Dynamika transportu fluwialnego górnej Parsêty jako odbicie funkcjonowania systemu zlewni

Dynamics of fluvial transport of the upper Parsêta River as a response of the catchment system

Andrzej Kostrzewski, Malgorzata Mazurek, Zbigniew Zwoliñski

6. Sources of material for fluvial transport

Like river runoff, the flow of solids is controlled by spatially and temporarily variable sources of supply (Fig. 6.1). The character and rhythm of the young-glacial relief, lithological diversification, drainage density, shape of the valley and channel, as well as the land-use pattern, are factors determining the magnitude of supply of the upper ParsÍta and the distribution of its sources. On completing geomorphological mapping of the area, five principal groups of sources of solid particles (mineral and organic) have been distinguished in the river channel. They are: the drainage system (supply through streams and groundwater), the wetted perimeter of the river channel (supply from the channel bed and banks), the floodplain (surface and underground supply), biogenic supply, and man-made supply. The results of the mapping of the upper ParsÍta channel are presented in Table 6.1.1.

The occurrence and intensity of processes responsible for supplying sediment for transport in the ParsÍta channel depends largely on lithology, channel morphology and conditions of river flow, hydrogeological conditions, and vegetation. In lowland rivers, bed and bank erosion are thought to be the primary processes responsible for the supply of material transported in the river channel. The particle-size distribution of the upper ParsÍta bed deposits (Fig. 6.1.3) indicates three basic lithofacies in the long profile of the river, viz. one with an even particle-size distribution in which fine sands predominate, one with the predominance of gravels, and one with the predominance of medium sand. The most important zone of suspended load supply is the wetted perimeter. Both the bed deposit facies and suspended load concentrations (Fig. 6.1.5) are clearly related to variations in the slope gradient in the long profile (Fig. 6.1.2). An important source of the suspended load and bedload is such washed-out features of channel accumulation as channel bars and point-bars. During efficient precipitation the area supplying the material expands to include terrain adjacent to the river channel. Substances dissolved in river water may come from the atmosphere, the biological cycle, and primarily from the processes of chemical weathering taking place in the soil and deeper down in the substratum (Fig. 6.1). Table 6.2.1 shows selected physical-chemical parameters of precipitation water registered in the meteorological section of the Storkowo Geoecological Station. The results of studies carried out in a pine-forest test area (in the K≥uda catchment) reveal significant variations in the physical-chemical properties of precipitation water (Table 6.2.2). The transformation of precipitation into runoff is associated with the constant change in the physical-chemical parameters of water supplying the river channel. Hydrochemical profiles of the main stream of the catchment (Figs. 6.2.1, 6.2.2) make it possible to establish the shares that various zones have in supplying the river channel with water. They also allow an assessment of the importance of the tributaries and the recognition of local sources of man-made pollution. When analysing the physical-chemical properties of water down the long profile of the upper ParsÍta, three zones of dissolved material supply can be distinguished. The first covers the 3 initial kilometres of the river course and is characterised by the highest ion concentration and a low SiO2 concentration. The high concentrations of dissolved material result from supplying from areas rich in calcium carbonate, and from the supply of readily soluble compounds in water drained from organic and mineral soil horizons. The water flowing along the next 5 kilometres of the ParsÍta course is made up, in varying proportions, of water from subcatchments supplied by different water-bearing horizons, each with its own duration of the hydrological cycle. The third zone, again 5 kilometres long, displays the least variability of dissolved components except for silica concentrations, which show an upward tendency. This is indicative of feeding by groundwater of fairly stable physical-chemical parameters. The hydrochemical profiles along the upper ParsÍta course have shown variations in the concentration of Ca+2, K+, SO4-2, and SiO2 ions to be useful as natural indicators when studying the mechanism through which precipitation is transformed into river runoff. They may also be used in the examination of spatial differences in the sources of supply and their geochemical properties.

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