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Anthropogenic changes in the suspended..

and 1990 by 30% and is now only 2,700,000 t yr^-1. Concurrently, the load at gauging stations on the Upper Vistula has been reduced by 20-50%, whereas, in the river stretch directly below the mouth of the last Carpathian tributary, it has decreased from about 1,450,000 to 1,300,000 tyr^-1. Simultaneously, the suspended load at the mouth of the Vistula has decreased from about 1,100,000 to 900,000 t yr^-1 in 1968, and, after completion of the Włocławek Reservoir, the load was reduced by 50%. This trend will doubtless continue. If those deep reservoirs planned and under construction on the Carpathian rivers are completed, the total suspended sediment supply to the Upper Vistula will reach only 1,100,0001 yr^-1, and the rates of the transportation in the Upper Vistula could be reduced by morę than 50%. At the mouth of the river, the load will be approximately 250,000 t yr^-1, and, if the reservoirs on the Vistula are completed, it could be reduced morę by five times (Fig. 11). Finally, when those constructions on the Vistula already planned are finished, river channel deepening will cease and the total suspended load entering the Baltic Sea could be reduced by a minimum of 10-fold, when compared with the present-day picture. The Vistula will no longer be the primary source of polluted matter in the Baltic Sea. Intensive dredging practices in the reservoirs on the river will prolong their useful lives and river loads will be much reduced.

CONCLUSIONS

The history of the recent alluviation of the Vistula floodplain is very similar to that of river valleys and alluvial plains (Wolman 1967; Trimble 1970, 1974, 1976; Walling 1974; Gregory 1987; Knox 1987; Dai 1988). The results presented show that river regulation introduces very significant and swift changes in the magnitude of the river load and sedimentation; this regulation is acknowledged as the most significant cause of the changes which have occurred in the Vistula catchment in the course of man’s impact on the fluvial processes operating here. Firstly, during the initial years after groyne construction had begun, the rates of transportation accelerated; secondly, the Cascade building system drastically reduces the rates of that transportation. The Vistula channel regulation work magnified the river load and initiated considerable overbank sedimentation within the inter-embankment floodplain of the Upper Vistula, together with intensive channel aggradation and overbank sedimentation in the river downstream, effects which occurred in a short period. Rates of alluviation of the Vistula valley floor, which were accelerating several decades ago, have now been slowing down for recent decades and this process will be intensified in the futurę. The history of alluviation in the Vistula valley floodplain, which was initiated about 150 years ago, may be compared with the eąually swift changes of