bluuebunny/crossref_metadata_2025 huggingface dataset:
Interrelationships between MODIS/Terra remotely sensed snow cover and the hydrometeorology of the Quesnel River Basin, British Columbia, Canada
Authors: Tong J. , Déry S. J. , Jackson P. L.
Published: April 2010

Abstract. A spatial filter (SF) method is adopted to reduce the cloud coverage from the Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day snow products (MOD10A2) between 2000–2007 in the Quesnel River Basin (QRB) of British Columbia, Canada. A threshold of k = 2 cm of snow depth measurements at four in-situ observation stations in the QRB are used to evaluate the accuracy of MODIS snow products MOD10A1, MOD10A2, and SF. Using the MOD10A2 and the SF, the relationships between snow ablation, snow cover extent (SCE), snow cover fraction (SCF), streamflow and climate variability are assessed. Based on our results we are able to draw several interesting conclusions. Firstly, the SF method reduces the average cloud coverage in the QRB from 15% for MOD10A2 to 9%. Secondly, the SF increases the overall accuracy (OA) based on the threshold k = 2 cm by about 2% compared to MOD10A2 and by about 10% compared to MOD10A1 at higher elevations. The OA for the four in-situ stations decreases with elevation with 93.1%, 87.9%, 84.0%, and 76.5% at 777 m, 1265 m, 1460 m, and 1670 m, respectively. Thirdly, an aggregated 1°C rise in average air temperature during spring leads to a 10-day advance in reaching 50% SCF (SCF50%) in the QRB. The correlation coefficient between normalized SCE of the SF and normalized streamflow is −0.84 (p<0.001) for snow ablation seasons. There is a 32-day time lag for snow ablation to impact the streamflow the strongest at the basin outlet. The linear correlation coefficient between SCF50% and 50% normalized accumulated runoff (R50%) attains 0.82 (p<0.01). This clearly demonstrates the strong links that exist between the SCF depletion and the hydrology of this sub-boreal, mountainous watershed.
Optimisation of LiDAR derived terrain models for river flow modelling
Authors: Mandlburger G. , Hauer C. , Höfle B. , Habersack H. , Pfeifer N.
Published: April 2010

Abstract. Airborne LiDAR (Light Detection And Ranging) combines cost efficiency, high degree of automation, high point density of typically 1–10 points per m2 and height accuracy of better than ±15 cm. For all these reasons LiDAR is particularly suitable for deriving precise Digital Terrain Models (DTM) as geometric basis for hydrodynamic-numerical (HN) simulations. The application of LiDAR for river flow modelling requires a series of preprocessing steps. Terrain points have to be filtered and merged with river bed data, e.g. from echo sounding. Then, a smooth Digital Terrain Model of the Watercourse (DTM-W) needs to be derived, preferably considering the random measurement error during surface interpolation. In a subsequent step, a hydraulic computation mesh has to be constructed. Hydraulic simulation software is often restricted to a limited number of nodes and elements, thus, data reduction and data conditioning of the high resolution LiDAR DTM-W becomes necessary. We will present a DTM thinning approach based on adaptive TIN refinement which allows a very effective compression of the point data (more than 95% in flood plains and up to 90% in steep areas) while preserving the most relevant topographic features (height tolerance ±20 cm). Traditional hydraulic mesh generators focus primarily on physical aspects of the computation grid like aspect ratio, expansion ratio and angle criterion. They often neglect the detailed shape of the topography as provided by LiDAR data. In contrast, our approach considers both the high geometric resolution of the LiDAR data and additional mesh quality parameters. It will be shown that the modelling results (flood extents, flow velocities, etc.) can vary remarkably by the availability of surface details. Thus, the inclusion of such geometric details in the hydraulic computation meshes is gaining importance in river flow modelling.
Combining semi-distributed process-based and data-driven models in flow simulation: a case study of the Meuse river basin
Authors: Corzo G. A. , Solomatine D. P. ,   Hidayat, de Wit M. , Werner M. , Uhlenbrook S. , Price R. K.
Published: April 2010

Abstract. One of the challenges in river flow simulation modelling is increasing the accuracy of forecasts. This paper explores the complementary use of data-driven models, e.g. artificial neural networks (ANN) to improve the flow simulation accuracy of a semi-distributed process-based model. The IHMS-HBV model of the Meuse river basin is used in this research. Two schemes are tested. The first one explores the replacement of sub-basin models by data-driven models. The second scheme is based on the replacement of the Muskingum-Cunge routing model, which integrates the multiple sub-basin models, by an ANN. The results show that: (1) after a step-wise spatial replacement of sub-basin conceptual models by ANNs it is possible to increase the accuracy of the overall basin model; (2) there are time periods when low and high flow conditions are better represented by ANNs; and (3) the improvement in terms of RMSE obtained by using ANN for routing is greater than that when using sub-basin replacements. It can be concluded that the presented two schemes can improve the performance of process-based models in the context of flow forecasting.
Improvement, calibration and validation of a distributed hydrological model over France
Authors: Quintana Seguí P. , Martin E. , Habets F. , Noilhan J.
Published: April 2010

