Monitoring of suspended mater with H-ADCP devices and comparison with sedimentation rates and soil properties in the Köhlfleethafen harbour basin of the Hamburg port

For future strategies in water depth maintenance in the Port of Hamburg, determining the navigability limit (i.e. the nautical safe depth) is of major importance. For this purpose, a project "Nautical Depth" was set up at the Hamburg Port Authority (HPA), which is dedicated to dealing with this issue. The aim is to measure a nautical safe depth under various boundary conditions and to identify limits for a safe passage of high concentrated soil suspensions. Among other things within the project monitoring data of suspended sediment fluxes and data from multibeam echo-sounders and sub-bottom profilers were analysed and compared.

Therefore, the backscatter along the cross-section of a long-term H-ADCP monitoring station was analysed and calibrated with water samples and data of optical backscatter sensors. The standard monitoring frequency of the data is 1 minute. The data were aggregated and summarized as half-tide values and flood-tide, ebb-tide and the residual sediment fluxes were calculated. These data sets were compared with hydroacoustic measurements of the bathymetry, including sub-bottom profilers, in the harbour basin Köhlfleethafen nearby the cross-section of the H-ADCP monitoring station. In a defined and shaped area volumetric calculations, layer densities and the amount of sedimented dry matter of the bottom layer were analysed.

The presentation will give a closer look to the sampling, monitoring and interpretation of the data. The data sets of sediment fluxes derived by the H-ADCP will be compared with the data sets of the hydroacoustic measurements. The influence of dredging campaigns will be shown, and an interpretation of the data will be given. The investigations also show, that the soil properties and analysed data sets are dependent from local and regional boundary conditions, as flow velocity, grain size distribution and especially in Hamburg from the organic matters and nutrients within the suspended and the soil material. All data sets are used to optimize the maintenance strategies of the nautical bottom in the Köhlfleethafen area, especial regarding sediment conditions methods with bed levellers or water injection dredgers.

References:

Nino Ohle, Thomas Thies, Rolf Lüschow, and Ulrich Schmekel - Sediment sampling and soil properties of sediments in the Hamburg port and the river Elbe in comparison with hydro-acoustic measurements , Proceedings of the EGU2020-16468, https://doi.org/10.5194/egusphere-egu2020-16468

Ahmad Shakeel, Claire Chassagne, Jasper Bornholdt, Nino Ohle, and Alex Kirichek - From fundamentals to implementation of yield stress for nautical bottom: Case study of the Port of Hamburg, Ocean Engineering, Volume 266, Part 2, 2022, 112772, ISSN 0029-8018, https://doi.org/10.1016/j.oceaneng.2022.112772