The conservation or restoration of ecosystem services has become a major topic in hydraulic engineering. Engineering practice lacks tools or design methods, which can be attributed to the lack of insight in processes at the interface of fluid mechanics, sediment transport and ecology. Examples include the re-establishment of sediment dynamics through river widenings, the design of riparian zones, the design of refuge areas, the rehabilitation of confluence areas into hotspots for biodiversity, the design of spawning areas for fish, the enrichment of the riverbed by adding large boulders or large wood.

Fig. Large wood in a river enhancing the heterogeneity in flow patterns, morphology and substrate

 

 

The focus of our research is on the eco-hydro-morphological processes and functions of large wood (Fig.). Large wood plays an important role in rivers. It creates heterogeneity in flow (stagnation zones, wakes, jets, vortex shedding, zones of increased turbulence, etc), morphology (zones of scour and deposition) and substrate (sediment sorting) and thereby improves habitat diversity. Moreover, there are also micro flow and habitat structures on the surface of the large wood itself. Large wood also creates transient storage of nutrients and contaminants. But large wood also has adverse effect: it causes additional flow resistance that leads to a rise in water surface elevation and in flooding risk. Large wood enriching has a high potential as a river restoration technique, but science-based design guidelines are at present lacking

The PhD of Théo Fernandez (started 08.2021) investigates in laboratory experiments how cylindrical obstacles in the river influence the flow, sediment transport, scour, morphology and inundation hazards. The application range goes beyond large wood in rivers: horizontal cylinders are also representative of pipelines across rivers, and vertical cylinders are also representative of bridge piers. This research is done in collaboration with the Institute for Hydromechanics at KIT, opens an external URL in a new window (Olivier Eiff). As an example of technological innovation, my team has developed low-cost load cells for measuring the total force acting on the cylinder, and an array of low-cost strain gauges for analysing the spatial-temporal coherence of vortex shedding in the wake of the cylinders.

The PhD of Iqbal Pratama (started 10.2021) investigates the formation of wood jams at bridges by means of laboratory experiments in combination with numerical simulations. Insight in the processes underlying the jam formation should lead to guidelines for an improved bridge design that minimizes the risks of jam formation.

Ingo Schnauder (Postdoc started 03.2019) investigates the hydro- and morphodynamics around large wood introduced in the river as a river restoration technique. The main focus is on the flow field and the development of the bathymetry in the vicinity of the wood, the retention in the wake of the wood, and the development of guidelines for the optimal design of in-stream wooden structures.