of knowledge and exchange of techniques. As a case study, the mountainous regions of Canada and China were compared. Vertical zonation is a characteristic feature of such regions, generating contrasts in microclimate, vegetation, soil and the resultant hydrological responses. An increase in precipitation with altitude is modified by aspect and other local factors. In temperate and colder latitudes, snow and ice are important, especially at higher elevations. Both countries have conducted many hydrological studies on snow and glaciers, but evaporation in mountainous terrain merits more attention. Runoff from mountainous catchments is often generated by a range of processes including rainfall, snowmelt and glacier melt, and runoff response to water input tends to be rapid. This study identifies some of the strengths and weaknesses of our current knowledge of mountain hydrology in both countries, and suggests that a more comprehensive treatment of the subject will improve the prediction of the hydrological behaviour of such regions.
Accuracy of kinematic wave and diffusion wave approximations for space‐independent flows on infiltrating surfaces
Authors: Singh V. P.
Published: February 2007

Error equations for the kinematic wave and diffusion wave approximations were derived under simplified conditions for space‐independent flows occurring on infiltrating planes or channels. These equations specify error as a function of time in the flow hydrograph. The kinematic wave, diffusion wave and dynamic wave solutions were parameterized through a dimensionless parameter γ which is dependent on the initial conditions. This parameter reflects the effect of initial flow depth, channel bed slope, lateral inflow and channel roughness when the initial condition is non‐vanishing; it reflects the effect of bed slope, channel roughness, lateral inflow and infiltration when the initial condition is vanishing. The error equations were found to be the Riccati equation.
Effect of mining and related activities on the sediment trace element geochemistry of Lake Coeur D'Alene, Idaho, USA part II: Subsurface sediments
Authors: Horowitz Arthur J. , Elrick Kent A. , Robbins John A. , Cook Robert B.
Published: February 2007

During the summer of 1990, 12 gravity cores were collected in Lake Coeur d'Alene, Idaho at various depths and in a variety of depositional environments. All core subsamples were analysed to determine the bulk sediment chemistry; selected subsamples were analysed for trace element partitioning and 137Cs activity. The purpose of these analyses was to determine the trace element concentrations and distributions in the sediment column and to try to establish a trace element geochemical history of the lake in relation to mining and mining‐related discharge operations in the area.

Substantial portions of the near‐surface sediments in Lake Coeur d'Alene are markedly enriched in Ag, As, Cd, Hg, Pb, Sb and Zn, and slightly enriched in Cu, Fe and Mn. Variations in the thickness of the trace element‐rich sediments, which range from more than 119 cm to as little as 17 cm, indicate that the source of much of this material is the Coeur d'Alene River. An estimated 75 million tonnes of trace element‐rich sediments have been deposited on or in the lake bed. Estimated trace element masses in excess of those considered representative of background conditions range from a high of 468 000 tonnes of Pb to a low of 260 tonnes of Hg.

The similarity between the trace element‐rich surface and subsurface sediments with respect to their location, their bulk chemistry, their interelement relations and their trace element partitioning indicate that the sources and/or concentrating mechanisms causing the trace element enrichment in the lake sediments have probably been the same through‐out their depositional history. Based on a Mt St Helens'ash layer from the 1980 eruption, ages estimated from 137Cs activity and the presence of 80 discernible and presumably annual layers in a core collected near the Coeur d'Alene River delta indicate that deposition rates for the trace element‐rich sediments have ranges from 2.1 to 1.3 cm/year. These data also indicate that the deposition of trace element‐rich sediments began, at least in the Coeur d'Alene River delta, some time between 1895 and 1910, dates consistent with the onset of mining and ore processing activities that began in the area in the 1880s.
Sensitivity to space and time resolution of a hydrological model using digital elevation data
Authors: Bruneau P. , Gascuel‐Odoux C. , Robin P. , Merot Ph. , Beven K.
Published: February 2007

