This paper presents a simple and highly accurate stability estimation method for armor units covering breakwater rubble mounds against tsunami overflow. In this method, overflow depth is used to represent the external force. This enables an easier and more robust estimation of the required mass of the armor units than the conventional method based on flow velocity. This method takes into account the influence of the impingement position of the overflow jet and the influence of harbor-side water depth, both of which are important factors for armor stability. Numerical computation is also carried out aiming at the establishment of a stability analysis method for armor units. The validity of the computation method is confirmed by comparing the measured current field. The stability of armor units is investigated by computing the hydraulic force acting on each armor unit.
A method to process high-resolution multispectral satellite data for seagrass mapping has been implemented based on an inversion of a bidirectional reflectance distribution function (BRDF) developed particularly for seagrass beds. The BRDF simulates radiative transfer from seagrass canopies approximated by assuming certain principles of geometric-optics and photon transport. Reflectance from seagrass canopies are considered to be linear mixtures of leaves and background signatures, which are moreover influenced by parameters such as seagrass leaf architecture and transmittance, seawater column inherent optical properties and substrate reflectance. To validate results of model estimates, transect line surveys along seagrass meadows were conducted to obtain actual seagrass percentage cover, species distribution, shoot density and abundance. Likewise, spectral profiles of the bottom cover, together with pigmentation and turbidity through the water column were measured using field underwater spectrometer and in-situ instruments. High-resolution satellite (Ikonos™) data taken at multiple angles were processed according to the inversion model protocol. Results from model simulations show reasonable agreement between values of modeled and observed spectral reflectance from in-situ and space sensors. Reasonable outcome of modeled against insitu reflectance data reveals that a relatively parsimonious set of variables is enough to assess seagrass biophysical properties with reasonable accuracy.
A series of hydraulic model experiments was systematically and carefully carried out to estimate the stability of various types of armor units for a harbor-side rubble mound of a composite breakwater against a water jet caused by an impinging bore-like tsunami. Armor stones of weight 1 ton were seen to be easily removed by the tsunami flow. Flat type concrete blocks with well-arranged holes showed high stability. In the case of using wave-dissipating blocks, the total stability of the armor layer was enhanced by placing heavier blocks along the toe of the slope. Numerical analysis was also carried out to investigate the effect of the shape of the blocks. The computed time series of water level and the behavior of the impinging jet agreed well with the experimental ones. The computational result of hydrodynamic forces acting on armor blocks revealed that the uplift forces were largely decreased by the holes in the blocks.
This paper presents a practical design method for armor units to cover a rubble mound at the rear side of a caisson breakwater against tsunami overflow. In this method, the overflow depth of tsunami is used to represent the external force. This enables the estimation of the required mass of the armor units to be done more robustly and easily than in the conventional method based on the flow velocity. Hydraulic model experiments were conducted to investigate the armor stability. We found two important factors for armor stability. These were the impingement position of the overflow jet and the harbor-side water level. These effects were taken into account in the method. Numerical analysis on the fluid forces acting on the armor blocks was also conducted to explore the fundamental expression of the new design formula for armor stability. Empirical formulae for the stability estimation were then derived based on the findings from experiments and numerical analysis. The overflow depths of the stability limit corresponding to two failure modes, overturning and sliding, were obtained by two formulae. The stability numbers for each armor unit were determined through the experiments. The estimated results by this method agreed well with the experimental ones.
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