Abstract. The hydrometeorological model SAFRAN-ISBA-MODCOU (SIM) computes water and energy budgets on the land surface and riverflows and the level of several aquifers at the scale of France. SIM is composed of a meteorological analysis system (SAFRAN), a land surface model (ISBA), and a hydrogeological model (MODCOU). In this study, an exponential profile of hydraulic conductivity at saturation is introduced to the model and its impact analysed. It is also studied how calibration modifies the performance of the model. A very simple method of calibration is implemented and applied to the parameters of hydraulic conductivity and subgrid runoff. The study shows that a better description of the hydraulic conductivity of the soil is important to simulate more realistic discharges. It also shows that the calibrated model is more robust than the original SIM. In fact, the calibration mainly affects the processes related to the dynamics of the flow (drainage and runoff), and the rest of relevant processes (like evaporation) remain stable. It is also proven that it is only worth introducing the new empirical parameterization of hydraulic conductivity if it is accompanied by a calibration of its parameters, otherwise the simulations can be degraded. In conclusion, it is shown that the new parameterization is necessary to obtain good simulations. Calibration is a tool that must be used to improve the performance of distributed models like SIM that have some empirical parameters.
Spatial rainfall variability and runoff response during an extreme event in a semi-arid catchment in the South Pare Mountains, Tanzania
Authors: Mul M. L. , Savenije H. H. G. , Uhlenbrook S.
Published: April 2010

Abstract. This paper describes an extreme flood event that occurred in the South Pare Mountains in northern Tanzania. A high spatial and temporal resolution data set has been gathered in a previously ungauged catchment. This data was analysed using a multi-method approach, to gather information about the processes that generated the flood event. On 1 March 2006, extreme rainfall occurred in the Makanya catchment, (300 km2), where up to 100 mm were recorded in Bangalala village in only 3 h. The flood was devastating, inundating large parts of the flood plain. The spatial variability of the rainfall during the event was very large, even in areas with the same altitude. The Vudee sub-catchment (25.8 km2) was in the centre of the rainfall event, receiving about 75 mm in 3 h divided over the two upstream tributaries: the Upper-Vudee and Ndolwa. The peak flow at the weir site has been determined using the slope-area method and gradually varied flow calculations, indicating a peak discharge of 32 m3 s−1. Rise and fall of the flood was very sharp, with the peak flow occurring just one hour after the peak of the rainfall. The flow receded to 1% of the maximum flow within 24 h. Hydrograph separation using hydrochemical parameters indicates that at the floodpeak 50% of the flow was generated by direct surface runoff (also indicated by the large amount of sediments in the samples), whereas the recession originated from displaced groundwater (>90%). The subsequent base flow in the river remained at 75 l s−1 for the rest of the season, which is substantially higher than the normal base flow observed during the previous rainy seasons (15 l s−1) indicating significant groundwater recharge during this extreme event.
Effects of intersite dependence of nested catchment structures on probabilistic regional envelope curves
Authors: Guse B. , Castellarin A. , Thieken A. H. , Merz B.
Published: April 2010

Abstract. This study analyses the intersite dependence of nested catchment structures by modelling cross-correlations for pairs of nested and unnested catchments separately. Probabilistic regional envelope curves are utilised to derive regional flood quantiles for 89 catchments located in Saxony, in the Southeast of Germany. The study area has a nested structure and the intersite correlation is much stronger for nested pairs of catchments than for unnested ones. Pooling groups of sites (regions) are constructed based on several candidate sets of catchment descriptors using the Region of Influence method. Probabilistic regional envelope curves are derived on the basis of flood flows observed within the pooling groups. Their estimated recurrence intervals are based on the number of effective sample years of data (i.e. equivalent number of uncorrelated data). The evaluation of the effective sample years of data requires the modelling of intersite dependence. We perform this globally, using a cross-correlation function for the whole study area as well as by using two different cross-correlation functions, one for nested pairs and another for unnested pairs. In the majority of the cases, these two modelling approaches yield significantly different estimates for the effective sample years of data, and therefore also for the recurrence intervals. The reduction of the recurrence interval when using two different cross-correlation functions is larger for larger pooling groups and for pooling groups with a higher fraction of nested catchments. A separation into nested and unnested pairs of catchments gives a more realistic representation of the characteristic river network structure and improves the estimation of regional information content. Hence, applying two different cross-correlation functions is recommended.
Root reinforcement and slope bioengineering stabilization by Spanish Broom (Spartium junceum L.)
Authors: Preti F. , Giadrossich F.
Published: April 2010