The space and time resolutions used for the input variables of a distributed hydrological model have a sufficient impact on the model results. This resolution depends on the required accuracy, experimental site and the processes and variables taken into account in the hydrological model. The influence of space and time resolution is studied here for the case of TOPMODEL, a model based on the variable contributing area concept, applied to an experimental 12 km2 catchment (Coët‐Dan, Brittany, France) during a two month winter period. A sensitivity analysis to space and time resolution is performed first for input variables derived from the digital elevation data, secondly for the optimized values of the TOPMODEL parameters and finally for modelling efficiency. This analysis clearly shows that a relevant domain of space and time resolutions where efficiency is fairly constant can be defined for the input topographic variables, as opposed to another domain of larger resolutions that induces a strong decrease of modelling efficiency. It also shows that the use of a single set of parameters, defined as mean values of parameters on this relevant domain of resolution, does not modify the accuracy of modelling. The sensitivity of the parameters to space and time resolution allows the physical significance of the parameter values to be discussed.
Potential of turbidity monitoring for measuring the transport of suspended solids in streams
Authors: Gippel Christopher James
Published: February 2007

Investigating the transport of suspended solids by water sampling usually leads to an underestimation of loads and an unrealistically high sampling frequency is required to properly characterize temporal trends. An alternative method is to use in situ optical turbidimeters to estimate the suspended solids concentration; however, the relationship between turbidity and suspended solids concentration is potentially confounded by variations in particle size, particle composition and water colour. Field measurements, and laboratory measurements using the type of natural material suspended in streamwater, were made to quantify the influences of these factors on nephelometric turbidity (Hach 2100A) and attenuance turbidity (Partech 7000 3RP MKII). The attenuance turbidity was approximately 2.5 times higher than nephelometric turbidity. The turbidity instruments were most sensitive to dispersions with a median diameter of 1.2‐1.4γm. Particle size variation can cause the turbidity to vary by a factor of four for the same concentration of suspended solids. However, the numerous close correlations between turbidity and suspended solids concentration reported previously suggests that either the particle size variations are not usually great, or that particle size variations are often associated with variations in suspended solids concentration. For the same concentration and particle size, organic particles gave attenuance turbidity values two to three times higher than mineral particles. However, shortterm temporal variations from purely organic to purely mineral particle loads are rare in nature, so variations in the percentage of organic matter in the paniculate load will not confound turbidity to this extent. Coloured dissolved organic matter is unlikely to alter the turbidity reading by more than 10%. An adequate relationship between turbidity measured in the field and suspended solids concentration should be expected in most situations. Some variance can be tolerated because a continuous estimate of suspended solids concentration overcomes the problem of infrequent sampling, which is the greatest source of error in the estimation of stream sediment loads.
Soil erosion and overland flow in forested areas with pine plantations at coastal mountain range, central chile
Authors: Oyarzun C. E. , Peña L.
Published: February 2007

The effects of timber‐cutting on sediment concentrations, soil loss and overland flow in an insigne pine (Pinus radiata) plantation were studied in a mountain watershed of the Cordillera de la Costa, central Chile. Soil formation rates for the lithological conditions of the watershed were estimated.

Soil loss measurements on the plantation were taken in 100 m2 plots, equipped with Coshocton samplers, during the years 1991 and 1992. Treatments were: clear‐cutting no residues/burned, clear‐cutting with residues and undisturbed controls.

First‐year soil losses were greater from the no residues/burned (2128 kg ha−1) than from the residues (1219 kg ha−1) or undisturbed (48 kg ha−1) plots. During the second post‐treatment year, soil loss was greater from the burned plots (1349 kg ha−1) than from the residues (243 kg ha−1) or the undisturbed (72 kg ha−1) plots. Sediment concentrations for the three treatments were 561, 340 and 59 mgl‐1 during the first year, and 400, 150 and 83 mgl−1 in the second year. Runoff from the no residues/burned plots was greater than from residues or undisturbed plots during the two post‐treatment years. Long‐term soil losses were projected to average 240 kg ha−1 yr−1 from areas without residues/burned and 120 kg ha−1 yr−1 in areas with residues treatment, over a 25 year rotation period, whereas control areas were projected to average 60 kg ha−1 yr−1.
Estimation of vertical water and heat fluxes in the semi‐confined aquifers in tokyo metropolitan area, japan
Authors: Dapaah‐Siakwan S. , Kayane Isamu
Published: February 2007

