bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional-scale hydrological modelling using multiple-parameter landscape zones and a quasi-distributed water balance model
Authors: Wooldridge S. A. , Kalma J. D.
Published: April 2010

Abstract. Regional-scale catchments are characterised typically by natural variability in climatic and land-surface features. This paper addresses the important question regarding the appropriate level of spatial disaggregation necessary to guarantee a hydrologically sound consideration of this variability. Using a simple hydrologic model along with physical catchment data, the problem is reconsidered as a model parameter identification problem. With this manner of thinking the subjective nature as to what to include in the disaggregation scheme is removed and the problem reconsidered in terms of what can be supported by the available data. With such an approach the relative merit of different catchment disaggregation schemes is viewed in terms of their ability to provide constrained parameterisations that can be explained in terms of the physical processes deemed active within a catchment. The outlined methodology was tested for a regional-scale catchment, located in eastern Australia, and involved using the quasi-distributed VIC catchment model to recover the characteristic responses resulting from the disaggregation of the catchment into combinations of climate, soil and vegetation characteristics. A land-surface classification based on a combination of soil depth and land cover type was found to provide the most accurate streamflow predictions during a 10-year validation period. Investigation of the uncertainty associated with the predictions due to weakly identified parameters however, revealed that a simpler classification based solely on land cover actually provided a more robust parameterisation of streamflow response. The result alludes to the hydrological importance of distinguishing between forested and non-forested land cover types at the regional-scale, and suggests that given additional information soil-depth / storage considerations may also have proved significant. Improvements to the outlined method are discussed in terms of increasing the informative content available to differentiate between competing catchment responses. Keywords: regional-scale, spatial variability, disaggregation, hydrotype, quasi-distributed, parameterisation, uncertainty
Rainfall dynamics at different temporal scales: A chaotic perspective
Authors: Sivakumar B.
Published: April 2010

Abstract. This study of the behaviour of rainfall dynamics at different temporal scales identifies the type of approach most suitable for transformation of rainfall data from one scale to another. Rainfall data of four different temporal scales, i.e. daily, 2-day, 4-day and 8-day, observed over a period of about 25 years at the Leaf River basin, Mississippi, USA, are analysed. The correlation dimension method is employed to identify the behaviour of rainfall dynamics. The finite correlation dimensions obtained for the four rainfall series (4.82, 5.26, 6.42 and 8.87, respectively) indicate the possible existence of chaotic behaviour in the rainfall observed at the four scales. A possible implication of this might be that the rainfall processes at these scales are related through a chaotic (scale-invariant) behaviour. However, a comparison of the correlation dimension and coefficient of variation of each of the time series reveals an inverse relationship between the two (higher dimension for lower coefficient of variation and vice versa). The presence of a large number of zeros in the higher resolution time series (that could result in an underestimation of the dimension) and the possible presence of a higher level of noise in the lower resolution time series (that could result in an overestimation of the dimension) might account for such results. In view of these problems, it is concluded that the results must be verified using other chaos identification methods and the existence of chaos must be substantiated with additional evidence. Keywords: rainfall, chaos, scaling, correlation dimension, number of variables, coefficient of variation, data size, noise, zeros
Regional analysis using the Geomorphoclimatic Instantaneous Unit Hydrograph
Authors: Hall M. J. , Zaki A. F. , Shahin M. M. A.
Published: April 2010

Abstract. The construction of design flood hydrographs for ungauged drainage areas has traditionally been approached by regionalisation, i.e. the transfer of information from the gauged to the ungauged catchments in a region. Such approaches invariably depend upon the use of multiple linear regression analysis to relate unit hydrograph parameters to catchment characteristics and generalised rainfall statistics. The concept of the geomorphological instantaneous unit hydrograph (GIUH), in relating the shape and scale of the catchment transfer function to stream network topology and channel characteristics, offers an alternative methodology. GIUH derivation depends upon a series of assumptions, including that of estimating a "characteristic velocity"; these continue to attract attention and debate. However, if this velocity is expressed in terms of the kinematic wave approximation, the peak and time-to-peak of the IUH may be expressed in terms of a group of catchment and channel characteristics and the intensity of rainfall excess, giving the so-called geomorphoclimatic IUH (GCIUH). Previous studies involving the GCIUH have developed a single IUH relating to the total duration of rainfall excess. In this study, the rainfall excess duration was divided into several (equal) time increments, with separate IUHs being generated for each interval. This quasi-linear approach was applied to 105 storm events from nine catchments in the south-west of England, ranging in size from 6 to 420 (km)2 . The results showed that, providing the time interval chosen is fine enough to capture the shape of the runoff hydrographs, a comparable level of goodness-of-fit can be obtained for catchments covering a range of about 1:75 in area. The modified GCIUH approach as described is therefore recommended for further investigation and intercomparison with regression-based regionalisation methods. Keywords: floods; geomorphology; rainfall-runoff modelling
Fingerprinting of bed sediment in the Tay Estuary, Scotland: an environmental magnetism approach
Authors: Jenkins P. A. , Duck R. W. , Rowan J. S. , Walden J.
Published: April 2010

