Simulation of diffraction of ocean waves by a submerged sphere in finite depth

Based on the linear diffraction theory, an investigation is made on the interaction of water waves with a completely submerged sphere in water of finite depth in this paper. The method of multipole expansions is used to obtain the fluid velocity potential in the form of double series of the associated Legendre functions with the unknown coefficients of the infinite set of infinite matrix equations. The truncation property of the matrices and the convergence of the multipole series coefficients are investigated for various wavelengths and depths. The systematic numerical simulation, based on our analytical solution, is carried out and the fields of the hydrodynamic diffraction pressure and fluid velocity around the sphere, the three-dimensional free surface elevation, and total exciting forces acting on the sphere are graphically presented for a wide range of the body submergences, ocean depths and wavelengths.     

Wave diffraction by large offshore structures: an exact second-order theory

An exact second order theory has been formulated in this paper to calculate the wave forces on offshore structures. Lighthill's method for deep water waves has been extended to shallow water waves. Exact expression for linear velocity potential applicable to the circular cylindrical strcutures for shallow water waves have been used in these calculations. These results have been verified with those obtained by direct perturbation technique reported recently by Rahman and Heaps. It is interesting to note that both the methods yield identical results.     

Climates of urbanization: local experiences of water security,conflict and cooperation in peri-urban South-Asia

ABSTRACT

This article explores changing water (in)securities in a context of urbanization and climate change in the peri-urban spaces of four South-Asian cities: Khulna (Bangladesh), Gurugram and Hyderabad (India), and Kathmandu (Nepal). As awareness of water challenges like intensifying use, deteriorating quality and climate change is growing, water security gets more scientific and policy attention. However, in peri-urban areas, the dynamic zones between the urban and the rural, it remains under-researched, despite the specific characteristics of these spaces: intensifying flows of goods, resources, people, and technologies; diversifying uses of, and growing pressures on land and water; and complex and often contradictory governance and jurisdictional institutions. This article analyses local experiences of water (in-)security, conflict and cooperation in relation to existing policies. It uses insights from the analysis of the case studies as a point of departure for a critical reflection on whether a ‘community resilience’ discourse contributes to better understanding these cases of water insecurity and conflict, and to better policy solutions. The authors argue that a community resilience focus risks neglecting important insights about how peri-urban water insecurity problems are experienced by peri-urban populations and produced or reproduced in specific socio-economic, political and policy contexts. Unless supported by in-depth hydro-social research, such a focus may depoliticize basically political questions of water (re) allocation, prioritization, and access for marginalized groups. Therefore, the authors plead for more critical awareness among researchers and policy-makers of the consequences of using a ‘community resilience’ discourse for making sense of peri-urban water (in-)security.

Key policy insights

• There is an urgent need for more (critical) policy and scientific attention to peri-urban water insecurity, conflict, and climate change.

• Although a changing climate will likely play a role, more attention is needed to how water insecurities and vulnerabilities in South Asia are socially produced.

• Researchers and policy-makers should avoid using depoliticized (community) resilience approaches for basically socio-political problems.

     

Modeling the Population Effects of Hypoxia on Atlantic Croaker (<Emphasis Type="Italic">Micropogonias undulatus</Emphasis>) in the Northwestern Gulf of Mexico: Part 2—Realistic Hypoxia and Eutrophication

Quantifying the population-level effects of hypoxia on coastal fish species has been challenging. In the companion paper (part 1), we described an individual-based population model (IBM) for Atlantic croaker in the northwestern Gulf of Mexico (NWGOM) designed to quantify the long-term population responses to low dissolved oxygen (DO) concentrations during the summer. Here in part 2, we replace the idealized hypoxia conditions with realistic DO concentrations generated from a 3-dimensional water quality model. Three years were used and randomly arranged into a time series based on the historical occurrence of mild, intermediate, and severe hypoxia year types. We also used another water quality model to generate multipliers of the chlorophyll concentrations to reflect that croaker food can be correlated to the severity of hypoxia. Simulations used 100 years under normoxia and hypoxia conditions to examine croaker population responses to the following: (1) hypoxia with food uncoupled and coupled to the severity of hypoxia, (2) hypoxia reducing benthos due to direct mortality, (3) how much hypoxia would need to be reduced to offset decreased croaker food expected under 25 and 50% reduction in nutrient loadings, and (4) key assumptions about avoidance movement. Direct mortality on benthos had no effect on long-term simulated croaker abundance, and the effect of hypoxia (about a 25% reduction in abundance) was consistent whether chlorophyll (food) varied with hypoxia or not. Reductions in hypoxia needed with a 25% reduction in nutrient loadings to result in minimal loss of croaker is feasible, and the croaker population will likely do as well as possible (approach abundance under normoxia) under the 50% reduction in nutrient loadings. We conclude with a discussion of why we consider our simulation-based estimates of hypoxia causing a 25% reduction the long-term population abundance of croaker in the NWGOM to be realistic and robust.     