Groundwater circulation is known to be one of the agents responsible for the redistribution of geothermal energy by acting as a source or sink in the course of its movement through porous media. Heat transport in groundwater systems is considered to be a coupled process and the theory based on this was used to analyse temperature profiles of 30 thermally stable observation wells in a deep, semi‐confined aquifer system in the Tokyo Metropolitan area. Vertical water fluxes in the semi‐confined aquifers and the associated upward heat fluxes were estimated from a heat flux equation that describes convection and conduction processes of heat transport in one dimension. The vertical downward water fluxes in Shitamachi lowland, Musashino and Tachikawa terraces were 0.69.26.91 × 10−9, 1.46‐70.92 × 10−9 and 2.61.2204 × 10−9 m/s, respectively. A vertical upward water flux of 1.80‐33.60 × 10−9 m/s was estimated in Shitamachi lowland. The water flux generally decreased with increasing depth for observation wells which intercepted more than one semi‐confining layer. The estimated upward heat fluxes for Shitamachi lowland, Musashino and Tachikawa terraces were 0.32‐1.12, 0.49‐1.21 and 1.00‐11.62 W/m2, respectively. The heat flux was highest in Tachikawa terrace where a major fault, the Tachikawa fault, is located. Generally, the estimated heat flux was higher in the semi‐confining layers than in the aquifers. Areas with heat sources and sinks as well as groundwater flow patterns in the semi‐confined aquifers were revealed by heat flux and temperature distributions in the study area.
Influence of sea salt on stream water chemistry in an upland afforested catchment
Authors: Soulsby Christopher
Published: February 2007

The chemistry of bulk precipitation and stream water was monitored in an acidic afforested catchment at Llyn Brianne in upland Wales between 1985 and 1990. Throughfall, stemflow and soil water chemistry were also monitored between 1988 and 1989. Marine‐derived solutes dominated the ionic composition of precipitation and stream water, which had mean Cl concentrations of 113 μequiv. 1−1 and 245 μequiv. 1−1, respectively. The higher concentrations in stream water reflect occult and dry deposition on the forest canopy and the effect of interception and transpiration losses. Chloride variations in stream water (112‐454μequiv. 1−1) were damped compared with bulk precipitation (28‐762μequiv. 1−1) due to the mixing of event (‘new’) water with pre‐event (‘old’) water in the catchment soils. A storm episode monitored in the catchment in April 1989 was associated with high sea salt inputs and Cl concentrations in throughfall (1466μequiv. 1−1) and storm runoff were exceptionally high (392μequiv. 1−1). The Cl signal in stream water during the episode was consistent with an event (‘new’) water contribution to the storm response. However, a short‐term hydrochemical budget estimated that although Cl outputs from the catchment during the event (1.17 kg ha−1) were equivalent to 8% of inputs in throughfall and stemflow, the storm runoff was equivalent to 32% of effective precipitation. This indicates that pre‐event (‘old’) water was the dominant source (> 75%) of storm runoff. Although sea salt inputs during the event had a marked impact on stream water chemistry, the anomalously high levels of acidity sometimes associated with sea salt events were not observed in this particular study.
Topographic zonation of infiltration in the hilly loess region, north china
Authors: Li Gang , Luk Shiu Hung , Cai Qiang Guo
Published: February 2007

Field infiltration tests using portable rainfall infiltrometers were conducted in the Wangjiagou experimental basin in the hilly loess region of north China. Based on data collected at 27 sites, a topographic zonation of infiltration characteristics was observed. The average steady infiltration rate and the average ponding time decreased from the hilltop to the hillslope and further decreased to the gully wall. Such a zonation is closely related to the variations of topography, soil and land use conditions in the study area. A general infiltration model is proposed. Collected field data are used to establish the applicability of the proposed model in the study area.
Scale issues in hydrological modelling: A review
Authors: Blöschl G. , Sivapalan M.
Published: February 2007

