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Morphological behaviour of trained rivers


Description of the work package 

What is morphology and morphological behaviour?

Morphology in Delft Cluster is a branch of geomorphology that deals with the forms of natural water bodies such as rivers, lakes, estuaries, lagoons, coastal zones and seas, as well as with the processes that create and modify these forms. These processes are the erosion, transport and deposition of sediment (cobbles, gravel, sand, silt, clay). In its operational meaning, morphology includes not only planform and bed topography but also bed sediment composition. Morphological behaviour is the manifestation of the changes in planform, bed topography and bed sediment composition.

  Forms of natural rivers


Morphological behaviour: outer-bend erosion and inner-bend accretion

What are trained rivers?

One of the morphological phenomena in natural rivers is that the planforms of these rivers change due to bank erosion and bank accretion. This creates beautiful patterns of meandering or braided rivers. However, such wild untrained rivers decrease the safety against flooding because they provide favourable conditions for ice jams and vegatation on the river bed. Therefore many rivers have been trained, which means that their planforms have been narrowed and stabilized by means of bank revetments and groynes. This stabilization also arrests the loss of land due to erosion. Moreover, the narrower width improves river navigability.


A river trained with groynes

Morphology and floods

Morphology is a key factor in the risk of flooding. Erosion may break down dunes or undermine dikes. Sedimentation may raise the bed and thereby increase flood water levels. Morphology can also be a part of solutions to increase the safety against flooding, for instance when promoting deltaic sedimentation in front of a coastline by opening new branches of the river. Furthermore, interventions to reduce flooding risks have morphological impacts that need to be assessed carefully before implementation.

Themes of the Delft Cluster work package

The work package Morphological behaviour of trained rivers consists of three themes that are important for the prediction of flood water levels and the impact assessment of measures to increase the safety from flooding:

1. The morphological behaviour of bifurcations, because it affects the design water levels (MHW) along the Rhine branches and because it will be affected by measures to increase the safety from flooding. Details of sediment transport processes and bed-form development in the case of sediment mixtures are of critical importance for this behaviour.
2. Morphological processes during floods, because they affect the conveyance capacity and the hydraulic resistance, and hence the flood water levels under design conditions (MHW).
3. Interactions between Room for the River measures in the floodplains (lowering, widening, nature development, secondary channels) and sediment transport, erosion and deposition, because Room for the River measures induce a combined response of vegetation growth and morphological evolution in the floodplains that affects the durability and sustainability of the measures. Detailed knowledge on these processes allows optimization of maintenance strategies (cyclic rejuvenation).


Rhine bifurcation at Pannerden

The Morphological Triangle (Morfologische Driehoek)

The research under the work package Morphological behaviour of trained rivers has been defined by the Morphological Triangle
(http://www.ncr-web.org/downloads/Doelstelling%20Driehoek.doc), a thematic subdivision of the Netherlands Centre for River Studies (http://www.ncr-web.org/) that co-ordinates fluvial morphological research in the Netherlands. The three angles of the Triangle represent Rijkswaterstaat RIZA, universities and the two technological institutes TNO-NITG and WL | Delft Hydraulics. The following themes have been selected as major areas of research:
• Morphological development and stability of river bifurcations;
• Biogeomorphology of floodplains;
• Morphological phenomena during floods;
• Sand-silt-clay interactions.

 

Safety against flooding  HOME


Related Ph.D. students:

M. Abdu Nabi (TU Delft)

A.P. Tuijnder (TU Twente)


Related publications

Related links


Contact:
Erik Mosselman
+31 (0)15 285 85 69