The Response of Macrobenthic Communities to Environmental Variability in Tropical Coastal Waters

The relative contributions of spatial and temporal fluctuations are different in shaping natural communities in a tropical coastal/estuarine system. Understanding how coastal communities respond to these fluctuations is still equivocal, and thus, available data are rare. Here, multiple analytical approaches were used to identify key spatial and temporal factors, and to quantify their relative roles in shaping a macrobenthic community through space (contamination degree, physical parameters, and sediment characteristics) and time (climatic factors, season, and year). A dataset of eight sampling times was analyzed over a period of 2 years, in which macrobenthic species abundances were sampled. A total of 33 species were identified, including 18 bivalves, 5 gastropods, and 4 crustaceans. The other taxa were less diverse. The results show that there were no significant temporal changes of macrobenthic community structure, but spatial changes were significant and synchronized with environmental factors (i.e., sediment characteristics, water depth, and the distance from anthropogenic sources). This study demonstrates that spatial factors played a primary role in structuring of macrobenthic assemblages, whereas the influence of temporal factors appeared less across geographically distinct sites. Thus, temporal variation of a coastal macrobenthic community appears to be controlled by partly different processes at different scales.     

Assessing the effect of future landslide on ecosystem services in Aqabat Al-Sulbat region,Saudi Arabia

Natural Hazards - Co-occurrence events of droughts and heatwaves characterized by abnormal low soil moisture (SM) and high temperatures may cause more significant impacts on society and natural...     

Assessing the long-term planform dynamics of Ganges–Jamuna confluence with the aid of remote sensing and GIS

Natural Hazards - The confluence of the Ganges, Jamuna, and Padma rivers is one of the most dynamic in the world, an internationally important research area because of the confluence of two of the...     

Liquefaction resistance evaluation of soils using artificial neural network for Dhaka City,Bangladesh

Natural Hazards - Soil liquefaction resistance evaluation is an important site investigation for seismically active areas. To minimize the loss of life and property, liquefaction hazard analysis is...     

The socioeconomic impact of climate-related hazards: flash flood impact assessment in Kuala Lumpur,Malaysia

Small-scale flash flood events are climate-related disasters which can put multiple aspects of the system at risk. The consequences of flash floods in densely populated cities are increasingly becoming problematic around the globe. However, they are largely ignored in disaster impact assessment studies, especially in assessing socioeconomic loss and damage, which can provide a significant insight for disaster risk reduction measures. Using a structured questionnaire survey, this study applied a statistical approach and developed a structural equation model (SEM) for assessing several socioeconomic dimensions including physical impacts, mobility disruption, lifeline facilities, health and income-related impacts. The study reveals that respondents have experienced a stronger impact on direct tangible elements such as household contents and buildings as well as direct intangible elements with β coefficients 0.703, 0.576 and 0.635, respectively, at p?<?0:001 level. The direct intangible impacts affect mobility disruption with β coefficients equal to 0.701 at p?<?0:001 level which then further cause adversity to income-generating activities with β 0.316 at significant p?<?0:001 as well. The overall model fit indices show highly acceptable scores of SRMR 0.068, RMSEA 0.055 and PClose 0.092. Thus, the SEM has successfully incorporated the socioeconomic dimensions of disaster impact and explained the impact phenomena reliably. This modeling approach will allow inclusion of various variables from different disciplines to assess hazard impact, vulnerability and resilience.

     

Storm protection service of the Sundarbans mangrove forest,Bangladesh

Natural Hazards - Storm protection service of mangrove is often undervalued. This paper empirically assessed the damage avoided by the Sundarbans mangrove forest in 15 villages of southwest coastal...