Fixation and distribution of bacterial activity in sand to induce carbonate precipitation for ground reinforcement

How ecological engineering can serve in coastal protection

In December 2004, a huge tsunami in SE Asia claimed many lives and caused catastrophic damage. This event has stimulated a debate about the role played by coastal ecosystems such as mangrove forests and coral reefs in protecting low-lying coastal areas. While some observers claim that these ecosystems play an important role, others are more sceptical and fear that financial resources may be diverted away from tsunami preparedness programmes to ecosystem rehabilitation schemes. Here, we review the role of coastal ecosystems in mitigating sea wave hazards. In particular, we examine the influence of coastal vegetation in severely affected parts of Aceh and Southern Thailand during the 2004 tsunami, and include direct observations made during two field visits in 2006. Numerous scientific studies illustrate that coastal ecosystems are important in protecting the coast against normal and extreme wind-driven waves, including cyclonic storm surges. However, much less information is available concerning the role of coastal ecosystems in protecting against tsunamis, and most studies have been too limited in scope to be able to generalise over large geographic areas and diverse conditions. In particular, few studies have taken account of the high variability in the energy and speed of tsunami waves along different coastline stretches, making it difficult to compare the role of ecosystems in different regions. Other aspects that have been little studied include the spatial patterns of impact, e.g. flow diversion and channelling as a result of hydraulic resistance, and the effects of tree breaking and flow debris. However, despite these limitations, some tentative conclusions can be drawn about the protection provided by ecosystems against tsunami waves: (1) The most important predictor variables of the tsunami hazard (i.e. set-up and inundation) at the regional and landscape levels are distance to the tsunami source and coastal topography, in particular near-shore bathymetry. (2) The influence of coral reefs on tsunami waves is complex. While closed, intact reefs can provide some protection, water may be accelerated through channels in fragmented reefs, causing even greater destruction on land. (3) In contrast, seagrass beds appear to provide a more consistent buffering against tsunamis, though more data are needed to quantify this effect. (4) In several locations (particularly farther away from the tsunami source), mangroves and other vegetation probably provided some protection against the 2004 tsunami; in numerous other locations, however, vegetation provided no protection or may in some cases even have increased the hazard (e.g. by contributing to flow debris, or by channelling water flows). It seems that whether or not vegetation does provide protection depends on many factors, including stand size, density, species composition, structure and homogeneity. Overall, the value of vegetation as a potential tsunami buffer is probably fairly minor, though it cannot be completely dismissed. Many more detailed spatial and hydro-dynamic analyses are needed before the hazard-vegetation interactions can be realistically modelled and visualised, e.g. on risk maps. (5) Tsunami greenbelts should not be treated as alternatives to early warning systems. Greenbelts may only be considered as an economical (and multi-functional) means to provide relative hazard protection for material assets (e.g. infrastructure, agriculture). We recommend a more holistic view, with tsunami hazard mitigation being seen as one of several services provided by coastal ecosystems. Equally, the value of other ecosystem services may be seen within the frame of risk management as they foster social stability and, in case of disaster, robustness. To assess the overall value of these services and to develop more accurate indicators of risk will require much more transdisciplinary research.

The 2004 tsunami in Aceh and Southern Thailand: A review on coastal ecosystems, wave hazards and vulnerability

Background 
Coastal landscapes are being transformed as a consequence of the increasing demand for infrastructures to sustain residential, commercial and tourist activities. Thus, intertidal and shallow marine habitats are largely being replaced by a variety of artificial substrata (e.g. breakwaters, seawalls, jetties). Understanding the ecological functioning of these artificial habitats is key to planning their design and management, in order to minimise their impacts and to improve their potential to contribute to marine biodiversity and ecosystem functioning. Nonetheless, little effort has been made to assess the role of human disturbances in shaping the structure of assemblages on marine artificial infrastructures. We tested the hypothesis that some negative impacts associated with the expansion of opportunistic and invasive species on urban infrastructures can be related to the severe human disturbances that are typical of these environments, such as those from maintenance and renovation works.


Methodology/Principal Findings 
Maintenance caused a marked decrease in the cover of dominant space occupiers, such as mussels and oysters, and a significant enhancement of opportunistic and invasive forms, such as biofilm and macroalgae. These effects were particularly pronounced on sheltered substrata compared to exposed substrata. Experimental application of the disturbance in winter reduced the magnitude of the impacts compared to application in spring or summer. We use these results to identify possible management strategies to inform the improvement of the ecological value of artificial marine infrastructures.


