bluuebunny/crossref_metadata_2025 huggingface dataset:
The Dutch secret: safe drinking water without chlorine in the Netherlands
Authors: Smeets P. W. M. H. , Medema G. J. , van Dijk J. C.
Published: April 2010

Abstract. The Netherlands is one of the few countries where chlorine is not used at all, neither for primary disinfection nor to maintain a residual disinfectant in the distribution network. The Dutch approach that allows production and distribution of drinking water without the use of chlorine while not compromising microbial safety at the tap, can be summarized as follows: Use the best source available, in order of preference: – microbiologically safe groundwater, – surface water with soil passage such as artificial recharge or bank filtration, – direct treatment of surface water in a multiple barrier treatment; Use a preferred physical process treatment such as sedimentation, filtration and UV-disinfection. If absolutely necessary, also oxidation by means of ozone or peroxide can be used, but chlorine is avoided; Prevent ingress of contamination during distribution; Prevent microbial growth in the distribution system by production and distribution of biologically stable (biostable) water and the use of biostable materials; Monitor for timely detection of any failure of the system to prevent significant health consequences. New developments in safe drinking water in the Netherlands include the adaptation of the Dutch drinking water decree, implementation of quantitative microbial risk assessment (QMRA) by water companies and research into source water quality, drinking water treatment efficacy, safe distribution and biostability of drinking water during distribution and \\textit{Legionella}. This paper summarizes how the Dutch water companies warrant the safety of the drinking water without chlorine.
Development of a predictive model to determine micropollutant removal using granular activated carbon
Authors: de Ridder D. J. , McConville M. , Verliefde A. R. D. , van der Aa L. T. J. , Heijman S. G. J. , Verberk J. Q. J. C. , Rietveld L. C. , van Dijk J. C.
Published: April 2010

Abstract. The occurrence of organic micropollutants in drinking water and its sources has opened up a field of study related to monitoring concentration levels in water sources, evaluating their toxicity and estimating their removal in drinking water treatment processes. Because a large number of organic micropollutants is currently present (although in relatively low concentrations) in drinking water sources, a method should be developed to select which micropollutants has to be evaluated with priority. In this paper, a screening model is presented that can predict solute removal by activated carbon, in ultrapure water and in natural water. Solute removal prediction is based on a combination of solute hydrophobicity (expressed as log D, the pH corrected log Kow), solute charge and the carbon dose. Solute molecular weight was also considered as model input parameter, but this solute property appeared to relate insufficiently to solute removal. Removal of negatively charged solutes by preloaded activated carbon was reduced while the removal of positively charged solutes was increased, compared with freshly regenerated activated carbon. Differences in charged solute removal by freshly regenerated activated carbon were small, indicating that charge interactions are an important mechanism in adsorption onto preloaded carbon. The predicted solute removal was within 20 removal-% deviation of experimentally measured values.
NOM characterization and removal at six Southern African water treatment plants
Authors: Haarhoff J. , Kubare M. , Mamba B. , Krause R. , Nkambule T. , Matsebula B. , Menge J.
Published: April 2010

Abstract. Organic pollution is a major concern during drinking water treatment. Major challenges attributed to organic pollution include the proliferation of pathogenic micro-organisms, prevalence of toxic and physiologically disruptive organic micropollutants, and quality deterioration in water distribution systems. A major component of organic pollution is natural organic matter (NOM). The operational mechanisms of most unit processes are well understood. However, their interaction with NOM is still the subject of scientific research. This paper takes the form of a metastudy to capture some of the experiences with NOM monitoring and analysis at a number of Southern African Water Treatment Plants. It is written from the perspective of practical process selection, to try and coax some pointers from the available data for the design of more detailed pilot work. NOM was tracked at six water treatment plants using dissolved organic carbon (DOC) measurements. Fractionation of the DOC based on biodegradability and molecular weight distribution was done at a water treatment plant in Namibia. A third fractionation technique using ion exchange resins was used to assess the impact of ozonation on DOC. DOC measurements alone did not give much insight into NOM evolution through the treatment train. The more detailed characterization techniques showed that different unit processes preferentially remove different NOM fractions. Therefore these techniques provide better information for process design and optimisation than the DOC measurement which is routinely done during full scale operation at these water treatment plants. Further work will focus on streamlining and improving the reproducibility of selected fractionation techniques, characterization of NOM from different water sources, and synthesis of the results into a systematic, practical guideline for process design and optimisation.
Technical Note: Community of bacteria attached on the PVDF MF membrane surface fouled from drinking water treatment, in Seoul, Korea
Authors:   Kyongmi Chon,   Kangmin Chon,   Jin-Soo Chang,   Heekyong Oh,   Euisin Lee,   Jaeweon Cho
Published: April 2010

