The run-up of long waves: laboratory-scaled geophysical reproduction and onshore interaction with macro-roughness elements
Goseberg, N.R. (2011). The run-up of long waves: laboratory-scaled geophysical reproduction and onshore interaction with macro-roughness elements. Mitteilungen des Franzius-Institut für Wasserbau und Küsteningenieurwesen der Universität Hannover, 97. PhD Thesis. Franzius-Institut für Wasserbau und Küsteningenieurwesen: Hannover. xxxiv, 260 pp.
Part of: Mitteilungen des Franzius-Institut für Wasserbau und Küsteningenieurwesen der Universität Hannover. Franzius-Institut für Wasserbau und Küsteningenieurwesen: Hannover. ISSN 0340-0077, more
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Document type: Dissertation
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| Keywords |
Long waves
Physical models
Water waves > Surface water waves > Tsunamis
Wave generation
Wave processes on beaches > Wave runup
Wave-shore interaction
Marine/Coastal |
| Abstract |
The evolution of long waves similar to tsunami on a 1=40 sloping beach and their interaction with idealized urban developments onshore is investigated by experimental means. The undisturbed wave run-up is firstly analyzed. Then the idealized urban development, which is represented by solid, cubic concrete blocks, is assessed. Four different configurations of those so-called macro-roughness elements are defined and the differences with regard to the effectiveness of reducing the long wave run-up are studied. Variations of the four macro-roughness element configurations are obtained through different distances between the individual obstacles and a variation of the number of obstacle rows in the onshore direction. As a result, empirical nomograms are proposed which relate the effective relative run-up and the associated run-up reduction to the surf similarity parameter and the non-linearity of the incident wave.
In contrast to commonly applied solitary waves, sinusoidal waves of one wave period with a leading depression wave are applied. Solitary waves are substituted by sinusoids of geophysically sound quantities. The correct reproduction of temporal and spatial wave properties is of major importance for the investigation of the nearand onshore interaction with macro-roughness elements and it is doubted that solitary waves comply best with these prerequisites specified by realistic events. The generation of the sinusoids is accomplished by a redeveloped, volume-driven wavemaker which is capable of reproducing waves of arbitrary wave length at laboratory scale as well as an intrinsic treatment of the reflected wave components.
The undisturbed long wave run-up is analyzed and good agreement with an existing theoretical approach to the two-dimensional run-up problem is found. An empirical fit of the experimental data on the basis of the existing theory can be expressed by a supplement of exponents. The reflection of long waves is analyzed on the basis of standard laboratory procedures. The resulting reflection coefficients, which are found to be fairly small, suggests that the reflection of long waves at mild sloping beaches should be re-examined.
The characteristic velocity flow pattern which arises during the inundation of the obstructed onshore area is illustrated qualitatively and quantitatively. Higher velocixvties occur during the run-up and run-down in cases of aligned macro-roughness configurations whereas velocities are smaller in staggered alignments. The rotation angle of the individual obstacles also contributes to the velocities to first order.
The acquired data sets of the experimental study, focusing on the wave run-up and the interaction with macro-roughness elements onshore, is well-suited for the validation and calibration of existing numerical models. |
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