A framework is provided for scaling and scale issues in hydrology. The first section gives some basic definitions. This is important as researchers do not seem to have agreed on the meaning of concepts such as scale or upscaling. ‘Process scale’, ‘observation scale’ and ‘modelling (working) scale’ require different definitions. The second section discusses heterogeneity and variability in catchments and touches on the implications of randomness and organization for scaling. The third section addresses the linkages across scales from a modelling point of view. It is argued that upscaling typically consists of two steps: distributing and aggregating. Conversely, downscaling involves disaggregation and singling out. Different approaches are discussed for linking state variables, parameters, inputs and conceptualizations across scales. This section also deals with distributed parameter models, which are one way of linking conceptualizations across scales. The fourth section addresses the linkages across scales from a more holistic perspective dealing with dimensional analysis and similarity concepts. The main difference to the modelling point of view is that dimensional analysis and similarity concepts deal with complex processes in a much simpler fashion. Examples of dimensional analysis, similarity analysis and functional normalization in catchment hydrology are given. This section also briefly discusses fractals, which are a popular tool for quantifying variability across scales. The fifth section focuses on one particular aspect of this holistic view, discussing stream network analysis. The paper concludes with identifying key issues and gives some directions for future research.
Investigating the representative elementary area concept: An approach based on field data
Authors: Woods Ross , Sivapalan Murugesu , Duncan Maurice
Published: February 2007

Changing the scale of observation or averaging has a significant, but poorly understood, impact on the apparent variability of hydrological quantities. The representative elementary area (REA) concept is used as a motivation for measuring inter‐storm streamflow and calculating wetness index distributions for the subcatchments of two small study areas in New Zealand. Small subcatchments are combined to provide larger scale samples, and then the variance of specific discharge between similar sized subcatchments is calculated. For small subcatchments (area less than ∼1 km2) this variance is found to decrease with area more quickly than might be expected if the catchments were random samples. Such behaviour is tentatively interpreted as evidence supporting the concept of ‘organization’. At larger scales, variance between catchments decreases in a way that is consistent with sampling from a stationary random field. The results from the streamflow data are reinforced by an analysis of topographic data for the two study areas, although some questions remain open.

Both the flow and topographic data support the idea that it is possible to find an averaging scale where the variability between catchments is sufficiently small for a ‘distribution function’ approach to be used in distributed rainfall‐runoff modelling. Consistent estimates of the scale at which the study areas become stationary (0.5 km2 for Little Akaloa, 2 km2 for Lewis) are obtained using both flow and topographic data. The data support a pragmatic REA concept which allows meaningful averages to be formed: this may be a useful base for further conceptual developments, but it is not appropriate for a classical continuum approach. Further conceptual development combined with field measurement and computer simulation are still required for the REA to have operational impacts. In particular, it is not clear which models are appropriate for use at the REA scale.
Scaling behaviour of hydrological fluxes and variables: Empirical studies using a hydrological model and remote sensing data
Authors: Wood Eric F.
Published: February 2007

