bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of monsoon rainfall for a mesoscale catchment in North-West India II: stochastic rainfall simulations
Authors: Zehe E. , Singh A. K. , Bárdossy A.
Published: April 2010

Abstract. Within this study we present a robust method for generating precipitation time series for the Anas catchment in North Western India. The method employs a multivariate stochastic simulation model that is driven by a time series of objectively classified circulation patterns (CPs). In a companion study (Zehe et al., 2006) it was already shown that CPs classified from the 500 or 700 Hpa levels are suitable to explain space-time variability of precipitation in that area. The model is calibrated using observed rainfall time series for the period 1985–1992 for two different CP time series, one from the 500 Hpa level and the over from the 700 Hpa level, and 200 realizations of daily rainfall are simulated for the period 85–94. Simulations using the CPs from the 500 Hpa level as input yield a good match of the observed averages and standard deviations of daily rainfall. They show furthermore good performance at the monthly scale. When used with the 700 Hpa level CPs as inputs the model clearly underestimates the standard deviation and performs much worse at the monthly scale, especially in the validation period 93–94. The presented results give evidence that CPs from the 500 Hpa, level in combination with a multivariate stochastic model, make up a suitable tool for reducing the sparsity of precipitation data in developing regions with sparse hydro-meteorological data sets.
Novel evaporation experiment to determine soil hydraulic properties
Authors: Schneider K. , Ippisch O. , Roth K.
Published: April 2010

Abstract. A novel experimental approach to determine soil hydraulic material properties for the dry and very dry range is presented. Evaporation from the surface of a soil column is controlled by a constant flux of preconditioned air and the resulting vapour flux is measured by infrared absorption spectroscopy. The data are inverted under the assumptions that (i) the simultaneous movement of water in the liquid and vapour is represented by Richards' equation with an effective hydraulic conductivity and that (ii) the coupling between the soil and the well-mixed atmosphere can be modelled by a boundary layer with a constant transfer resistance. The optimised model fits the data exceptionally well. Remaining deviations during the initial phase of an experiment are thought to be well-understood and are attributed to the onset of the heat flow through the column which compensates the latent heat of evaporation.
Physically-based modelling of hydrological processes in a tropical headwater catchment (West Africa) – process representation and multi-criteria validation
Authors: Giertz S. , Diekkrüger B. , Steup G.
Published: April 2010

Abstract. The aim of the study was to test the applicability of a physically-based model to simulate the hydrological processes in a headwater catchment in Benin. Field investigations in the catchment have shown that lateral processes such as surface runoff and interflow are most important. Therefore, the 1-D SVAT-model SIMULAT was modified to a semi-distributed hillslope version (SIMULAT-H). Based on a good database, the model was evaluated in a multi-criteria validation using discharge, discharge components and soil moisture data. For the validation of discharge, good results were achieved for dry and wet years. The main differences were observable in the beginning of the rainy season. A comparison of the discharge components determined by hydro-chemical measurements with the simulation revealed that the model simulated the ratio of groundwater fluxes and fast runoff components correctly. For the validation of the discharge components of single events, larger differences were observable, which was partly caused by uncertainties in the precipitation data. The representation of the soil moisture dynamics by the model was good for the top soil layer. For deeper soil horizons, which are characterized by higher gravel content, the differences between simulated and measured soil moisture were larger. A good agreement of simulation results and field investigations was achieved for the runoff generation processes. Interflow is the predominant process on the upper and the middle slopes, while at the bottom of the hillslope groundwater recharge and – during the rainy season – saturated overland flow are important processes.
Simplified stochastic soil-moisture models: a look at infiltration
Authors: Rigby J. R. , Porporato A.
Published: April 2010

Abstract. A simplified, vertically-averaged model of soil moisture interpreted at the daily time scale and forced by a stochastic process of instantaneous rainfall events is compared with a vertically-averaged model which uses a non-overlapping rectangular pulse rainfall model and a more physically based description of infiltration. The models are compared with respect to the importance of short time-scale (intra-storm) variable infiltration in determining the probabilistic structure of soil-moisture dynamics at the daily time-scale. Differences in approach to infiltration modelling show only minor effects on the probabilistic structure of soil-moisture dynamics as simulated in the two models. The partitioning of losses during a single rainfall event are examined closely and the conditions under which surface-controlled runoff is significant, as a proportion of total losses, are delineated.
Measuring methods for groundwater – surface water interactions: a review
Authors: Kalbus E. , Reinstorf F. , Schirmer M.
Published: April 2010