Abstract. Sediment fingerprinting is commonly used for sediment provenance studies in lakes, rivers and reservoirs and on hillslopes and floodplains. This investigation explores the mixing of terrestrial and marine-derived sediment in the Tay Estuary, Scotland, using mineral magnetic attributes for fingerprinting. Samples representative of the estuary sediments and of four sources (end-members) were subjected to a suite of magnetic susceptibility and remanence measurements. Sediment samples from the beds of the Rivers Tay and Earn represented fluvial inputs while samples from the Angus and Fife coasts represented marine input. Multivariate discriminant and factor analysis showed that the sources could be separated on the basis of six magnetic parameters in a simple multivariate unmixing model to identify source contributions to estuarine bed sediments. Multi-domain magnetite signatures, characteristic of unweathered bedrock, dominate the magnetic measurements. Overall contributions of 3% from the River Earn, 17% from the River Tay, 29% from the Angus coast and 51% from the Fife coast source end-members, demonstrated the present-day regime of marine sediment derivation in the Tay Estuary. However, this conceals considerable spatial variability both along-estuary and in terms of sub-environments, with small-scale variations in sediment provenance reflecting local morphology, particularly areas of channel convergence. Keywords: bed sediment, environmental magnetism, fingerprinting, Tay Estuary, Scotland
Identification of a change in climate state using regional flood data
Authors: Franks S. W.
Published: April 2010

Abstract. Flood frequency analysis typically assumes that annual floods arise from a single distribution and are independent. However, there is significant evidence for the existence of persistent climate modes. Timescales associated with climate variability range from inter-annual through to longer, multi-decadal time scales. In the case of the Australian climate, previous studies of the Indian and Pacific Oceans have indicated marked multi-decadal variability in both mean Sea Surface Temperatures (SST) and typical circulation patterns. In this light, data from 40 stream gauges around New South Wales are examined to determine whether flood frequency data are indeed independent and distributed identically. Given likely correlation in flood records between gauges, an assessment of the regional significance of observed changes in flood frequency is required. To achieve this, flood observations are aggregated into a regional index. A simple non-parametric test is then employed to identify the timing and magnitude of any change in mean annual flood. Finally, it is shown that the identified change in flood frequency corresponds directly to an observed shift in SST and mean circulation. These results demonstrate the role of natural variability in climate parameters and the need for an improved conceptual framework for flood frequency estimation. Keywords: Floods, flood frequency, climate variability, IPO, PDO, climate change
Application of a plane-stratified emission model to predict the effects of vegetation in passive microwave radiometry
Authors: Lee K. , Chawn Harlow R. , Burke E. J. , Shuttleworth W. J.
Published: April 2010

Abstract. This paper reports the application to vegetation canopies of a coherent model for the propagation of electromagnetic radiation through a stratified medium. The resulting multi-layer vegetation model is plausibly realistic in that it recognises the dielectric permittivity of the vegetation matter, the mixing of the dielectric permittivities for vegetation and air within the canopy and, in simplified terms, the overall vertical distribution of dielectric permittivity and temperature through the canopy. Any sharp changes in the dielectric profile of the canopy resulted in interference effects manifested as oscillations in the microwave brightness temperature as a function of canopy height or look angle. However, when Gaussian broadening of the top and bottom of the canopy (reflecting the natural variability between plants) was included within the model, these oscillations were eliminated. The model parameters required to specify the dielectric profile within the canopy, particularly the parameters that quantify the dielectric mixing between vegetation and air in the canopy, are not usually available in typical field experiments. Thus, the feasibility of specifying these parameters using an advanced single-criterion, multiple-parameter optimisation technique was investigated by automatically minimizing the difference between the modelled and measured brightness temperatures. The results imply that the mixing parameters can be so determined but only if other parameters that specify vegetation dry matter and water content are measured independently. The new model was then applied to investigate the sensitivity of microwave emission to specific vegetation parameters. Keywords: passive microwave, soil moisture, vegetation, SMOS, retrieval
Influence of vegetation on SMOS mission retrievals
Authors: Lee K. , Burke Eleanor J. , Shuttleworth W. , Harlow R.
Published: April 2010