The effects of small‐scale heterogeneity in land surface characteristics on the large‐scale fluxes of water and energy in the land‐atmosphere system has become a central focus of many of the climatology research experiments. The acquisition of high resolution land surface data through remote sensing and intensive land‐climatology field experiments (such as HAPEX and FIFE) has provided data to investigate the interactions between microscale land‐atmosphere interactions and macroscale models. One essential research question is how to account for the small‐scale heterogeneities and whether ‘effective’ parameters can be used in the macroscale models. To address this question of scaling, it is important to carry out modelling studies by analysing the spatial behaviour of process‐based, distributed land‐atmospheric models and available data from land surface climate experiments such as those designed under ISLSCP (e.g. FIFE and BOREAS) and HAPEX (e.g. HAPEX‐MOBILY, HAPEX‐SAHEL) and GEWEX (e.g. GCIP) and from smaller scale remote sensing experiments. Using data from FIFE'87 and WASHITA'92, a soil moisture remote sensing experiment, analyses are presented on how the land surface hydrology during rain events and between rain event varies; specifically, runoff during rain events, evaporation between rain events and soil moisture. The analysis with FIFE'87 data suggests that the scale at which a macroscale model becomes valid, the representative elementary scale (REA), is of the order of 1.5‐3 correlation lengths, which for the land processes investigated appear to be about 750‐1250 m. For the Washita catchment data, analysis of soil‐based infiltration data supports an REA of this spatial scale, but model derived and remotely sensed soil moisture data appear to suggest a larger scale. Statistical self‐similarity is investigated to further understand how soil moisture scales over the Washita catchment and to provide a basis for macroscale models.
Effects of vertical resolution and map scale of digital elevation models on geomorphological parameters used in hydrology
Authors: Gyasi‐Agyei Yeboah , Willgoose Garry , De Troch Francois P.
Published: February 2007

The advent of digital elevation models (DEMs) has made it possible to objectively extract, calculate and store geomorphological parameters for hydrological modelling at several scales. For a grid‐based DEM, the threshold area used to extract the channel network is analogous to the scale of the map produced. In addition to the map scale, the effects of the vertical resolution of the DEM on some frequently used geomorphological parameters in hydrology are examined using high‐resolution DEMs of two natural and two artificial catchments. The vertical resolution was varied between 1 cm and 1 m, the most common vertical resolution of DEMs. At a fixed map scale, the mean absolute percentage error in the geomorphological parameters caused by a decrease in vertical resolution is within the range 0–5% for the medium‐sized catchments and 0–10% for the small catchments studied. Although it is true that a change in vertical resolution may cause a change in the individual pixel slope, area and topographic index (area/slope), particularly in low relief terrain, their cumulative distributions do not show any significant change with the vertical resolution. The shape of the normalized width function is not very sensitive to the vertical resolution and the map scale. For small catchments order change may occur at different map scales for the different vertical resolution DEMs of the same catchment, causing a significant change in order‐related parameters such as Horton ratios. It is suggested that the vertical resolution of the DEM of a catchment be considered satisfactory for most hydrological applications if the ratio of the average drop per pixel and vertical resolution is greater than unity. This ratio criterion could be used to define the minimum pixel area for reliable channel network definition for any given vertical resolution. The minimum pixel area places a lower bound on the horizontal resolution with which a channel network can be extracted from a DEM. These results could potentially be used to assess the adequacy for hydrological purposes of existing and proposed digital elevation databases.
Predicting catchment‐scale soil moisture status with limited field measurements
Authors: Kalma J. D. , Bates B. C. , Woods R. A.
Published: February 2007

A catchment‐wide soil moisture index based on spatially distributed point measurements of soil moisture is used to describe the temporal trend in regional soil moisture status in a 26 km2 catchment in south‐eastern Australia. The temporal variation in runoff, evaporation and soil moisture storage is simulated with a modification of the lumped SFB water balance model of Boughton (1984), which assumes a fixed bucket size, and with the variable infiltration capacity (VIC) model of Wood et al. (1992), which assumes a variable bucket representation. Comparison of simulated catchment soil moisture storage and the soil moisture index based on measurements indicates that both models can make useful predictions of soil moisture status at the catchment scale, with the VIC model performing slightly better than the SFB model. It is also shown that the quasi‐distributed VIC model can predict the relative wetness at individual locations, given their relative frequency of occurrence, thus allowing the disaggregation of catchment‐scale storage values to point‐scale soil moisture values.
Application of the meta‐channel concept: Construction of the meta‐channel hydraulic geometry for a natural catchment
Authors: Snell John , Sivapalan Murugesu
Published: February 2007