Abstract. Interactions between groundwater and surface water play a fundamental role in the functioning of riparian ecosystems. In the context of sustainable river basin management it is crucial to understand and quantify exchange processes between groundwater and surface water. Numerous well-known methods exist for parameter estimation and process identification in aquifers and surface waters. Only in recent years has the transition zone become a subject of major research interest; thus, the need has evolved for appropriate methods applicable in this zone. This article provides an overview of the methods that are currently applied and described in the literature for estimating fluxes at the groundwater – surface water interface. Considerations for choosing appropriate methods are given including spatial and temporal scales, uncertainties, and limitations in application. It is concluded that a multi-scale approach combining multiple measuring methods may considerably constrain estimates of fluxes between groundwater and surface water.
Curvature distribution within hillslopes and catchments and its effect on the hydrological response
Authors: Bogaart P. W. , Troch P. A.
Published: April 2010

Abstract. Topographic convergence and divergence are first order controls on the hillslope and catchment hydrological response, as evidenced by similarity parameter analyses. Hydrological models often do not take convergence as measured by contour curvature directly into account; instead they use comparable measures like the topographic index, or the hillslope width function. This paper focuses on the question how hillslope width functions and contour curvature are related within the Plynlimon catchments, Wales. It is shown that the total width function of all hillslopes combined suggest that the catchments are divergent in overall shape, which is in contrast to the perception that catchments should be overall convergent. This so-called convergence paradox is explained by the effect of skewed curvature distributions and extreme curvatures near the channel network. The hillslope-storage Bossiness (hsB) model is used to asses the effect of within-hillslope convergence variability on the hydrological response. It is concluded that this effect is small, even when the soil saturation threshold is exceeded. Also described in this paper is a novel algorithm to compute flow path lengths on hillslopes towards the drainage network, using the multidirectional flow redistribution method.
Modelling subsurface storm flow with the Representative Elementary Watershed (REW) approach: application to the Alzette River Basin
Authors: Zhang G. P. , Savenije H. H. G. , Fenicia F. , Pfister L.
Published: April 2010

Abstract. A new domain, the macropore domain describing subsurface storm flow, has been introduced to the Representative Elementary Watershed (REW) approach. The mass balance equations have been reformulated and the closure relations associated with subsurface storm flow have been developed. The model code, REWASH, has been revised accordingly. With the revised REWASH, a rainfall-runoff model has been built for the Hesperange catchment, a sub-catchment of the Alzette River Basin. This meso-scale catchment is characterised by fast catchment response to precipitation, and subsurface storm flow is one of the dominant runoff generation processes. The model has been evaluated by a multi-criteria approach using both discharge and groundwater table data measured at various locations in the study site. It is demonstrated that subsurface storm flow contributes considerably to stream flow in the study area. Simulation results show that discharges measured along the main river course are well simulated and groundwater dynamics is well captured, suggesting that the model is a useful tool for catchment-scale hydrological analysis.
Biotic pump of atmospheric moisture as driver of the hydrological cycle on land
Authors: Makarieva A. M. , Gorshkov V. G.
Published: April 2010

Abstract. In this paper the basic geophysical and ecological principles are jointly analyzed that allow the landmasses of Earth to remain moistened sufficiently for terrestrial life to be possible. 1. Under gravity, land inevitably loses water to the ocean. To keep land moistened, the gravitational water runoff must be continuously compensated by the atmospheric ocean-to-land moisture transport. Using data for five terrestrial transects of the International Geosphere Biosphere Program we show that the mean distance to which air fluxes can transport moisture over non-forested areas, does not exceed several hundred kilometers; precipitation decreases exponentially with distance from the ocean. 2. In contrast, precipitation over extensive natural forests does not depend on the distance from the ocean along several thousand kilometers, as illustrated for the Amazon and Yenisey river basins and Equatorial Africa. This points to the existence of an active biotic pump transporting atmospheric moisture inland from the ocean. 3. Physical principles of the biotic moisture pump are investigated based on the previously unstudied properties of atmospheric water vapor, which can be either in or out of aerostatic equilibrium depending on the lapse rate of air temperature. A novel physical principle is formulated according to which the low-level air moves from areas with weak evaporation to areas with more intensive evaporation. Due to the high leaf area index, natural forests maintain high evaporation fluxes, which support the ascending air motion over the forest and "suck in" moist air from the ocean, which is the essence of the biotic pump of atmospheric moisture. In the result, the gravitational runoff water losses from the optimally moistened forest soil can be fully compensated by the biotically enhanced precipitation at any distance from the ocean. 4. It is discussed how a continent-scale biotic water pump mechanism could be produced by natural selection acting on individual trees. 5. Replacement of the natural forest cover by a low leaf index vegetation leads to an up to tenfold reduction in the mean continental precipitation and runoff, in contrast to the previously available estimates made without accounting for the biotic moisture pump. The analyzed body of evidence testifies that the long-term stability of an intense terrestrial water cycle is unachievable without the recovery of natural, self-sustaining forests on continent-wide areas.
Verification tools for probabilistic forecasts of continuous hydrological variables
Authors: Laio F. , Tamea S.
Published: April 2010

