Time filter

Source Type

Shoresh, Israel

Bauman A.G.,James Cook University | Baird A.H.,James Cook University | Cavalcante G.H.,WaterWays
Coral Reefs | Year: 2011

Despite extensive research on coral reproduction from numerous geographic locations, there remains limited knowledge within the Persian Gulf. Given that corals in the Persian Gulf exist in one of the most stressful environments for reef corals, with annual variations in sea surface temperature (SST) of 12°C and maximum summer mean SSTs of 36°C, understanding coral reproductive biology in the Gulf may provide clues as to how corals may cope with global warming. In this study, we examined six locally common coral species on two shallow reef sites in Dubai, United Arab Emirates (UAE), in 2008 and 2009 to investigate the patterns of reproduction, in particular the timing and synchrony of spawning. In total, 71% colonies in April 2008 and 63% colonies in April 2009 contained mature oocytes. However, the presence of mature gametes in May indicated that spawning was potentially split between April and May in all species. These results demonstrate that coral reproduction patterns within this region are highly seasonal and that multi-species spawning synchrony is highly probable. Acropora downingi, Cyphastrea microphthalma and Platygyra daedalea were all hermaphroditic broadcast spawners with a single annual gametogenic cycle. Furthermore, fecundity and mature oocyte sizes were comparable to those in other regions. We conclude that the reproductive biology of corals in the southern Persian Gulf is similar to other regions, indicating that these species have adapted to the extreme environmental conditions in the southern Persian Gulf. © 2011 Springer-Verlag.

Kosters F.,WaterWays | Winter C.,University of Bremen
Geo-Marine Letters | Year: 2014

The prediction of large-scale coastal and estuarine morphodynamics requires a sound understanding of the relevant driving processes and forcing factors. Data- and process-based methods and models suffer from limitations when applied individually to investigate these systems and, therefore, a combined approach is needed. The morphodynamics of coastal environments can be assessed in terms of a mean bed elevation range (BER), which is the difference of the lowest to highest seabed elevation occurring within a defined time interval. In this study of the coastal sector of the German Bight, North Sea, the highly variable distribution of observed BER for the period 1984-2006 is correlated to local bed shear stresses based on hindcast simulations with a well-validated high-resolution (typically 1,000 m in coastal settings) process-based numerical model of the North Sea. A significant correlation of the 95th percentile of bed shear stress and BER was found, explaining between 49 % and 60 % of the observed variance of the BER under realistic forcing conditions. The model then was applied to differentiate the effects of three main hydrodynamic drivers, i.e. tides, wind-induced currents, and waves. Large-scale mapping of these model results quantify previous qualitative suggestions: tides act as main drivers of the East Frisian coast, whereas waves are more relevant for the morphodynamics of the German west coast. Tidal currents are the main driver of the very high morphological activity of the tidal channels of the Ems, Weser and Elbe estuaries, the Jade Bay, and tidal inlets between the islands. This also holds for the backbarrier tidal flats of the North Frisian Wadden Sea. The morphodynamics of the foreshore areas of the barrier island systems are mainly wave-driven; in the deeper areas tides, waves and wind-driven currents have a combined effect. The open tidal flats (outer Ems, Neuwerker Watt, Dithmarschen Bight) are affected by a combination of tides, wind-driven currents and waves. Model performance should be measurably improved by integrating the roles of other key drivers, notably sediment dynamics and salt marsh stabilisation. © 2013 Springer-Verlag Berlin Heidelberg.

Naulin M.,WaterWays | Kortenhaus A.,Ghent University | Oumeraci H.,TU Braunschweig
Coastal Engineering Journal | Year: 2015

