The solutions for construction of sea dike and sea embankments system as the sandy mud trap to support mangrove plants in the coastal zone of Hai Phong city, Vietnam

Mangrove plants play a viral role in protecting the coast, retraining erosion. Especially in areas considered the variable wave conditions, complex dynamic conditions such as the coastal region of Hai Phong city. However, due to various reasons, the development/additional planting of mangrove forests in the coastal area of Hai Phong in some locations has not achieved the desired result. This study was conducted survey measurements of mangroves, terrain, and practical experience to assess the ecological impact of certain dynamic and sedimentary conditions on mangroves. Thereby proposing several solutions to build sea dykes/embankments suitable to Hai Phong conditions, strengthen sediment traps, and create favorable conditions for developing mangrove trees in this area.

Measuring soil erosion resistance on coastal dikes linking hyperspectral UAV-data, plant traits and soil information

<p>The integrity of a sea dike, especially its surface soil and biological revetment, is indispensable for coastal protection, as a dike breach would result in damages and economic losses. Estimates of the condition of a sea dike are typically established by on-site inspections and expert judgement at regular intervals. These status assessments of the protection level of the sea dike evaluate grass coverage and animal burrows, since structural inconsistencies deter the overall safety levels on coastal protection. In laboratory settings, erosion resistance of a sea dike is often determined by means of assessing critical shear stress induced by wave-run up and overtopping. Whereby the grain size distribution and soil aggregate formation on the one hand and the root penetration of the sample on the other are significant factors influencing critical shear stress and therefore erosion resistance. <br>Drone-/UAV-based remote sensing can be used to easily determine the degree of coverage of the dike revetment via green value detection. Thermal spectroscopy is also already used in agriculture to detect the state of health of plants at an early stage, for example due to a shortage of water. In addition, plants can be classified using hyperspectral imaging data. <br>We aim to derive transfer functions correlating ground truthing data, drawn from coastal real world- and a full scale laboratory dike, with plant species, its characteristic taxonomic traits and assessed top soil parameters. This approach bears the advantage of yielding an erosion-resistance estimate of the dike cover based on the plant classification using UAV-derived hyperspectral information. Furthermore, taxonomic species are sought to be paired with their respective, site specific, root architecture. Soil parameters such as nutrient availability and humidity will be observed and integrated into the approach, as they bear an impact on subterranean vegetation growth in that plants with lower nutrient availability develop a higher root network (high root length density [cm/cm³]). Finally, grazing livestock on the dike impacts the root system and soil structure as well and both aspects will be investigated comparing mowed against grazed areas as preliminary results show a dike cover void of grazing livestock exhibits a higher root shoot ratio than one with grazing. We hypothesize that classifying plants based on optical, hyperspectral UAV-derived data and the knowledge about the composition of the subsoil, the correlation of plant-specific root architecture and root growth with nutrient availability and agricultural maintenance could provide valuable information about erosion resistance of the dike cover to support dike inspection on an objective basis.</p>

Study on climate change impacts of sea level rise on the Saemangeum Sea Dike using the EEMD method

<p>The Saemangeum Sea Dike, completed in 2011 in South Korea, is the longest sea dike in the world. One of the most pressing issues of today, climate change leads to sea level rise that could increase the risk of sea dike overflow. However, what impact climate change will have on the Saemangeum Sea Dike has not been verified yet. Here, we estimate the impacts of sea level rise on the Saemangeum Sea Dike, using the Linear Regression Analysis method and the Ensemble Empirical Mode Decomposition (EEMD) method. The sea level data of the Saemangeum area of the last 30 years was analysed and the results showed that the maximum rate of sea level rise of the Saemangeum Sea Dike is at 2.51 mm/year when the EEMD method was applied. It means that the impact of sea level rise on the Saemangeum sea dike is reasonably low because the sea level rise will exceed the freeboard after 366 years, so there is currently no clear sign that it poses a problem.</p>

WAVE FORCE OF TSUNAMI KRAKATAU 1883 ON THE OUTER SEA DIKE IN JAKARTA BAY

Volcanic activity of Mount Anak Krakatau has been increased in the recent years. One of the consequences was Tsunami Sunda Strait in 2018. This heightened the awareness of the potential impact of a tsunami induced by Anak Krakatau for the construction of NCICD Project. This research is aimed to calculate the potential impact in the terms of wave force. Tsunami Krakatau 1883 was used as reference for two reasons. First, the comprehensive research has been conducted for this event. Second, the magnitude of Mount Anak Krakatau-induced tsunami will not be higher than that of Tsunami Krakatau 1883. Non shallow water equation-based numerical model is applied to simulate the tsunami. Time series from the model result is extracted as an input to calculate the wave force. There are four different method used such as Rule of Thumb, Linear Theory, Sainflou Method and Goda Method. The results show that the tsunami will hit the outer sea dike with a minimal force of 100 kN and a maximum force of 400 kN. OSD1-A is the safest sea dike since the tsunami only will hit the structure with a half force.

Wave Run-Up on Mortar-Grouted Riprap Revetments

The wave run-up height is a crucial design parameter that determines the crest height of a sea dike and is used for estimating the number of overtopping waves. Therefore, a reduction of the wave run-up height is generally aspired in the design of dikes, which can be achieved by mortar-grouted riprap revetments (MGRR). Although MGRRs are widely utilized revetments along the German North Sea coast, no investigations into the wave run-up height on this revetment type are available to date. Full-scale hydraulic model tests were hence conducted to investigate wave run-up heights on partially grouted and fully grouted MGRRs. The wave run-up was determined using 2D-LIDAR measurements, which were validated by video data. Partially grouted MGRRs, due to their roughness, porosity, and permeability, reduce wave run-up heights from 21% to 28%, and fully grouted MGRRs due to their roughness reduce wave run-up heights from 12% to 14% compared to smooth impermeable revetments. Influence factors have been determined for four widely used revetment configurations, which can now be used for design purposes. A comparison and subsequent discussion about the representation of the physics of wave run-up by different parameters is carried out with the results presented.