This is the second in a series of three papers about the meta‐channel concept which illustrates the derivation of the principles behind the concept, the construction of the hydraulic geometry and the application of the concept to flood routing, respectively. It was shown in the first of these that a channel network in a catchment can be conceptualized into a single ‘effective channel’ representation: a meta‐channel. This study uses this conceptualization to show how such a meta‐channel can be constructed. The techniques derived are applied to one catchment in New Zealand. We derive hydraulic geometries expressed as functions of flow distance throughout this catchment based on the Leopold and Maddock power laws. This derivation uses classical published values for hydraulic geometry coefficients and exponents, regional parameterization of the index flood relationship for New Zealand as a whole, together with local knowledge regarding the order of magnitude of the channel roughness. Conservation principles derived from the continuity and mechanical energy balance equations are used to construct the hydraulic geometry of the meta‐channel of this catchment. A meta‐channel long profile is established and compared against the mainstream long profile. The effectiveness of the Leopold and Maddock power law assumptions is tested by comparing the derived hydraulic geometry against available field cross‐sectional data for the gauging site at the outlet of the catchment.
Scaling theory to extrapolate individual tree water use to stand water use
Authors: Hatton Thomas J. , Wu Hsin‐I
Published: February 2007

Extrapolation of measurements of water use by individual trees to that for a stand of trees is a critical step in linking plant physiology and hydrology. Limitations in sampling resources and variation in tree sizes within a stand necessitate the use of some scaling relationship. Further, to scale tree water use in space as well as time, the relationship must reflect the changing availabilities of energy and water supply. It is argued here that tree leaf area is the most appropriate covariate of water use to achieve this aim. However, empirical results show that the relationship is not always linear. A theory is developed, based on the concepts of hydrological equilibrium (sensu Nemani and Running, 1989) and ecological field theory (Walker et al., 1989) which accounts for (occasional) non‐linear behaviour of the flux/ leaf area relationship in evergreen trees. A key feature of this theory is the notion of a non‐linear, quasi‐equilibrium reflecting plant water stress. An equation is derived from these concepts and a standard, explicit treatment of tree water use (Landsberg and McMurtrie, 1984), which is used to characterise this relationship. This equation has the form Q = aIA + bΨsAf. The theory is tested against field data and published reports on Eucalyptus tree water use.
Estimation of terrestrial water and energy balances over heterogeneous catchments
Authors: Silberstein R. P. , Sivapalan M.
Published: February 2007

Modelling experiments have been undertaken to address the effects of land surface heterogeneity on the energy and water fluxes at catchment scales. The simulation results indicate that in the presence of strong contrasts (i.e. patchiness) in the land surface characteristics (for example, soil moisture, leaf area index or vegetation type) significant inter‐patch advection can result. For example, small areas with high levels of soil moisture surrounded by drier areas have a disproportionately high latent heat flux. The sensible heat flux showed a complementary suppression. The response to changes in leaf area index, however, was found to be much more complex. At constant soil moisture levels, it was found that under some conditions the latent heat flux of patches of high leaf area index increased as its proportion of the surface increased as a result of the increase in net radiation and roughness. There was also an increase in sensible heat flux. This effect was also found on surfaces with low moisture levels and strong contrasts in surface vegetation. Although these results do depend on the initial boundary layer and terrestrial conditions, a consequence of this is that significant biases can be generated in modelling catchment output if the heterogeneity effects are not fully accounted for. The model simulations demonstrate that the fluxes from a ‘homogenized’ surface with catchment‐average land surface properties (e.g. soil moisture) can be significantly higher than that for a heterogeneous surface with explicitly modelled inter‐patch interactions. These results have particular implications for nested catchment models where the responses of individual subcatchments are as important as that of the total catchment. They are also significant in efforts towards developing lumped land surface parameterizations for use in atmospheric models such as general circulation models.
Meteorlogical impact of replacing native perennial vegetation with annual agricultural species
Authors: Xinmei Huang , Lyons T. J. , Smith R. C. G.
Published: February 2007