Abstract. In the present paper we describe some methods for verifying and evaluating probabilistic forecasts of hydrological variables. We propose an extension to continuous-valued variables of a verification method originated in the meteorological literature for the analysis of binary variables, and based on the use of a suitable cost-loss function to evaluate the quality of the forecasts. We find that this procedure is useful and reliable when it is complemented with other verification tools, borrowed from the economic literature, which are addressed to verify the statistical correctness of the probabilistic forecast. We illustrate our findings with a detailed application to the evaluation of probabilistic and deterministic forecasts of hourly discharge values.
Defining the climatic signal in stream salinity trends using the Interdecadal Pacific Oscillation and its rate of change
Authors: McNeil V. H. , Cox M. E.
Published: April 2010

Abstract. The impact of landuse on stream salinity is currently difficult to separate from the effect of climate, as the decadal scale climatic cycles in groundwater and stream hydrology have similar wavelengths to the landuse pattern. These hydrological cycles determine the stream salinity through accumulation or release of salt in the landscape. Widespread patterns apparent in stream salinity are discussed, and a link is demonstrated between stream salinity, groundwater levels and global climatic indicators. The Interdecadal Pacific Oscillation (IPO) has previously been investigated as a contributory climatic indicator for hydrological and related time series in the Southern Hemisphere. This study presents an approach which explores the rate of change in the IPO, in addition to its value, to define an indicator for the climate component of ambient shallow groundwater levels and corresponding stream salinity. Composite time series of groundwater level and stream salinity are compiled using an extensive but irregular database covering a wide geographical area. These are modelled with respect to the IPO and its rate of change to derive control time series. A example is given of how a stream salinity trend changes when the decadal climatic influence is removed.
The effectiveness of polder systems on peak discharge capping of floods along the middle reaches of the Elbe River in Germany
Authors: Huang S. , Rauberg J. , Apel H. , Disse M. , Lindenschmidt K.-E.
Published: April 2010

Abstract. In flood modelling, many one-dimensional (1-D) hydrodynamic models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2-D) models are very demanding in data requirements and computational resources. The latter is an important consideration when uncertainty analyses using the Monte Carlo techniques are to complement the modelling exercises. This paper describes the development of a quasi-2-D modeling approach, which still calculates the dynamic wave in 1-D but the discretisation of the computational units are in 2-D, allowing a better spatial representation of the flow in polders and avoiding large additional expenditure on data pre-processing and computational time. The model DYNHYD (1-D hydrodynamics) from the WASP5 modeling package was used as a basis for the simulations and extended to incorporate the quasi-2-D approach. A local sensitivity analysis shows the sensitivity of parameters and boundary conditions on the filling volume of polders and capping of the peak discharge in the main river system. Two flood events on the Elbe River, Germany were used to calibrate and test the model. The results show a good capping effect on the flood peak by the proposed systems. The effect of capping reduces as the flood wave propagates down stream from the polders (up to 0.5 cm of capping is decreased for each additional kilometer from the polder).
A conceptual investigation of process controls upon flood frequency: role of thresholds
Authors: Struthers I. , Sivapalan M.
Published: April 2010

Abstract. Traditional statistical approaches to flood frequency inherently assume homogeneity and stationarity in the flood generation process. This study illustrates the impact of heterogeneity associated with threshold non-linearities in the storage-discharge relationship associated with the rainfall-runoff process upon flood frequency behaviour. For a simplified, non-threshold (i.e. homogeneous) scenario, flood frequency can be characterised in terms of rainfall frequency, the characteristic response time of the catchment, and storm intermittency, modified by the relative strength of evaporation. The flood frequency curve is then a consistent transformation of the rainfall frequency curve, and could be readily described by traditional statistical methods. The introduction of storage thresholds, namely a field capacity storage and a catchment storage capacity, however, results in different flood frequency "regions" associated with distinctly different rainfall-runoff response behaviour and different process controls. The return period associated with the transition between these regions is directly related to the frequency of threshold exceedence. Where threshold exceedence is relatively rare, statistical extrapolation of flood frequency on the basis of short historical flood records risks ignoring this heterogeneity, and therefore significantly underestimating the magnitude of extreme flood peaks.
Towards a hydrological classification of European soils: preliminary test of its predictive power for the base flow index using river discharge data
Authors: Schneider M. K. , Brunner F. , Hollis J. M. , Stamm C.
Published: April 2010