Abstract. Alpha, beta, and gamma proteobacteria comprise approximate 68, 16, and 7% of all identified bacteria. In this study, bacterial communities that had fouled polyvinylidene fluoride microfiltration membranes, which are used for drinking water treatment, over an 18 month period were analyzed using the 16s rRNA gene clone library method. The alpha, beta, and gamma proteobacteria were composed of mainly Bradyrhizobium and Rhodopseudomonas, Ralstonia, and Legionella, respectively. The presence of a relatively high amount of alpha proteobacteria was due to the oligotrophic condition of the drinking water source, the Han River, tested in this specific case study. The second most prominent bacteria community was the beta proteobacteria, which are typically found in a freshwater environment. This finding supports the notion that the drinking water source was relatively clean. Analyses of the organic foulants indicated that the they were most likely from extra cellular polymers and/or cell fractured chemicals from bacteria or micro-organisms, as identified using organic characterizing tools, including 3 dimensional fluorescence excitation-emission matrix and Fourier transform IR analyses.
A bottom-up approach of stochastic demand allocation in water quality modelling
Authors: Blokker E. J. M. , Vreeburg J. H. G. , Beverloo H. , Klein Arfman M. , van Dijk J. C.
Published: April 2010

Abstract. An "all pipes" hydraulic model of a DMA-sized drinking water distribution system was constructed with two types of demand allocations. One is constructed with the conventional top-down approach, i.e. a demand multiplier pattern from the booster station is allocated to all demand nodes with a correction factor to account for the average water demand on that node. The other is constructed with a bottom-up approach of demand allocation, i.e., each individual home is represented by one demand node with its own stochastic water demand pattern. The stochastic water demand patterns are constructed with an end-use model on a per second basis and per individual home. The flow entering the test area was measured and a tracer test with sodium chloride was performed to measure travel times. The two models were evaluated on the predicted sum of demands and travel times, compared with what was measured in the test area. The new bottom-up approach performs at least as well as the conventional top-down approach with respect to total demand and travel times, without the need for any flow measurements or calibration measurements. The bottom-up approach leads to a stochastic method of hydraulic modelling and gives insight into the variability of travel times as an added feature beyond the conventional way of modelling.
Negative pressures in full-scale distribution system: field investigation, modelling, estimation of intrusion volumes and risk for public health
Authors: Besner M. C. , Ebacher G. , Jung B. S. , Karney B. , Lavoie J. , Payment P. , Prévost M.
Published: April 2010

Abstract. Various investigations encompassing microbial characterization of external sources of contamination (soil and trenchwater surrounding water mains, flooded air-valve vaults), field pressure monitoring, and hydraulic and transient analyses were conducted in the same distribution system where two epidemiological studies showing an increase in gastrointestinal illness for people drinking tap water were conducted in the 1990's. Interesting results include the detection of microorganisms indicators of fecal contamination in all external sources investigated but at a higher frequency in the water from flooded air-valve vaults, and the recording of 18 negative pressure events in the distribution system during a 17-month monitoring period. Transient analysis of this large and complex distribution system was challenging and highlighted the need to consider field pressure data in the process.
Understanding and managing large sensor networks
Authors: Ediriweera D. D. , Marshall I. W.
Published: April 2010

Abstract. The water supply industry is trialing a range of sensor network designs for monitoring distributed infrastructure. The paper investigates the performance of such a sensor system deployed to monitor a water distribution network. The study reveals up to one fifth of the data intended to be collected either to be missing or erroneous. Findings reinforce the importance of in-depth design consideration of all aspects of large scale sensor systems, and the necessity for expertise on every detail of the system, or access to a rule set which embeds this knowledge allowing non-specialists to make near optimal choices. First steps towards defining such a rule set is presented here with supporting evidence.
I-WARP: individual water main renewal planner
Authors: Kleiner Y. , Rajani B.
Published: April 2010

Abstract. I-WARP is based upon a nonhomogeneous Poisson approach to model breakage rates in individual water mains. The structural deterioration of water mains and their subsequent failure are affected by many factors, both static (e.g., pipe material, pipe size, age (vintage), soil type) and dynamic (e.g., climate, cathodic protection, pressure zone changes). I-WARP allows for the consideration of both static and dynamic factors in the statistical analysis of historical breakage patterns. This paper describes the mathematical approach and demonstrates its application with the help of a case study. The research project within which I-WARP was developed, was jointly funded by the National Research Council of Canada (NRC), and the Water Research foundation (formerly known as the American Water Works Association Research Foundation – AwwaRF) and supported by water utilities from USA and Canada.
MUWS (Microbiology in Urban Water Systems) – an interdisciplinary approach to study microbial communities in urban water systems
Authors: Deines P. , Sekar R. , Jensen H. S. , Tait S. , Boxall J. B. , Osborn A. M. , Biggs C. A.
Published: April 2010