Abstract. The present paper deals with the root system's characteristics of Spanish Broom (Spartium junceum L.), a species whose capacity for adaptating and resisting to drought is worth investigating. In particular, the aims of the study were 1) to investigate the plant's bio-mechanical aspects and 2) to verify whether root reinforcement and the field rooting ability of stem cuttings enhance its potential for use in slope stabilization and soil bio-engineering techniques, particularly in the Mediterranean areas. Single root specimens were sampled and tested for tensile strength, obtaining classic tensile strength-diameter relationships. Analysis were performed on the root systems in order to assess root density distribution. The Root Area Ratio (RAR) was analyzed by taking both direct and indirect measurements, the latter relying on image processing. The data obtained were used to analyze the stability of an artificial slope (landfill) and the root reinforcement. The measurement and calculation of mean root number, mean root diameter, RAR, root cohesion and Factor of safety are presented in order to distinguish the effect of plant origin and propagation. Furthermore, tests were performed to assess the possibility of agamic propagation (survival rate of root-ball endowed plants, rooting from stem cuttings). These tests confirmed that agamic propagation is difficult, even though roots were produced from some buried stems, and for practical purposes it has been ruled out. Our results show that Spanish Broom has good bio-mechanical characteristics with regard to slope stabilization, even in critical pedoclimatic conditions and where inclinations are quite steep, and it is effective on soil depths up to about 50 cm, in agreement with other studies on Mediterranean species. It is effective in slope stabilization, but less suitable for soil bio-engineering or for triggering natural plant succession.
Mapping rainfall erosivity at a regional scale: a comparison of interpolation methods in the Ebro Basin (NE Spain)
Authors: Angulo-Martínez M. , López-Vicente M. , Vicente-Serrano S. M. , Beguería S.
Published: April 2010

Abstract. Rainfall erosivity is a major causal factor of soil erosion, and it is included in many prediction models. Maps of rainfall erosivity indices are required for assessing soil erosion at the regional scale. In this study a comparison is made between several techniques for mapping the rainfall erosivity indices: i) the RUSLE R factor and ii) the average EI30 index of the erosive events over the Ebro basin (NE Spain). A spatially dense precipitation data base with a high temporal resolution (15 min) was used. Global, local and geostatistical interpolation techniques were employed to produce maps of the rainfall erosivity indices, as well as mixed methods. To determine the reliability of the maps several goodness-of-fit and error statistics were computed, using a cross-validation scheme, as well as the uncertainty of the predictions, modeled by Gaussian geostatistical simulation. All methods were able to capture the general spatial pattern of both erosivity indices. The semivariogram analysis revealed that spatial autocorrelation only affected at distances of ~15 km around the observatories. Therefore, local interpolation techniques tended to be better overall considering the validation statistics. All models showed high uncertainty, caused by the high variability of rainfall erosivity indices both in time and space, what stresses the importance of having long data series with a dense spatial coverage.
Hydrological model performance and parameter estimation in the wavelet-domain
Authors: Schaefli B. , Zehe E.
Published: April 2010

Abstract. This paper proposes a method for rainfall-runoff model calibration and performance analysis in the wavelet-domain by fitting the estimated wavelet-power spectrum (a representation of the time-varying frequency content of a time series) of a simulated discharge series to the one of the corresponding observed time series. As discussed in this paper, calibrating hydrological models so as to reproduce the time-varying frequency content of the observed signal can lead to different results than parameter estimation in the time-domain. Therefore, wavelet-domain parameter estimation has the potential to give new insights into model performance and to reveal model structural deficiencies. We apply the proposed method to synthetic case studies and a real-world discharge modeling case study and discuss how model diagnosis can benefit from an analysis in the wavelet-domain. The results show that for the real-world case study of precipitation – runoff modeling for a high alpine catchment, the calibrated discharge simulation captures the dynamics of the observed time series better than the results obtained through calibration in the time-domain. In addition, the wavelet-domain performance assessment of this case study highlights the frequencies that are not well reproduced by the model, which gives specific indications about how to improve the model structure.
HESS Opinions "Classification of hydrological models for flood management"
Authors: Plate E. J.
Published: April 2010

