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The runoff coefficient is one of the basic hydrological characteristics of the catchment. It can be determined using multiannual, periodic, or annual data measurement sequences. The variability of the runoff coefficient can be influenced by the terrain, the land cover, and the land-use in the catchment, among other things. The present study is an attempt to analyse changes in the runoff coefficient over a period of 30 years (1984–2013) for 49 gauging sections located in the Carpathian part of the Upper Vistula catchment. An additional analysis was carried out to study the impact of changes in the land cover and land-use of the catchment on the value of the runoff coefficient. Rainfall and daily flows data was made available by IMGW-PIB, whereas land cover and land-use data of the catchment come from the CORINE Land Cover system (1990, 2000, 2000, and 2012).
The aim of the work is to present a new hydrological model, developed at the Institute of Technology and Life Sciences (Instytut Technologiczno-Przyrodniczy), which can be used to simulate and study the formation of total runoff and its components from a small lowland agricultural catchment, in various meteorological conditions, taking into account the different initial retention status of the catchment and the impact of urbanized areas on the said runoff. The study involved the necessity of choosing the type of the model, and the manner of describing hydrological processes. Based on studying subject literature, as well as on the results of previous research and observations conducted in the upper Mławka river catchment (left tributary of the Wkra river), it was assumed that the most appropriate tool for prognostic and simulation purposes would be a conceptual model, that – in its structure and description of hydrological processes – would take into account the theory of active areas (variable source areas). It was assumed that a simple model would be developed as far as possible, that would create the possibility of simulating hydrographs of total runoff, surface runoff, subsurface runoff, and ground runoff from a natural catchment, and from catchments which have been urbanized to varying degrees. The work also includes the presentation of proposed principles for the classification of urbanized areas, taking into account their location within the catchment area and the way of draining rainwater, as well as a description of adequate modules of the model that would make it possible to simulate the runoff from the urbanized sub-catchments. The model is described by the state-space representations (differential equations) and output equations. It works with a one-hour time interval. The input is total precipitation and reference evapotranspiration. On the output end, we receive the total runoff hydrograph, and the hydrographs of the components of this runoff. The model includes 10 optimized parameters, occurring in procedures simulating processes in the natural, non-transformed part of the catchment, and 10 measurable parameters used to describe partially urbanized catchments. The article presents the results of identifying the parameters for the model, and of its verification. For this purpose, 5 hydrographs of total runoff were used, between 192 and 432 hours long, including storm surges. They were recorded in the catchment of the upper-course Mławka river. The obtained values of the criterion functions lead us to conclude that the quality of the model is very good. The model has been used for simulation studies of the impact of urbanization of the agricultural catchment on the parameters of river runoff (Krężałek 2018).
Wind, flow and wave measurements were performed in November–December in 2008 in the relatively narrow and shallow Suur Strait connecting the waters of the V¨ainameri and the Gulf of Riga. During the measurement period wind conditions were extremely variable, including a severe storm on 23 November. The flow speed along the strait varied between ±0.2 m s−1, except for the 0.4 m s−1 that occurred after the storm as a result of the sea level gradient. The mean and maximum significant wave heights were 0.53 m and 1.6 m respectively. Because of their longer fetch, southerly winds generated higher waves in the strait than winds from the north. All wave events caused by the stronger southerly winds induced sediment resuspension, whereas the current-induced shear velocity slightly exceeded the critical value for resuspension only when the current speed was 0.4 m s−1. A triplenested two-dimensional high resolution (100 m in the Suur Strait) circulation model and the SWAN wave model were used to simulate water exchange in 2008 and the wave-induced shear velocity field in the Suur Strait respectively. Circulation model simulations demonstrated that water exchange was highly variable, that cumulative transport followed an evident seasonal cycle, and that there was an gross annual outflow of 23 km3 from the Gulf of Riga. The horizontal distribution of waveinduced shear velocity during the strong southerly wind event indicated large shear velocities and substantial horizontal variability. The shear velocities were less than the critical value for resuspension in the deep area of the Suur Strait.
Displacement of fertilizer elements from arable soils to ground and surface waters is discussed. The rate of chemical elements leaching from soils was assessed by measuring their concentrations and outflow in drainage waters, and by measuring ion concentrations and outflow in surface runoff and watercourses draining farming areas.
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