Following the clearing of native perennial vegetation for agriculture based on winter growing annual species, the surface characteristics of south‐western Australia have been significantly altered. Analysis of the annual variation of these characteristics based on satellite data and a one‐dimensional boundary layer model suggests that convective mixing over the cleared land is no longer able to reach the lifting condensation level for a significant period of the year. This implies a decrease in convective cloud formation and a reduction in the convective enhancement of rainfall.
Scaling of land‐atmosphere interactions: An atmospheric modelling perspective
Authors: Avissar Roni
Published: February 2007

Investigations of the impact of the ground surface on energy and mass fluxes in the atmosphere as well as on the dynamic response of the atmosphere at different scales are reviewed to emphasize the requirements for hydrological schemes for atmospheric models. Based on these investigations, a discussion on the scaling of the most important land processes and characteristics, from an atmospheric modelling perspective, is provided. It appears that because of the strong, non‐linear response of the atmosphere to the spatial variability of land‐surface characteristics, the scaling of hydrological processes and parameters is not linear. This implies that appropriate hydrological schemes for atmospheric models need to provide higher statistical moments and characteristic length scales of the spatial distribution of water availability for evapotranspiration.
Simulating heterogeneous vegetation in climate models. Identifying when secondary vegetation becomes important
Authors: Pitman A. J.
Published: February 2007

To parameterize the land surface in global climate models (GCMs) data must be provided at a variety of resolutions. In GCMs, high‐resolution data must be aggregated to the coarser resolution of the GCM. The method used for parameter aggregation can lead to the simulation of very different land surface climatologies. It is shown that the most important transition from a simulation of homogeneous tundra to one of homogeneous coniferous forest is the initial increase in forest. The differences between the simulation of tundra and the simulation of tundra with two‐ninths coniferous forest are considerable. This suggests that the land surface is sensitive to the aggregated parameters in non‐linear ways. It suggests that more care is needed in data aggregation, and that improved algorithms for data aggregation must be developed, because these data sets represent the foundations on which advanced land surface parameterizations are built. Finally, it shows that the influence of relatively small amounts of secondary vegetation should be represented in GCMs.
Estimating macropore and matrix flow using the hydrograph separation procedure in an experimental forest plot
Authors: Návar José , Turton Donald J. , Miller Edwin L.
Published: February 2007

This study was conducted to estimate macropore space, macropore flow and matrix flow in an experimental forest plot in the Ouachita Mountains of Arkansas. Lateral soil water fluxes and soil capillary potentials were observed in the isolated plot during applied rainfall experiments. Rainfalls were applied 17 times during the period 17 July to 10 October 1991. The subsurface hydrograph separation technique was used to estimate macropore space, macropore flux and matrix flux. The boundary between macropore and matrix flow was statistically determined by covariance analysis. The maximum estimated lateral macropore space was approximately 0.006 (cm3 cm−3). The maximum estimated lateral macropore and matrix flow were 0.042 and 0.00066 cm s−1, respectively. This report also emphasizes the need for further research on the hydrograph separation procedure for estimating macropores and macropore flow.
Modelling the growth of cyanobacteria (GrowSCUM)
Authors: Howard A. , Kirkby M. J. , Kneale P. E. , McDonald A. T.
Published: February 2007

Toxic cyanobacteria have become a common nuisance in freshwater lakes and reservoirs throughout the world, sometimes resulting in the closure of sites with high amenity value. Cyanobacteria are able to regulate their buoyancy state in response to changing photosynthetic rates. Additionally, the cyanobacteria are liable to become entrained within wind‐induced near‐surface turbulent currents, resulting in mixing and mass transport. These movement processes have been modelled. A mathematical function is presented which describes light‐ and nutrient‐limited cyanobacterial growth. The growth model is integrated with a previous movement model (SCUM: simulation of cyanobacterial underwater movement) as movement patterns and wind‐induced lake mixing strongly affect the intensity and duration of light received by the cyanobacteria and thereby determine the photosynthetic potential. Results of the model suggest that cyanobacteria are resistant to periods of lake mixing and continue to increase their biomass, but at a depressed rate. Growth is most rapid under calm conditions. The results agree well with field‐based findings, confirming the validity of the growth function.
On the concept of a representative elementary area in catchment runoff
Authors: Fan Ying , Bras Rafael L.
Published: February 2007