Abstract. Microbiology in Urban Water Systems (MUWS) is an integrated project, which aims to characterize the microorganisms found in both potable water distribution systems and sewer networks. These large infrastructure systems have a major impact on our quality of life, and despite the importance of these systems as major components of the water cycle, little is known about their microbial ecology. Potable water distribution systems are large, highly interconnected and dynamic, and difficult to control. Sewer systems are also large and subject to time varying inputs and demands. Their performance also faces increasing loading due to increasing urbanization and longer-term environmental changes. Therefore, understanding the link between microbial ecology and any potential impacts on short or long-term engineering performance is important. By combining the strengths and research expertise of civil-, biochemical engineers and molecular microbial ecologists, we aim to link the abundance and diversity of microorganisms to physical and engineering variables so that novel insights into the ecology of microorganisms within both water distribution systems and sewer networks can be explored. By presenting the details of this multidisciplinary approach, and the principals behind the molecular microbiological methods and techniques that we use, this paper will demonstrate the potential of an integrated approach to better understand urban water system function and so meet future challenges.
Rapid evaluation of water supply project feasibility in Kolkata, India
Authors: Dutta Roy K. , Thakur B. , Konar T. S. , Chakrabarty S. N.
Published: April 2010

Abstract. Mega cities in developing countries are mostly dependent on external funding for improving the civic infrastructures like water supply. International and sometimes national agencies stipulate financial justifications for infrastructure funding. Expansion of drinking water network with external funding therefore requires explicit economic estimates. A methodology suitable for local condition has been developed in this study. Relevant field data were collected for estimating the cost of supply. The artificial neural network technique has been used for cost estimate. The willingness to pay survey has been used for estimating the benefits. Cost and benefit have been compared with consideration of time value of money. The risk and uncertainty have been investigated by Monte Carlo's simulation and sensitivity analysis. The results in this case indicated that consumers were willing to pay for supply of drinking water. It has been also found that supply up to 20 km from the treatment plant is economical after which new plants should be considered. The study would help to plan for economically optimal improvement of water supply. It could be also used for estimating the water tariff structure for the city.
Historical reconstruction of the Aral Sea shrinking by a full 3-D wetting and drying model ECOSMO
Authors: Alekseeva I. , Schrum C.
Published: April 2010

Abstract. Several decades ago, the Aral Sea was the fourth out of the biggest lakes all over the world. Due to intense irrigation in the Aral Sea basin an imbalance in the water budget occurred and caused dramatic shrinking of the Aral Sea. With the present paper a sea-ice model for the Aral Sea has been developed, aiming in resolving the long-term development of the sea including drastic volume and surface area changes. The necessary requirement for such a model is a mass conservative wetting and drying scheme which has been developed in the application. By performing sensitivity experiments on different implementations of wetting and drying schemes, a significant influence of waggling on the volume and salt budget was identified for a hindcast under realistic forcing and the need for a volume and mass conserving scheme was demonstrated. Using a mass conserving implementation a model hindcast was performed for 1979–1993 by using the ECMWF re-analysis (ERA-15) meteorological data and modeled evaporation. Consideration of surface area changes in a temporal resolution of the model time step allowed for a realistic description of non-linear interactions between volume loss and evaporation changes. The sea-ice model was able to successfully simulate sea level and sea surface area decrease as well as sea-ice dynamics on a multiyear to decadal time scale. Model predicted evaporation was found to result in significantly improved volume budgets for the Aral Sea and in realistic predictions of the Aral Sea shrinking. Furthermore, by comparing the simulated average salinities to observed ones, it could be shown that the present model concept neglecting additional salt flux effects such as salt precipitation and salinity deposition on the dried sea bed, is adequate to reproduce observed mean salinities during the period of investigation.
Simplified aerosol modeling for variational data assimilation
Authors: Huneeus N. , Boucher O. , Chevallier F.
Published: April 2010

Abstract. We have developed a simplified aerosol model together with its tangent linear and adjoint versions for variational assimilation of aerosol optical depth with the aim to optimize aerosol emissions over the globe. The model was derived from the general circulation model LMDz; it groups together the 24 aerosol species simulated in LMDz into 4 species, namely gaseous precursors, fine mode aerosols, coarse mode desert dust and coarse mode sea salt. The emissions have been kept as in the original model. Modifications, however, were introduced in the computation of aerosol optical depth and in the processes of sedimentation, dry and wet deposition and sulfur chemistry to ensure consistency with the new set of species and their composition. The simplified model successfully manages to reproduce the main features of the aerosol distribution in LMDz. Differences between the original and simplified models are mainly associated to the new deposition and sedimentation velocities consistent with the definition of species in the simplified model and the simplification of the sulfur chemistry. Furthermore, simulated aerosol optical depth remains within the variability of AERONET observations for all aerosol types and all sites throughout most of the year. Sensitivity analyses with the tangent linear version show that the simplified sulfur chemistry is the dominant process responsible for the strong non-linearity of the model.
Derivation of a numerical solution of the 3D coupled velocity field for an ice sheet – ice shelf system, incorporating both full and approximate stress solutions
Authors: Reerink T. J. , van de Wal R. S. W. , Borsboom P.-P.
Published: April 2010