Abstract. Using the proposed Soil Moisture and Ocean Salinity (SMOS) mission as a case study, this paper investigates how the presence and nature of vegetation influence the values of geophysical variables retrieved from multi-angle microwave radiometer observations. Synthetic microwave brightness temperatures were generated using a model for the coherent propagation of electromagnetic radiation through a stratified medium applied to account simultaneously for the emission from both the soil and any vegetation canopy present. The synthetic data were calculated at the look-angles proposed for the SMOS mission for three different soil-moisture states (wet, medium wet and dry) and four different vegetation covers (nominally grass, crop, shrub and forest). A retrieval mimicking that proposed for SMOS was then used to retrieve soil moisture, vegetation water content and effective temperature for each set of synthetic observations. For the case of a bare soil with a uniform profile, the simpler Fresnel model proposed for use with SMOS gave identical estimates of brightness temperatures to the coherent model. However, to retrieve accurate geophysical parameters in the presence of vegetation, the opacity coefficient (one of two parameters used to describe the effect of vegetation on emission from the soil surface) used within the SMOS retrieval algorithm needed to be a function of look-angle, soil-moisture status, and vegetation cover. The effect of errors in the initial specification of the vegetation parameters within the coherent model was explored by imposing random errors in the values of these parameters before generating synthetic data and evaluating the errors in the geophysical parameters retrieved. Random errors of 10% result in systematic errors (up to 0.5°K, 3%, and ~0.2 kg m-2 for temperature, soil moisture, and vegetation content, respectively) and random errors (up to ~2°K, ~8%, and ~2 kg m-2 for temperature, soil moisture and vegetation content, respectively) that depend on vegetation cover and soil-moisture status. Keywords: passive microwave, soil moisture, vegetation, SMOS, retrieval
Fitting and testing the significance of linear trends in Gumbel-distributed data
Authors: Clarke R. T.
Published: April 2010

Abstract. The widely-used hydrological procedures for calculating events with T-year return periods from data that follow a Gumbel distribution assume that the data sequence from which the Gumbel distribution is fitted remains stationary in time. If non-stationarity is suspected, whether as a consequence of changes in land-use practices or climate, it is common practice to test the significance of trend by either of two methods: linear regression, which assumes that data in the record have a Normal distribution with mean value that possibly varies with time; or a non-parametric test such as that of Mann-Kendall, which makes no assumption about the distribution of the data. Thus, the hypothesis that the data are Gumbel-distributed is temporarily abandoned while testing for trend, but is re-adopted if the trend proves to be not significant, when events with T-year return periods are then calculated. This is illogical. The paper describes an alternative model in which the Gumbel distribution has a (possibly) time-variant mean, the time-trend in mean value being determined, for the present purpose, by a single parameter β estimated by Maximum Likelihood (ML). The large-sample variance of the ML estimate ˆβMR is compared with the variance of the trend βLR calculated by linear regression; the latter is found to be 64% greater. Simulated samples from a standard Gumbel distribution were given superimposed linear trends of different magnitudes, and the power of each of three trend-testing procedures (Maximum Likelihood, Linear Regression, and the non-parametric Mann-Kendall test) were compared. The ML test was always more powerful than either the Linear Regression or Mann-Kendall test, whatever the (positive) value of the trend β; the power of the MK test was always least, for all values of β. Keywords: Extreme value probability distribution, Gumbel distribution, statistical stationarity, trend-testing procedures
Climate change impacts on nutrient loads in the Yorkshire Ouse catchment (UK)
Authors: Bouraoui F. , Galbiati L. , Bidoglio G.
Published: April 2010

Abstract. This study assessed the impact of potential climate change on the nutrient loads to surface and sub-surface waters from agricultural areas and was conducted using the Soil and Water Assessment Tool (SWAT) model. The study focused on a 3500 km2 catchment located in northern England, the Yorkshire Ouse. The SWAT model was calibrated and validated using sets of five years' measurements of nitrate and ortho-phosphorus concentrations and water flow. To increase the reliability of the hydrological model predictions, an uncertainty analysis was conducted by perturbing input parameters using a Monte-Carlo technique. The SWAT model was then run using a baseline scenario corresponding to an actual measured time series of daily temperature and precipitation, and six climate change scenarios. Because of the increase in temperature, all climate scenarios introduced an increase of actual evapotranspiration. Faster crop growth and an increased nutrient uptake resulted, as did an increase of annual losses of total nitrogen and phosphorus, however, with strong seasonal differences. Keywords: SWAT model, climate change, nutrient loads
Incorporation of groundwater losses and well level data in rainfall-runoff models illustrated using the PDM
Authors: Moore R. J. , Bell V. A.
Published: April 2010

Abstract. Intermittent streamflow is a common occurrence in permeable catchments, especially where there are pumped abstractions to water supply. Many rainfall-runoff models are not formulated so as to represent ephemeral streamflow behaviour or to allow for the possibility of negative recharge arising from groundwater pumping. A groundwater model component is formulated here for use in extending existing rainfall-runoff models to accommodate such ephemeral behaviour. Solutions to the Horton-Izzard equation resulting from the conceptual model of groundwater storage are adapted and the form of nonlinear storage extended to accommodate negative inputs, water storage below which outflow ceases, and losses to external springs and underflows below the gauged catchment outlet. The groundwater model component is demonstrated through using it as an extension of the PDM rainfall-runoff model. It is applied to the River Lavant, a catchment in Southern England on the English Chalk, where it successfully simulates the ephemeral streamflow behaviour and flood response together with well level variations. Keywords: groundwater, rainfall-runoff model, ephemeral stream, well level, spring, abstraction
An integrated simulation method for flash-flood risk assessment: 1. Frequency predictions in the Bisagno River by combining stochastic and deterministic methods
Authors: Rulli M.C. , Rosso R.
Published: April 2010