Abstract. Hydrological models for flood management are components of flood risk management, which is the set of actions to be taken to prevent flood disasters. It is a cyclical process: initiated by occurrence of an extreme flood it leads through the reconstruction and rehabilitation phase to risk assessment and project planning and implementation, and finally to operation and preparedness for a next extreme flood when the cycle starts again. We subdivide the tasks of flood management into two consecutive parts: planning and operation, which basically require different kinds of hydrological models. For planning, real time runoff is not needed, one works with design scenarios. For this task models should be used appropriate to the tasks at hand, which reflect characteristics of landscape as well as of hydrological scale. For operation, hydrological forecast models are needed which have to meet a different set of conditions. In this paper, requirements for hydrological models as functions of application, geology and topography, and of area size are surveyed and classified, as a first approach for guiding users to the correct type of model to be used in a given location. It is suggested that one always should start flood modeling with an analysis of local conditions and select or develop task and locality specific models.
Field-scale apparent hydraulic parameterisation obtained from TDR time series and inverse modelling
Authors: Wollschläger U. , Pfaff T. , Roth K.
Published: April 2010

Abstract. Due to the large heterogeneity in the hydraulic properties of natural soils, estimation of field-scale hydraulic parameters is difficult. Past research revealed that data from accurate but small-scale laboratory measurements could hardly ever be transferred to the field scale. In this study, we explore an alternative approach where apparent hydraulic properties of a layered soil profile are directly estimated from hydraulic inverse modelling of a time series of in situ measured soil water contents obtained from time domain reflectometry. The data covered a one-year period with both wet and dry soil conditions. For the time period used for inversion, the model is able to reproduce the general evolution of water content in the different soil layers reasonably well. However, distinct drying and wetting events could not be reproduced in detail which we explain by the complicated natural processes that are not fully represented in the rather simple model. The study emphasises the importance of a correct average representation of the soil-atmosphere interaction.
Examining the effect of pore size distribution and shape on flow through unsaturated peat using computed tomography
Authors: Rezanezhad F. , Quinton W. L. , Price J. S. , Elrick D. , Elliot T. R. , Heck R. J.
Published: April 2010

Abstract. The hydraulic conductivity of unsaturated peat soil is controlled by the air-filled porosity, pore size and geometric distribution as well as other physical properties of peat materials. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT), at 45 μm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a sharp decline in hydraulic conductivity. This is because the large pores readily lose water, the peat rapidly becomes less conductive and the flow path among pores, more tortuous.
Modelling water-harvesting systems in the arid south of Tunisia using SWAT
Authors: Ouessar M. , Bruggeman A. , Abdelli F. , Mohtar R. H. , Gabriels D. , Cornelis W. M.
Published: April 2010

Abstract. In many arid countries, runoff water-harvesting systems support the livelihood of the rural population. Little is known, however, about the effect of these systems on the water balance components of arid watersheds. The objective of this study was to adapt and evaluate the GIS-based watershed model SWAT (Soil Water Assessment Tool) for simulating the main hydrologic processes in arid environments. The model was applied to the 270-km2 watershed of wadi Koutine in southeast Tunisia, which receives about 200 mm annual rain. The main adjustment for adapting the model to this dry Mediterranean environment was the inclusion of water-harvesting systems, which capture and use surface runoff for crop production in upstream subbasins, and a modification of the crop growth processes. The adjusted version of the model was named SWAT-WH. Model evaluation was performed based on 38 runoff events recorded at the Koutine station between 1973 and 1985. The model predicted that the average annual watershed rainfall of the 12-year evaluation period (209 mm) was split into ET (72%), groundwater recharge (22%) and outflow (6%). The evaluation coefficients for calibration and validation were, respectively, R2 (coefficient of determination) 0.77 and 0.44; E (Nash-Sutcliffe coefficient) 0.73 and 0.43; and MAE (Mean Absolute Error) 2.6 mm and 3.0 mm, indicating that the model could reproduce the observed events reasonably well. However, the runoff record was dominated by two extreme events, which had a strong effect on the evaluation criteria. Discrepancies remained mainly due to uncertainties in the observed daily rainfall and runoff data. Recommendations for future research include the installation of additional rainfall and runoff gauges with continuous data logging and the collection of more field data to represent the soils and land use. In addition, crop growth and yield monitoring is needed for a proper evaluation of crop production, to allow an economic assessment of the different water uses in the watershed.
Snow distribution over the Namco lake area of the Tibetan Plateau
Authors: Li M. , Ma Y. , Hu Z. , Ishikawa H. , Oku Y.
Published: April 2010

