Procesy brzegowe i osady denne wybranych zbiorników wodnych w warunkach zróżnicowanej antropopresji : na przykładzie Wyżyny Śląskiej i jej obrzeży

Abstract

Formation of artificial water reservoirs has caused the appearance of qualitatively new morphogenetic processes, conditioning morphological evolution of concave landforms. Anthropogenically shaped - even as a whole - reservoir basins (Fig. 3-6, 7-10), are often not more than several dozen years old and are relatively young element of the geographical environment. Simultaneously these changes are unusually dynamic and prove the reaction of the natural relief-forming processes on the relief anthropogenisation, and concern three characteristic zones of artificial water reservoirs basins, i.e. contact area of river and lake waters, littoral zone and the bottom. Investigation carried out in the years 1993-2000 (Tab. 1-3) particularly concerned four artificial lakes (Fig. 2; Tab. 8). The first of them is reservoir Pogoria III (Fig. 6) in the catchment of the Pogoria (Tab. 4), the second one - Przeczyce (Fig. 5) in the catchment of the Czarna Przemsza (Tab. 4), the next Świerklaniec, which is also called Kozłowa Góra water reservoir (Fig. 4), located in the Brynica catchment (Tab. 4) and Dzierżno Duże reservoir (Fig. 3) in the Kłodnica catchment. The subjects of carried out investigation were also several dozen other water reservoirs in the area of Silesian Upland and its borders (Fig. 1). Identification of research problems, based on the initial morphological and limnological study, allowed designating the range of elaboration and formulating aims of this work, which particularly concern: 1) distinguishing of types, presenting reasons and conditions of shore landforms formation within water reservoirs, 2) evaluation of both formation conditions and differentiation of bottom deposits within water reservoirs; 3) influence of varied anthropopression on the course of changes in shores morphology and reservoir basin bottom; 4) evaluation of morphological stage of artificial water reservoirs development; 5) course of morphological changes in basins of selected water reservoirs in Silesian Upland and its borders in the bearing of similar processes occurring within other artificial water reservoirs. Artificial water reservoirs in Silesian Upland are characterised by the occurrence of shore processes. Their intensity and range are conditioned by many factors. To the most important of them belong - apart from the size and shape of lake basin (Tab. 5; Fig. 3-6) - waving connected with local anemological conditions (Tab. 6, 7), fluctuations of water levels (Fig. 11) and lithology of the direct neighbourhood of the reservoir (Fig. 12-15), very often having very simple transmission on the character of shore configuration and relative heights (Tab. 9). The most spectacular changes in littoral are observed within post-exploitation and dam reservoirs, whereas smaller changes - within the range of shore zones of reservoirs in subsidence basins. All reservoirs (post-exploitation, dam, in subsidence basins) are convenient place of rock waste accumulation in contact zone of river and lake waters. The change in energy of flowing waters occurs here and in result of rock waste sedimentation deltas or alluvial fans are formed (Fig. 3, 28; Phot. 1), which are eroded (cut) in periods of low water levels in reservoirs. In later period the processes of organic matter sedentation are of significant importance, which are especially morpho-shaping at periodically dried surfaces. The most spectacular example is the delta of the Kłodnica, formed in the mouth zone of this stream into Dzierżno Duże water reservoir (Fig. 3), characterised by large size. Other landforms are decidedly less striking (e.g. deltas of reservoirs Rogoźnik and Pogoria I), but they also document spontaneous reaction into the process of relief anthropogenisation (Fig. 28; Phot. 1). Deltas or alluvial fans are often replaced by zones of accumulation, occupying large areas. Deltas unusually rarely can be observed within shores of water reservoirs in subsidence depressions and collapse depressions (Phot. 10), considering the character of reservoirs without drainage and connected with it the lack of waste rock supply. The sign of intensive morphological changes are relatively not numerous abrasion landforms at shores of dam reservoirs, plenty of them within post-exploitation reservoirs (Fig. 16-21) and lack within shore zone of reservoir in subsidence depressions. Active cliffs (or only periodical of dead cliff features) can be mostly met in the place of former edge of exploitation field of reservoirs: Dzierżno Duże, Pławniowice, Dziećkowice. At shores of Świerklaniec they do not occur. At shores of Przeczyce they are rare in the place of contact of lake waters with valley slope-foots of terrace scarp features. The majority of dam reservoirs is characterised at the very most by terrace levels, which are usual landforms occurring under conditions