| 1. |
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| 2. |
- Beldring, Stein, et al.
(författare)
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Kinematic wave approximations to hillslope hydrological processes in tills
- 2000
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Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 14:4, s. 727-745
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Tidskriftsartikel (refereegranskat)abstract
- This work has been carried out within the framework of NOPEX - a NOrthern hemisphere climate Processes land surface EXperiment. Its purpose is to describe the spatial variability of groundwater levels and soil moisture content and their influence on runoff generation in small catchments in a landscape dominated by boreal forest and till soils, which is characteristic for the Nordic countries. Kinematic wave approximations have been used to describe saturated subsurface flow and saturation overland flow in hillslopes with a thin soil layer overlying a relatively impermeable bedrock. Simultaneous analyses of catchment runoff, groundwater-table depths and soil moisture in the unsaturated zone have been performed by including the kinematic wave descriptions in a precipitation-runoff model. The results have been compared with observed hydrographs and spatial patterns of groundwater levels and soil moisture content in two small experimental catchments. Results from this study indicate that is reasonable to apply the same parameter set when describing hydrological processes in computational elements with similar characteristics at a scale of about 1 km(2) in the NOPEX area.
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| 3. |
- Bishop, Kevin, et al.
(författare)
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The hydrology of the covered catchment
- 1998
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Ingår i: Experimental Reversal of Acid Rain Effects: the Gårdsjön Project. - : John Wiley & Sons. ; , s. 109-135
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Bokkapitel (refereegranskat)
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| 4. |
- Bishop, Kevin, et al.
(författare)
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Water storage in a till catchment. II : Implications of transmissivity feedback for flow paths and turnover times
- 2011
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:25, s. 3950-3959
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the flow paths and turnover times within a catchment characterized by the transmissivity feedback mechanism where there is a strong increase in the saturated hydraulic conductivity towards the soil surface and precipitation inputs saturate progressively more superficial layers of the soil profile. The analysis is facilitated by the correlation between catchment water storage and groundwater levels, which made it possible to model the daily spatial distribution of water storage, both vertically in different soil horizons and horizontally across a 6300-m2 till catchment. Soil properties and episodic precipitation input dynamics, combined with the influence of topographic features, concentrate flow in the horizontal, vertical, and temporal dimensions. Within the soil profile, there was a vertical concentration of lateral flow to superficial soil horizons (upper 30?cm of the soil), where much of the annual flow occurred during runoff episodes. Overland flow from a limited portion of the catchment can contribute to peak flows but is not a necessary condition for runoff episodes. The spatial concentration of flow, and the episodic nature of runoff events, resulted in a strong and spatially structured differentiation of local flow velocities within the catchment. There were large differences in the time spent by the laterally flowing water at different depths, with turnover times of lateral flow across a 1-m-wide soil pedon ranging from under 1?h at 10- to 20-cm depth to a month at 70- to 80-cm depth. In many regards, the hydrology of this catchment appears typical of the hydrology in till soils, which are widespread in Fenno-Scandia. Copyright (c) 2011 John Wiley & Sons, Ltd.
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| 5. |
- Bockgård, Niclas, et al.
(författare)
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Accuracy of CFC groundwater dating in a crystalline bedrock aquifer: Data from a site in southern Sweden
- 2004
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 12:2, s. 171-183
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) and tritium were determined in groundwater in fractured crystalline bedrock at Finnsjon, Sweden. The specific goal was to investigate the accuracy of CFC dating in such an environment, taking potential degradation and mixing of water into consideration. The water was sampled to a depth of 42 m in three boreholes along an 800-m transect, from a recharge area to a local discharge area. The CFC-113 concentration was at the detection limit in most samples. The apparent recharge date obtained from CFC-11 was earlier than from CFC-12 for all samples, with a difference of over 20 years for some samples. The difference was probably caused by degradation of CFC-11. The CFC-12 dating of the samples ranged from before 1945 to 1975, with the exception of a sample from the water table, which had a present-day concentration. Conclusions about flow paths or groundwater velocity could not be drawn from the CFCs. The comparison between CFC-12 and tritium concentrations showed that most samples could be unmixed or mixtures of waters with different ages, and the binary mixtures that matched the measured concentrations were determined. The mixing model approach can be extended with additional tracers.
