Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 16

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
Winter conditions of low air temperature cause development of ice phenomena at rivers and reservoirs, creating often problems in their exploitation. There is a need to continuously monitor the spatial extension of ice phenomena and their different forms. Local water authority (RZGW Warszawa) prepares for rivers under their administration a daily reports on ice conditions in winter. Ice reports are prepared from visual inspection of the RZGW personnel visiting selected sections of the river course. This is specially problematic in holidays and weekends when usually data from observations are missing. In this study it is tested application of microwave remote sensing data from Sentinel-1 platform to observe the development and recession of the ice cover at the Dębe reservoir in winter 2017. Satellite Sentinel-1 radar images are distributed by the European Space Agency (ESA) on the open access policy. These are two satellites A and B which every 2 days collect images in SAR active remote sensing technique. Dębe reservoir was created in 1963 by closing by the barrage Narew river below its confluence with Bug river. Maximum water head is 7.10 m, and average 6.8 m. Area of the reservoir is 30.3 km2 average discharge of Bug river at Wyszków gauge is 162 m³ ·s⁻¹, and Narew river at Zambski Kościelne gauge 139 m³ ·s⁻¹. Retention time of water in the reservoir is 3–4 days. Comparison of the average water temperature at gauge Zambski Kościelne and Wyszków from the winter half-year of the period 1963–1981 shows the increase of water temperature by 0.5–1 C after the year 1972 when Ostrołęka power station was put in to operation.. This difference in the temperature between Narew and Bug rivers is reflected by the ice conditions at the end of winter season. Sentinel-1 SAR instrument emits electromagnetic wavelength of 6 cm (C band), and are use two polarizations VH and VV. Using SNAP program geometric correction and color composite was created for selected images at the beginning and end of ice cover at Dębe reservoir on Narew river, covering period January 5-March 6, 2017. It has been found that interpretation of the Sentinel-1 images is most problematic if we want to detect boundary between open calm water and new fast ice. The flow of pancake ice on January 5, 2017 had been recorded and the pattern of ice distribution compared to flow lines calculated by the hydrodynamic CCHE2D model. Result of the hydrodynamic modeling shows circulation pattern in the widest part of the reservoir where are also the most favorable conditions for lake type of ice cover formation. End of ice cover is represented by the image of February 26, 2017 which shows the Narew river free from ice due to higher temperature of the water. Relatively simple visual interpretation of the Sentinel-1 VH and VV images can by used in the study of ice phenomena on major rivers and lakes.
In the hydrological cycle of river valley a vertical water fluxes are controlled by climate (precipitation and evapotranspiration). In the Vistula river valley near Plock periods of water recharge, surplus and deficit in the valley landscape units has been determined using Thornthwaite water balance method. A good tracer of that process is Cl and NO3 concentration in the ground water. Concentration of these elements in ground water varies depending on the landscape unit, under the dune fields is lowest due to a good recharge ratio. In all units lowest concentration of NO3 in the ground water are observed in a spring time due to a dilution effect in the period of water surplus in the fluvial system. In the chemistry of small creek Nida representing lateral river runoff reaching main valley a similar to ground water chemistry pattern has been observed. A lowest concentration of Cl (30-40 mg dm-3) and PO4 (0.25-1 mg dm-3) occur in spring time due to a dilution effect. Highest concentrations of Cl (50-70 mg dm-3) occur in late summer and fall. Spring time with a high runoff produces the highest loads of nutrients. Wetland on the floor of the Vistula river valley located in the lower reach of Nida catchment acts as a natural trap of the nutrients. It lowers concentration of PO4 during low flows by 55% and NO3 by 35 % Efficiency of reduction depends on the river discharge.
6
63%
With the use of two-dimensional hydrodynamic model CCHE2D it has been calculated a flood passage through the contemporary Vistula River channel in Warsaw. The channel reach is between km 501-521 and limited by flood protective dikes. For the model calibration it has been used a measurement of water surface of the 1997 year flood. To study the floodplain high vegetation influence on the river flow resistance it has been calculated two scenarios of flood passage. Scenario zero of recently existing vegetation and scenario one of tall trees clearance at the right bank between km 509-519. Simulations have been run for the discharges Qp1% = 6430 m³/s i Qp0,1 % = 8250 m³/s. Obtained results shows that the highest lowering of the water surface by 0,56 m due to trees cutting occurs at discharge Q0,1% on km 510. In the river reach km 511-516 river flow has a very high average velocities in vertical, exceeding in some places 3,7 m/s. Verification of these results has been done by comparison with hydrometrie measurements.