Abstract. A stochastic rainfall generator and a deterministic rainfall-runoff model, both distributed in space and time, are combined to provide accurate flood frequency prediction in the Bisagno River basin (Thyrrenian Liguria, N.W. Italy). The inadequacy of streamflow records with respect to the return period of the required flow discharges makes the stochastic simulation methodology a useful operational alternative to a regionalisation procedure for flood frequency analysis and derived distribution techniques. The rainfall generator is the Generalized Neyman-Scott Rectangular Pulses (GNSRP) model. The rainfall-runoff model is the FEST98 model. The GNSRP generator was calibrated using a continuous 7-years' record of hourly precipitation measurements at five raingauges scattered over the Bisagno basin. The calibrated rainfall model was then used to generate a 1000 years' series of continuous rainfall data at the gauging sites and a flood-oriented model validation procedure was developed to evaluate the agreement between observed and simulated extreme values of rainfall at different scales of temporal aggregation. The synthetic precipitation series were input to the FEST98 model to provide flood hydrographs at selected cross-sections across the river network. Flood frequency analysis of the annual flood series (AFS) obtained from these simulations was undertaken using L-moment estimations of Generalized Extreme Value (GEV) distributions. The results are compared with those determined by applying a regional flood analysis in Thyrrhenian Liguria and the derived distribution techniques to the Bisagno river basin. This approach is also useful to assess the effects of changes in land use on flood frequency regime (see Rosso and Rulli, 2002). Keywords: flood frequency, stochastic rainfall generator, distributed rainfall runoff model, derived distribution
Excess nitrogen leaching and C/N decline in the Tillingbourne catchment, southern England: INCA process modelling for current and historic time series
Authors: Whitehead P. G. , Lapworth D. J. , Skeffington R. A. , Wade A.
Published: April 2010

Abstract. Measurements of nitrate deposition and streamwater chemistry in the Tillingbourne Catchment, in Southern England, made in 1979-1982 and 1999-2001 show a 216% increase in Nitrogen leaching despite a reduction in N inputs. Both the historical and current data sets have been modelled using the Integrated Nitrogen Model in Catchments (INCA). The process-based model is shown to reproduce the historical patterns of N release from the catchment. However, modelling the increased leaching of N during recent years required an increase of the mineralisation control parameter in the model, suggesting enhanced mineralisation rates. Comparing historic and current soils data for C/N ratios shows that there has been a reduction in C/N from 38 to 26% in the humus layer and a reduction from 33 to 26% in the mineral soil horizon. This significant fall in C/N is consistent with the increase in N saturation in the H and Ah horizons of the major catchment soil. Keywords: acid deposition, recovery, nitrogen, Carbon-Nitrogen ratios, Tillingbourne, Thames, catchment studies, nutrient leaching, modelling
INCA Modelling of the Lee System: strategies for the reduction of nitrogen loads
Authors: Flynn N. J. , Paddison T. , Whitehead P. G.
Published: April 2010

Abstract. The Integrated Nitrogen Catchment model (INCA) was applied successfully to simulate nitrogen concentrations in the River Lee, a northern tributary of the River Thames for 1995-1999. Leaching from urban and agricultural areas was found to control nitrogen dynamics in reaches unaffected by effluent discharges and abstractions; the occurrence of minimal flows resulted in an upward trend in nitrate concentration. Sewage treatment works (STW) discharging into the River Lee raised nitrate concentrations substantially, a problem which was compounded by abstractions in the Lower Lee. The average concentration of nitrate (NO3) for the simulation period 1995-96 was 7.87 mg N l-1. Ammonium (NH4) concentrations were simulated less successfully. However, concentrations of ammonium rarely rose to levels which would be of environmental concern. Scenarios were run through INCA to assess strategies for the reduction of nitrate concentrations in the catchment. The conversion of arable land to ungrazed vegetation or to woodland would reduce nitrate concentrations substantially, whilst inclusion of riparian buffer strips would be unsuccessful in reducing nitrate loading. A 50% reduction in nitrate loading from Luton STW would result in a fall of up to 5 mg N l-1 in the reach directly affected (concentrations fell from maxima of 13 to 8 mg N l-1 , nearly a 40 % reduction), whilst a 20% reduction in abstractions would reduce maximum peaks in concentration in the lower Lee by up to 4 mg l-1 (from 17 to 13 mg N l-1, nearly a 25 % reduction),. Keywords: modelling, water quality, nitrogen, nitrate, ammonium, INCA, River Lee, River Thames, land-use.
The influence of riparian-hyporheic zone on the hydrological responses in an intermittent stream
Authors: Butturini A. , Bernal S. , Sabater S. , Sabater F.
Published: April 2010