Abstract. To overcome the mechanical coupling of an ice sheet with an ice shelf, one single set of velocity equations is presented covering both the sheet and the shelf. This set is obtained by applying shared sheet-shelf approximations. The hydrostatic approximation and a constant density are the only approximations that are applied to the full-Stokes momentum equations. The remaining stress terms from the momentum equations and the stress terms from the usual ice-flow law are multiplied by coefficients which can be put to zero or one, facilitating several stress approximations per domain within one model. In addition we derived a matrix format for the discretized set of the fully coupled velocity equations on a three-dimensional vertically scaled grid, in which all linear derivative terms are treated implicitly. The compact vector format of this sparse matrix equation is developed, including the boundary conditions.
Surface water process and groundwater flow within a hydrologically complex floodplain wetland, Norfolk Broads, U.K.
Authors: Gilvear D. J. , Sadler P. J. K. , Tellam J. H. , Lloyd J. W.
Published: April 2010

Abstract. The patterns of variation in water quality for an acidic stream draining plantation forest overlying acidic and acid sensitive gley soils with shale and slate bedrock changed following the introduction of a 45 m deep borchole near to the stream. During drilling, air flushing of debris from the borehole cleared fracture routes for groundwater penetration to the stream via the stream bed. Consequently, there were and there remain marked increases in pH, alkalinity and calcium concentrations in the stream water. The extent of this water quality improvement varies according to flow. Under extreme highfiow conditions, most of the stream water is supplied from near surface soil water sources and acidic stream waters (pH about 4.2) result. Under baseflow conditions, the stream water pH is about 7.0 upstream and about 7.5 downstream of the borehole. Under intermediate flow conditions, the improvement in pH is most marked and values increase from around 5 to around 6.3. For acid sensitive "hard rock" areas such as those studied here, the bedrock has frequently been assumed to be both impermeable and low in base cations. This study illustrates that this view may be incorrect, and that groundwater may provide an important modifier of streamwater quality, at least for slate and shale dominated hard rock areas. Indeed, the work demonstrates clearly the potential for water quality remediation through groundwater manipulation.
An Assessment of the Capabilities of the ERS Satellites' Active Microwave Instruments for Monitoring Soil Moisture Change
Authors: Blyth K.
Published: April 2010

Abstract. The launch of the European Remote sensing Satellite (ERS-1) in July 1991 represented an important turning point in the development of Earth observation as it was the first of a series of satellites which would carry high resolution active microwave (radar) sensors which could operate through the thickest cloudeover and provide continuity of data for at least a decade. This was of particular relevance to hydrological applications, such as soil moisture monitoring, which generally require frequent satellite observations to monitor changes in state. ERS-1 and its successor ERS-2 carry the active microwave instrument (AMI) which operates in 3 modes (synthetic aperture radar, wind scatterometer and wave seatterometer) together with the radar altimeter which may all be useful for the observation of soil moisture. This paper assesses the utility of these sensors through a comprehensive review of work in this field. Two approaches to soil moisture retrieval are identified: 1) inversion modelling, where the physical effects of vegetation and soil roughness on radar backscatter are quantified through the use of multi-frequency and/or multi-polarization sensors and 2) change detection where these effects are normalized through frequent satellite observation, the residual effects being attributed to short-term changes in soil moisture. Both approaches will be better supported by the future European Envisat-l satellite which will provide both multi-polarization SAR and low resolution products which should facilitate more frequent temporal observation.
The aggregate description of semi-arid vegetation with precipitation-generated soil moisture heterogeneity
Authors: White C. B. , Houser P. R. , Arain A. M. , Yang Z.-L. , Syed K. , Shuttleworth W. J.
Published: April 2010

