Kerlin, T.

Musall, M.

Nestmann, F.

Oberle, P.

English

KITopen

EGU21-256https://doi.org/10.5194/egusphere-egu21-256EGU General Assembly 2021© Author(s) 2022. This work is distributed underthe Creative Commons Attribution 4.0 License.HIPPO – In situ device to monitor the remobilization process of finesedimentsTim Kerlin, Mark Musall, Peter Oberle, and Franz NestmannKarlsruhe Institute of Technology, Institute for Water and River Basin Management, Department for Hydraulic and RuralEngineering, Germany (tim.kerlin@kit.edu)Within the joint project Integrated Water Governance Support System (iWaGSS) funded by theGerman Federal Ministry for Education and Research (BMBF, reference numer: 02WGR1424C) theInstitute of Water and River Basin Management (IWG) of the Karlsruhe Institute of Technology (KIT)developed a benthic flume. The benthic flume HIPPO (Hydro-morphological Investigation ofriverbed Particle Performance On-site) is an adjustable in situ device to reliably determine the startof erosion of fine sediments.In advance 3D-CFD simulations have been carried out to optimize the components and the setupof the measurement system. The final product is primarily a benthic flume, which has adownwardly opened sampling area at the bottom and is placed on the river or reservoir bed. Thisunderwater flow channel can be adapted to the local conditions with further components and isconnected via a tube system to a measurement boat or raft. On the boat a pump creates a steadyflow velocity in the system. The velocity in the benthic flume is gradually increased at fixed timeintervals and is monitored using a built-in flow velocity meter (Acoustic Doppler Velocimeter). Inaddition the entire erosion process is recorded visually with video cameras. Also the turbidity ofthe water flowing through the system is continuously measured by a turbidity probe installedbehind the pump. The amount of flow induced by the pump is controlled by a valve close to theend of the system. With the pump currently installed flow velocities of up to v = 0.8 m/s at thesampling area can be achieved, which is sufficient for the determination of the critical flow rate forerosion of most types of clay, silty and fine sandy sediments. During the process of erosion alsothe remobilization of fluid mud can be monitored. The critical flow velocity for the start ofsediment transport is determined on the basis of the turbidity of the pumped water and data fromthe flow velocity probe and is verified using the camera system.In addition to the critical threshold flow velocities, the critical bed shear stress is often required asinput or evaluation variables for morhpodynamic numerical models. The conversion can be made,for example, using the quadratic velocity approach originally used in pipe hydraulics. Thedetermination of the required resistance coefficient λ is based on the Moody Chart. However, itshould be considered that this procedure entails some uncertainties with regard to themeasurement system presented here. Still for cohesive sediments, the natural values measured inthis way represent a significant added value compared to common estimates based on onlypartially known bed parameters, since factors such as vegetative cover, consolidation or even adeveloped biofilm can influence the timing of erosion. Especially against this background, possibleeffects of the change of hydraulics by the measuring system (geometry, velocity profile) seem tobe small compared to the uncertainties of contemporary morphodynamic analyses.Powered by TCPDF (www.tcpdf.org)

HIPPO – In situ device to monitor the remobilization process of fine sediments

https://publikationen.bibliothek.kit.edu/1000135519/148515181

HIPPO – In situ device to monitor the remobilization process of fine sediments

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