of changing damming up. The problem of recession rate of rocky walls, expressed by hitherto existing amount of material originating from abrasion of cliff shore is similarly presented. Regarding even very overestimated values for Dzierżno Duże, it can be amounted about to 60 000 c. m., whereas for the Pogoria III only 3000 cm. This amount for the reservoir Przeczyce is minimal, in relation to Świerklaniec it is difficult to say something because of the lack of cliff shore. These data indicate the large importance of shore denivelation in geodynamics of littoral zone, and confirm numerous examples of shore landforms from other water reservoirs, e.g. Żywiec in Tresna, Dobczyce on the Raba, Czorsztyn. The significant example on the scale of country, presenting abrasion processes is reservoir at Włocławek, and other examples are related to Siberian dam reservoirs (Phot. 7), reservoir on the Volga or reservoirs in Czech Republic (Phot. 8, 9). But accumulation landforms within water reservoirs in Silesian Upland and its borders occur mostly at shores of basins of dam and postexploitation objects (or their parts) of mature coast relief and varied biogenic shores of reservoirs in subsidence basins (Phot. 10). They are relatively often element of morphology of littoral zones of dam reservoirs - Goczałkowice, Przeczyce, Świerklaniec - and of some post-exploitation - e.g. Pogoria III. There are landforms (sandy tips, beaches, shore embankments, dried areas, zones of material accumulation, fixed with vegetation) built of mineral and organic material in dependence on local lithological conditions (Fig. 21-24, 26; Phot. 2-4). In Upper Silesian Region accumulative landforms relatively rarely make permanent element of coast relief and decidedly larger dynamic of changes is typical for accumulative ephemeral landforms (Fig. 25; Phot. 5, 6). Carried out investigations on the character and intensity of shore processes determine to distinguish four stages of littoral zone development, which in relation to morphological evolution of reservoirs are treated as geosystems. These stages are labelled as: abrasional shoreline varying, abrasional-ccumulative shoreline levelling, accumulative shoreline varying, biogenic fixation of shoreline. The first from abovementioned stages was finished for the object investigated, but it will be soon typical for now projected objects (e.g. Kuźnica Warężyńska), the second stage is related to reservoir Dzierżno Duże, the example of the third is Pogoria III and Przeczyce, whereas the four one - Świerklaniec. Carried out calculations of load balance in system - alimentation-outflow in the reservoir only slightly correspond with results of calculation capacity of bottom deposits (Tab. 10). It can be supposed that the size of reservoir silting amounts to: 0,2% of basin capacity - Pogoria III; 5,4% - Przeczyce; 7,5% - Świerklaniec; Dzierżno Duże - 2,3%, but the largest silting rate is significant for Dzierżno Duże and next: Przeczyce, Świerklaniec, Pogoria III. It can be admitted that the silting rate is adequate to the degree of catchment anthropogenisation. In mechanical composition of bottom deposits (Fig. 27) most often dusty and silty fractions predominate, and sandy fraction is characterised by decidedly less participation (with exception of Pogoria III water reservoirs). Mean depth of bottom deposits most often reaches from some cm (e.g. Pogoria III, Łąka, Pławniowice) to several dozen cm (Dierżno Duże, Przeczyce, Świerklaniec) in a case of flow reservoirs and from some a dozen or so, rarely several dozen cm in reservoirs devoid of clear flow character (e.g. Borki, Stawiki, Czechowice) and their spatial occurrence is highly varied. Interesting data were obtained in result of carrying out basic analyses of physico-chemical properties (Tab. 11) and mineralogical-petrographical analyses (Tab. 12) of bottom deposits. Content of some heavy metals especially confirms that the essential problem is the geochemical background level exceeding (Tab. 13). On the base of made calculations and at the assumption of stable character of the environment conditions it is possible to make conclusions of the time of the given objects life (Tab. 14), which is varied and amounts about to: 1 thousand years (Przeczyce), 1.26 thousand years (Świerklaniec); 1.48 thousand years (Dzierżno Duże); above 22 thousand years (Pogoria III). With except for Pogoria III the time of investigated objects life is comparable to life of some other water reservoirs of the Upper Silesian Region (e.g. Pogoria 1-1,6 thousand years, Goczałkowice - 3 thousand years, Dzierżno Małe - 2 thousand years), and - with time of further existence of the majority of Polish water reservoirs, which function already nothing less than some thousand years. It proves unusually rapid rate of water reservoirs evolution in the Upper Silesian Region. This rate is - thanks to anthropogenic stimulation - decidedly faster in comparison to natural objects, which are devoid of anthropopression.