RIVER ENGINEERING
As the consequences of massive interventions over the last centuries become increasingly apparent, the use of river landscapes and hydropower continues to grow, posing significant challenges for river engineering. A holistic consideration of the water and sediment cycle, both in river construction and restoration, and the optimization of river engineering measures to fulfill and maintain multiple functions are more necessary than ever.
In rivers, hydraulic structures interact with the flow and morphology and, on a larger scale, with the entire water and sediment cycle. The consequences of the unilateral pursuit of objectives in past river engineering measures are increasingly being felt worldwide. The situation of accelerated sediment transport in straightened and confined rivers is exacerbated by the increasing retention of sediments (e.g., through the expansion of hydropower). On the one hand, ecological problems arise due to the loss of habitat for animals and plants, for example, when sediment banks disappear due to morphological changes or floodplains dry out as the groundwater level drops due to erosion of the riverbed. On the other hand, human technical infrastructure can be affected, for example, if deepening of the riverbed destabilizes bridge piers or built-up banks, changes the effect of hydraulic structures such as groynes, or restricts the supply of groundwater for agriculture or as drinking water. The IWA contributes to research on innovative river engineering and optimized solutions to preserve or restore the diverse functions of rivers for humans and nature. As a starting point for problem-solving, process understanding, and success monitoring, the IWA also uses various methods to gain insights into the morphological changes and the current state of the rivers.
In the field of river engineering, the IWA contributes to the following topics:
Morphological River Development
Imbalances between the input and output of sediment lead to changes in average bed levels, which can lead to technical or ecological problems in the long term and restrict the functions of rivers for humans and nature. The IWA uses survey data and data concerning sediment transport to balance sediment, assess the morphological state of the water body, trace potential problems back to their cause, and derive solutions. Numerical models and laboratory experiments are also used for this purpose.
Restoration
The restoration of rivers requires allowing for morphodynamic processes, which present new challenges to the planning, implementation, and maintenance of river engineering measures and necessitate improved predictability of these processes. The IWA develops and uses numerical models for hydrodynamics, sediment transport, and bank erosion, as well as for their interaction with vegetation. Tools that are partly derived from their own investigations are also used. Laboratory model experiments, for example, are conducted to infer the width and sediment requirements of river corridors. The optimization of measures takes into account expected ecosystem services such as flood protection, or ecohydraulic and morphodynamic requirements for providing habitats.
Innovative River Engineering Measures – Longitudinal Structures
Longitudinal structures are used, for example, to confine parts of the river course (e.g., bank protection, guide structures) or to control the discharge of flood events (e.g., dikes). Increasing conflicts of use and adverse developments of previous river engineering measures require innovative solutions that fulfill diverse functions. The effects of the measures should be predictable despite the increased involvement of morphodynamic processes and vegetation. The IWA accompanies integrative hydraulic engineering projects in which, for example, regulatory structures are modified so that the effect of regulation is optimized while at the same time natural morphodynamic processes are restored. For instance, the IWA conducts measurements on bank erodibility and develops both simple, applicable tools and more complex, multidimensional numerical models to model lateral morphodynamic processes as well.
Innovative River Engineering Measures – Transverse Structures
In confined spaces, transverse structures can serve the controlled transformation of energy and reduction of the capacity to transport sediments. The impact on the sediment continuum, as well as the possibility for fish migration, must be considered in the design of the transverse structure. At the IWA, research is being conducted on the optimization of various innovative variants that minimize the impact on connectivity, such as the “pendulum ramp” or the “rhombus carpet.”
Innovative River Engineering Measures – Sediment Replenishment
If the sediment continuum cannot be restored or sediment supplied through natural processes, artificial sediment additions may become necessary to maintain or restore the bed level or habitat-relevant structures. Ship-based additions can only occur in navigable flows and may therefore not be sufficient, making alternative sediment addition methods through dumpings or conveyor belt additions necessary. The IWA investigates such sediment addition methods in field experiments, in the laboratory, and numerically, in order to be able to use them effectively in nature. In addition to the removal from the addition site, the spread of the sediment is also of interest, where at the IWA the process understanding is advanced thanks to extensive expertise and formulas derived from field and laboratory experiments.