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1.
  • Singh, V.P., et al. (författare)
  • Kinematic wave modelling of saturated basal flow in a snowpack
  • 1997
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 11:2, s. 177-187
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Movement of snowmelt water through a thin saturated layer at the infiltrating base of a snowpack is modelled by applying the kinematic wave theory. Analytical solutions are obtained for flow depth, velocity and discharge assuming that the rate of input to the saturated layer due to vertical percolation is constant. This assumption results in a linear rise and recession of the snowmelt hydrograph. The solutions are extended to the case of time-varying input. An explicit consideration of infiltration leads to a free boundary problem</p>
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2.
  • Singh, V.P., et al. (författare)
  • Kinematic wave modelling of vertical movement of snowmelt water through a snowpack
  • 1997
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 11:2, s. 149-167
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Vertical movement of snowmelt water through snowpacks is modelled by applying the kinematic wave theory. Analytical solutions are obtained for moisture flux, particle velocity, time history and velocity of meltwater front and total moisture content for a single melt event assuming that the melt rate is constant. These solutions are extended to the case involving more than one event.</p>
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3.
  • Westerström, Göran, et al. (författare)
  • An investigation of snowmelt runoff on experimental plots in Lulea, Sweden
  • 2000
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 14:10, s. 1869-85
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Empirical characteristics of snowmelt runoff are derived from observations made during snowmelt in a six-year period from 1980 to 1985 on three experimental plots and three plates located on the campus of the Lulea University of Technology in Lulea, Sweden. The plots had asphalt, gravel and grass surfaces. The plates were of different designs with one having the bottom cut out so that it was more like a frame. With the assumption that the asphalt surface of the plots was impervious, infiltration of meltwater into gravel and grass surfaces was deduced. Unlike rainfall infiltration, the graph of snowmelt infiltration rate resembled a flow hydrograph, with a distinct rise, a peak and a distinct recession. A strong linear relationship between the snowmelt runoff hydrograph peak and the snowmelt amount was found, which explained more than 90% of the variability in the snowmelt peak. This is in contrast with rainfall runoff where the relationship between runoff peak and volume is decidedly nonlinear. Hourly snowmelt runoff peak and daily snowmelt amount were found to exhibit nearly constant skew and follow approximately a Gumbel frequency distribution.</p>
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4.
  • Beldring, Stein, et al. (författare)
  • Kinematic wave approximations to hillslope hydrological processes in tills
  • 2000
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 14:4, s. 727-745
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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. </p><p></p>
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5.
  • Nyberg, Lars, et al. (författare)
  • Water transit times and flow paths from two line injections of 3H and 36Cl in a microcatchment at Gårdsjön, Sweden
  • 1999
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 13:11, s. 1557-1575
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>To investigate groundwater transit times and flow paths in shallow till soil, within an acidification study at Gardsjon, Sweden, two line injections of Cl-36 and H-3 Were made in groundwater during 1992. The first injection in January, when the two tracers were injected at the same depth, gave tracer transit times from injection line to outlet of some hours due to a runoff event on the first day. The subsequent recession period left a considerable amount of tracer in the unsaturated zone, which had transit times that ranged from weeks to months. Tracer recovery at the outlet was 78% for H-3 and 47% for Cl-36. Cl retention was indicated. The second injection in November, when H-3 was injected at 30 cm depth and 36C1 at 60 cm depth, gave recoveries of 96% for H-3 and 83% for Cl-36. Apart from an advective flow-dependent tracer transport, very fast tracer pulses occurred. The velocities for those pulses were of the order of tens of metres per hour. Highest tracer concentrations were observed in the superficial soil layers, which suggest that these layers were the dominant flow paths. </p>
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6.
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7.