Abstract. Meteorological measurements in the Walnut Gulch catchment in Arizona were used to synthesize a distributed, hourly-average time series of data across a 26.9 by 12.5 km area with a grid resolution of 480 m for a continuous 18-month period which included two seasons of monsoonal rainfall. Coupled surface-atmosphere model runs established the acceptability (for modelling purposes) of assuming uniformity in all meteorological variables other than rainfall. Rainfall was interpolated onto the grid from an array of 82 recording rain gauges. These meteorological data were used as forcing variables for an equivalent array of stand-alone Biosphere-Atmosphere Transfer Scheme (BATS) models to describe the evolution of soil moisture and surface energy fluxes in response to the prevalent, heterogeneous pattern of convective precipitation. The calculated area-average behaviour was compared with that given by a single aggregate BATS simulation forced with area-average meteorological data. Heterogeneous rainfall gives rise to significant but partly compensating differences in the transpiration and the intercepted rainfall components of total evaporation during rain storms. However, the calculated area-average surface energy fluxes given by the two simulations in rain-free conditions with strong heterogeneity in soil moisture were always close to identical, a result which is independent of whether default or site-specific vegetation and soil parameters were used. Because the spatial variability in soil moisture throughout the catchment has the same order of magnitude as the amount of rain falling in a typical convective storm (commonly 10% of the vegetation's root zone saturation) in a semi-arid environment, non-linearity in the relationship between transpiration and the soil moisture available to the vegetation has limited influence on area-average surface fluxes.
Aggregation rules for surface parameters in global models
Authors: Shuttleworth W. J. , Yang Z.-L. , Arain M. A.
Published: April 2010

Abstract. Aggregation rules are derived for calculating the effective value of parameters that determine the exchange of momentum and energy between the land surface and the atmosphere at the length scales used in General Circulation Models (GCMs). The derivation involves starting from theories that link parameters relevant at grid scale and patch scale, and then imposing the limitations necessarily present when models are operated in a free-standing, predictive mode. The application of these rules is illustrated by example for the case of the Biosphere-Atmosphere Transfer Scheme (BATS). Remotely sensed global maps of land cover classes at 1 km x 1 km pixel scale for North America, South America, and Africa are used with these new aggregation rules to calculate area-average values of parameters for the 3° x 3° grid mesh used in the National Center for Atmospheric Research Community Climate Model. There are significant differences between the parameters calculated using aggregation rules and the values selected on the basis of the dominant vegetation cover in each grid, this being the selection procedure conventionally applied with BATS.
Eucalyptus water use greater than rainfall input - possible explanation from southern India
Authors: Calder I. R. , Rosier P. T. W. , Prasanna K. T. , Parameswarappa S.
Published: April 2010

Abstract. Hydrological and silvicultural studies carried out in southern India on the effects of plantations of Eucalyptus and other fast growing exotic tree species have determined the impacts of these plantations on water resources, erosion, soil nutrient status and growth rates at sites of differing rainfall and soil depth in Karnataka. Whilst providing new information on these issues, the studies also raised two important questions: what was the explanation for the anomalous result that the water use of 3400 mm from Eucalyptus plantations at Hosakote over a three year period exceeded the rainfall of 2100 mm over the same period and why were growth rates of woodlots on most farmer's fields higher than those of plantations on land owned by the Karnataka Forest Department? The records of the soil moisture depletion patterns under these plantations from the day of planting provide the basis for the answers to both questions: i) whilst roots are penetrating into deeper soil layers, they are able to extract from a reservoir of water additional to that available from the rainfall each year, ii) farmer's land on which short rooted agricultural crops have been grown previously is likely to have a much higher soil water status than land previously under forest or scrub vegetation. These new studies have also established that the development of the drying front under the Eucalyptus camaldulensis plantations is very rapid, indicating average root extension rates in excess of 2.5 m per year, whilst those under Tectona grandis and Artocarpus heterophyllus advanced at approximately half the rate. These results have obvious implications for the long term sustainability of growth rates from these plantations and the recharge of groundwater. The authors believe that this study may be the first to report neutron probe soil moisture depletion observations, from the date of planting, beneath tree plantations in a dry climate. The extent to which the roots were able to penetrate raises the question of whether other studies, which have estimated water use from soil moisture observations in dry climates, may have seriously underestimated both the actual soil moisture depletion and the water use through having soil moisture measurements located to insufficient depth.
Towards a rational definition of potential evaporation
Authors: Lhomme J.-P.
Published: April 2010