Abstract. Stream and riparian groundwater hydrology has been studied in a small intermittent stream draining a forested catchment for a system representative of a Mediterranean climate. The relationship between precipitation and stream runoff and the interactions between stream water and the surrounding riparian groundwater have been analysed under a wide spectrum of meteorological conditions. The hypothesis that the hydrological condition of the near-stream groundwater compartment can regulate the runoff generation during precipitation events was tested. Stream runoff is characterised by a summer dry period, and precipitation input explained only 25% of runoff variability over the study period (r2 =0.25, d.f.=51, p<0.001). The variability of precipitation v. stream runoff is explained partly by the hydrogeological properties of the riparian near-stream zone. This zone is characterised by high hydrological conductivity values and abrupt changes in groundwater level in summer. The summer dry period begins with a rapid decrease in near-stream groundwater level, and ends just after the first autumnal rain when the original groundwater level recovers suddenly. Within this period, storms do not cause major stream runoff since water infiltrates rapidly into the riparian compartment until it is refilled during the subsequent winter and spring; then the precipitation explains the 80% of the stream runoff variability (r2=0.80, d.f.=34, p<0.001). These results suggest that the hydrological interaction between the riparian groundwater compartment and the stream channel is important in elucidating the hydrological responses during drought periods in small Mediterranean streams. Keywords: riparian zone, groundwater hydrology, runoff, intermittent stream, Mediterranean climate
A nitrogen model for European catchments: INCA, new model structure and equations
Authors: Wade A. J. , Durand P. , Beaujouan V. , Wessel W. W. , Raat K. J. , Whitehead P. G. , Butterfield D. , Rankinen K. , Lepisto A.
Published: April 2010

Abstract. A new version of the Integrated Nitrogen in Catchments model (INCA) was developed and tested using flow and streamwater nitrate concentration data collected from the River Kennet during 1998. INCA is a process-based model of the nitrogen cycle in the plant/soil and in-stream systems. The model simulates the nitrogen export from different land-use types within a river system, and the in-stream nitrate and ammonium concentrations at a daily time-step. The structure of the new version differs from the original, in that soil-water retention volumes have been added and the interface adapted to permit multiple crop and vegetation growth periods and fertiliser applications. The process equations are now written in terms of loads rather than concentrations allowing a more robust tracking of mass conservation when using numerical integration. The new version is able to reproduce the seasonal dynamics observed in the streamwater nitrogen concentration data, and the loads associated with plant/soil system nitrogen processes reported in the literature. As such, the model results suggest that the new structure is appropriate for the simulation of nitrogen in the River Kennet and an improvement on the original model. The utility of the INCA model is discussed in terms of improving scientific understanding and catchment management. Keywords: modelling, water quality, nitrogen, nitrate, River Kennet, River Thames
A region of influence approach to predicting flow duration curves within ungauged catchments
Authors: Holmes M. G. R. , Young A. R. , Gustard A. , Grew R.
Published: April 2010

Abstract. The development of regionalised hydrological models or procedures for estimating flow duration statistics has been the subject of international research since the 1970s. Historically these models have been based on multivariate statistical models that relate flow statistics to the physical and climatic characteristics of a catchment. The a priori classification of catchments has often been a component of this analysis. This paper discusses the background to the development of such models, with particular emphasis on the United Kingdom; it describes a new region of influence approach to estimating flow duration statistics and compares the performance of this method with current multivariate regression based methods for estimating flow duration statistics within the United Kingdom. Keywords: hydrological models, regionalisation, river networks, water resources, flow duration curves, region of influence
Strontium isotopic record of signatures of Holocene fluvial sediments in the Loire valley, France
Authors: Négrel P. , Kloppman W. , Garcin M. , Giot D.
Published: April 2010

Abstract. The distribution of Sr contents and isotopes of strontium Sr in the labile fraction of sediments from a channel fillings infill in the Middle Loire alluvial plain is used to highlight aspects of the evolution of the basin over the period from 10 000 yr. BP to the present. The acid extractable matter (AEM) in the sediment samples is variable in amount and in trace element contents. Carbonates and Fe–Mn oxyhydroxides are the principal carrying phases in the labile fraction. The historical record of 87Sr/86Sr ratio variations in AEM shows two components. In the first, the AEM is consistently low (around 10%) and the 87Sr/86Sr ratios range from around 0.7086 to 0.710. This corresponds to the hydrous Fe-Mn oxides endmember. Fe–Mn oxyhydroxides originate from the Massif Central and their 87Sr/86Sr ratios display a larger range than present day Fe–Mn oxides. Furthermore, the mixing proportions between Fe–Mn oxides generated on granitoids and on basalts fluctuated only weakly in the past. The second component has greater AEM (20–50%) and the 87Sr/86Sr ratio is almost constant at 0.709–0.7095. This corresponds to a carbonate endmember, clearly different from present day carbonates and may reflect the influence of both authigenic and detrital origins. The low 87Sr/86Sr ratio suggests a dominantly authigenic source for the carbonate endmember; this may be linked to groundwater inputs, although a minor influence from a secondary detrital source cannot be discounted. This reflects a different functioning of the river between deposition in the channel and the present day. Keywords: River Loire, Holocene, fluvial dynamics, geochemistry, strontium isotopes
Towards a comprehensive physically-based rainfall-runoff model
Authors: Liu Z. , Todini E.
Published: April 2010

