Colmation – Unravelling physical interactions of surface and subsurface processes

• Applicants: Professor Dr.-Ing. Markus Noack; Professorin Dr.-Ing. Silke Wieprecht
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445027764

The long history of research on fine sediment infiltration and accumulation into gravel riverbeds and the more recent research that relates these processes to the phenomena called colmation has shown the importance to understand the basic physics behind colmation processes; especially given their immense impact on river ecology. There is a consensus that surface and subsurface processes including hydraulic, sedimentary and biogeochemical processes provoke the spatio-temporal behaviour of colmation processes. However, substantial knowledge gaps exist regarding the interactions and the dynamics of the involved processes. The interactions between turbulences at the water-sediment interface, interstitial flows and progressive occlusion of pores with fine sediments are so far unexplored but fundamental to understand the dynamic behaviour of colmation processes. Hence, a general physical description of the interacting surface and subsurface processes and their effect on sediment infiltration and accumulation is still missing.The proposed work will focus on laboratory flume experiments to separate and investigate distinct processes involved in colmation by applying new and innovative measuring techniques (PIV and endoscopic PIV, gamma-ray-attenuation, 3D printing for defined bed configurations) that will result in a detailed and so far unique dataset. The key aspects of the proposed work include investigations on the role of turbulences at the water-sediment interface on infiltration rates and how they influence and interact with the interstitial flow fields in the pores. Next to vertical infiltration processes, the hydraulic forces acting on already infiltrated particles will be examined to derive thresholds for the initiation of interstitial sediment transport processes. Finally, experiments will be conducted to explore the dynamic effect of progressive pore occlusion due to sediment infiltration (dynamic development of clogging) on infiltration rates and on the flow fields in the pores as well as on the water-sediment interface. Thereby, variations of key parameters such as the riverbed configuration (particle size distribution, packing arrangement), hydraulic boundaries and supplied infiltration material will be related to the flow fields, infiltration rates and masses. Thus, the results of the proposed work have a high potential to describe the interactions and dynamics of colmation processes on a fundamental and physical basis. Especially the specific investigations on the interactions between surface and subsurface processes contribute to a deeper understanding of the phenomena colmation. The high-resolution measurement data on flow and sedimentation (also in the pore space) that will be obtained by the experiment represent an ideal data set for the development of further (numerical) modelling techiques.

• DFG Programme: Research Grants
• International Connection: Italy, United Kingdom, USA
• Cooperation Partners: Professor Gianluca Blois, Ph.D.; Professor Dr. Maurizio Righetti; Professor Dr.-Ing. Thorsten Stößer