Evolution of the embanked floodplains
The evolution of the embanked floodplains has been studied extensively by Middelkoop (1998), Asselman (1998), Wolfert (2001) and Hesselink (2002). The studies of Middelkoop and Asselman are also concerned with the effects of climate change on the sedimentation of the rivers Rhine and Meuse. Kwadijk (1993) modeled the effects of climate change on discharge of the Rhine.
- Figure 1 Historic evolution of the embanked floodplains (Middelkoop 1998), as a a result of human interference.
A large part of the embanked floodplains was formed only during the last 3 or 4 centuries. Their development has been strongly influenced by humans: in fact they can largely be seen as the result of land reclamations from the river bed. Figure 1 schematically shows the step wise development of such a floodplain of the river Waal (Middelkoop 1998).
The geomorphology shows a typical point bar geomorphology of scroll bars and swales, and some residual channels (Figure 3). Analysis of historic river maps (the oldest from 1600 AD) shows, that sand bars, formed in the river beds, were planted with willows, which enhanced the trapping of sediments. New sand bars were successively formed in a downstream direction. The development began when a high sand bar or an island in the river bed was formed close to the river dike (1634). Dams were built to connect the island to the land. The channel between the former island and the dike was closed off and gradually filled up with clay. During several phases (1723-1921) the floodplain became larger when new islands were reclaimed and merged with the floodplain. The vegetation shows a sequence, related to the geomorphological development of the floodplains: in the beginning, the island was covered with a natural vegetation of reed and willow shoots (1723, 1773). After a few decades this vegetation was replaced by willows, while reed and young willows were still growing in the low and wet parts. Finally, the willows were cut and were replaced by grasslands (1873, 1921). This succession of vegetation was repeated for each new phase of embanked floodplain growth. The resulting morphological pattern of these floodplains therefore was formed during subsequent stages of floodplain growth under the influence of humans. It is not reflecting a former braided river or a set of parallel active channels in the past. In other embanked floodplains, the original point bar and swale topography is still visible, for example near Maasbommel-Nieuwe Schans (Figure 2 and 3).
- Figure 2 Maps of the embanked floodplain of the river Maas around 1850 near Maasbommel and present location of the Maas residual channel (topographical maps 1: 50.000).
- Figure 3 Picture of the embanked floodplain near Maasbommel (location see Figure 2). The view is from the north to Ooijen in the south. In 1860 the first depression was still the main channel of the Meuse. The channel was cut off artificially. The residual channel fill is 6 m thick and consists of clay and peat.
- Figure 4 Map of the Heerewaarden area in the 17th century.
- Figure 5 Geological map of the Heerewaarden area (after Middelkoop 1998).
Figure 4 shows the area around the former confluence of Maas and Waal, near Heerewaarden. In the 17th century, the two rivers were connected at three locations. At the southernmost location, the Spaniards built a fortress in 1599, during the 80-year war between the Dutch and the Spanish. The other fortresses on the map were built later. The geological map (Figure 5) still shows the connections between the two rivers, by the presence of channel deposits.The construction of the Pannerdens Canal in 1707 (Figure 6) was a major engineering work, that fixed the discharge distribution among the three branches of the Rhine: Waal (6/9 of total Rhine discharge), Nederrijn-Lek (2/9 of total Rhine discharge) and IJssel (1/9 of total Rhine discharge).
- Figure 6 Construction of the Pannerdens Canal in 1707 AD.
- Asselman, N.E.M. (1997), Suspended sediment in the river Rhine. The impact of climate change on erosion, transport and deposition. Netherlands Geographical Studies 234, 257 pp. KNAG/Faculteit Ruimtelijke Wetenschappen Universiteit Utrecht.
- Hesselink, A.W. (2002), Morphological development of the embanked floodplains of the Rhine and Meuse in the Netherlands in historical time. Netherlands Geographical Studies 292, 190 pp. KNAG/Faculteit Ruimtelijke Wetenschappen Universiteit Utrecht.
- Kwadijk, J. (1993), The impact of climate change on the discharge of the River Rhine. Netherlands Geographical Studies 171, 208 pp. KNAG/Faculteit Ruimtelijke Wetenschappen Universiteit Utrecht.
- Middelkoop, H. (1997), Embanked floodplains in the Netherlands. Netherlands Geographical Studies 224, 341 pp. KNAG/Faculteit Ruimtelijke Wetenschappen Universiteit Utrecht.
- Wolfert, H. (2001), Geomorphological change and river rehabilitation. Case studies on lowland fluvial systems in the Netherlands. Ph. D. Thesis Universiteit Utrecht. Alterra Scientific Contributions 6, 200 pp.