Abstract. Predicting discharge in ungauged catchments or contaminant movement through soil requires knowledge of the distribution and spatial heterogeneity of hydrological soil properties. Because hydrological soil information is not available at a European scale, we reclassified the Soil Geographical Database of Europe (SGDBE) at 1:1 million in a hydrological manner by adopting the Hydrology Of Soil Types (HOST) system developed in the UK. The HOST classification describes dominant pathways of water movement through soil and was related to the base flow index (BFI) of a catchment (the long-term proportion of base flow on total stream flow). In the original UK study, a linear regression of the coverage of HOST classes in a catchment explained 79% of BFI variability. We found that a hydrological soil classification can be built based on the information present in the SGDBE. The reclassified SGDBE and the regression coefficients from the original UK study were used to predict BFIs for 103 catchments spread throughout Europe. The predicted BFI explained around 65% of the variability in measured BFI in catchments in Northern Europe, but the explained variance decreased from North to South. We therefore estimated new regression coefficients from the European discharge data and found that these were qualitatively similar to the original estimates from the UK. This suggests little variation across Europe in the hydrological effect of particular HOST classes, but decreasing influence of soil on BFI towards Southern Europe. Our preliminary study showed that pedological information is useful for characterising soil hydrology within Europe and the long-term discharge regime of catchments in Northern Europe. Based on these results, we draft a roadmap for a refined hydrological classification of European soils.
Threshold effects in catchment storm response and the occurrence and magnitude of flood events: implications for flood frequency
Authors: Kusumastuti D. I. , Struthers I. , Sivapalan M. , Reynolds D. A.
Published: April 2010

Abstract. The aim of this paper is to illustrate the effects of selected catchment storage thresholds upon runoff behaviour, and specifically their impact upon flood frequency. The analysis is carried out with the use of a stochastic rainfall model, incorporating rainfall variability at intra-event, inter-event and seasonal timescales, as well as infrequent summer tropical cyclones, coupled with deterministic rainfall-runoff models that incorporate runoff generation by both saturation excess and subsurface stormflow mechanisms. Changing runoff generation mechanisms (i.e. from subsurface flow to surface runoff) associated with a given threshold (i.e. saturation storage capacity) is shown to be manifested in the flood frequency curve as a break in slope. It is observed that the inclusion of infrequent summer storm events increases the temporal frequency occurrence and magnitude of surface runoff events, in this way contributing to steeper flood frequency curves, and an additional break in the slope of the flood frequency curve. The results of this study highlight the importance of thresholds on flood frequency, and provide insights into the complex interactions between rainfall variability and threshold nonlinearities in the rainfall-runoff process, which are shown to have a significant impact on the resulting flood frequency curves.
Modelling the spatial variability of snow water equivalent at the catchment scale
Authors: Skaugen T.
Published: April 2010

Abstract. The spatial distribution of snow water equivalent (SWE) is modelled as a two parameter gamma distribution. The parameters of the distribution are dynamical in that they are functions of the number of accumulation and melting events and the temporal correlation of accumulation and melting events. The estimated spatial variability is compared to snow course observations from the alpine catchments Norefjell and Aursunden in Southern Norway. A fixed snow course at Norefjell was measured 26 times during the snow season and showed that the spatial coefficient of variation change during the snow season with a decreasing trend from the start of the accumulation period and a sharp increase in the melting period. The gamma distribution with dynamical parameters reproduced the observed spatial statistical features of SWE well both at Norefjell and Aursunden. Also the shape of simulated spatial distribution of SWE agreed well with the observed at Norefjell. The temporal correlation tends to be positive for both accumulation and melting events. However, at the start of melting, a better fit between modelled and observed spatial standard deviation of SWE is obtained by using negative correlation between SWE and melt.
Neural network modelling of non-linear hydrological relationships
Authors: Abrahart R. J. , See L. M.
Published: April 2010

Abstract. Two recent studies have suggested that neural network modelling offers no worthwhile improvements in comparison to the application of weighted linear transfer functions for capturing the non-linear nature of hydrological relationships. The potential of an artificial neural network to perform simple non-linear hydrological transformations under controlled conditions is examined in this paper. Eight neural network models were developed: four full or partial emulations of a recognised non-linear hydrological rainfall-runoff model; four solutions developed on an identical set of inputs and a calculated runoff coefficient output. The use of different input combinations enabled the competencies of solutions developed on a reduced number of parameters to be assessed. The selected hydrological model had a limited number of inputs and contained no temporal component. The modelling process was based on a set of random inputs that had a uniform distribution and spanned a modest range of possibilities. The initial cloning operations permitted a direct comparison to be performed with the equation-based relationship. It also provided more general information about the power of a neural network to replicate mathematical equations and model modest non-linear relationships. The second group of experiments explored a different relationship that is of hydrological interest; the target surface contained a stronger set of non-linear properties and was more challenging. Linear modelling comparisons were performed against traditional least squares multiple linear regression solutions developed on identical datasets. The reported results demonstrate that neural networks are capable of modelling non-linear hydrological processes and are therefore appropriate tools for hydrological modelling.
Riverine transport of biogenic elements to the Baltic Sea – past and possible future perspectives
Authors: Humborg C. , Mörth C.-M. , Sundbom M. , Wulff F.
Published: April 2010

