Tsunami Hazard Assessment Along Chinese Coast Using Scaling Relations Developed for Tsunami Prediction

Potential tsunamis in the western Pacific Ocean pose great threats to the Chinese coastal areas. Among all possible tsunami source regions, the Manila subduction zone draws the most attention and there have been many research works on the tsunami hazards in the South China Sea. In this study, we evaluate the tsunami hazard along the Chinese coast by investigating more potential sources, including the subduction zones of Manila, Ryukyu, Nankai, Izu–Bonin and Mariana. Two tsunami scenarios are considered for each subduction zone, a worst scenario of earthquake magnitude 9.0 and a scenario of largest earthquake magnitude known in history in this zone. Earthquake source parameters are calculated using scaling relations that have been shown to be suitable for tsunami generation. Our results show that for the Chinese coast, tsunami hazards from the Manila and Ryukyu subduction zones are severe in the worst scenarios, and tsunami hazards from the Nankai, Izu–Bonin and Mariana subduction zones are mild. Using the largest earthquake magnitude in history, tsunami hazards from all the investigated subduction zones are almost negligible. Through a sensitivity test on earthquake magnitude, we find that earthquakes of magnitude of 8.5 or larger in the Manila and Ryukyu subduction zones cause severe tsunami hazard along the Chinese coast with wave amplitude over 2 m.

Numerical Modeling of Beach Morphological Change: A Case Study of Kaanapali Beach, Maui, Hawaii

This case study reports results from field observations and numerical simulations of waves and morphological changes along a portion of Kaanapali Beach on West Maui, Hawaii, which is protected by a hard coral reef and experiences shoreline changes from season to season. The SWAN spectral wave model shows reasonable agreement with ADCP observations of wave-heights for the winter months. Simulated beach profile change over one-month time frame was able to reasonably capture the trend of beach face migration (accretion or erosion); the modeled shoreline also shows satisfactory agreement with beach survey data. This case study suggests that Delft3D is able to capture key features of sediment transport along a narrow beach protected by a fringing reef.

Experimental Study of Turbulence and Entrained Air Characteristics in a Plunging Breaking Solitary Wave

The entrained air and turbulence characteristics under a breaking solitary wave on a 1:20 sloping beach are investigated through laboratory measurement. Free surface elevation is obtained from wave gauge measurements. Wave breaking process is captured in detail by a high-speed camera. The bubble image velocimetry (BIV) is used to measure the velocity and the fiber optic reflectometer (FOR) is used to capture instantaneous void fraction in the aerated region. The mean void fraction and velocities in the aerated region are obtained by ensemble averaging over 22 repetitions. Results show that the maximum mean void fraction is 0.6 in the collapsing cavity region and is 0.35 in the splash up region. The time series of the mean void fraction has good synchronization with the instantaneous images taken by high-speed camera. The maximum horizontal velocity occurs in the splash up region and reaches 1.17C shortly after the plunging jet hits the water surface, with C being the phase speed of the primary wave. The turbulence intensities over the entire aerated region are presented and discussed. The measured data can be used for the calibration and verification of the numerical model for aerated flows simulation under breaking waves in the surf zone.

Downstream Water Management Strategy in Murray–Darling Basin to Improve Adelaide’s Water Quality and Agricultural Output — Feasibility Analysis of a Dual-Purpose Coastal Reservoir

Australia is the driest country in the world, and the lower Murray–Darling Basin and Adelaide have experienced extreme water scarcity crisis, especially during the Millennium Drought (2000–2010). Many counter measures have been proposed or implemented like desalination plants and water buyback, etc., some progress has been made, but far away from a complete solution. Different from existing measures, this research aims at using coastal reservoir technology to shift from upstream water development to downstream development, in order to solve a series of water supply and ecological environment problems by redesigning a coastal reservoir in the downstream area. It is suggested that high-quality water is stored in a “coastal reservoir” inside the Alexandrina Lake for Adelaide’s water supply. The lake water outside the “coastal reservoir” is used for agricultural development. A preliminary feasibility study was conducted in terms of water quantity and water quality, river’s environmental flow and agricultural output. The results show that if a small size (550–630[Formula: see text]GL) coastal reservoir was created inside the Lake Alexandrina in the mouth of Murray River, the Adelaide’s water supply could be secured and its water quality be improved even during droughts like the Millennium Drought. Besides, if the agricultural development is concentrated around the lake, its water demand can be fully met from the lake, rather than the river, thus the agricultural development has little negative impacts on the river’s ecosystem, it is a win-win solution for agricultural development and river ecosystem. It is suggested that Australian government should provide stimulus package for upstream farmers to relocate to areas around the lake.

Strategic Analysis on the Potential of Coastal Reservoirs in Reshaping Indian Coastal Economic Corridor

In general, people like to live near the coast because of a better aesthetical pleasing living environment, access to a variety of recreational activities and more job opportunities. Consequently, more than 50% of the world’s population live within 200[Formula: see text]km of the coast, and ¾ of the world’s megacities are situated by the shore. Significant pressure on land, water supply, waste management and other infrastructures appear in these coastal cities. India, which hosts one-sixth of the world’s population is looking for strategies to manage India’s coastal cities, water, land and human resources. This paper reviews China’s experience in water resources development for coastal cities. China’s coastal economic corridor (CEC) contributes 60% of the national GDP, which needs plentiful water supply to sustain its coastal cities. The present investigation shows that India has better natural conditions to develop its CEC. Among the coastal infrastructures, coastal reservoirs (i.e., CRs) should be the priority, which nourishes the coastal prosperity. This paper also discusses the feasibility of water–oil exchange project between India and Persian Gulf countries.

Anthropogenic Activities and its Impact along the Coastal Region of Mangaluru, India

Mangaluru coast belt spreads about 22 Kms with Arabian Sea in the West and the Western Ghats in the East. Coastal anthropogenic activities such as disposal of untreated or partially treated sewage and industrial effluents and their possible impacts hinder the coastal environment. Huge amount of pollution load from the major industries located nearby are discharged into the sea directly or through the west flowing rivers of the area i.e. Gurupura and Nethravathi. Due to this, the soil properties also get affected. The preliminary study was carried out at the study area by considering surface water samples, i.e. stream water, river water, sea water and also soil samples to study the physicochemical characteristics. The study reveals that most of the surface water samples have low dissolved oxygen concentration and are high in BOD, COD, TDS, Electrical Conductivity (EC) and Chlorides Concentration. Very low dissolved oxygen concentration was observed in the Gurupura–Nethravathi Estuary point. With respect to fertility of the soil, most of the soil samples were below the normal range for the various parameters.

Tsunami Risk in Japanese Coast and Recent Mitigation Technique using Removable Breakwater

In this paper, the tsunami risk in the west coast of Japan is introduced. Especially, the inundation risk in Osaka city is discussed. Three visor gates are installed at the mouths of main rivers in the city. The gates are mainly installed to prevent the storm surge due to typhoons but they are effective to reduce the tsunami height at the mouth point of river. Though the gates are necessary to prevent the tsunami inundation, the stability against tsunami forces is not enough because the gates were constructed in 1960s. Therefore, the removable breakwater is now under consideration to reduce the tsunami force. The hydraulic experiment was carried out in order to investigate the applicability of the removable breakwater. The reduction rate by the breakwater was derived from the experiment.