Reconstruction of the Late Holocene river channel shifts in the North-Eastern part of the Lower Danube Plain based on historical data

Abstract

Several periods of increased fluvial activity and accelerated runoff / deposition have been identified during the Holocene in different regions of Europe (Macklin et al, 2006). According to Starkel (2002) the older phases were characterized by an incision of deeper and wider tracks and, since Roman period, especially during the past millennium, tendency had changed to aggradation, braiding and river avulsions. The turn to a more stable fluvial regime caused further incisions and the development of narrow and smaller meanders. All these fluvial responses can be mainly correlated with the climatic fluctuations (cooler and wetter phases alternating with drier and warmer ones), socio-economic changes (increased anthropic pressure) or both. The last major period of concentration of extreme meteorological and hydrological events is the Little Ice Age (LIA), which conventionally took place between the 16th and mid 19th century (Lamb, 1984). However in Romania the study of LIA and the associate fluvial effects is rather poor. The data regarding hydro-climatological events (weather conditions, floods) in the medieval period (mostly collected by Topor, 1960) is scarce and based on the few local chronicles and diaries of the foreign travelers. However these confirm the increased frequency and magnitude of the rainfalls in the summer (with several important peaks in the 1590 – 1690 interval) as well as the hard winters well documented for the rest of the continent. Changes in the configuration of the stream network, due to avulsions, can be evaluated based on historical maps only with the first half of the 17th century and the dating of the fluvial records is still missing.
The North-Eastern part of the Lower Danube Plain (Fig. 1) is a large alluvial floodplain where Siret River collects several major tributary streams draining SE Carpathians (Putna, Râmnicu Sărat, Buzău) or the Moldavian Tableland (Bârlad), before joining Danube, near Galaţi. Surprisingly Siret’s floodplain (until the confluence with Buzău) it is larger by a couple of kilometers than Danube’s, despite the anastomosed character of the last one. This can indicate a progressive Holocene shift of the Siret’s river course from the Carpathians to the eastern edge of the floodplain or a transformation from a multi-channel to a single channel pattern. The instability was also specific to main tributaries, as is confirmed by the presence of multiple abandoned sinuous courses and relict meander belts in the area. An important shift of the Siret River’s lower course to a more eastern position during medieval times was briefly discussed, for the first time, by Antonovici (1929) based on couple of historical documents. The few questions we will try to answer to in this study are: When was formed the actual configuration of the river network in the study region? What was the impact of the LIA? How relevant can be the analysis of the historical data in the assessment of the river channel shifts?