Abstract. The paper reviews critical processes for the land-sea fluxes of biogenic elements (C, N, P, Si) in the Baltic Sea catchment and discusses possible future scenarios as a consequence of improved sewage treatment, agricultural practices and increased hydropower demand (for N, P and Si) and of global warming, i.e., changes in hydrological patterns (for C). These most significant drivers will not only change the total amount of nutrient inputs and fluxes of organic and inorganic forms of carbon to the Baltic Sea, their ratio (C:N:P:Si) will alter as well with consequences for phytoplankton species composition in the Baltic Sea. In summary, we propose that N fluxes may increase due to higher livestock densities in those countries recently acceded to the EU, whereas P and Si fluxes may decrease due to an improved sewage treatment in these new EU member states and with further damming and still eutrophic states of many lakes in the entire Baltic Sea catchment. This might eventually decrease cyanobacteria blooms in the Baltic but increase the potential for other nuisance blooms. Dinoflagellates could eventually substitute diatoms that even today grow below their optimal growth conditions due to low Si concentrations in some regions of the Baltic Sea. C fluxes will probably increase from the boreal part of the Baltic Sea catchment due to the expected higher temperatures and heavier rainfall. However, it is not clear whether dissolved organic carbon and alkalinity, which have opposite feedbacks to global warming, will increase in similar amounts, because the spring flow peak will be smoothed out in time due to higher temperatures that cause less snow cover and deeper soil infiltration.
Unsupervised classification of saturated areas using a time series of remotely sensed images
Authors: de Alwis D. A. , Easton Z. M. , Dahlke H. E. , Philpot W. D. , Steenhuis T. S.
Published: April 2010

Abstract. The spatial distribution of saturated areas is an important consideration in numerous applications, such as water resource planning or siting of management practices. However, in humid well vegetated climates where runoff is produced by saturation excess processes on hydrologically active areas (HAA) the delineation of these areas can be difficult and time consuming. A technique that can simply and reliably predict these areas would be a powerful tool for scientists and watershed managers tasked with implementing practices to improve water quality. Remotely sensed data is a source of spatial information and could be used to identify HAAs. This study describes a methodology to determine the spatial variability of saturated areas using a temporal sequence of remotely sensed images. The Normalized Difference Water Index (NDWI) was derived from medium resolution Landsat 7 ETM+ imagery collected over seven months in the Town Brook watershed in the Catskill Mountains of New York State and used to characterize the areas susceptible to saturation. We found that within a single land cover, saturated areas were characterized by the soil surface water content when the vegetation was dormant and leaf water content of the vegetation during the growing season. The resulting HAA map agreed well with both observed and spatially distributed computer simulated saturated areas (accuracies from 49 to 79%). This methodology shows that remote sensing can be used to capture temporal variations in vegetation phenology as well as spatial/temporal variation in surface water content, and appears promising for delineating saturated areas in the landscape.
Controls on runoff generation and scale-dependence in a distributed hydrologic model
Authors: Vivoni E. R. , Entekhabi D. , Bras R. L. , Ivanov V. Y.
Published: April 2010

Abstract. Hydrologic response in natural catchments is controlled by a set of complex interactions between storm properties, basin characteristics and antecedent wetness conditions. This study investigates the transient runoff response to spatially-uniform storms of varying properties using a distributed model of the coupled surface-subsurface system, which treats heterogeneities in topography, soils and vegetation. We demonstrate the control that the partitioning into multiple runoff mechanisms (infiltration-excess, saturation-excess, perched return flow and groundwater exfiltration) has on nonlinearities in the rainfall-runoff transformation and its scale-dependence. Antecedent wetness imposed through a distributed water table position is varied to illustrate its effect on runoff generation. Results indicate that transitions observed in basin flood response and its nonlinear and scale-dependent behavior can be explained by shifts in the surface-subsurface partitioning. An analysis of the spatial organization of runoff production also shows that multiple mechanisms have specific catchment niches and can occur simultaneously in the basin. In addition, catchment scale plays an important role in the distribution of runoff production as basin characteristics (soils, vegetation, topography and initial wetness) are varied with basin area. For example, we illustrate how storm characteristics and antecedent wetness play an important role in the scaling properties of the catchment runoff ratio.
Rivers we can't bring ourselves to clean – historical insights into the pollution of the Moselle River (France), 1850–2000
Authors: Garcier R. J.
Published: April 2010

