Coastal Engineering Journal

The December 26, 2004 tsunami has caused extensive damage in the Union Territory of Andaman & Nicobar Islands, India, affecting 115.36 km of coastline. In order to identify the impacts of tsunami in South Andaman of the Andaman Islands, the study has been carried out using satellite data for pre-tsunami (Feb. 2003) and post-tsunami (March 2005). This paper provides an assessment of damages caused by tsunami and suitable resettlement places for the people using remote sensing and GIS technology. Assessment of tsunami inflicted damage to island ecosystems assumes greater importance owing to their life-sustaining and livelihood support abilities. Apart from the reparation caused to life and property, significant damage has afflicted the ecosystem, which will have long lasting effects. The tsunami-induced damage to coastal ecosystems was studied based on coastal landuse, geomorphology and coastal critical habitat for South Andaman Island using remote sensing and GIS. An area of 3,366 ha of land area was affected by tsunami. Within the coastal ecosystem, coral reef and mangrove were also severely affected. The study of landforms shows that the land is submerged. The severity of damages and their consequences suggest the need for a definite restoration ecology programme.

Intermittent breaching of sand barriers at temporary open estuaries plays a key role in the functioning of these systems. In addition to their ecological impacts, breaching events can cause significant morphological changes because high breach outflows result in the scouring of significant amounts of accumulated sediments from an estuary. Estimation and modeling of these processes requires insight into the parameters that determine features of the breach such as its size and the timescales for the breach formation. The latter is particularly important for characterizing the outflow hydrograph and for estimating sediment transport effects. Simple laboratory experiments are reported that investigated the temporal evolution of the breach and the scaling of the breach formation time T_F and peak outflow Q_P. The experiments were specifically designed to investigate the influence of the outflow volume S, the hydraulic head H, and the barrier breadth B. A scaling is suggested that gives a good description of the experimental data. The scaling is shown to be consistent with observed breach characteristics for actual estuaries (or coastal lagoons) and earth-dam failures where outflow volumes are several orders of magnitude larger than the models.

If the Rayleigh distribution of wave heights is valid, the representative wave heights can all be converted one to another through the known relationships. In shallow water, it has been pointed out by many researchers that the wave height distribution deviates from the Rayleigh distribution. However, it is not clear whether this deviation can lead to significant errors on the estimation of representative wave heights or not. Experimental data from small-scale, large-scale, and field experiments were used to examine the errors of the relationships derived from the Rayleigh distribution on estimating representative wave heights. The examination indicates that if H_rms is given, the relationships give overall very good estimations on and H_1/3, good estimation on H_1/10 but fair estimation on H_max. The effect of wave breaking was empirically incorporated into the relationships. The new relationships give better estimation than the relationships derived from the Rayleigh distribution.

Distributions of individual wave heights approximately follow the Rayleigh distribution regardless of the bandwidth of frequency spectra, even though Longuet-Higgins derived the theory on the condition of narrow-band spectrum in 1952. The spectral width parameter does not affect the wave height distribution, but it merely provides a measure of the minuteness of data sampling interval relative to mean wave period for waves in the sea. A spectral shape parameter introduced by Rice in 1945 for wave envelope amplitude is a better measure to describe a slight departure of wave height distribution from the Rayleigh. Several sets of linearly simulated wave profiles and field measurement records have been re-analyzed to verify the above findings. The spectral shape parameter also governs the spread of wave period distribution for single peaked spectral waves.

A 3D interfacing zonal (TDIZ) model was developed for the submerged bottom-flow-discharge from a sea-bottom freshwater drainage facility and used to analyze both initial mixing in the near field and the advection-dispersion process in the far field with ambient water flow. The mixing characteristics of the freshwater discharge and the applicability of the model for each field were verified using data from field measurements. The predicted salinity distribution and the minimum dilution at the water surface were generally in agreement with the field measurement data, and the vertical concentration distribution of the discharged water and the mixing behavior were also well simulated. When the advection-dispersion process by ambient water flow was analyzed, the TDIZ model in which initial mixing in the near field was considered gave better results than a far-field advection-dispersion model, which considered the discharge boundary conditions in terms of a simple point source.