Abstract. The mesoscale snow distribution over the Namco lake area of the Tibetan Plateau on October 2005 has been investigated in this paper. The base and revised experiments were conducted using the Weather Research Model (WRF) with three nested grids that included a 1 km finest grid centered on the Namco station. Our simulation ran from 6 October through to 10 October 2005, which was concurrent with long term meteorological observations. Evaluation against boundary layer meteorological tower measurements and flux observations showed that the model captured the observed 2 m temperature and 10 m winds reasonably well in the revised experiment. The results suggest that output snow depth maximum amounts from two simulated experiments were centered downwind of the Namco lakeshore. Modified surface state variable, for example, surface skin temperature on the lake help to increase simulated credibility.
On the role of storm duration in the mapping of rainfall to flood return periods
Authors: Viglione A. , Blöschl G.
Published: April 2010

Abstract. While the correspondence of rainfall return period TP and flood return period TQ is at the heart of the design storm procedure, their relationship is still poorly understood. The purpose of this paper is to shed light on the controls on this relationship. To better understand the interplay of the controlling factors we assume a simplified world with block rainfall, constant runoff coefficient and linear catchment response. We use an analytical derived flood frequency approach in which, following design practise, TP is defined as the return period of the intensity-duration-frequency (IDF) curve given storm duration and depth. Results suggest that the main control on the mapping of rainfall to flood return periods is the ratio of storm duration and catchment response time, as would be expected. In the simple world assumed in this work, TQ is always smaller or equal than TP of the associated storm, i.e., TQ/TP≤1. This is because of the difference in the selectiveness of the rectangular filters used to construct the IDF curves and the unit hydrograph (UH) together with the fact that different rectangular filters are used when evaluating the storm return periods. The critical storm duration that maximises TQ/TP is, in descending importance, a function of the catchment response time and the distribution of storm duration, while the maximum value of TQ/TP is mainly a function of the coefficient of variation of storm duration. The study provides the basis for future analyses, where more complex cases will be examined.
Comparison of different base flow separation methods in a lowland catchment
Authors: Gonzales A. L. , Nonner J. , Heijkers J. , Uhlenbrook S.
Published: April 2010

Abstract. Assessment of water resources available in different storages and moving along different pathways in a catchment is important for its optimal use and protection, and also for the prediction of floods and low flows. Moreover, understanding of the runoff generation processes is essential for assessing the impacts of climate and land use changes on the hydrological response of a catchment. Many methods for base flow separation exist, but hardly one focuses on the specific behaviour of temperate lowland areas. This paper presents the results of a base flow separation study carried out in a lowland area in the Netherlands. In this study, field observations of precipitation, groundwater and surface water levels and discharges, together with tracer analysis are used to understand the runoff generation processes in the catchment. Several tracer and non-tracer based base flow separation methods were applied to the discharge time series, and their results are compared. The results show that groundwater levels react fast to precipitation events in this lowland area with shallow groundwater tables. Moreover, a good correlation was found between groundwater levels and discharges suggesting that most of the measured discharge also during floods comes from groundwater storage. It was estimated using tracer hydrological approaches that approximately 90% of the total discharge is groundwater displaced by event water mainly infiltrating in the northern part of the catchment, and only the remaining 10% is surface runoff. The impact of remote recharge causing displacement of near channel groundwater during floods could also be motivated with hydraulic approximations. The results show further that when base flow separation is meant to identify groundwater contributions to stream flow, process based methods (e.g. the rating curve method; Kliner and Knezek, 1974) are more reliable than other simple non-tracer based methods. Also, the recursive filtering method (proposed by Eckhardt, 2005) can be calibrated well using the results of tracer investigation giving good results. Consequently, non-tracer based base flow separation methods that can be validated for some events may provide a powerful tool for groundwater assessment or model calibration/validation in lowland areas.
Comparative predictions of discharge from an artificial catchment (Chicken Creek) using sparse data
Authors: Holländer H. M. , Blume T. , Bormann H. , Buytaert W. , Chirico G.B. , Exbrayat J.-F. , Gustafsson D. , Hölzel H. , Kraft P. , Stamm C. , Stoll S. , Blöschl G. , Flühler H.
Published: April 2010

Abstract. Ten conceptually different models in predicting discharge from the artificial Chicken Creek catchment in North-East Germany were used for this study. Soil texture and topography data were given to the modellers, but discharge data was withheld. We compare the predictions with the measurements from the 6 ha catchment and discuss the conceptualization and parameterization of the models. The predictions vary in a wide range, e.g. with the predicted actual evapotranspiration ranging from 88 to 579 mm/y and the discharge from 19 to 346 mm/y. The predicted components of the hydrological cycle deviated systematically from the observations, which were not known to the modellers. Discharge was mainly predicted as subsurface discharge with little direct runoff. In reality, surface runoff was a major flow component despite the fairly coarse soil texture. The actual evapotranspiration (AET) and the ratio between actual and potential ET was systematically overestimated by nine of the ten models. None of the model simulations came even close to the observed water balance for the entire 3-year study period. The comparison indicates that the personal judgement of the modellers was a major source of the differences between the model results. The most important parameters to be presumed were the soil parameters and the initial soil-water content while plant parameterization had, in this particular case of sparse vegetation, only a minor influence on the results.
Relative impacts of key drivers on the response of the water table to a major alley farming experiment
Authors: Noorduijn S. L. , Smettem K. R. J. , Vogwill R. , Ghadouani A.
Published: April 2010