Abstract. As products of both natural and social systems, rivers are highly complex historical objects. We show in this paper that historical analysis works on two different levels: one level, which we call "structural", shows the materiality of the riverine environment as the spatial-temporal product of natural factors and human impacts (bed and course alterations, pollution, etc.). On a second level –"semiotic" – we show that river systems are also social constructs and the subjects of ancient and diverse management practices. The quality of a river will be a function of the dialectical interaction between both levels. Historical analysis can uncover the inherited constraints that bear upon current management practices. To help substantiate this analytical framework, we analyse the case of the Moselle river in eastern France by using archival sources and statistical data. Severely impaired by industrial discharges from iron, coal and salt industries between the 1875s and the early 1980s, the waters of the Moselle became the subject of a social consensus between stakeholders that prevented the implementation of efficient pollution management policies until the 1990s. The example urges caution on the pervasiveness of participatory approaches to river management: social consensus does not necessarily benefit the environment.
Determination of the historical variation of the trophic state in lakes using sediment stratigraphies
Authors: Olli G.
Published: April 2010

Abstract. Biogenic silica (BSi) and phosphorous (P) accumulation were investigated in sediment cores from Karlskärsviken, a bay of Lake Mälaren. The aim was to make use of BSi and P relations in sediment stratigraphies in order to investigate the historical nutrient trophy in a near shore lake environment since the Middle Ages, with focus on industrial times, and to evaluate anthropogenic influences on the bay's trophic state. The BSi accumulation in the sediments is a better indicator of former nutrient pelagic trophy than P accumulation in sediments and for this reason a BSi inferred P (BSi-P) water concentration is calculated. This method enables the determination of the background total phosphorous (TP) concentration (which is related to the reference conditions) in the investigated bay; this background TP is determined equal to 0.020–0.022 mg L−1. There is an increasing trend of BSi-P concentration in the bay since the Middle Ages to the present, about 0.025 mg L−1, with a small decrease in the inner bay section during the last decades. The P accumulation rate is not found to have changed since the 1960s and 1970s, which indicates that the P loading to Karlskärsviken has not decreased. In Karlskärsviken, the shallow inner section of the bay, where the water quality is dominated by loading from the bay catchment area, is less nutritious than the water in the outer section, which is influenced by the main streams from the western part of Lake Mälaren.
Soft combination of local models in a multi-objective framework
Authors: Fenicia F. , Solomatine D. P. , Savenije H. H. G. , Matgen P.
Published: April 2010

Abstract. Conceptual hydrologic models are useful tools as they provide an interpretable representation of the hydrologic behaviour of a catchment. Their representation of catchment's hydrological processes and physical characteristics, however, implies a simplification of the complexity and heterogeneity of reality. As a result, these models may show a lack of flexibility in reproducing the vast spectrum of catchment responses. Hence, the accuracy in reproducing certain aspects of the system behaviour may be paid in terms of a lack of accuracy in the representation of other aspects. By acknowledging the structural limitations of these models, we propose a modular approach to hydrological simulation. Instead of using a single model to reproduce the full range of catchment responses, multiple models are used, each of them assigned to a specific task. While a modular approach has been previously used in the development of data driven models, in this study we show an application to conceptual models. The approach is here demonstrated in the case where the different models are associated with different parameter realizations within a fixed model structure. We show that using a "composite" model, obtained by a combination of individual "local" models, the accuracy of the simulation is improved. We argue that this approach can be useful because it partially overcomes the structural limitations that a conceptual model may exhibit. The approach is shown in application to the discharge simulation of the experimental Alzette River basin in Luxembourg, with a conceptual model that follows the structure of the HBV model.
Assessment of alternative land management practices using hydrological simulation and a decision support tool: Arborea agricultural region, Sardinia
Authors: Cau P. , Paniconi C.
Published: April 2010

Abstract. Quantifying the impact of land use on water supply and quality is a primary focus of environmental management. In this work we apply a semidistributed hydrological model (SWAT) to predict the impact of different land management practices on water and agricultural chemical yield over a long period of time for a study site situated in the Arborea region of central Sardinia, Italy. The physical processes associated with water movement, crop growth, and nutrient cycling are directly modeled by SWAT. The model simulations are used to identify indicators that reflect critical processes related to the integrity and sustainability of the ecosystem. Specifically we focus on stream quality and quantity indicators associated with anthropogenic and natural sources of pollution. A multicriteria decision support system is then used to develop the analysis matrix where water quality and quantity indicators for the rivers, lagoons, and soil are combined with socio-economic variables. The DSS is used to assess four options involving alternative watersheds designated for intensive agriculture and dairy farming and the use or not of treated wastewater for irrigation. Our analysis suggests that of the four options, the most widely acceptable consists in the transfer of intensive agricultural practices to the larger watershed, which is less vulnerable, in tandem with wastewater reuse, which rates highly due to water scarcity in this region of the Mediterranean. More generally, the work demonstrates how both qualitative and quantitative methods and information can assist decision making in complex settings.
Hydrological model coupling with ANNs
Authors: Kamp R. G. , Savenije H. H. G.
Published: April 2010