Abstract. This paper introduces TOPKAPI (TOPographic Kinematic APproximation and Integration), a new physically-based distributed rainfall-runoff model deriving from the integration in space of the kinematic wave model. The TOPKAPI approach transforms the rainfall-runoff and runoff routing processes into three ‘structurally-similar’ non-linear reservoir differential equations describing different hydrological and hydraulic processes. The geometry of the catchment is described by a lattice of cells over which the equations are integrated to lead to a cascade of non-linear reservoirs. The parameter values of the TOPKAPI model are shown to be scale independent and obtainable from digital elevation maps, soil maps and vegetation or land use maps in terms of slope, soil permeability, roughness and topology. It can be shown, under simplifying assumptions, that the non-linear reservoirs aggregate into three reservoir cascades at the basin scale representing the soil, the surface and the drainage network, following the topographic and geomorphologic elements of the catchment, with parameter values which can be estimated directly from the small scale ones. The main advantage of this approach lies in its capability of being applied at increasing spatial scales without losing model and parameter physical interpretation. The model is foreseen to be suitable for land-use and climate change impact assessment; for extreme flood analysis, given the possibility of its extension to ungauged catchments; and last but not least as a promising tool for use with General Circulation Models (GCMs). To demonstrate the quality of the comprehensive distributed/lumped TOPKAPI approach, this paper presents a case study application to the Upper Reno river basin with an area of 1051 km2 based on a DEM grid scale of 200 m. In addition, a real-world case of applying the TOPKAPI model to the Arno river basin, with an area of 8135 km2 and using a DEM grid scale of 1000 m, for the development of the real-time flood forecasting system of the Arno river will be described. The TOPKAPI model results demonstrate good agreement between observed and simulated responses in the two catchments, which encourages further developments of the model. Keywords: rainfall-runoff modelling, topographic, kinematic wave approximation, spatial integration, physical meaning, non-linear reservoir model, distributed and lumped
Bayesian estimation of parameters in a regional hydrological model
Authors: Engeland K. , Gottschalk L.
Published: April 2010

Abstract. This study evaluates the applicability of the distributed, process-oriented Ecomag model for prediction of daily streamflow in ungauged basins. The Ecomag model is applied as a regional model to nine catchments in the NOPEX area, using Bayesian statistics to estimate the posterior distribution of the model parameters conditioned on the observed streamflow. The distribution is calculated by Markov Chain Monte Carlo (MCMC) analysis. The Bayesian method requires formulation of a likelihood function for the parameters and three alternative formulations are used. The first is a subjectively chosen objective function that describes the goodness of fit between the simulated and observed streamflow, as defined in the GLUE framework. The second and third formulations are more statistically correct likelihood models that describe the simulation errors. The full statistical likelihood model describes the simulation errors as an AR(1) process, whereas the simple model excludes the auto-regressive part. The statistical parameters depend on the catchments and the hydrological processes and the statistical and the hydrological parameters are estimated simultaneously. The results show that the simple likelihood model gives the most robust parameter estimates. The simulation error may be explained to a large extent by the catchment characteristics and climatic conditions, so it is possible to transfer knowledge about them to ungauged catchments. The statistical models for the simulation errors indicate that structural errors in the model are more important than parameter uncertainties. Keywords: regional hydrological model, model uncertainty, Bayesian analysis, Markov Chain Monte Carlo analysis
Assessment of terrigenous organic carbon input to the total organic carbon in sediments from Scottish transitional waters (sea lochs): methodology and preliminary results
Authors: Loh P. S. , Reeves A. D. , Overnell J. , Harvey S. M. , Miller A. E. J.
Published: April 2010

Abstract. This paper addresses the assessment of terrestrially derived organic carbon in sediments from two Scottish sea lochs. The results illustrate a smooth decrease in area-specific sediment oxygen uptake rates along a transect of six stations from the head of Loch Creran to the sea, from 18.7 mmol O2m-2d-1 to 6.6 mmol O2m-2d-1. Measurement of the losses on ignition at two temperatures (250°C and 500°C) of the sediment fraction from 1–2 cm depth at the same stations enabled the proportion of weight loss that occurred over the high temperature range to be calculated. These show a smooth increase from 0.33 to 0.62. These observations indicate that (a) the amount of easily biodegradable organic material in the sediment decreases by two-thirds along the transect and (b) the proportion of refractory organic material in the sediment increases along the same transect. This suggests strongly that terrigenous organic material, brought down by the River Creran is a very important fuel for sediment diagenetic processes in this system. Preliminary analyses of the lignin composition of the same sediments indicate the predominance of non-woody gymnosperm tissue. Lignin is used as a proxy for terrigenous allochthonous material. Comparative data for Loch Etive are also presented. Keywords: sedimentary organic carbon, Loch Creran, Loch Etive, oxygen uptake, lignin analysis
Wetland restoration and nitrate reduction: the example of the peri-urban wetland of Vitoria-Gasteiz (Basque Country, North Spain)
Authors: García-Linares C. , Martínez-Santos M. , Martínez-Bilbao V. , Sánchez-Pérez J. M. , Antiguedad I.
Published: April 2010

