The diversity of fluvial system response to the Holocene hydrological changes using the Vistula River catchment as an example

Abstract

Złożoność reagowania systemu fluwialnego na zmiany hydrologiczne w holocenie (na przykładzie dorzecza Wisły) Hydrological changes during the Holocene are expressed in the variable frequency of extreme events and reflected in fluvial sediments and landforms. The diversity of fluvial system response depends on rainfall and runoff-sediment load regime, but is specifically related to the landscape type, size of catchment, and connectivity of valley reaches in the long profile, as well as to increasing human impact. This diversity is exemplified by the Vistula River catchment, investigated in detail during the last decades, providing a basis for demonstrating how various fluvial sequences are expressing palaeohydrological changes. Various types of flood events, ranging from those connected with heavy downpours to continuous rains and to snowmelt floods, play a leading role in catchments of various size and landscape type. Three main models of Holocene transformation of valley floors were distinguished: an incisional one in the mountain headwaters, an aggradational one in low-gradient river valleys, and transitional one reflecting phases of various frequency of extreme events (and their clusters) represented in sequences of cuts and fills. This last transitional type should characterise the middle valley courses, but is best developed slightly upstream on the direct foreland of the Carpathians, where the greatest fluctuations in the river discharge, bed load and suspended load are observed. The presence of many gaps in alluvial sequences requires a better recognition of Holocene hydrological changes and it is recommended to correlate fluvial data with other palaeorecords.