Wave - Induced Suspended Sediment Flux Degradation due to Emergent Vegetation

It is well known that sediment movement is affected by aquatic vegetation under flow and wave conditions. However this impact is not fully understood yet. The aim of this study is to determine the effect of emergent vegetation on suspended sediment flux under wave conditions. In this context, an experimental study was conducted and wave orbital velocities and suspended sediment concentrations are measured through 4 m long emergent reeds under regular waves. Suspended sediment fluxes were calculated and the results of these calculations were evaluated. The results showed that the depth integrated suspended sediment flux were retained 75% to 90% due to vegetation

The effect of reed beds on wave attenuation and suspended sediment concentration

The effect of emergent and submerged vegetation on uniform and oscillatory flow conditions has been intensively studied by researchers in the last two decades. It has been determined that vegetation affects wave characteristics and cause wave attenuation especially in shallow waters where wave orbitals are in interaction with vegetation. Consequently they affect sediment deposition and resuspension acting as a sink. The aim of this study is to determine wave attenuation due to vegetation, and to identify the effect of emergent vegetation on suspended sediment concentration. In this experimental study, a reed bed was established on a sandy bottom in a wave flume in ITU Hydraulics Laboratory. Regular waves with different wave steepness were generated in the flume and water surface elevations through the reed bed were measured using resistance type wave gauges. Suspended sediment concentration time series were measured using OPCON along depth. The gradual wave attenuation due to reed bed was determined and wave transmission coefficients for different waves were found between 0.35 and 0.55 and these values are reversely proportional with wave steepness. It has been found out that wave attenuation also decreases with increasing KC numbers. Suspended sediment concentration measurements inside the reed bed were a little bit harder to interpret, but a decrease in concentration; before the waves reach the reed bed and after the waves left the reed bed, was determined. In spite of many studies on effects of vegetation on flow conditions there is still a lack of understanding vegetation-flow interaction and sedimentation around them. This study is an attempt to make a contribution on this topic

An experimental study on geotextile usage for protection of scour under submarine pipelines

Scour is a process that is occurring by reason of disturbed flow conditions in the case of existence of submarine pipeline on the seabed. When pipelines are placed on the erodible seabed changing flow (wave/current) conditions cause scour around pipes and this leads the system to stability problems. Geotextiles are permeable textiles which are produced as either woven or non-woven and used in lots of industrial areas. They also have a wide usage in coastal engineering such as for coastal erosion control and in reefs, breakwaters, revetments. In this study, it is aimed to determine the effect of usage of geotextile material for scour protection of submarine pipelines experimentally. In this context, scour is examined in the wave flume by using two pipes and placing geotextile material under regular wave conditions

Methodology for Integrated Socio-economic Assessment of Multi-use Offshore Platforms

This chapter presents the methodology employed for the Integrated Socio-Economic Assessment (MISEA) of different designs of Multi-Use Offshore Platforms (MUOPs). The methodology allows for the identification, the valuation and the assessment of the potential impacts and their magnitude. The analysis considers a number of feasible designs of MUOP investments, and the likely responses of those impacted by the investment project. The approach provides decision-makers with a valuable tool to assess whether a MUOP project increases the overall social welfare and hence should be undertaken. This is performed under alternative specifications regarding platform design, the discount rate and the stream of net benefits, if a Cost-Benefit Analysis (CBA) is to be followed or a sensitivity analysis of selected criteria in a Multi-Criteria Decision Analysis (MCDA) framework. The methodology can support the implementation of policies aiming at achieving a good environmental status of the EU’s marine waters and the protection of the resource base upon which marine-related economic and social activities depend