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Dynamic Bed Causes Irregular Course Of River

How can you manage and design rivers such that no floods occur, whilst still ensuring navigation for shipping and a continuation of the agricultural, ecological and recreational functions? Dutch researcher Saskia van Vuren discovered that uncertainties in the behaviour of the riverbed play an important role in predicting the effects of design measures, such as lowering floodplains.

     
 Van Vuren investigated the effect of the riverbed on the water level. The photos show high water in the River Waal in 2002 between Brakel and Zaltbommel. (Image courtesy of Netherlands Organization for Scientific Research)
 
In view of future large-scale projects, such as river improvement measures in the project 'Ruimte voor de rivier' [Room for the River], the societal relevance of responsible river management is increasing. The large-scale spatial redesigning of the Rhine Branches could result in greater dynamics in the riverbed, which could give rise to more problems for shipping. That might lead to increasing costs for maintenance dredging. Moreover an increase in the riverbed dynamics might also affect the high-water levels. Saskia van Vuren investigated the uncertainty in riverbed dynamics.

Changes in the riverbed elevation can give rise to high-water problems and flooding, drought problems which hinder shipping, problems with respect to the discharge distribution at bifurcation points, and erosion problems. Fluctuations in the groundwater level caused by these so-called morphological changes can exert an influence on the local ecology and agriculture. In her thesis, Van Vuren uses examples to illustrate how insights into the uncertain behaviour of the riverbed can support managers in the design, management and maintenance of the river.

A closer look at the Rhine

The researcher evaluated the effect of various river improvement measures along the Rhine on the riverbed, such as lowering floodplains, constructing secondary channels, and setting back dikes. Some locations were found to be more sensitive to management measures than others. This comes to light in the average changes, the variability and the seasonal dependency of the shape of the riverbed.

At present, the hydraulic models used by river managers for high-water level predictions often assume a fixed bed elevation. Van Vuren discovered that mid-term variations in the bed elevation and bed activity around bifurcation points influence high-water levels. This being the case the researcher argues that in future, high-water level predictions must take morphological dynamics (how the riverbed changes in response to altered circumstances) into account.

Saskia van Vuren's research was funded by Technology Foundation STW.

 

Source: Netherlands Organization for Scientific Research. December 2005


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