Abstract

Avulsion parameters greatly influence alluvial architecture, because they determine channel density and interconnectedness. Reliable data on avulsion parameters is still scarce. From a detailed reconstruction of the Holocene avulsion history of the whole Rhine-Meuse delta we determined quantitative values for the avulsion parameters: avulsion frequency, avulsion duration, and interavulsion period. In the Rhine-Meuse delta the number of coeval channels is related to the avulsion frequency. Calibrated 14C intensity histograms are used to analyze 14C dates of beginning and ending river activity. The histograms show that instantaneous and gradual avulsions were almost equally important in the Rhine-Meuse delta. A high avulsion frequency occurred from 8000 to 7300 cal yr BP (a total of 17 avulsions, i.e., 2.43 avulsions/100 years). During this period the avulsion frequency was related to the high rate of sea-level rise, which induced fluvial sedimentation in the present near-coastal area. After 7300 cal yr BP avulsion frequency decreased as a result of a continuously decreasing rate of sea-level rise. From 7300 to 3200 cal yr BP avulsion frequency was low; 35 avulsions took place within 4100 years (0.85 avulsions/100 years). Approximately 5000 cal yr BP the coastal barriers became closed and large-scale peat formation occurred. This resulted in fixation of the river channels and low cross-valley gradients, reducing the chances for avulsion. Between 3200 and 1400 cal yr BP avulsion frequency was high again (a total of 34 avulsions, i.e., 1.89 avulsions/100 years) as a result of increased discharge and/or within-channel sedimentation, which enhanced chances for avulsion. The period of activity of channel belts shows no significant trend on the time scale of the Holocene. It is highly variable and averages 1280 ± 820 cal yr. The avulsion duration fluctuates between less than 200 and 1250 cal years and averages 335 cal years. The avulsion duration shows no significant trend through time and remained constant until at least 1900 cal yr BP. Avulsion duration seems not to be influenced by aggradation rate. Average interavulsion period is shorter than the period of activity of channel belts, and is approximately 945 cal years. In the Rhine-Meuse delta, on the time scale of the Holocene, interavulsion period and avulsion duration are on average constant. Therefore, the number of coeval channels is directly related to avulsion frequency. Available evidence from other rivers and deltas around the world, however, suggests that the relationship between these avulsion parameters is not everywhere the same.

You do not currently have access to this article.