A qualitative discussion is presented on the concept of a representative elementary area (REA) proposed by Wood et al. (1988). Their work represents a systematic effort of looking at spatial variability as functions of scale, and over the past few years has stimulated new thoughts and research findings. However, it is argued here that the REA concept has limited utility in catchment hydrology for the following reasons. Firstly, the method of finding the REA using distributed modelling appears flawed. In estimating local runoff, point‐process models are applied to elements of 30 × 30 m2 or larger, but the effect of this particular upscaling on the calculated REA has not been addressed. This causes the REA to be relative to the resolution of the modelling. Secondly, an REA does not seem to exist in a natural environment because of its relativeness in the presence of multi‐scale heterogeneity and its dependence on individual storm events. Based on the above arguments and following a discussion of the hydrological implications of REA, it is pointed out that the REA does not provide a definite and robust measure of the inherent spatial variability in runoff and that its utility in formulating large‐scale hydrology is not as clear as it was first envisioned.
Hydrological and hydrochemical response of a small canadian shield catchment to late winter rain‐on‐snow events
Authors: Maclean R. A. , English M. C. , Schiff S. L.
Published: February 2007

A study was undertaken during the winter of 1990–1991 in a small (3.7 ha) Canadian Shield catchment to examine the hydrological and hydrochemical response during rain‐on‐snow events. The results are presented of two large (37.9 and 34.6 mm) rain‐on‐snow events occurring in early and late March 1991. Peak and total runoff and the groundwater response from the two events are significantly different. Hydrological data indicate that these differences can be attributed to a combination of meteorological (temperature) and physical conditions (antecedent snowpack ripeness, soil moisture and groundwater levels). An immature snowpack (low temperature and density) combined with low antecedent soil moisture conditions significantly reduced the magnitude of the net hydrological input and runoff from the catchment during the early March event, whereas a more mature snowpack and high antecedent soil moisture conditions led to a large runoff event during late March.

During both rain‐on‐snow events a significant portion of the pre‐event snowpack chemical load was lost. Based on the maximum snowpack chemical load measured before the events, the two large rain‐on‐snow events and a brief mid‐March warm period during which there were two much smaller rain‐on‐snow events removed 78% of the hydrogen ion and 63% of the sulphate and nitrate load from the snowpack, while only reducing snowpack water equivalence by 7%. A two‐component (rain and snowmelt) isotopic (δ18O SMOW %0) separation of snowmelt lysimeter water during the two events indicated that snowmelt was an important (50 and 65%, respectively) water source available for infiltration and runoff at the snow‐soil interface. Considering the high hydrogen ion loadings to the catchment during these two events (3.3 and 3.0 mequiv.m−2, respectively) streamflow pH was not significantly reduced due to an increase in the discharge of well‐buffered groundwater. A two‐component isotopic hydrograph separation of peak stream discharge during the 2–3 March event indicated that 75% of the total flow was groundwater. In mid‐latitude acid‐sensitive catchments, winter rain‐on‐snow events are an important hydrological occurrence due to their ability to elute much of the chemical load (H+, SO4, NO3) from the snowpack before the onset of spring melt when the maximum annual hydrological input typically occurs.
Accuracy of tretyakov precipitation gauge: Result of wmo intercomparison
Authors: Yang Daqing , Goodison Barry E. , Metcalfe John R. , Golubev Valentin S. , Elomaa Esko , Gunther Thilo , Bates Roy , Pangburn Timothy , Hanson Clayton L. , Emerson Douglas , Copaciu Voilete , Milkovic Janja
Published: February 2007

The Tretyakov non‐recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period.

The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge‐measured precipitation data over large regions of the former USSR and central Europe.