Abstract. There is an increasing need for model coupling. However, model coupling is complicated. Scientists develop and improve models to represent physical processes occurring in nature. These models are built in different software programs required to run the model. A software program or application represents part of the system knowledge. This knowledge is however encapsulated in the program and often difficult to access. In integrated water resources management it is often necessary to connect hydrological, hydraulic or ecological models. Model coupling can in practice be difficult for many reasons related to data formats, compatibility of scales, ability to modify source codes, etc. Hence, there is a need for an efficient and cost effective approach to model-coupling. Artificial neural networks (ANNs) can be used as an alternative to replace a model and simulate the model's output and connect it to other models. In this paper, we investigate an alternative to traditional model coupling techniques. ANNs are four different models: a rainfall runoff model, a river channel routing model, an estuarine salt intrusion model, and an ecological model. The output results of each model is simulated by a neural network that is trained on corresponding input and output data sets. The models are connected in cascade and their input and output variables are connected. To test the results of the coupled neural network also a coupled system of four sub-system models has been set-up. These results have been compared to the results of the coupled neural networks. The results show that it is possible to train neural networks and connect these models. The results of the salt intrusion model was however not very accurate. It was difficult for the neural network to represent both short term (tidal) and long term (hydrological) processes.
Dissolved iodine in rainfall, cloud, stream and groundwater in the Plynlimon area of mid-Wales
Authors: Neal C. , Neal M. , Wickham H. , Hill L. , Harman S.
Published: April 2010

Abstract. Iodine concentrations in rainfall, cloud water, throughfall, stemflow, stream water and groundwater are described for the upper River Severn Plynlimon catchments in mid-Wales. Iodine concentrations average 1.55 µg l−1 in rainfall while the corresponding averages of iodine concentrations in cloud water, throughfall and stemflow iodine concentrations are three to eight times higher. For the atmospheric inputs, there are both marine and anthropogenic sources while, for stemflow and throughfall, humic substances may be a dominant component. The average concentrations in the streams and groundwaters vary between 1.00 to 4.22 µg l−1 and 0.57 to 8.51 µg l−1, respectively. The higher averages are for waters associated with gley soils that are high in dissolved organic carbon (DOC). For the streams draining forested catchments, iodine concentrations have increased over time, probably due to wetting up of the soils because of reduction in transpiration as the trees are maturing and felling activities. The increases vary between 0.025±0.003 and 0.044±0.010 µg l−1 per year and are associated partly with an increase in DOC concentration: adjusted for the effect of DOC, the increases range between 0.013±0.003 and 0.023±0.009 µg l−1 per year. For the moorland areas, no such trend is observed but the value is lower. For most of the Plynlimon catchments, a net uptake of iodine of around 40% is lower for streams draining gley soils with even a net export for the smaller streams. Within the streams, iodine concentrations are highly correlated with DOC and there is an annual cycle of iodine and DOC concentration change, with maxima between July and November. For the groundwaters, a loss of iodine and DOC relative to the streams probably reflects within catchment losses in the lower inorganic soils and bedrock areas. However, in one case, groundwater iodine concentrations were relatively high and this coincided with high DOC concentrations.
The role of catchment characteristics in determining surface water nitrogen in four upland regions in the UK
Authors: Helliwell R. C. , Coull M. C. , Davies J. J. L. , Evans C. D. , Norris D. , Ferrier R. C. , Jenkins A. , Reynolds B.
Published: April 2010

Abstract. Hydrochemical and catchment data from 80 upland moorland sites in four regions with contrasting climate, soils, geology and geomorphology have been analysed to assess the key catchment attributes that influence enhanced leaching of soluble nitrogen to surface waters. The regions are the South Pennines of northern England, the Snowdonia National Park in north Wales, the Galloway region of south-west Scotland and the Mourne Mountains in Northern Ireland, all highly acidified, with median pH values of <5.5. Linear regression of mean summer and winter concentrations for nitrate (NO3−), ammonium (NH4+), dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) were expressed as functions of catchment attributes. Nitrate concentrations in waters draining catchments dominated by peaty soils (large C pool) were much less than those in catchments dominated by mineral soils (small C pool). Hence, if future N deposition levels are maintained or increase, high-altitude catchments with small carbon pools are potentially more susceptible to NO3− leaching. All N species exhibit seasonality; this is most marked in Galloway and least marked in the South Pennines, which implies that the South Pennines have reached an advanced stage of N saturation. Surface water inorganic N concentrations and the ratio of dissolved organic carbon (DOC) to dissolved organic N (DON) can be related to deposition inputs, although relationships differ throughout the year. If the DOC/DON ratio is indicative of catchment N saturation, levels of N retention are at least partially determined by deposition levels. This study identifies N deposition as a major inter-regional control on the degree of catchment N saturation and on N leaching to surface waters; it stresses the importance of catchment factors in modifying the relationship between N deposition and leaching in acid sensitive UK upland catchments.
Estimating nutrient concentrations from catchment characteristics across the UK
Authors: Davies H. , Neal C.
Published: April 2010

