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
5. Geoecosystem of the upper ParsÍta catchment
The upper ParsÍta catchment extends along the northern slope of the Central Pomeranian chain of end moraines within the so-called ParsÍta lobe. The relief of this area is the product of deglaciation during the Pomeranian Phase of the Vistulian, and of the processes of the Holocene morphogenetic cycle. The available relief of the particular subcatchments is diversified (Table 5.1.1). Their morphological character directs the flow of surface and ground water. The largest area of the upper ParsÍta catchment is occupied by deposits left by the accumulation of the ice-sheet, namely tills, sometimes with a very high sand content (Fig. 5.2.1). An important source supplying the ParsÍta with its bedload and suspended load is sands and gravels of fluvioglacial origin. The physical-chemical properties of the river water are directly influenced by zones of organic deposits. Surface deposits of the upper ParsÍta catchment display big variations in their mechanical composition. The dominant soils in the catchment are brown earths (Table 5.3.1), which occupy 46.1 % of its area. Next are black earths, which occupy 2.62 % of the area. In river valleys there are patches of alluvial soils proper (0.4 %), while podzols can be found in the woodland. A characteristic feature of the catchment is the mosaic land-use pattern conforming to the main forms of the young-glacial relief. Because of the high proportion of arable land and woodland (Figs. 5.4.1, 5.4.2), which together occupy as much as 77% of the area, the upper ParsÍta catchment can be classified as an agricultural-woodland one.
The two hydrological years under analysis, 1992 and 1993, can be regarded as average climatic years in relation to the 1951-1993 period (Fig. 5.5.1). However, 1992 was a much warmer and drier year than 1993 (Table 5.5.1, Figs. 5.5.2, 5.5.3). In 1992 the mean annual air temperature was 8.3įC, while in 1993 the respective figure was 7.6įC. The annual precipitation totals were 543.6 mm and 699.9 mm, respectively (Figs. 5.5.4, 5.5.5). Like other rivers of the coastal region, the ParsÍta has an even hydrological regime, being feeding by groundwater, rain and snow as well as spring floods. Mean annual stages were similar: 50.9 cm in 1992 and 50.3 cm in 1993 (Tables 5.6.1) but the mean annual stage for 1992 was the highest in the hydrological period 1986-1993 (Fig. 5.6.7). The upper ParsÍta discharges varied between 0.297 m3s-1 and 3.089 m3s-1 in the two years (Figs. 5.6.1, 5.6.3), and averaged 0.944 m3s-1. The dominance of the winter half-year over
the summer one in this respect results not only from the distribution and intensity of precipitation, but also to a large extent from the specific operation of the upper ParsÍta geoecosystem (Fig. 5.6.5). Over the two years there were 38 discharges that can be treated as floods. In only 11 of them the increment of discharge from the start of the flood to the peak exceeded 0.5 m3s-1 (Table 5.6.3). Maximum flood discharges ranged from 0.593 m3s-1 to 3.083 m3s-1. The most frequent causes of flood discharges are falls of rain and snow, as well as mid-winter and spring thaws. The two hydrological years 1992 and 1993, with their variable discharge scale and dynamics, provided a good opportunity to study the mechanism and magnitude of river transport under different modes of feeding of the ParsÍta.