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| 6. |
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| 7. |
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| 8. |
- Bockgård, Niclas, 1974-
(författare)
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Groundwater Recharge in Crystalline Bedrock : Processes, Estimation, and Modelling
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Kunskap om grundvattenbildningen är nödvändig för att man ska kunna förutsäga konsekvenserna av grundvattenuttag och underjordsbyggande. Grundvattenbildningen i berggrunden är dock svår att uppskatta. Syftet med avhandlingen var att öka förståelsen av grundvattenbildningen i kristallin berggrund, att undersöka hur grundvattenbildningen ska uppskattas samt att utveckla nya modeller för att beskriva grundvattenbildningen. Studien grundades på tre angreppssätt: grundvattendatering med freoner (CFC), geohydrauliska observationer och matematisk modellering.Koncentrationerna av CFC-11 och CFC-113 befanns vara låga i det undersökta berggrundvattnet, vilket i kombination med låga syrgashalter tyder på anaerob nedbrytning. Koncentrationerna av CFC-12 och tritium överensstämde ganska väl, vilket betyder att den skenbara åldern kan vara den sanna åldern. Resultaten tyder på att CFC-datering inte är pålitlig i skogsmiljöer med finkornigt jordtäcke.Vid nederbörd observerades ett snabbt gensvar i den hydrauliska potentialen i den studerade bergakviferen, trots det 10 m mäktiga moräntäcket. En avsevärd del av de observerade potentialvariationerna befanns vara belastningseffekter, som inte innebar någon magasinsförändring eller något vattenflöde. Berggrundens belastningseffektivitet uppskattades, ur potentialens svar på lufttrycksförändringar, till 0,95. Ytbelastningen beräknades från mätningar av lufttryck, vatten i jordtäcket och snö. Omkring 20 % av årstidsvariationen hos den hydrauliska potentialen uppskattades bero på enbart belastningsförändringar. En enkel begreppsmässig modell kunde användas för att simulera den observerade hydrauliska potentialen. För att beskriva enskilda grundvattenbildningstillfällen på bästa sätt var det nödvändigt att ta hänsyn till effekten av ytbelastningen.Numeriska experiment gjordes med en modell av en jord–bergprofil. När berget modellerades som ett heterogent kontinuum bildades omättade zoner i berget vid stora hydrauliska gradienter. Fenomenet uppträdde i områden där låggenomsläppliga zoner låg uppströms höggenomsläppliga zoner, och ledde till minskad hydraulisk konduktivitet i berget.
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| 9. |
- Davies, Jessica, et al.
(författare)
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A discrete particle representation of hillslope hydrology : hypothesis testing in reproducing a tracer experiment at Gardsjon, Sweden
- 2011
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:23, s. 3602-3612
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Tidskriftsartikel (refereegranskat)abstract
- Despite the long history of the continuum equation approach in hydrology, it is not a necessary approach to the formulation of a physically based representation of hillslope hydrology. The Multiple Interacting Pathways ( MIPs) model is a discrete realization that allows hillslope response and transport to be simultaneously explored in a way that reflects the potential occurrence of preferential flows and lengths of pathways. The MIPs model uses random particle tracking methods to represent the flow of water within the subsurface alongside velocity distributions that acknowledge preferential flows and transition probability matrices, which control flow pathways. An initial realization of this model is presented here in application to a tracer experiment carried out in Gardsjon, Sweden. The model is used as an exploratory tool, testing several hypotheses in relation to this experiment.
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| 10. |
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| 11. |
- Davies, J., et al.
(författare)
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Integrated modeling of flow and residence times at the catchment scale with multiple interacting pathways
- 2013
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:8, s. 4738-4750
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Tidskriftsartikel (refereegranskat)abstract
- There is still a need for catchment hydrological and transport models that properly integrate the effects of preferential flows while accounting for differences in velocities and celerities. A modeling methodology is presented here which uses particle tracking methods to simulate both flow and transport in multiple pathways in a single consistent solution. Water fluxes and storages are determined by the volume and density of particles and transport is attained by labeling the particles with information that may be tracked throughout the lifetime of that particle in the catchment. The methodology allows representation of preferential flows through the use of particle velocity distributions, and mixing between pathways can be achieved with pathway transition probabilities. A transferable 3-D modeling methodology is presented for the first time and applied to a unique step-shift isotope experiment that was carried out at the 0.63 ha G1 catchment in Gardsjon, Sweden. This application highlights the importance of combining flow and transport in hydrological representations, and the importance of pathway velocity distributions and interactions in obtaining a satisfactory representation of the observations.
