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Anthropogenic changes in the suspended..

DATA USED AND CALCULATION METHODS

Analysis of the present-day transportation and sedimentation rates of the Vistula is based on detailed measurements madę over the last 90 years. The following data have been recorded: the daily suspended load transportation at all gauging stations in its drainage basin (from 1946-1990); records of daily water discharges at all gauging stations on the river (from 1931-1990); results from repeated levelling of all gauging profiles on the river (from 1905—1990).

The average rates for suspended load show a decreasing trend along those river stretches which do not have a large tributary in flows (Fig. 3). A balance in the suspended load has permitted an estimation of the average

Fig. 3. Average rates of suspended load transportation, R, along the longitudinal profile of the Vistula. Lower continuous linę presents the current State of transportation rates, upper continuous linę presents estimated rates of that transportation, when the suspended load is not trapped by dams (before 1938). Broken linę presents the rates of transportation of the Lower

Vistula before 1968 (without the Włocławek Reservoir)

Cj — reduced rates of transportation from the 1930s until 1968, C₂ — reduced rates of transportation after 1969; C₃ — reduced rates of suspended load supply by the Vistula to the Baltic Sea due to sedimentation processes in reservoirs; (a-p) — gauging stations with suspended load measurements on the river. Mouths of main tributaries to the river are marked

rates of the overbank suspended matter which has been deposited, AS, to be madę. On this basis, it is possible to obtain information about changes in sedimentation rates sińce 1946. Balances have been computed separately for each stretch of the Vistula between successive suspended load gauging stations. The methodology for this is explained in the author’s paper (Łajczak 1995b). Information relating to the sedimentation rates which occurred before 1950 has been derived from analysis of repeated cross-section levelling of the inter-embankment zonę at successive gauging stations on the river, from