There are always major events which determine a professional career. They can be looked at as a challenge and a chance to improve specific knowledge. The milestones described herein contributed to my professional experience as a river engineer. One is never alone to take up these challenges and to present solutions. I would like to thank all those who made such experience possible and who worked with me in these decisive moments.
Martin Jaeggi
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New Zealand braided rivers |
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Leave spent from Oct. 1978 to July 1979 at Lincoln University, Canterbury, New Zealand. Many opportunities to study wild braided gravel rivers. In a way, they are what Swiss rivers might have looked like in a natural stage. In a way I discovered there the field of river morphology. The acquired knowledge proved to be extremely useful for teaching and for a series of river restoration projects. |
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The Reussdelta project |
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In autumn 1980, the idea presented by ILU of giving up the channelized river mouth of the Reuss into Lake of Lucerne and to restore a natural delta. Such an idea was then not conceivable at all from a traditional river engineering point of view. A feasibility study in a hydraulic model finally convinced about everyone concerned. Between 1988 and 1991 the project was realised. The area is now considered to be an alluvial zone of national importance. |
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The Emme investigation |
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From 1985 to 1987, the Laboratory of Hydraulics, Hydrology and Glaciology of the ETH Zurich and the Geographical Institute of the University of Bern were in charge of a fundamental investigation of the Emme river and its catchment. This triggered the development of the computer programme MORMO able to simulate bed load transport and river bed changes. A major result of the study was the fact river bed erosion was a long term effect of the 19th century river regulation and was not induced by recent disturbances. Local river widenings were proposed as an alternative to drop structures to control channel incision. A first widening was realised near Utzenstorf in 1991/1992. |
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The Reuss flood in Uri 1987 |
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On August 24, 1987, the Reuss river flooded a large part of the canton of Uri in Central Switzerland. In the steeper reaches, channel widening and meander migration damaged railway and motorway structures. It became apparent that in such rivers big boulders contribute to a certain bed stability for minor floods, whereas such extreme floods may just continue to model the valley topography. In the lower part, the flood showed the limits of conventional river training design. Development in the alluvial plain behind the river dikes had taken place based an a somehow exaggerated safety feeling. The channelised river was able to carry a 100 year flood. However, this flood exceeded the design flood by about 25 %. The system totally collapsed. Three dam breaches were the consequence. Obstacles in the alluvial plain like a motorway embankment made the damage heavier. New guidelines for flood protection have since then been developed in Switzerland (see FOWG). For increasingly higher and rare floods progressive increase of damage may be accepted. Categories of objects are introduced with variable degree of protection. Floods have to be managed beyond the design discharge of river channels. The scheme should not collapse for extreme floods. Residual risk has to be made transparent. |
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The Saltina event in Brig 1993 |
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On September 24, 1993, the Saltina river flooded the centre of the township of Brig - Glis in the canton of Valais. The bridge built at the upper end of the alluvial fan was the major cause. It had been lowered in 1958. Although nothing happened during minor floods, this time deposition of sediment occurred in the bridge section. Soon, water spilled over the bridge and away form the channel. This caused a further loss of transport capacity and amplified the deposition process. This event made evident the role of sediment transport for floods of low frequency and the need for appropriate design of the structures concerned.
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