  • Ali, Genevieve, et al. (författare)
  • Comparison of threshold hydrologic response across northern catchments
  • 2015
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 29:16, s. 3575-3591
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Nine mid-latitude to high-latitude headwater catchments - part of the Northern Watershed Ecosystem Response to Climate Change (North-Watch) programme - were used to analyze threshold response to rainfall and snowmelt-driven events and link the different responses to the catchment characteristics of the nine sites. The North-Watch data include daily time-series of various lengths of multiple variables such as air temperature, precipitation and discharge. Rainfall and meltwater inputs were differentiated using a degree-day snowmelt approach. Distinct hydrological events were identified, and precipitation-runoff response curves were visually assessed. Results showed that eight of nine catchments showed runoff initiation thresholds and effective precipitation input thresholds. For rainfall-triggered events, catchment hydroclimatic and physical characteristics (e.g. mean annual air temperature, median flow path distance to the stream, median sub-catchment area) were strong predictors of threshold strength. For snowmelt-driven events, however, thresholds and the factors controlling precipitation-runoff response were difficult to identify. The variability in catchments responses to snowmelt was not fully explained by runoff initiation thresholds and input magnitude thresholds. The quantification of input intensity thresholds (e.g. snow melting and permafrost thawing rates) is likely required for an adequate characterization of nonlinear spring runoff generation in such northern environments.</p>
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8.
  • Ameli, A. A., et al. (författare)
  • The exponential decline in saturated hydraulic conductivity with depth : a novel method for exploring its effect on water flow paths and transit time distribution
  • 2016
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 30:14, s. 2438-2450
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The strong vertical gradient in soil and subsoil saturated hydraulic conductivity is characteristic feature of the hydrology of catchments. Despite the potential importance of these strong gradients, they have proven difficult to model using robust physically based schemes. This has hampered the testing of hypotheses about the implications of such vertical gradients for subsurface flow paths, residence times and transit time distribution. Here we present a general semi-analytical solution for the simulation of 2D steady-state saturated-unsaturated flow in hillslopes with saturated hydraulic conductivity that declines exponentially with depth. The grid-free solution satisfies mass balance exactly over the entire saturated and unsaturated zones. The new method provides continuous solutions for head, flow and velocity in both saturated and unsaturated zones without any interpolation process as is common in discrete numerical schemes. This solution efficiently generates flow pathlines and transit time distributions in hillslopes with the assumption of depth-varying saturated hydraulic conductivity. The model outputs reveal the pronounced effect that changing the strength of the exponential decline in saturated hydraulic conductivity has on the flow pathlines, residence time and transit time distribution. This new steady-state model may be useful to others for posing hypotheses about how different depth functions for hydraulic conductivity influence catchment hydrological response.</p>
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9.
  • Andersson, Jan-Olov, 1966-, et al. (författare)
  • Spatial variation of wetlands and flux of dissolved organic carbon in boreal headwater streams
  • 2008
  • Ingår i: Hydrological Processes. - 0885-6087 .- 1099-1085. ; :22, s. 1965-1975
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>In order to investigate the relation between water chemistry and functional landscape elements, spatial data sets of characteristics for 68 small (0·2–1·5 km<sup>2</sup>) boreal forest catchments in western central Sweden were analysed in a geographical information system (GIS). The geographic data used were extracted from official topographic maps. Water sampled four times at different flow situations was analysed chemically. This paper focuses on one phenomenon that has an important influence on headwater quality in boreal, coniferous forest streams: generation and export of dissolved organic carbon (DOC). It is known that wetland cover (bogs and fens) in the catchment is a major source of DOC. In this study, a comparison was made between a large number of headwater catchments with varying spatial locations and areas of wetlands. How this variation, together with a number of other spatial variables, influences the DOC flux in the streamwater was analysed by statistical methods. There were significant, but not strong, correlations between the total percentages of wetland area and DOC flux measured at a medium flow situation, but not at high flow. Neither were there any significant correlations between the percentage of wetland area connected to streams, nor the percentage of wetland area within a zone 50 m from the stream and the DOC flux. There were, however, correlations between catchment mean slope and the DOC flux in all but one flow situations. This study showed that, considering geographical data retrieved from official sources, the topography of a catchment better explains the variation in DOC flux than the percentage and locations of distinct wetland areas. This emphasizes the need for high-resolution elevation models accurate enough to reveal the sources of DOC found in headwater streams.</p>
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10.
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