Abstract. The concept of potential evaporation is defined on the basis of the following criteria: (i) it must establish an upper limit to the evaporation process in a given environment (the term "environment" including meteorological and surface conditions), and (ii) this upper limit must be readily calculated from measured input data. It is shown that this upper limit is perfectly defined and is given by the Penman equation, applied with the corresponding meteorological data (incoming radiation and air characteristics measured at a reference height) and the appropriate surface characteristics (albedo, roughness length, soil heat flux). Since each surface has its own potential evaporation, a function of its own surface characteristics, it is useful to define a reference potential evaporation as a short green grass completely shading the ground. Although the potential evaporation from a given surface is readily calculated from the Penman equation, its physical significance or interpretation is not so straightforward, because it represents only an idealized situation, not a real one. Potential evaporation is the evaporation from this surface, when saturated and extensive enough to obviate any effect of local advection, under the same meteorological conditions. Due to the feedback effects of evaporation on air characteristics, it does not represent the "real" evaporation (i.e. the evaporation which could be physically observed in the real world) from such an extensive saturated surface in these given meteorological conditions (if this saturated surface were substituted for an unsaturated one previously existing). From a rigorous standpoint, this calculated potential evaporation is not physically observable. Nevertheless, an approximate representation can be given by the evaporation from a limited saturated area, the dimension of which depends on the height of measurement of the air characteristics used as input in the Penman equation. If they are taken at a height of 2 m (the height of the meteorological observations), the dimension of the saturated surface in the direction of the wind ranges roughly from 50 to 200 m for a short green grass completely shading the ground.
Plotting positions via maximum-likelihood for a non-standard situation
Authors: Jones D. A.
Published: April 2010

Abstract. A new approach is developed for the specification of the plotting positions used in the frequency analysis of extreme flows, rainfalls or similar data. The approach is based on the concept of maximum likelihood estimation and it is applied here to provide plotting positions for a range of problems which concern non-standard versions of annual-maximum data. This range covers the inclusion of incomplete years of data and also the treatment of cases involving regional maxima, where the number of sites considered varies from year to year. These problems, together with a not-to-be-recommended approach to using historical information, can be treated as special cases of a non-standard situation in which observations arise from different statistical distributions which vary in a simple, known, way.
A combined Pòlya process and mixture distribution approach to rainfall modelling
Authors: Todini E. , di Bacco M.
Published: April 2010

Abstract. A new probabilistic interpretation of at site rainfall sequences is introduced for the development of a stochastic model of rain. The model, is divided into two sub models; the first one describing the total number of rainfall spells within a window of time is described by a Pòlya process in order to reproduce better the variable probability of occurrence of rainfall during storm events (due to the presence of different numbers of rainfall cells); the second sub model, conditional on the first one, describes the total quantity of rainfall in the time window, given a number of rainfall spells. The probabilistic rainfall model, which has shown interesting properties in reproducing the probability distribution of observed data at time scales ranging from one hour to twenty-four hours, may be the basis for a number of applications which include the development of a conditional stochastic generator of rain, within the frame of real-time flood forecasting, and the derivation of a probabilistic distribution of rainfall extremes at the various time scales.
The Plynlimon water balance 1969-1995: the impact of forest and moorland vegetation on evaporation and streamflow in upland catchments
Authors: Hudson J. A. , Crane S. B. , Blackie J. R.
Published: April 2010

Abstract. The Plynlimon experiment in mid-Wales, designed to determine the extent to which coniferous plantation increases evaporation losses and reduces streamflow relative to upland grassland, has now been yielding data since 1969 from the grassland Wye and the 67% forested Severn catchments. Water balance analyses of the early data indicated significantly higher evaporation rates from the forested catchment and studies of the hydrological processes involved attributed this to the high loss rates of precipitation intercepted by the forest canopy. Models based on these process studies predicted losses from the forested catchment that were similar but marginally higher than those determined by the catchment water balance. As the data sets from the catchments increased in length and a detailed reassessment of the ratings of the streamflow gauging structures was completed the updated water balances continued to show a significantly greater evaporation loss from the forested catchment, but the gap between the forest water balance and the model predictions widened. Furthermore Hudson and Gilman (1993), using the best data sets then available, identified downward trends in the evaporation from both catchments which the models did not reproduce and for which no obvious physical or physiological explanation was forthcoming. This dictated a major reassessment of the longer data sets, using the more powerful data processing techniques now available, to identify and eliminate any errors and inconsistencies. This paper describes the reassessment of the precipitation data and the estimates of potential evaporation and presents the water balance results emerging from the revised data sets. The revised results indicate that the evaporation losses from the grassland Wye catchment remained broadly similar to the potential evaporation estimates throughout the 1969-1995 period. The losses from the forested area of the Severn catchment declined from a level some 61% above that of the grassland in 1972 to a level only 18% higher before the start of felling in 1985. This downward trend continued as the felling and re-planting progressed. Over the period  since 1990 the forest catchment losses appear to have stabilised at some 5-10% below those of  the grassland catchment. Using the revised precipitation and potential evaporation data, process based models over-predict the forest catchment evaporation throughout the period and do not mirror the re-felling decline. Possible reasons for this apparent decline in evaporation rates are discussed.
Fish populations in Plynlimon streams
Authors: Crisp D. T. , Beaumont W. R. C.
Published: April 2010

