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The article deals with the auto-naturalization problems of regulated streams in Lithuania. Research on such streams overgrown with woody vegetation was conducted in the Neris River basin in the Baltic Highlands. We chose to investigate the most urbanized rough terrain area of southeastern Lithuania. The regulated streams found in this area include stretches with a relatively high reserve of hydraulic conductivity. Therefore, with reference to the Water Framework Directive for improving the ecological situation, we assessed the possibilities of promoting the naturalization process. The average density of woody vegetation on the investigated slopes of regulated streams is T = 1.26±0.20 items m-2. The slopes with northeastern exposure point to the average density of woody vegetation counting TNE = 0.91 items m-2, which is 2.42 times more than that observed on the slopes with eastern exposure and 2.30 times more than those with southern exposure (TS = 0.39 items m-2). Under the presence of the recent density of woody vegetation, hydraulic measurements established Manning’s roughness coefficient that varied from 0.030 to 0.094. The conducted simulation indicates that the studied stretches of regulated streams lose a margin of hydraulic conductivity when Manning’s roughness coefficient reaches a threshold of 0.060-0.080. Planning the naturalization of regulated streams is first offered in the stretches of higher slopes (S0>0.003), where the maintenance of the adequate roughness of the bed may assist in designing the overgrowth of both slopes with woody vegetation.
Due to the recently increasing frequency of extreme changes in river runoff regime, scientific literature has dealt with the characteristics of runoff formation. Studies have been carried out on analyzing climate change and a lot of attention has fallen on land-use structures. Migration of precipitation through the river basin is influenced by the lithological composition of sediments. Its structure is determined by analyzing geological and geomorphological maps and by drilling boreholes in the selected area. With the help of boreholes the level of groundwater and lithological composition of sediments can be assessed. An installed system of lysimeters and piezometers in the borehole allows us to monitor the change of groundwater level and the amount of water moving through the unsaturated zone of sediments over time. The set of lysimeter boreholes allows us to capture and map the spacial change of these parameters. Following thorough analysis of the lithological structure of river basins in separate costal zones, this article aims at evaluating river runoff formation characteristics. The basin lithological factor was calculated based on large-scale maps using ArcGis software. In order to carry out more thorough analysis of the influence of lithology in given territories, sections of 0-50 m, 50-200 m, 200-500 m, 500-800 m, 800-1000 m, and >1000 m were established, calculating the distance in meters from the riverbank. Eight river basins of typical lithological structure (sandy, loamy, argillaceous) were selected and examined. The period of the year 1960-2013 was analyzed as this period and the relationship between the runoff and precipitation with correlation of 0.72-0.83 was established, as well as that with the lithological structure, established following the derivation of a hydromodule.
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