Abstract. Changes in land use and agricultural intensification caused wetlands on the quaternary aquifer of Vitoria-Gasteiz (Basque Country) to disappear some years ago and nitrate concentration in groundwaters increased very quickly. The Basque Government recently declared the East Sector of this aquifer a Vulnerable Zone according to the 91/676/CEE European Directive. Recently, the wetlands have been restored through the closure of the main drainage ditches, the consequent elevation of the water table and the abondonment of agricultural practices near the wetlands. This is the case of the Zurbano wetland. Restoration has allowed the recovery of its biogeochemical function, which has reduced nitrate concentrations in waters. Nitrate concentrations which exceed 50 mg l–1 in groundwaters entering into the wetland are less than 10 mg l–1 at the outlet. Conditions in the wetland are conducive to the loss of nitrates: organic matter rich wetted soils, clay presence allowing a local semiconfined flow and very low hydraulic gradient. Water quality monitoring at several points around the wetland showed the processes involved in nitrate loss, although some aspects still remain unresolved. However, during storm events, the wetland effectively reduces the nitrate concentration entering the Alegria River, the most important river on the quaternary aquifer. Keywords: restored wetland functionality, nitrate losses, Basque Country
Mitigation of negative ecological and socio-economic impacts of the Diama dam on the Senegal River Delta wetland (Mauritania), using a model based decision support system
Authors: Duvail S. , Hamerlynck O.
Published: April 2010

Abstract. Abstract: The delta of the River Senegal was modified substantially by the construction of the Diama dam in 1986 and the floodplain and estuarine areas on the Mauritanian bank were affected severely by the absence of floods. In 1994, managed flood releases were initiated in the Bell basin (4000 ha) of the Diawling National Park, as part of a rehabilitation effort. The basin was designated as a joint management area between traditional users and the Park authority and a revised management plan was developed through a participatory approach based on a topographical, hydro-climatic, ecological and socio-economic data. Hydraulic modelling was developed as a tool to support stakeholder negotiations on the desired characteristics of the managed flood releases. Initially, a water balance model was developed. The data were then integrated into a one-dimensional hydraulic model, MIKE 11 (DHI, 2000). When associated with a Digital Elevation Model and a Geographic Information System, (Arc View), the model provided a dynamic description of floods. Flood extent, water depth and flood duration data were combined with ecological and socio-economic data. The water requirements of the different stakeholders were converted to flood scenarios and the benefits and constraints analysed. A consensus scenario was reached through a participatory process. The volume of flood release required to restore the delta does not affect hydro-power generation, navigation or intensive irrigation, for which the dams in the basin were constructed. Hydraulic modelling provided useful inputs to stakeholder discussions and allows investigation of untested flood scenarios. Keywords: wetland restoration, water use conflicts, equity, Senegal River delta, Mauritania, Diawling National Park
The O and H stable isotope composition of freshwaters in the British Isles. 2. Surface waters and groundwater
Authors: Darling W. G. , Bath A. H. , Talbot J. C.
Published: April 2010

Abstract. The utility of stable isotopes as tracers of the water molecule has a long pedigree. The study reported here is part of an attempt to establish a comprehensive isotopic "baseline" for the British Isles as background data for a range of applications. Part 1 of this study (Darling and Talbot, 2003) considered the isotopic composition of rainfall in Britain and Ireland. The present paper is concerned with the composition of surface waters and groundwater. In isotopic terms, surface waters (other than some upland streams) are poorly characterised in the British Isles; their potential variability has yet to be widely used as an aid in hydrological research. In what may be the first study of a major British river, a monthly isotopic record of the upper River Thames during 1998 was obtained. This shows high damping of the isotopic variation compared to that in rainfall over most of the year, though significant fluctuations were seen for the autumn months. Smaller rivers such as the Stour and Darent show a more subdued response to the balance between runoff and baseflow. The relationship between the isotopic composition of rainfall and groundwater is also considered. From a limited database, it appears that whereas Chalk groundwater is a representative mixture of weighted average annual rainfall, for Triassic sandstone groundwater there is a seasonal selection of rainfall biased towards isotopically-depleted winter recharge. This may be primarily the result of physical differences between the infiltration characteristics of rock types, though other factors (vegetation, glacial history) could be involved. In the main, however, groundwaters appear to be representative of bulk rainfall within an error band of 0.5‰ δ18O. Contour maps of the δ18O and δ2H content of recent groundwaters in the British Isles show a fundamental SW-NE depletion effect modified by topography. The range of measured values, while much smaller than those for rainfall, still covers some ‰ for δ18O and 30‰ for δ2H. Over lowland areas the "altitude effect" is of little significance, but in upland areas is consistent with a range of –0.2 to –0.3‰ per 100 m increase in altitude. Groundwaters dating from the late Pleistocene are usually modified in δ18O and δ2H owing to the effects of climate change on the isotopic composition of rainfall and thus of recharge. Contour maps of isotopic variability prior to 10 ka BP, based on the relatively limited information available from the British Isles, allow a first comparison between groundwaters now and at the end of the last Ice Age. The position of the British Isles in the context of the stable isotope systematics of NW Europe is reviewed briefly. Keywords: Stable isotopes, surfacewaters, groundwater, British Isles
Estimation of parameters in a distributed precipitation-runoff model for Norway
Authors: Beldring S. , Engeland K. , Roald L. A. , Sælthun N. R. , Voksø A.
Published: April 2010