Abstract. In Plynlimon streams, brown trout (Salmo trutta L.) are widespread in the upper Wye at population densities of 0.03 to 0.32 fish m-2 and show evidence of successful recruitment in most years. In the upper Severn, brown trout are found only in an area of c. 1670 -2 downstream of Blaenhafren Falls at densities of 0.03 to 0.24 fish -2 and the evidence suggests very variable year to year success in recruitment (Crisp & Beaumont, 1996). Analyses of the data show that temperature differences between afforested and unafforested streams may affect the rates of trout incubation and growth but are not likely to influence species survival. Simple analyses of stream discharge data suggest, but do not prove, that good years for recruitment in the Hafren population were years of low stream discharge. This may be linked to groundwater inputs detected in other studies in this stream. More research is needed to explain the survival of the apparently isolated trout population in the Hafren.
Relationships between spruce plantation age, solute and soil chemistry in Hafren forest
Authors: Stevens P. A. , Reynolds B. , Hughes S. , Norris D. A. , Dickinson A. L.
Published: April 2010

Abstract. Rain, throughfall, soil waters from surface peaty O horizon and deeper mineral B horizon, and stream water, were collected every four weeks for one year in a moorland catchment, and in four forested catchments. The four forested catchments represented an age sequence of first rotation Sitka spruce plantations, aged 14, 28, 37 and 53 years. All water samples were analysed for all major solutes, including dissolved organic nitrogen (DON-N); stream water and B horizon soil waters were also subjected to aluminium speciation. In each catchment, soil samples were collected on one occasion and pH was measured. Concentrations of most solutes were substantially higher in the 37 year old forest stand than in the moorland catchment, with intermediate concentrations in the two younger stands and 53 year old stand. In particular, higher nitrate-N concentrations were found in the soils and streams of the older forests, although these concentrations tended to be highest in the 37 year old stand. Acid neutralizing capacity (ANC) of soil waters was lower in the B horizon of the forest stands than in the moorland, and tended to decline with increasing forest age. Soil water from both O and B horizons was most acid in the 37 year old stand, and the water from the soil O horizon in all four forest stands was more acid than that in moorland sites. The pH of the soil itself (as measured in a deionised water slurry) was lower in the forest stands than in moorland, although trends with forest age were complex.
Scale dependence of the episodic hydrochemical response of nested catchments at Plynlimon
Authors: Foster H. J. , Alexander S. , Locks T. , Wheater H. S. , Lees M. J. , Reynolds B.
Published: April 2010

Abstract. Previous monitoring of the surface water chemistry of the forested catchments at Plynlimon has concentrated on weekly measurements. Hence, peak values and details of the rapid changes in chemistry occurring during events tend to be missed, particularly for smaller catchments. Knowledge of the detailed hydrochemical response is necessary to predict effects on stream ecology and to quantify processes occurring within the catchment. This information is vital if the likely impacts of changes in landuse and pollutant input on episodic hydrochemical variations are to be modelled. A summary of daily and three-hourly chemistry for the River Severn headwaters at Plynlimon, central Wales is presented. Data are from the summer and autumn of 1995 and the winter and summer of 1996. The effects of antecedent conditions, soiltype, landuse and groundwater and tributary inflow on stream episodic hydrochemical response are discussed for a range of spatial scales, including first, second and third order streams. Detailed information on the chemical changes due to a discrete groundwater inflow into the bed of one stream shows that, during episodes, its influence on stream chemistry is overridden by that of event water. A comparison of drainage ditch chemistry with main stream chemistry during storm events is used to consider the importance of tributary inflow at these times. The contrast in results between sites is assessed, to evaluate the effects of clearfelling and soil type on stream event chemistry.
Predicting soil acidification trends at Plynlimon using the SAFE model
Authors: Reynolds B.
Published: April 2010

Abstract. The SAFE model has been applied to an acid grassland site, located on base-poor stagnopodzol soils derived from Lower Palaeozoic greywackes. The model predicts that acidification of the soil has occurred in response to increased acid deposition following the industrial revolution. Limited recovery is predicted following the decline in sulphur deposition during the mid to late 1970s. Reducing excess sulphur and NOx deposition in 1998 to 40% and 70% of 1980 levels results in further recovery but soil chemical conditions (base saturation, soil water pH and ANC) do not return to values predicted in pre-industrial times. The SAFE model predicts that critical loads (expressed in terms of the (Ca+Mg+K):Alcrit ratio) for six vegetation species found in acid grassland communities are not exceeded despite the increase in deposited acidity following the industrial revolution. The relative growth response of selected vegetation species characteristic of acid grassland swards has been predicted using a damage function linking growth to soil solution base cation to aluminium ratio. The results show that very small growth reductions can be expected for "acid tolerant" plants growing in acid upland soils. For more sensitive species such as Holcus lanatus, SAFE predicts that growth would have been reduced by about 20% between 1951 and 1983, when acid inputs were greatest. Recovery to c. 90% of normal growth (under laboratory conditions) is predicted as acidic inputs decline.
A parameterization of momentum roughness length and displacement height for a wide range of canopy densities
Authors: Verhoef A. , McNaughton K. G. , Jacobs A. F. G.
Published: April 2010