Conclusions/Significance 
We demonstrate that some of the impacts of globally expanding marine urban infrastructures, such as those related to the spread of opportunistic, and invasive species could be mitigated through ecologically-driven planning and management of long-term maintenance of these structures. Impact mitigation is a possible outcome of policies that consider the ecological features of built infrastructures and the fundamental value of controlling biodiversity in marine urban systems.

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Anthropogenic Disturbance Can Determine the Magnitude of Opportunistic Species Responses on Marine Urban Infrastructures

This study focuses on the shoreline change detection along the North Sinai coast in Egypt using geographic information system and digital shoreline analysis system (DSAS) during the elapsed period ...

Shoreline change detection using DSAS technique: Case of North Sinai coast, Egypt

Rosetta Promontory, Egypt has been suffering from a continuous erosion problem. The dramatic retreatment was observed during the last century. It is basically due to the construction of Aswan High Dam in 1964, which reduced the flow and sediment discharges. In this paper, four Landsat images (two Thematic Mapper and two Enhanced Thematic Mapper) covering the period from 1984 to 2014 were used. These Landsat images were radio-metrically and geometrically corrected, and then, multi-temporal post-classification analysis was performed to detect land cover changes, extracting shoreline positions to estimate shoreline change rates of the Nile delta coast around Rosetta Promontory. This method provides a viable means for examining long-term shoreline changes. Four categories, including seawater, developed (agriculture and urban), sabkhas (salt-flat), and undeveloped areas, were selected to evaluate their temporal changes by comparing the four selected images. Supervised classification technique was used with support vector machine algorithm to detect temporal changes. The overall accuracy assessment of this method ranged from 97% to 100%. In addition, the shoreline was extracted by applying two different techniques. The first method is based on a histogram threshold of Band 5, and the other uses the combination of histogram threshold of Band 5 and two band ratios (Band 2/Band 4 and Band 2/Band 5). For land cover change detection from 1984 to 2014, it was found that the developed area that increased by 9% although the land in the study area has been contracted by 1.6% due to coastal erosion. The shoreline retreat rate has decreased more than 70% from 1984 to 2014. Nevertheless, it still suffers from significant erosion with a maximum rate of 37 m/year. In comparison to ground survey and different remote sensing techniques, the established trend of shoreline change extracted using histogram threshold was found to be closely consistent with these studies rather than combining band ratio with histogram threshold.

Detection of Shoreline and Land Cover Changes around Rosetta Promontory, Egypt, Based on Remote Sensing Analysis

The role of fringing coral reef in beach protection of Hurghada, Gulf of Suez, Red Sea of Egypt

The rapid erosion in most coastlines is considered a major problem not only in Egypt, but also around the world. The main causes are due to anthropogenic activities and/or coastal hydrodynamics. The coastal zone suffers from sedimentation, accretion, and pollution problems as well as the side effect of climate change. The climate change will increase sea level rise, salt water intrusions, and storm surge. Major efforts has been exerted to manage coastal erosion problems and to restore coastal capacity in order to protect housing, infrastructure and the cultivated land. These problems were encountered with various types of hard structures, but most of these methods response were limited due to lack in evaluation of the entire ecological situation. This encouraged the coastal engineers to think about new types of environmental friendly structures work better with ecological situation. In this study, the protection measures worldwide is reviewed and divided mainly into four groups, hard, soft, combined, innovative measures. The usage and side effect of each type is mentioned briefly. It is clear that there is a predominant approach towards the soft engineering, the eco-engineering techniques, or combination between them in order to enhance the ecological situation. Recently, there are several efforts to apply these new technologies to protect the coastal zone as well as the environment by taking into consideration the effect of climate change. These new approaches in coastal protection are multi used, environmentally friendly, easy to modify and maintain, and efficient from an economic perspective. Previous efforts in solving coastal problems in Egypt are analyzed and discussed taking into consideration the experience of similar cases worldwide. It is clear that the environmental friendly coastal structure is more suitable to solve most of our coastal problems with saving our ecosystem and reduce the protection cost.

Moheb Iskander

Papers

Detection of Shoreline and Land Cover Changes around Rosetta Promontory, Egypt, Based on Remote Sensing Analysis

The role of fringing coral reef in beach protection of Hurghada, Gulf of Suez, Red Sea of Egypt

Coastal protection measures, case study (Mediterranean zone, Egypt)

Hydrodynamic performance of double rows of piles suspending horizontal c shaped bars

Beach impacts of shore-parallel breakwaters backing offshore submerged ridges, Western Mediterranean Coast of Egypt