Abstract. Widespread clearing of native vegetation in Southwest Western Australia has led to land degradation associated with rising groundwater, secondary salinisation and waterlogging. Re-establishing deep-rooted perennial vegetation across parts of the landscape is one technique for managing land degradation. Alley farming is an agroforestry practice where multiple perennial tree belts are planted in alternation with traditional agricultural crops. To identify the best configuration (belt width versus alley width) for controlling rising groundwater levels and providing viable economic returns, a large scale experiment was established in 1995. The experiment contains seven different alley farming designs, each with transects of piezometers running across tree belts into adjacent alleys to monitor changes in the groundwater level. Two control piezometers were also installed in an adjacent paddock. Groundwater at the site is shallow (<3 m) and of poor quality (pH 3–5, Ec 2.1–45.9 mS cm−1) so root water uptake from the saturated zone is limited. Simple hydrograph analysis could not separate treatment effects on the water table response. Subsequent statistical analysis revealed that 20–30% of the variability in the water table data over the 12 year study period was attributable to the alley farming experiment. To futher investigate the effect of the experiment on groundwater response, additional hydrograph analysis was conducted to compare the trends in the control piezometers in relation to those located within the belts. A difference of 0.9 m was observed between the mean groundwater levels in the control piezometers and the mean levels in the perennial belt piezometers. For a mean specific yield of 0.03 m3 m−3 (standard deviation of 0.03 m3 m−3) this equates to an additional average annual water use of 27 mm yr−1 (standard deviation of 33 mm yr−1) by the perennial agroforestry system. It is concluded that declining annual rainfall is the principal control on hydrograph response at the site, whilst perennial biomass development has a lesser impact on water table depth.
A framework for assessing flood frequency based on climate projection information
Authors: Raff D. A. , Pruitt T. , Brekke L. D.
Published: April 2010

Abstract. Flood safety is of the utmost concern for water resources management agencies charged with operating and maintaining reservoir systems. Risk evaluations guide design of infrastructure alterations or lead to potential changes in operations. Changes in climate may change the risk due to floods and therefore decisions to alter infrastructure with a life span of decades or longer may benefit from the use of climate projections as opposed to use of only historical observations. This manuscript presents a set of methods meant to support flood frequency evaluation based on current downscaled climate projections and the potential implications of changing flood risk on how evaluations are made. Methods are demonstrated in four case study basins: the Boise River above Lucky Peak Dam, the San Joaquin River above Friant Dam, the James River above Jamestown Dam, and the Gunnison River above Blue Mesa Dam. The analytical design includes three core elements: (1) a rationale for selecting climate projections to represent available climate projections; (2) generation of runoff projections consistent with climate projections using a process-based hydrologic model and temporal disaggregation of monthly downscaled climate projections into 6-h weather forcings required by the hydrologic model; and (3) analysis of flood frequency distributions based on runoff projection results. In addition to demonstrating the methodology, this paper also presents method choices under each analytical element, and the resulting implications to how flood frequencies are evaluated. The methods used reproduce the antecedent calibration period well. The approach results in a unidirectional shift in modeled flood magnitudes. The comparison between an expanding retrospective (current paradigm for flood frequency estimation) and a lookahead flood frequency approach indicate potential for significant biases in flood frequency estimation.
Modelling runoff at the plot scale taking into account rainfall partitioning by vegetation: application to stemflow of banana (Musa spp.) plant
Authors: Charlier J.-B. , Moussa R. , Cattan P. , Cabidoche Y.-M. , Voltz M.
Published: April 2010