Abstract. Values of the momentum roughness length, z0, and displacement height, d, derived from wind profiles and momentum flux measurements, are selected from the literature for a variety of sparse canopies. These include savannah, tiger-bush and several row crops. A quality assessment of these data, conducted using criteria such as available fetch, height of wind speed measurement and homogeneity of the experimental site, reduced the initial total of fourteen sites to eight. These datapoints, combined with values carried forward from earlier studies on the parameterization of z0 and d, led to a maximum number of 16 and 24 datapoints available for d and z0, respectively. The data are compared with estimates of roughness length and displacement height as predicted from a detailed drag partition model, R92 (Raupach, 1992), and a simplified version of this model, R94 (Raupach, 1994). A key parameter in these models is the roughness density or frontal area index, λ. Both the comprehensive and the simplified model give accurate predictions of measured z0 and d values, but the optimal model coefficients are significantly different from the ones originally proposed in R92 and R94. The original model coefficients are based predominantly on measured aerodynamic parameters of relatively closed canopies and they were fitted `by eye'. In this paper, best-fit coefficients are found from a least squares minimization using the z0 and d values of selected good-quality data for sparse canopies and for the added, mainly closed canopies. According to a statistical analysis, based on the coefficient of determination (r2), the number of observations and the number of fitted model coefficients, the simplified model, R94, is deemed to be the most appropriate for future z0 and d predictions. A CR value of 0.35 and a cd1 value of about 20 are found to be appropriate for a large range of canopies varying in density from closed to very sparse. In this case, 99% of the total variance occurring in the d-data across 16 selected canopies can be explained, whereas the analogous value for the z0-data (24 datapoints available) is 81%. This makes the R94 model, with only two coefficients and its relatively simple equations, a useful universal tool for predicting z0 and d values for all kinds of canopies. For comparison, a similar fitting exercise is made using simple linear equations based on obstacle height only (e.g. Brutsaert, 1982) and another formula involving canopy height as well as roughness density (Lettau, 1969). The fitted Brutsaert equations explain 98% and 62% of the variance in the d and z0-data, respectively. Lettau's equation for prediction of z0 performs unsatisfactorily (r2 values <0, even after fitting of the coefficient) and so it is concluded that the drag partition model is definitely the most effective for prediction of the momentum roughness lengths for a wide rang of canopy densities.
Comparison of three stream tube models predicting field-scale solute transport
Authors: Jacques D. , Vanderborght J. , Mallants D. , Kim D.-J. , Vereecken H. , Feyen J.
Published: April 2010

Abstract. In this paper the relation between local- and field-scale solute transport parameters in an unsaturated soil profile is investigated. At two experimental sites, local-scale steady-state solute transport was measured in-situ using 120 horizontally installed TDR probes at 5 depths. Local-scale solute transport parameters determined from BTCs were used to predict field-scale solute transport using stochastic stream tube models (STM). Local-scale solute transport was described by two transport models: (1) the convection-dispersion transport model (CDE), and (2) the stochastic convective lognormat transfer model (CLT). The parameters of the CDE-model were found to be lognormally distributed, whereas the parameters of the CLT model were normally distributed. Local-scale solute transport heterogeneity within the measurement volume of a TDR-probe was an important factor causing field-scale solute dispersion. The study of the horizontal scale-dependency revealed that the variability in the solute transport parameters contributes more to the field-scale dispersion at deeper depths than at depths near the surface. Three STMs were used to upscale the local transport parameters: (i) the stochastic piston flow STM-I assuming local piston flow transport, (ii) the convective-dispersive STM-II assuming local CDE transport, and (iii) the stochastic convective lognormal STM-III assuming local CLT. The STM-I considerably underpredicted the field-scale solute dispersion indicating that local-scale dispersion processes, which are captured within the measurement volume of the TDR-probe, are important to predict field-scale solute transport. STM-II and STM-III both described the field-scale breakthrough curves (BTC) accurately if depth dependent parameters were used. In addition, a reasonable description of the horizontal variance of the local BTCs was found. STM-III was (more) superior to STM-II if only one set of parameters from one depth is used to predict the field-scale solute BTCs at several depths. This indicates that the local-scale solute transport process, as measured with TDR in this study, is in agreement with the CLT-hypothesis.