Abstract. Within a Geographical Information System (GIS) framework, the distributions of nitrate and orthophosphate concentrations at monitoring sites across the UK were examined and empirical relationships with catchment characteristics were established. The mean orthophosphate concentrations were linked strongly with the urban component, and less significantly with effective rainfall and agricultural coverage. This is of strategic importance in relation to phosphorus and the Water Framework Directive. Correspondingly, mean nitrate concentrations were linked to land-use types, base flow index and effective rainfall. Within-catchment residence times and effective-rainfall (runoff) were important in relation to nitrate. The issue of nitrate and the Water Framework Directive is more complex than that for orthophosphate and involves a strong agricultural as well as an urban component.
Towards benchmarking an in-stream water quality model
Authors: Boorman D. B.
Published: April 2010

Abstract. A method of model evaluation is presented which utilises a comparison with a benchmark model. The proposed benchmarking concept is one that can be applied to many hydrological models but, in this instance, is implemented in the context of an in-stream water quality model. The benchmark model is defined in such a way that it is easily implemented within the framework of the test model, i.e. the approach relies on two applications of the same model code rather than the application of two separate model codes. This is illustrated using two case studies from the UK, the Rivers Aire and Ouse, with the objective of simulating a water quality classification, general quality assessment (GQA), which is based on dissolved oxygen, biochemical oxygen demand and ammonium. Comparisons between the benchmark and test models are made based on GQA, as well as a step-wise assessment against the components required in its derivation. The benchmarking process yields a great deal of important information about the performance of the test model and raises issues about a priori definition of the assessment criteria.
Self-similar pattern formation and continuous mechanics of self-similar systems
Authors: Dyskin A. V.
Published: April 2010

Abstract. In many cases, the critical state of systems that reached the threshold is characterised by self-similar pattern formation. We produce an example of pattern formation of this kind – formation of self-similar distribution of interacting fractures. Their formation starts with the crack growth due to the action of stress fluctuations. It is shown that even when the fluctuations have zero average the cracks generated by them could grow far beyond the scale of stress fluctuations. Further development of the fracture system is controlled by crack interaction leading to the emergence of self-similar crack distributions. As a result, the medium with fractures becomes discontinuous at any scale. We develop a continuum fractal mechanics to model its physical behaviour. We introduce a continuous sequence of continua of increasing scales covering this range of scales. The continuum of each scale is specified by the representative averaging volume elements of the corresponding size. These elements determine the resolution of the continuum. Each continuum hides the cracks of scales smaller than the volume element size while larger fractures are modelled explicitly. Using the developed formalism we investigate the stability of self-similar crack distributions with respect to crack growth and show that while the self-similar distribution of isotropically oriented cracks is stable, the distribution of parallel cracks is not. For the isotropically oriented cracks scaling of permeability is determined. For permeable materials (rocks) with self-similar crack distributions permeability scales as cube of crack radius. This property could be used for detecting this specific mechanism of formation of self-similar crack distributions.
New technique to measure forest floor interception – an application in a beech forest in Luxembourg
Authors: Gerrits A. M. J. , Savenije H. H. G. , Hoffmann L. , Pfister L.
Published: April 2010

Abstract. In hydrological models, evaporation from interception is often disregarded, combined with transpiration, or taken as a fixed percentage of rainfall. In general interception is not considered to be a significant process in rainfall-runoff modelling. However, it appears that on average interception can amount to 20–50% of the precipitation. Therefore, knowledge about the process of interception is important. Traditional research on interception mainly focuses on canopy interception and almost completely denies forest floor interception, although this is an important mechanism that precedes infiltration or runoff. Forest floor interception consists partly of interception by dry soil, partly of interception by short vegetation (mosses, grasses and creeping vegetation) and partly of interception by litter. This research project concentrates on litter interception: to measure its quantities at point scale and subsequently to upscale it to that of a hydrotope. A special measuring device has been developed, which consists of a permeable upper basin filled with forest floor, and a watertight lower basin. Both are weighed continuously. The device has been tested in the Huewelerbach catchment (Luxembourg). The preliminary measuring results show that the device is working properly. For November 2004, evaporation from interception was calculated to be 14 mm of 42 mm throughfall (i.e., 34%).