Process of sedimentation in Włocławek Reservoir has been described using echo-soundings made by Hydroprojekt on 1971 and 1992. Cross sections from echosounding have been registered to cartographic coordinates and bottom contour lines drawn. Digital model of river bottom has been calculated and raster map of bottom relief from year 1971 and 1992 have been subtracted giving the map of sedimentation balance. Hydraulic parameters such as channel width, average velocity and average depth at the cross-sections of the reservoir have been calculated using NCCHE2D model. Results are giving better understanding of the sedimentation conditions and allows to delineate three different zones of the reservoir - riverine, transitional and lacustrine.
Poland belongs to main sources of pollution reaching Baltic Sea. From Polish territory with a river runoff it is transported 11 % of N load and 37% of P load. Most of the nutrients come from non-point sources, which are generated from agriculture areas of the river basins. It is known that Polish agriculture is in a phase of recession due to economical changes after year 1989 transformation. To understand what is an influence of these changes and environment protection investments in Poland on an improvement of river water quality this study has been performed. River basins at Polish coast (Rega, Parsęta, Słupia, Reda, Pasłęka), and at Swedish coast (Rönne, Lagan, Nissan, Ätran, Viskan) have been compared. Main criteria of the river basins selection was their size, dominance of agriculture in land-use, similar hydrological conditions, and available data on river runoff and chemistry. Temporal changes in water quality has been studied using averaged environmental monitoring data from periods 1990-1993 and 1994-1997, as well as socioeconomic data from census survey in 1988 versus 1997 (1995 in Sweden). It has been found that in Polish basins reduction of point pollution sources took place, combined with extension of water supply systems. Agriculture shows a decrease in production intensity, which results in lower nutrients loads reaching rivers. These two factors can explain a radical decrease of nutrients loads reaching Baltic from Polish basins. This is visible especially in case of P. Further improvement of water quality in case of Polish basins can be achieved by increase of volume of sewage treated in the countryside, and reduction of non point pollution in ecotone zones.
Geomorphology of the Vistula River Valley in Warsaw has been presented, as well as history of flood protective dikes and channel regulation works. From historical sources we have the description of catastrophic flood of 1635. The level of the flood of 1844 has been preserved in the form of high water mark. Using two dimensional hydrodynamic model CCHE2D the simulation of thousand years recurrence flood has been performed. It has been compared the result of the calculations with historical chronic and high water mark. It has been calculated the pattern of flood water flow over Praga district terrace, showing also the possibility of flood flow directly to Narew river through the relive channels leading by a terrain depressions of today's Zeranski Canal and Bródnowski Canal.
The paper presents a possibility of an application of Imaging Spectroscopy to acquire thematic maps of water quality. Thanks to very high spectral, radiometric and spatial resolution of AISA hyperspectral images, which allow to identify zones of water with different properties. An analysis of the spatial distribution of physico-chemical parameters of water was made in 2014 for the Zegrzyńskie Lake. A Hhyperspectral image was acquired by the MGGP Aero aircraft and the Finnish AISA Eagle scanner. Remote sensing indices of water quality (Secchi Disk Depth (SDD), Colored Dissolved Organic Matter (CDOM)) and vegetation index – Carotenoid Reflectance Index 1 (CRI 1), which determines the content of chlorophyll and other plant pigments in the water, was calculated on the image. Based on spatial distribution of water quality indices the IsoData classification was performed. The result was a set of maps with five zones of concentrations of different substances in of the Zegrzyńskie Lake. The verification was made based on in-situ acquired samples of water during airborne data imaging. Due to differences in suspended substances load and different water velocity Bug and Narew water flow in separate streams and mix in the middle of the artificial lake. Following research showed a high correlation between the calculated indices and field measurements. They also confirmed the usability of AISA hyperspectral images to create thematic maps of water quality.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.