Dispersal pattern of coral larvae in Kuantan coastal waters, Malaysia

Understanding source and sink pattern of coral larvae is among the key elements for effective ecosystem management and future habitat restoration. This study examined dispersal pattern of coral larvae among three known inshore reefs (Pulau Ular, Balok Reef and Raja Muda reef) in Kuantan coastal waters by simulating virtual larvae trajectories during spawning event in 2018. Dispersal pathways were mod elled and constructed by incorporating biological traits (timing of spawning and pelagic larvae duration) using Langragian particle tracking module integrated with 2-dimensional, hydrodynamic, flexible network model (MIKE 21 FM). Results indicated that Acroporid larvae moved in southward direction throughout dispersal period. Source and sink dynamic suggested that Pulau Ular has high larvae retention (70%) in which most of larvae originated from natal reef. Balok reef was dominant source of larvae for Raja Muda reef. Results also indicated that patches reefs near Raja Muda was ideal sink site for coral larvae and sh ould be prioritized for future ecosystem management action

Model Numerik Lintasan Sebaran Larva Karang di Kandidat Lokasi Penempatan Bekas Struktur Anjungan Migas Lepas Pantai (Rig To Reef)

Anjungan migas lepas pantai yang sudah dibongkar ketika telah memasuki masa akhir produksinya dapat dimanfaatkan sebagai terumbu karang buatan (artificial reef).  Program ini di beberapa negara dikenal dengan sebutan Rigs-to-Reef (R2R).  Salah satu faktor penting yang harus dipertimbangkan dalam penempatan struktur rigs untuk terumbu buatan ini adalah konektivitas antara habitat asli sebagai sumber larva karang dan kandidat lokasi agar larva karang dapat menyebar, tumbuh dan berkembang dengan baik. Faktor penting yang mempengaruhi planulasi (pelepasan dan penyebaran larva karang ke laut sekitar) adalah sirkulasi arus laut di lapisan permukaan. Penelitian ini bertujuan untuk membuat simulasi sebaran larva karang dan memetakan pola konektivitas antara kawasan konservasi Perairan Daerah (KKPD) Bontang (source) dan lokasi baru untuk penempatan struktur rigs (sink).  Sebaran larva karang diperoleh dengan menggunakan pemodelan biofisik untuk mendapatkan skenario rekruitmen dan jejak penyebaran larva.  Pemodelan biofisik digunakan sebagai alat prediksi penyebaran larva untuk menilai konektivitas antar kawasan konservasi dan untuk evaluasi umum dari berbagai faktor yang berperan dalam pergerakan larva.  Simulasi sebaran larva dibuat dengan menggunakan modul Agent Based Modelling (Passive Drifter) menggunakan MIKE 21 FM untuk memprediksi sebaran larva karang di kandidat lokasi.  Simulasi sebaran larva dilakukan di beberapa bulan yang mewakili puncak 4 musim yang berbeda, yakni musim barat (bulan Januari), musim Peralihan I (bulan Mei), musim Timur (bulan Agustus) dan musim Peralihan II (bulan Oktober).  Hasil dari model sebaran larva mengindikasikan bahwa proses penyebaran larva karang di kawasan konservasi Bontang dipengaruhi oleh arus permukaan yang dibangkitkan oleh pasang surut serta variasi angin musiman dan menyebar dengan baik ke kandidat lokasi R2R

Pemodelan Pasang Surut dengan Menggunakan Metode Flexible Mesh untuk Mengetahui Genangan Rob di Pesisir Karawang

ABSTRAKPasang surut air laut merupakan salah satu gejala alam yang tampak di laut, yakni gerakan naik turunnya muka air laut. Gerakan tersebut disebabkan oleh pengaruh gaya tarik menarik antara bumi, bulan dan matahari. Data pasang surut dapat memberikan gambaran hidrodinamika di daerah pesisir dan dapat digunakan untuk perencanaan pembangunan dan mitigasi bencana di wilayah pesisir. Untuk mengetahui pasang surut dapat dilakukan dengan pengukuran langsung di lapangan atau dapat dilakukan dengan pemodelan. Penelitian ini bertujuan untuk membuat pemodelan pasang surut pantai Karawang dan dimanfaatkan untuk mengetahui genangan rob yang sering terjadi di pesisir Karawang. Metode yang digunakan dalam pemodelan pasang surut ini adalah Metode Flexible Mesh Simulasi yang terdapat pada Software Mike 2 dengan mengunakan data batimetri, garis pantai dan topografi. Hasil pemodelan pasang surut di perairan Karawang diketahui tipe pasang surut adalah tipe campuran condong harian tunggal dengan nilai Fomzhal adalah 2.854. Pasang tertinggi terjadi pada 8 Maret 2021 dengan interval waktu selama 2 jam dan elevasi berkisar 0.20-0.42m. Prediksi genangan banjir rob tertingi terjadi pada pada 13 Maret 2021 dengan interval waktu selama 3 jam dan nilai elevasi berkisar 0.11-0.15 m berada pada pesisir Kecamatan Pedes dengan dengan luasan genangan 38,69 km2.ABSTRACTThe tides are one of the natural phenomena that appear in the sea, namely the movement of rising and falling sea levels. The movement is caused by the influence of the attractive forces between the earth, moon and sun. Tidal data can provide an overview of hydrodynamics in coastal areas and can be used for development planning and disaster mitigation in coastal areas. To find out the tides can be done by direct measurements in the field or can be done by modeling. This study aims to model the tides of the Karawang coast and is used to determine the tidal inundation that often occurs on the coast of Karawang. The method used in this tidal modeling is the Flexible Mesh Simulation Method found in Mike 2 Software using bathymetry, coastline and topography data. From the results of tidal modeling in the Karawang Waters, it is known that the tidal type is a mixed type with a single daily slope and the Fomzhal value is 2.85. The highest tide will occur on March 8, 2021 with an interval of 2 hours and an elevation of 0.20-0.42m. Prediction of the highest tidal flood inundation will occur on March 13, 2021 with an interval of 3 hours and an elevation value ranging from 0.11-0.15 m on the coast of Pedes District with an inundation area of 38.69 km2

