Problems Related to Important Changes in River Regime Following Intensive River Training Works
During the 19th century intensive efforts were made in Switzerland — as well as in the adjacent Central European Countries — to control the major rivers within their alluvial plains. The land reclaimed from the river beds and flood plains greatly favoured
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PROBLEMS RELATED TO IMPORTANT CHANGES IN RIVER REGIME FOLLOWING INTENSIVE RIVER TRAINING WORKS Martin N.R. Jaeggi Laboratory of Hydraulics, Federal Institute of Technology, Zurich, Switzerland GENERAL DESCRIPTION OF SWISS RIVER CONTROL During the 19th century intensive efforts were made in Switzerland -as well as in the adjacent Central European Countries to control the major rivers within their alluvial plains. The land reclaimed from the river beds and flood plains greatly favoured progress in agricultural production, and later on in the industrial revolution. The traffic infrastructure of our days could not be imagined if these rivers had not been controlled and regulated. Life in the 20th century now relies to a big part on the safety of these alluvial plains. The population pressure on these regions has always been higher in these zones in Switzerland than in countries with a different topographic structure. This may explain differences in the practice of river training between different countries, e.g. Switzerland and the U.K. In Switzerland, river training ~n the 19th century mostly consisted of straightening and extensive narrowing of the river courses (width reductions from 1 to 2 km to about 100 m) and building of flood proof dykes. Since most of the alluvial plains are located upstream of lakes, one purpose of such river regulation was to improve sediment transport capacity so that the usually aggrading streams could carry their sediment to a lake and drop it there. In several cases rivers were artificially diverted to lakes in order to reduce the threat of sediment deposits to the alluvial plains. Sometimes an ideal cross-section could be found only after several attempts. The first regulation works with a certain but not sufficient width reduction resulted in accelerated aggradation. In more recent times, due to intensive gravel extraction (which was at first welcomed from a river engineering point of view), the trend reversed and bed degradation occurred. This K. V. H. Smith (ed.), Channels and Channel Control Structures © Springer-Verlag Berlin Heidelberg 1984
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made necessary the insertion of drop structures to fix the bed. One aim of river straightening was to achieve a stable plane bed. As can be expected from the present state of knowledge, many of those river beds deformed into alternate bars, so that the expected reduction of foundation works for bank protection remained an illusion. For other rivers plane beds were found to remain stable. After decades of operation the accelerated and localised sediment input to the lakes created new problems. This paper deals with a research programme on alternate bar formation and a model study for a new solution at a river mouth to a lake. Both problems may be seen to be a consequence of intensive river training. ALTERNATE BAR FORMATION IN STRAIGHT RIVERS 2.1 Description, Experimental Programme
Fig. 1
Alternate bars in the regulated Alpine Rhine
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Fig. 2
Regulated Rhone River with stable plane bed.
As figures 1 and 2 illustrate, some of the co
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