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Mangroves thrive in sheltered intertidal areas in the tropics and sub-tropics. Due to this position at the interface between land and sea, mangroves play an important role in the attenuation of waves. Dissipation of wave energy in mangrove forests is an interesting feature from the viewpoint of coastal protection. Nevertheless, field data are sparse and modeling attempts reveal the need for additional data. This paper presents the results of an extensive field campaign, lasting 6 months, in mangroves along the Andaman coast of Trang Province in southern Thailand. Wave attenuation has been studied along two contrasting transects with different elevation and vegetation characteristics and different orientations towards the Andaman Sea. Along the Kantang transect, which is mostly exposed to swell waves, vegetation densities increased from 4.5 to 9.3 volume-‰ along the transect and on average 63% of the incident wave energy was attenuated over a distance of 246 m. Along the Palian transect, mostly exposed to sea waves instead, vegetation increased from 4.3 to 19 volume-‰ and 72% of the incident wave energy was attenuated over this 98 m transect. It was found that standardized wave attenuation correlates well with incident wave energy, when attenuation is analyzed per vegetation zone. Energy reduction rates of these zones, defined by the gradient of the correlations between the standardized wave attenuation and incident wave energy, are found to increase significantly with vegetation density. Consistently, wave reduction rates, expressing the gradient of the correlation between wave height reduction and incident wave heights, are found to be 0.001-0.014 for the study sites and also show a significant and increasing trend with vegetation densities.

The coastal zones management not only relies on a profound knowledge of the shoreline but also on a good assessment of morphodynamics, sediments transport and coastal interventions required. Many coastal studies, such as beach slope estimates, equilibrium beach profile definition or sediment transport analysis, depend on the sediment grain size at the site. This paper aims to gain a better understanding of grain size distribution along the cross-shore profile and variation of d 50 , allowing to define a representative d 50 to characterize the beaches. On the study site chosen, Barra beach, Aveiro, an extensive field campaign was performed, from October 2010 to May 2011. In a weekly basis, samples from 5 points along a cross-shore profile were collected. During this period, data related to wave climate was collected from the Portuguese Hydrographic Institute in temporal series of 10 min. Tidal projections from Hydrographic Institute were also identified for the period of the field campaigns. The sediment grain size distributions showed that, although the mass-median-diameter does not usually pass the 1 mm, d 50 presented a great variation during winter, in the intertidal zone. On the other side, the first and last points of the cross-shore profile, located far from the intertidal zone, presented the smaller d 50 and variation through time. The significant wave height presented a mean value of 2.16 m. The most energetic wave climates happened in November, January and February. During those months, an increase of d 50 in the wave breaking zone was noticed. Generally, the expected behavior of the cross-shore sediment grain size distribution is in line with the data collected in this paper and it was verified that the grain size is coarser on the intertidal zone and after storm periods. Also, despite the complexity of defining a characteristic d 50 due to its great temporal and spatial variation, sensitivity analysis on the data obtained helped the identification of the upper foreshore limit, at high tide, as the better location for a sediment sample collection representative of a cross-shore profile.

There are no sequential and integrated approaches that include the steps needed to perform an adequate management and planning of the coastal zones to mitigate coastal erosion problems and climate change effects. Important numerical model packs are available for users, but often looking deeply to the physical processes, demanding big computational efforts and focusing on specific problems. Thus, it is important to provide adequate tools to the decision-makers, which can be easily interpreted by populations, promoting discussions of optimal intervention scenarios in medium to long-term horizons. COMASO (coastal management software) intends to fill this gap, presenting a group of tools that can be applied in standalone mode, or in a sequential order. The first tool should map the coastal erosion vulnerability and risk, also including the climate change effects, defining a hierarchy of priorities where coastal defense interventions should be performed, or limiting/constraining some land uses or activities. In the locations identified as priorities, a more detailed analysis should consider the application of shoreline and cross-shore evolution models (second tool), allowing discussing intervention scenarios, in medium to long-term horizons. After the defined scenarios, the design of the intervention should be discussed, both in case of being a hard coastal structure or an artificial nourishment (third type of tools). Finally, a cost-benefit assessment tool should optimize the decisions, forecasting costs and benefits for each different scenario, through definition of economic values to the interventions and to the land/services/ecosystems, weighting all the environmental, cultural, social and historical aspects. It is considered that COMASO tools can help giving answers to the major problems of the coastal planning and management entities, integrating transversal knowledge in risk assessment, physical processes, engineering and economic evaluations. The integrated coastal zone management needs these tools to ensure sustainable coastal zones, mitigating erosion and climate change effects.

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