Abstract. Rainfall partitioning by vegetation modifies the intensity of rainwater reaching the ground, which affects runoff generation. Incident rainfall is intercepted by the plant canopy and then redistributed into throughfall and stemflow. Rainfall intensities at the soil surface are therefore not spatially uniform, generating local variations of runoff production that are disregarded in runoff models. The aim of this paper was to model runoff at the plot scale, accounting for rainfall partitioning by vegetation in the case of plants concentrating rainwater at the plant foot and promoting stemflow. We developed a lumped modelling approach, including a stemflow function that divided the plot into two compartments: one compartment including stemflow and the related water pathways and one compartment for the rest of the plot. This stemflow function was coupled with a production function and a transfer function to simulate a flood hydrograph using the MHYDAS model. Calibrated parameters were a "stemflow coefficient", which compartmented the plot; the saturated hydraulic conductivity (Ks), which controls infiltration and runoff; and the two parameters of the diffusive wave equation. We tested our model on a banana plot of 3000 m2 on permeable Andosol (mean Ks=75 mm h−1) under tropical rainfalls, in Guadeloupe (FWI). Runoff simulations without and with the stemflow function were performed and compared to 18 flood events from 10 to 140 rainfall mm depth. Modelling results showed that the stemflow function improved the calibration of hydrographs according to the error criteria on volume and on peakflow, to the Nash and Sutcliffe coefficient, and to the root mean square error. This was particularly the case for low flows observed during residual rainfall, for which the stemflow function allowed runoff to be simulated for rainfall intensities lower than the Ks measured at the soil surface. This approach also allowed us to take into account the experimental data, without needing to calibrate the runoff volume on Ks parameter. Finally, the results suggest a rainwater redistribution module should be included in distributed runoff models at a larger scale of the catchment.
An evaluation of the Canadian global meteorological ensemble prediction system for short-term hydrological forecasting
Authors: Velázquez J. A. , Petit T. , Lavoie A. , Boucher M.-A. , Turcotte R. , Fortin V. , Anctil F.
Published: April 2010

Abstract. Hydrological forecasting consists in the assessment of future streamflow. Current deterministic forecasts do not give any information concerning the uncertainty, which might be limiting in a decision-making process. Ensemble forecasts are expected to fill this gap. In July 2007, the Meteorological Service of Canada has improved its ensemble prediction system, which has been operational since 1998. It uses the GEM model to generate a 20-member ensemble on a 100 km grid, at mid-latitudes. This improved system is used for the first time for hydrological ensemble predictions. Five watersheds in Quebec (Canada) are studied: Chaudière, Châteauguay, Du Nord, Kénogami and Du Lièvre. An interesting 17-day rainfall event has been selected in October 2007. Forecasts are produced in a 3 h time step for a 3-day forecast horizon. The deterministic forecast is also available and it is compared with the ensemble ones. In order to correct the bias of the ensemble, an updating procedure has been applied to the output data. Results showed that ensemble forecasts are more skilful than the deterministic ones, as measured by the Continuous Ranked Probability Score (CRPS), especially for 72 h forecasts. However, the hydrological ensemble forecasts are under dispersed: a situation that improves with the increasing length of the prediction horizons. We conjecture that this is due in part to the fact that uncertainty in the initial conditions of the hydrological model is not taken into account.
Deriving a global river network map and its sub-grid topographic characteristics from a fine-resolution flow direction map
Authors: Yamazaki D. , Oki T. , Kanae S.
Published: April 2010

Abstract. This paper proposes an improved method for converting a fine-resolution flow direction map into a coarse-resolution river network map for use in global river routing models. The proposed method attempts to preserve the river network structure of an original fine-resolution map in the upscaling procedure, as this has not been achieved with previous upscaling methods. We describe an improved method in which a downstream cell can be flexibly located on any cell in the river network map. The improved method preserves the river network structure of the original flow direction map and allows automated construction of river network maps at any resolution. Automated construction of a river network map is helpful for attaching sub-grid topographic information, such as realistic river meanderings and drainage boundaries, onto the upscaled river network map. The advantages of the proposed method are expected to enhance the ability of global river routing models by providing ways to more precisely represent surface water storage and movement.
Solid phase evolution in the Biosphere 2 hillslope experiment as predicted by modeling of hydrologic and geochemical fluxes
Authors: Dontsova K. , Steefel C. I. , Desilets S. , Thompson A. , Chorover J.
Published: April 2010

Abstract. A reactive transport geochemical modeling study was conducted to help predict the mineral transformations occurring over a ten year time-scale that are expected to impact soil hydraulic properties in the Biosphere 2 (B2) synthetic hillslope experiment. The modeling sought to predict the rate and extent of weathering of a granular basalt (selected for hillslope construction) as a function of climatic drivers, and to assess the feedback effects of such weathering processes on the hydraulic properties of the hillslope. Flow vectors were imported from HYDRUS into a reactive transport code, CrunchFlow2007, which was then used to model mineral weathering coupled to reactive solute transport. Associated particle size evolution was translated into changes in saturated hydraulic conductivity using Rosetta software. We found that flow characteristics, including velocity and saturation, strongly influenced the predicted extent of incongruent mineral weathering and neo-phase precipitation on the hillslope. Results were also highly sensitive to specific surface areas of the soil media, consistent with surface reaction controls on dissolution. Effects of fluid flow on weathering resulted in significant differences in the prediction of soil particle size distributions, which should feedback to alter hillslope hydraulic conductivities.
Linking soil- and stream-water chemistry based on a Riparian Flow-Concentration Integration Model
Authors: Seibert J. , Grabs T. , Köhler S. , Laudon H. , Winterdahl M. , Bishop K.
Published: April 2010

