Spatial and temporal trends in bed elevation and surface grain size in the upper Rhine delta and Niederrhein

Abstract

This study analyzes and compares data for interventions (river training works, dredging and nourishment), discharge statistics, bed elevation and slope spatially and temporally in the Niederrhein, Bovenrijn, Pannerdensch Kanaal and Waal branches. River training works have actively taken place in the study area so far. Meander cutoffs and normalizations had mainly taken place between 16th and 19th centuries for navigability, and fixed layers, channel widening and side channels have been constructed in 20th and 21st centuries to mitigate river bed degradation and defend hinterland from flood. Dredging and nourishment have been actively conducted in the study area as well, and nourishment is more dominant than dredging in Niederrhein and Bovenrijn. Characteristic yearly discharges are estimated, which is highly fluctuating in time, and Bovenrijn discharge is distributed to about 64% and 36% for Waal river and Pannerdensch Kanaal respectively. According to data, discharge at Rees (Rkm 837) is higher than discharge at Lobith (Rkm 862) which is the most downstream station in the study area. This is probably because of the difference of Q-H relations in the Netherlands and Germany, and more research on the Q-H relations is needed to understand this phenomenon. The bed elevation of the study area is degrading, and it is still ongoing. Bed slope in the Niederrhein and Bovenrijn has steepened between 1934 and 1991, and after the moment bed slope is relatively stable and somewhat constant. Degradation rate is decreasing in time, but it is expected to take more time to reach equilibrium state. It is also confirmed that slope of Pannerdensch Kanaal and Waal is increasing in time.