Failures of flood defenses have been one of the major reasons in the past leading to flooding of the hinterland behind flood defenses along rivers and at the sea. It is therefore inevitable to investigate the reliability of such defenses for extreme events as have occurred in the past and are discussed to happen more frequently in the future and due to climate changes. The first subproject in XtremRisK (SP 1) and the related papers in this issue [Gönnert, G. and Gerkensmeier, B. [2015] "A multi-method approach to develop extreme storm surge events to strengthen the resilience of highly vulnerable coastal areas," Coast. Eng. J., this special issue; Wahl, T. et al. [2015] "Statistical assessment of storm surge scenarios within integrated risk analyses," Coast. Eng. J., this special issue; Tayel, M. and Oumeraci, H. [2015] "A hybrid approach using hydrodynamic modelling and artificial neural networks for extreme storm surge prediction, Coast. Eng. J., this special issue] have investigated the components of storm surges and their statistical occurrence, also in relation to the wave parameters. These results can now be used as input for investigating the reliability of flood defenses and provide an overall failure probability for different types of defenses and different failure modes. This paper therefore summarizes the key findings of the "risk pathway" analysis of XtremRisK Subproject 2 (SP 2) which comprise a reliability analysis and breach modeling of coastal and estuarine flood defenses using storm surge scenarios and sea states, including their occurrence probabilities provided by XtremRisK SP 1. The paper discusses the key results, the progress, and challenges in reliability analysis and breach modeling of flood defenses. The developed and advanced methods were applied to pilot sites in Hamburg (Elbe Estuary) and the Island of Sylt (North Sea). These pilot sites are mainly protected by linear flood defenses such as sea dikes, estuarine dikes, coastal dunes, and flood defense walls. Results have shown that under extreme conditions many dikes may fail simply from wave overtopping and even overflow but also from dike breaching due to the severe loading of the dike slopes when heavy overtopping and overflow occurs. The inflowing water volumes were calculated based on time-dependent water levels and then used for inundation modeling of the hinterland in Subproject 3 (SP 3) of XtremRisK. Furthermore, the limit state equations for wave overtopping and overflow had been adapted to time-dependent simulations. An importance factor was introduced for the probability of breaching of sea dikes leading to significantly different failure probabilities. The length effect considering the different homogeneous segments in the dike ring of Hamburg-Wilhelmsburg was estimated using an upper and lower bound approach showing the importance of the segmentation of the dike ring. © 2015 World Scientific Publishing Company and Japan Society of Civil Engineers.

The interaction of water and soil has been both a blessing and a curse in all times within living memory. Water is the origin of life but is also threatening life when appearing unboundedly. Therefore mankind has always worked hard to benefit from water resources on one hand and to deal with the threat of flooding on the other hand. For both, to protect the land and to allow for beneficial uses like irrigation or navigation, often special measures are necessary to keep the water within certain bounds. Structures to achieve a permanently stable situation like irrigation and navigational canals, river training or flood protection measures need suitable material, carefully thought out design and accurate execution. Often a decision has to be made among competitive approaches to optimize such structures. In many cases, geosynthetics can support or improve the functionality and sometimes only with geosynthetics the desired result can be achieved. Geosynthetics can provide strength and flexibility, imperviousness and drainage, durability and robustness or controlled degradation. All these properties can be of use to handle the many occurrences of interaction of water and soil. Surface water has to be guided or to be kept off; percolating water should be controlled to avoid internal erosion effects should be restrained by appropriate filtration. To guarantee well functioning in general, also chemical and biological aspects have to be considered like ochre formation, root penetration and population by any kind of species. The German Federal Waterways Engineering and Research Institute (BAW) has gathered experience with geosynthetics in hydraulic applications since more than 40 years. These years revealed the capabilities of geosynthetic solutions and simultaneously emphasized the need of careful selection, design and execution.A large variety of geosynthetic fabric and structures is available. To control the interaction of water and soil many different attributes are required, e.g. membranes for impervious lining, filter sheets for erosion control, different kinds of mattresses or wrap-around structures, voluminous elements from sandbags to mega containers for protection, training or immediate repair. In many cases geosynthetics can be designed to control the interaction of water and soil according to the individual and local requirements to allow for an excellent execution of waterways and flood protection structures. © 2014 Elsevier Ltd.

Knoch D.,WaterWays | Malcherek A.,Max Planck Institute for Physics
Ocean Dynamics | Year: 2011

In this paper, a three-dimensional isopycnal approach is presented to simulate the dynamics of fluid mud covering the formation, development, transport, and disappearance of fluid mud. The basic assumption is the assignment of the fluid's density as the indicating parameter for the rheological behavior. Considering stable stratification, as is usually the case for fluid mud, layers of constant density discretize the vertical domain. The non-Newtonian dynamics of fluid mud is simulated by solving the Cauchy equations for general continuum dynamics. Instead of using a turbulent viscosity approach, the viscosity is allowed to vary according to the rheological behavior of mud suspensions. This apparent viscosity can be determined for different rheological formulations in dependence of the volume solid fraction and the shear rate. An existing three-dimensional isopycnal hydrodynamic model was extended for vertical mass transport processes and was applied on a schematic system with hindered settling. For including the rheological behavior of fluid mud, the Worrall-Tuliani approach was parameterized and implemented. The resulting flow behavior is shown on a model application of fluid mud layers moving down an inclined plane. With these changes, it is demonstrated that the isopycnal model is capable of simulating fluid mud dynamics. © 2010 Springer-Verlag.

Discover hidden collaborations