Abstract
The wave overtopping discharge at coastal defense structures is directly linked to the freeboard height. By means of physical modelling, experiments on wave overtopping volumes at sloped coastal structures are customarily determined for constant water levels and static wave steepness conditions (e.g., specific wave spectrum). These experiments are the basis for the formulation of empirically derived and widely acknowledged wave overtopping estimations for practical design purposes. By analysis and laboratory reproduction of typical features from exemplarily regarded real storm surge time series in German coastal waters, the role of non-stationary water level and wave steepness were analyzed and adjusted in experiments. The robustness of wave overtopping estimation formulae (i.e., the capabilities and limitations of such a static projection of dynamic boundary conditions) are outlined. Therefore, the classic static approach is contrasted with data stemming from tests in which both water level and wave steepness were dynamically altered in representative arrangements. The analysis reveals that mean overtopping discharges for simple sloping structures in an almost deep water environment could be robustly estimated for dynamic water level changes by means of the present design formulae. In contrast, the role of dynamic changes of the wave steepness led to a substantial discrepancy of overtopping volumes by a factor of two. This finding opens new discussion on methodology and criteria design of coastal protection infrastructure under dynamic exposure to storm surges and in lieu of alterations stemming from projected sea level rise.
Highlights
The required design freeboard height of a costal defense structure is usually determined by hydraulic model tests
The analysis reveals that mean overtopping discharges for simple sloping structures in an almost deep water environment could be robustly estimated for dynamic water level changes by means of the present design formulae
We analyzed to what degree the influence of variations in the static design water level (SWL) and the wave steepness is already covered by existing design formulae [2]
Summary
The required design freeboard height of a costal defense structure is usually determined by hydraulic model tests. Standard laboratory routines focus on wave overtopping prediction by means of translating a corresponding static design water level (SWL) in a wave flume or basin. The real non-stationary water levels or changes in wave steepness during storm surges are not mimicked. The common standard in wave overtopping prediction are model tests with different constant design water levels and wave characteristics during a single test [2,3]. The objective of the present paper was to derive or develop a more realistic approach in hydraulic model testing, as water levels and wave characteristics are rarely constant in nature. The new approach considers dynamic changes of the SWL and the wave steepness in a hydraulic model tests. We analyzed to what degree the influence of variations in the SWL and the wave steepness is already covered by existing design formulae [2].
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