Field measurements of wave run-up on coastal structures with a pressure step gauge

Wave run-up field measurements on German sea dikes have been carried out at the German North Sea coast in the last decade by the local authority responsible for coastal protection of the federal state of Schleswig-Holstein (LKN-SH) in cooperation with the Institute of River and Coastal Engineering of TUHH (see e.g. DREIER and FRÖHLE 2019). Lately, TUHH has developed a new prototype for wave run-up field measurements (see Fig. 2). Among others, the results of the wave run-up measurements have been used to validate and improve empirical formulas proposed in the well-known EurOtop manual.
Under the course of the project, another prototype for a wave run-up gauge was installed near Tallinn at the Estonian Baltic Sea coast on a local rubble mound breakwater (see Fig. 1). The breakwater is adapted to ice conditions with a smooth slope (similar to German sea dikes).
Moreover, the wave conditions near the breakwater are monitored with the help of a prototype for a miniature wave buoy (d=50cm, see Fig. 3) which will be validated and improved within an international research cooperation between scientists and engineers from Taiwan, Estonia and Germany.
The aims of the project are:

i) implementation and optimization of the wave run-up gauge,

ii) validation and improvement wave run-up formulas (e.g. EurOtop),

iii) joint analysis and assessment of measurements at the North Sea and Baltic Sea, and finally

iv) dissemination of results (public seminars and preparation of a joint scientific publication). The public seminars were cancelled due to the Corona virus pandemic.

The results are expected to have influence on empirical wave run-up calculations in Nordic and Baltic countries and thus improving cost-effective coastal engineering and management as well as early-warning systems.

The project participants know each other from scientific exchanges (e.g. a guest stay of Mr. Rain Männikus at TUHH in 2019) and the interests are based on joint research on the hydrodynamic conditions in the Baltic Sea and the consequences for coastal protection structures. A first joint publication of the participants of the project was submitted to the International Coastal Symposium 2020 (DREIER et al. 2020). One of the scientific aims of the project is the deepening of the relations between project partners and to exchange knowledge on the scientific questions for the preparation of future joint-project applications respectively joint-publications of the partners.

See also: Laboratory of Wave Engineering, Estonia

• Description of measurements in Haven Kakumäe, 2020 (Rain Männikus)
  The measurement devices in Haven Kakumäe were set up in August 2020. Due to Covid-19 restrictions, the travelling of German scientists and specialists from Hamburg was not possible. Therefore, an Estonian electrician company was asked to set up the pressure sensors on the slope of the breakwater and the data logger and devices in Haven Kakumäe. At the same time, a directional wave buoy which was ordered from Institute of Hydrological and Oceanic Sciences at the National Central University in Taiwan, was set up approximately 100 m seaward of the breakwater (see Fig. 4). As of December 2020 the measurements are ongoing and are planned to continue at least throughout the winter 2021 and longer if possible.

• Field measurements of wave run-up on coastel structures with a pressure step gauge (Norman Dreier)
  The successful implementation of the wave run-up step gauge based on pressure sensors and wave measurements at the Estonian coast provide a unique basis for further joint analysis of wave run-up events both at the German North Sea coast and the Estonian Baltic sea coast. First wave run-up events have been analysed during a storm on 17^th September 2020 with maximum run-up heights up to 1.8m. The field measurements of wave run-up and waves will be continued and the step gauge will be optimized for the detection and analysis of the wave run-up events. The results of the analysis will be used for the comparison between the measured average wave run-up heights (Ru2%) and the hindcast of average wave run-up heights calculated with the empirical EurOtop (2016) approach. Moreover the results are being used for the improvement of the wave run-up forecast as a basis for coastal hazard early warning systems that take into account different loads on and the resistance of coastal structures.