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| 12. |
- Gong, Lebing
(författare)
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Large-scale Runoff Generation and Routing : Efficient Parameterisation using High-resolution Topography and Hydrography
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water has always had a controlling influence on the earth’s evolution. Understanding and modelling the large-scale hydrological cycle is important for climate prediction and water-resources studies. In recent years large-scale hydrological models, including the WASMOD-M evaluated in the thesis, have increasingly become a main assessment tool for global water resources.The monthly version of WASMOD-M, the starting point of the thesis, revealed restraints imposed by limited hydrological and climate data quality and the need to reduce model-structure uncertainties. The model simulated the global water balance with a small volume error but was less successful in capturing the dynamics. In the last years, global high-quality, high-resolution topographies and hydrographies have become available. The main thrust of the thesis was the development of a daily WASMOD-M making use of these data to better capture the global water dynamics and to parameterise local non-linear processes into the large-scale model. Scale independency, parsimonious model structure, and computational efficiency were main concerns throughout the model development.A new scale-independent routing algorithm, named NRF for network-response function, using two aggregated high-resolution hydrographies, HYDRO1k and HydroSHEDS, was developed and tested in three river basins with different climates in China and North America. The algorithm preserves the spatially distributed time-delay information in the form of simple network-response functions for any low-resolution grid cell in a large-scale hydrological model.A distributed runoff-generation algorithm, named TRG for topography-derived runoff generation, was developed to represent the highly non-linear process at large scales. The algorithm, when inserted into the daily WASMOD-M and tested in same three basins, led to the same or a slightly improved performance compared to a one-layer VIC model, with one parameter less to be calibrated. The TRG algorithm also offered a more realistic spatial pattern for runoff generation.The thesis identified significant improvements in model performance when 1) local instead of global climate data were used, and 2) when the scale-independent NRF routing algorithm was used instead of a traditional storage-based routing algorithm. In the same time, spatial resolution of climate input and choice of high-resolution hydrography have secondary effects on model performance.Two high-resolution topographies and hydrographies were used and compared, and new techniques were developed to aggregate their information for use at large scales. The advantages and numerical efficiency of feeding high-resolution information into low-resolution global models were highlighted.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Harris, David M., et al.
(författare)
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Hydrograph Separation Using Continuous Open System Isotope Mixing
- 1995
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 31:1, s. 157-171
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new hydrograph separation method for runoff source modeling based on continuous open system isotope mixing using a variable source area and three isotopic reservoirs. The three reservoirs are (1) direct precipitation on saturated areas, (2) a near-stream saturated zone, and (3) subsurface water in upslope areas. The reservoir sizes and isotopic compositions evolve due to continuous, open system mixing. Streamflow is composed of rainfall on saturated areas and water exfiltrated from the near-stream Saturated zone. The contributing source fractions are determined using the observed isotopic compositions of the stream and the modeled isotopic compositions of the contributing reservoirs, which are functions of time. The near-stream saturated zone receives inflow from upslope areas which are not Surface saturated. The surface-saturated area changes dynamically based on the difference between lateral inflow and contributions to streamflow from the near-stream saturated zone. The upslope zone (reservoir 3) evolves by mixing with rainfall. This hydrograph separation method requires (1) a function which relates the amount of water stored in the near-stream saturated zone to saturated area, (2) a function which relates saturated area fraction to total streamflow, and (3) knowledge of the water storage capacity in reservoirs 2 and 3. The hydrograph separation method was applied to oxygen isotope data for rainfall and runoff during a 36-hour storm at the Gardsjon Fl catchment in southwestern Sweden, The hydrograph separation method was used to estimate time-dependent streamflow contributions due to overland flow of storm rainfall and. subsurface flow of mainly preevent water. We also used the separation method to estimate parameters for relations between saturated area fraction and streamflow, and saturated area and subsurface water storage. We show that streamflow contributions from overland flow may be described by a simple analytic function of antecedent conditions and catchment parameters.
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| 18. |
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| 19. |
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| 20. |
- Hjerdt, K.N., et al.
(författare)
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A new topographic index to quantify downslope controls on local drainage
- 2004
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Ingår i: Water Resources Research. - 0043-1397 .- 1944-7973. ; 40:5, s. W056021-W056026
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Tidskriftsartikel (refereegranskat)abstract
- Topography is an important control on hydrological processes. One approach to quantify this control is the topographic ln(a/tan< beta >) index. This index has become widely used in hydrology, but it utilizes a relatively small portion of the information contained in a digital elevation model (DEM). One potentially important feature not considered in the implementation of the ln(a/tan< beta >) index is the enhancement or impedance of local drainage by downslope topography. This effect could be important in some terrain for controlling hydraulic gradients. We propose a new way of estimating the hydraulic gradient by calculating how far downhill (Ld, [m]) a parcel of water must move in order to lose a certain amount of potential energy (d, [m]). Expressed as a gradient, tan< alpha >d = d/Ld, values tend to be lower on concave slope profiles and higher on convex slope profiles compared with the local gradient, tan< beta >. We argue that the parameter d controls the deviation of hydraulic gradient from surface slope. While we determine this subjectively, landscape relief, DEM resolution, and soil transmissivity should be considered at the selection of d. We found the downslope index values to be less affected by changes in DEM resolution than local slope. Three applications are presented where the new index is shown to be useful for hydrological, geomorphological, and biogeochemical applications.