Abstract. A distributed version of the HBV-model using 1 km2 grid cells and daily time step was used to simulate runoff from the entire land surface of Norway for the period 1961-1990. The model was sensitive to changes in small scale properties of the land surface and the climatic input data, through explicit representation of differences between model elements, and by implicit consideration of sub-grid variations in moisture status. A geographically transferable set of model parameters was determined by a multi-criteria calibration strategy, which simultaneously minimised the residuals between model simulated and observed runoff from 141 Norwegian catchments located in areas with different runoff regimes and landscape characteristics. Model discretisation units with identical landscape classification were assigned similar parameter values. Model performance was evaluated by simulating discharge from 43 independent catchments. Finally, a river routing procedure using a kinematic wave approximation to open channel flow was introduced in the model, and discharges from three additional catchments were calculated and compared with observations. The model was used to produce a map of average annual runoff for Norway for the period 1961-1990. Keywords: distributed model, multi-criteria calibration, global parameters, ungauged catchments.
The role of a dambo in the hydrology of a catchment and the river network downstream
Authors: von der Heyden C. J. , New M. G.
Published: April 2010

Abstract. Dambos are shallow, seasonally inundated wetlands and are a widespread landform in Central and Southern Africa. Owing to their importance in local agriculture and as a water resource, the hydrology of dambos is of considerable interest: varied, and sometimes contradictory, hydrological characteristics have been described in the literature. The issues in contention focus on the role of the dambo in (i) the catchment evapotranspiration (ET) budget, (ii) flood flow retardation and attenuation, and (iii) sustaining dry season flow to the river down-stream. In addition, both rainfall and groundwater have been identified as the dominant source of water to the dambo and various hydrogeological models have been proposed to describe the hydrological functions of the landform. In this paper, hydrological and geochemical data collected over a full hydrological year are used to investigate and describe the hydrological functions of a dambo in north-western Zambia. The Penman estimate of wetland ET was less than the ET from the miombo-wooded interfluve and the wetland has been shown to have little effect on flood flow retardation or attenuation. Discharge of water stored within the wetland contributed little to the dry season flow from the dambo, which was sustained primarily by groundwater discharge. Flow in a perched aquifer within the catchment soils contributed a large portion of baseflow during the rains and early dry season. This source ceased by the mid dry season, implying that the sustained middle to late dry season streamflow from the wetland is through discharge of a deeper aquifer within the underlying regolith or bedrock. This hypothesis is tested through an analysis of groundwater and wetland geochemistry. Various physical parameters, PHREEQC model results and end member mixing analysis (EMMA) suggest strongly that the deep Upper Roan dolomite aquifer is the source of sustained discharge from the wetland. Keywords: dambo, hydrology, hydrogeology, stormflow, evapotranspiration, baseflow, sponge effect, Zambia
The role of wetlands in the hydrological cycle
Authors: Bullock A. , Acreman M.
Published: April 2010

Abstract. It is widely accepted that wetlands have a significant influence on the hydrological cycle. Wetlands have therefore become important elements in water management policy at national, regional and international level. There are many examples where wetlands reduce floods, recharge groundwater or augment low flows. Less recognised are the many examples where wetlands increase floods, act as a barrier to recharge, or reduce low flows. This paper presents a database of 439 published statements on the water quantity functions of wetlands from 169 studies worldwide. This establishes a benchmark of the aggregated knowledge of wetland influences upon downstream river flows and groundwater aquifers. Emphasis is placed on hydrological functions relating to gross water balance, groundwater recharge, base flow and low flows, flood response and river flow variability. The functional statements are structured according to wetland hydrological type and the manner in which functional conclusions have been drawn. A synthesis of functional statements establishes the balance of scientific evidence for particular hydrological measures. The evidence reveals strong concurrence for some hydrological measures for certain wetland types. For other hydrological measures, there is diversity of functions for apparently similar wetlands. The balance of scientific evidence that emerges gives only limited support to the generalised model of flood control, recharge promotion and flow maintenance by wetlands portrayed throughout the 1990s as one component of the basis for wetland policy formulation. That support is confined largely to floodplain wetlands, while many other wetland types perform alternate functions – partly or fully. This paper provides the first step towards a more scientifically defensible functional assessment system. Keywords: wetlands, hydrological functions, flood reduction, groundwater recharge, low flows, evaporation