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The paper presents the results of estimation and comparison of risk of extreme floods on rivers of various hydrological regimes. The hypothesis that extreme events occur with the same frequency in all rivers has been refuted. The borderline between extreme and common floods on 30 rivers from various geographical regions of Poland was defined on the basis of the standardized flow-duration curve for 1971-2006. The analyses resulted in grouping the curves into 6 groups. Four measures of flood magnitude have been proposed. The time distribution of extreme events during the last decades was estimated for the most dynamic rivers.
In the paper the Horton and Schumm laws have been tested in the kontext of their application for spatial description of river basin water run-off. In addition the possibility of the geomorphlogical instantaneous unit hydropraph (GIUH) application for the run-off simulation has been investigated. Special attention has been paid to the interpretation of the laws and their parameters. The problem of the empirical correctness of th laws in the various physiographic conditions has been also studied. The methods of the Horton and Schumm laws parameters evaluation have been compared and some recommendations have been given having in mind the standardization needs. The studies have been based on a 13 basins in the area of the Sudetian and Carpathian mountains. The results have been compared with a recorded 22 flood waves in a 17 gauging stations.
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One of the phenomena related to intensive urbanisation is the human settlement in the flood endangered area as well as increase of flood frequency and magnitude. This coincidence cause rise of the economical loses. As a counter measure usually it would be to build storage reservoirs or increase of storage capacity of the catchment. That problem has been illustrated by a case study on a south east part of Warsaw comprising catchment of a small stream (14 km long)- Potok Służewski. Rainfall water of the urban area is drained by that stream. Storage capacity of the catchment, mainly small ponds, located in the valley bottom, has been for a long time neglected. The intensive summer rainfall has caused flooding of the urban area at the Arbuzowa street. Looking for a solution to increase storage capacity it has been considered use of 12 ponds, located in the middle reach of the stream. These ponds form a natural feature of the landscape. It has been analysed a maximum capacity of the ponds as a possible retention element of the catchment. It has been shown, that existing capacity of the ponds is not sufficient for considerable reduction of the flood wave peak flows. It is recommended to look for additional storage in the catchment especially in the period of foreseen growth of urbanisation.
The paper focuses on the problem of natural water lifting in small river-lake systems caused by the different hydrological regime of the recipient (fig. 2B). The problem is shown on the example of Seven Lakes Stream flowing into Charzykowskie Lake (fig. 1, tab. 1, 2). The aim of the research was to investigate the range of the recipient backwater and its influence on the level and slope of water in the lower course of Seven Lakes Stream (fig. 4, 5, 6). The study was supported by statistical analyse of daily water stages measurements made in four water-gauging stations from 01.05.2000 till 31.10.2001. This period was characterised by favourable conditions to rebuilding the water storage after the years of water deficit (fig. 3). The lakes stages were significantly risen which allowed to find the events of backwater influence. Particular attention was paid on defining these Charzykowskie Lake stages which could cause the equalization or rising the water stages of the stream. This was the background to appreciate the number of events with the water lifting in two lakes localised in the lowest course of the investigated river-lake system in the period 1991-2005 (fig. 7). Prediction of backwater occurence in a longer period was developed on the basis of the analyse of the data from IMGW water-gauging station localised on Charzykowskie Lake.
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