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| 21. |
- Jenkins, A., et al.
(författare)
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HYDROLOGY
- 1994
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Ingår i: BIOGEOCHEMISTRY OF SMALL CATCHMENTS. - 0471937231 ; , s. 31-54
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Konferensbidrag (refereegranskat)
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| 22. |
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| 23. |
- Kauffeldt, Anna, 1981-
(författare)
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Disinformative and Uncertain Data in Global Hydrology : Challenges for Modelling and Regionalisation
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water is essential for human well-being and healthy ecosystems, but population growth and changes in climate and land-use are putting increased stress on water resources in many regions. To ensure water security, knowledge about the spatiotemporal distribution of these resources is of great importance. However, estimates of global water resources are constrained by limitations in availability and quality of data. This thesis explores the quality of both observational and modelled data, gives an overview of models used for large-scale hydrological modelling, and explores the possibilities to deal with the scarcity of data by prediction of flow-duration curves.The evaluation of the quality of observational data for large-scale hydrological modelling was based on both hydrographic data, and model forcing and evaluation data for basins worldwide. The results showed that a GIS polygon dataset outperformed all gridded hydrographic products analysed in terms of representation of basin areas. Through a screening methodology based on the long-term water-balance equation it was shown that as many as 8–43% of the basins analysed displayed inconsistencies between forcing (precipitation and potential evaporation) and evaluation (discharge) data depending on how datasets were combined. These data could prove disinformative in hydrological model inference and analysis.The quality of key hydrological variables from a numerical weather prediction model was assessed by benchmarking against observational datasets and by analysis of the internal land-surface water budgets of several different model setups. Long-term imbalances were found between precipitation and evaporation on the global scale and between precipitation, evaporation and runoff on both cell and basin scales. These imbalances were mainly attributed to the data assimilation system in which soil moisture is used as a nudge factor to improve weather forecasts.Regionalisation, i.e. transfer of information from data-rich areas to data-sparse areas, is a necessity in hydrology because of a lack of observed data in many areas. In this thesis, the possibility to predict flow-duration curves in ungauged basins was explored by testing several different methodologies including machine learning. The results were mixed, with some well predicted curves, but many predicted curves exhibited large biases and several methods resulted in unrealistic curves.
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| 24. |
- Kauffeldt, Anna, et al.
(författare)
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Disinformative data in large-scale hydrological modelling
- 2013
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 17:7, s. 2845-2857
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale hydrological modelling has become an important tool for the study of global and regional water resources, climate impacts, and water-resources management. However, modelling efforts over large spatial domains are fraught with problems of data scarcity, uncertainties and inconsistencies between model forcing and evaluation data. Model-independent methods to screen and analyse data for such problems are needed. This study aimed at identifying data inconsistencies in global datasets using a pre-modelling analysis, inconsistencies that can be disinformative for subsequent modelling. The consistency between (i) basin areas for different hydrographic datasets, and (ii) between climate data (precipitation and potential evaporation) and discharge data, was examined in terms of how well basin areas were represented in the flow networks and the possibility of water-balance closure. It was found that (i) most basins could be well represented in both gridded basin delineations and polygon-based ones, but some basins exhibited large area discrepancies between flow-network datasets and archived basin areas, (ii) basins exhibiting too-high runoff coefficients were abundant in areas where precipitation data were likely affected by snow undercatch, and (iii) the occurrence of basins exhibiting losses exceeding the potential-evaporation limit was strongly dependent on the potential-evaporation data, both in terms of numbers and geographical distribution. Some inconsistencies may be resolved by considering subgrid variability in climate data, surface-dependent potential-evaporation estimates, etc., but further studies are needed to determine the reasons for the inconsistencies found. Our results emphasise the need for pre-modelling data analysis to identify dataset inconsistencies as an important first step in any large-scale study. Applying data-screening methods before modelling should also increase our chances to draw robust conclusions from subsequent model simulations.
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| 25. |
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