Abstract. The riparian zone, the last few metres of soil through which water flows before entering a gaining stream, has been identified as a first order control on key aspects of stream water chemistry dynamics. We propose that the distribution of lateral flow of water across the vertical profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates. This paper presents a mathematical implementation of this concept as well as the model assumptions. We also present an analytical solution, which provides a physical basis for the commonly used power-law flow-load equation. This approach quantifies the concept of riparian control on stream-water chemistry providing a basis for testing the concept of riparian control. By backward calculation of soil-water-chemistry profiles, and comparing those with observed profiles we demonstrate that the simple juxtaposition of the vertical profiles of water flux and soil water chemistry provides a plausible explanation for observed variations in stream water chemistry of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride. The "static" implementation of the model structure presented here provides a basis for further development to account for seasonal influences and hydrological hysteresis in the representation of hyporheic, riparian, and hillslope processes.
Variability of the groundwater sulfate concentration in fractured rock slopes: a tool to identify active unstable areas
Authors: Binet S. , Spadini L. , Bertrand C. , Guglielmi Y. , Mudry J. , Scavia C.
Published: April 2010

Abstract. Water chemical analysis of 100 springs from the Orco and the Tinée valleys (Western Italy and Southern France) and a 7 year groundwater chemistry monitoring of the 5 main springs were performed. All these springs drain from crystalline rock slopes. Some of these drain from currently active gravitational slope deformations. All groundwaters flowing through presently unstable slopes show anomalies in the sulfate concentrations compared to stable aquifers. Particularly, an increase of sulfate concentrations was observed repeatedly after each of five consecutive landslides on the La Clapière slope, thus attesting to the mechanical deformations are at the origin of this concentration change. Significant changes in the water chemistry are produced even from slow (mm/year) and low magnitude deformations of the geological settings. Pyrite nuclei in open fractures were found to be coated by iron oxides. This suggests that the increase of dissolved sulfate relates to oxidative dissolution of Pyrite. Speciation calculations of Pyrite versus Gypsum confirmed that observed changes in the sulfate concentrations is predominantly provided from Pyrite. Calculated amounts of dissolved minerals in the springs water was obtained through inverse modelling of the major ion water analysis data. It is shown that the concentration ratio of calculated dissolved Pyrite versus calculated dissolved gneiss rock allows us to unambiguously distinguish water from stable and unstable areas. This result opens an interesting perspective for the follow-up of sliding or friction dynamic in landslides or in (a) seismic faults.
Spatial variation in soil active-layer geochemistry across hydrologic margins in polar desert ecosystems
Authors: Barrett J. E. , Gooseff M. N. , Takacs-Vesbach C.
Published: April 2010

Abstract. Polar deserts are characterized by severe spatial-temporal limitations of liquid water. In soil active layers of the Antarctic Dry Valleys, liquid water is infrequently available over most of the arid terrestrial landscape. However, soils on the margins of glacial melt-water streams and lakes are visibly wet during the brief Austral summer when temperatures permit the existence of liquid water. We examined the role of these hydrologic margins as preferential zones for the transformation and transport of nutrient elements and solutes in an environment where geochemical weathering and biological activity is strictly limited by the dearth of liquid water. We report on hydropedological investigations of aquatic-terrestrial transition zones adjacent to 11 stream and lake systems in the Antarctic Dry Valleys. Our results show that wetted zones extended 1–11 m from the edges of lotic and lentic systems. While capillary demand and surface evaporation drive a one-way flux of water through these zones, the scale of these transition zones is determined by the topography and physical characteristics of the surrounding soils. Nutrient concentrations and fluxes appear to be influenced by both the hydrology and microbial-mediated biogeochemical processes. Salt concentrations are enriched near the distal boundary of the wetted fronts due to evapo-concentration of pore water in lake margin soils, while organic matter, ammonium and phosphate concentrations are highest in stream channel sediments where potential for biological activity is greatest. Thus, in the Antarctic Dry Valleys, intermittently wet soils on the margins of streams and lakes are important zones of both geochemical cycling and biological activity.