Assessment of Wave Attenuation Performance of the Tanjung Piai Breakwater Using Spectral Wave Analysis

Tanjung Piai is one of Malaysian heritage sites situated at the southernmost tip of the Asian continent. Tanjung Piai provides a conducive coastal habitat for many mangrove species, including the rare species of Bruguiera hainesii and Bruguiera sexangula. Coastal erosion resulting in shoreline retreat that was detected dating back to the 1930s. Due to uncontrolled coastal development ij the vicinity of Tanjung Piai, the erosion rate at the mangrove site had accelerated since the recent decades. This led to significant land mass loss that threatens the eco-system. Various measures have been undertaken to mitigate the erosion problems. Some measures were adopted to permanently harden the shoreline preventing sea water from reaching the mangroves. However, this resulted in mangroves gradually dying along the coast.. A series of offshore breakwaters were subsequently planned to reduce wave energy, mitigate the erosion and protect the existing mangroves growing along the wave-exposed coastline. This study aims to assess the impact of offshore waves, squalls and wind-generated waves to the Tanjung Piai coastline (with and without the breakwaters) using a two-dimensional numerical model. A survey of the site and details of the breakwaters’ design were incorporated in the modelling. The numerical results show that the breakwaters are able to reduce offshore wave heights up to 66%. The breakwaters can attenuate offshore waves more effectively compared to squalls and wind-generated waves. The breakwaters were completed in 2019. They were proven to be able to provide protection to the mangroves along the coast of Tanjung Pia

Assessment of Wave Attenuation Performance of the Tanjung Piai Breakwater Using Spectral Wave Analysis

Tanjung Piai is one of Malaysian heritage sites situated at the southernmost tip of the Asian continent. Tanjung Piai provides a conducive coastal habitat for many mangrove species, including the rare species of Bruguiera hainesii and Bruguiera sexangula. Coastal erosion resulting in shoreline retreat that was detected dating back to the 1930s. Due to uncontrolled coastal development ij the vicinity of Tanjung Piai, the erosion rate at the mangrove site had accelerated since the recent decades. This led to significant land mass loss that threatens the eco-system. Various measures have been undertaken to mitigate the erosion problems. Some measures were adopted to permanently harden the shoreline preventing sea water from reaching the mangroves. However, this resulted in mangroves gradually dying along the coast.. A series of offshore breakwaters were subsequently planned to reduce wave energy, mitigate the erosion and protect the existing mangroves growing along the wave-exposed coastline. This study aims to assess the impact of offshore waves, squalls and wind-generated waves to the Tanjung Piai coastline (with and without the breakwaters) using a two-dimensional numerical model. A survey of the site and details of the breakwaters’ design were incorporated in the modelling. The numerical results show that the breakwaters are able to reduce offshore wave heights up to 66%. The breakwaters can attenuate offshore waves more effectively compared to squalls and wind-generated waves. The breakwaters were completed in 2019. They were proven to be able to provide protection to the mangroves along the coast of Tanjung Pia

NUMERICAL MODELLING OF THE MORPHODYNAMICS OF THE PLOČE GRAVEL BEACH IN RIJEKA

The morphodynamics of an artificial gravel beach in the Bay of Rijeka (Ploče Beach) was analyzed. The morphological changes of the beach face were monitored through an intense situation of gravitational surface wind waves from the incident SSW direction. A numerical modeling technique was applied, after initially establishing a numerical model for wave deformation. A model for sediment transport was established based on its results. Both models were based on the finite volume method. In addition, the partial contribution of the longshore component of sediment transport was analyzed based on empirical formulae. The modeling results were verified by comparing the positions and amounts of eroded/accumulated material along the beach with the processing of terrain images in the form of point clouds. The erosion and accumulation positions of the beach sediment material, obtained by numerical model simulations, corresponded to the surveyed positions. The total volume of eroded and accumulated material based on terrain image processing corresponded to the model values

A new approach for handling complex morphologies in hybrid shoreline evolution models

Hybrid shoreline evolution models are being increasingly used to inform the management of sandy coastal systems. These models generally apply a two-dimensional physics-driven approach to calculate littoral drift and the one-line theory to update the shoreline morphology. As per the one-line theory, the calculated littoral drift is uniformly distributed over the active coastal profile. A key challenge facing the application of hybrid models is that they fail to consider complex morphologies when updating the shoreline morphology. Complex morphologies are defined herein by non-parallel depth contours to the shoreline, a characteristic feature of many vulnerable sandy coastal systems. This study illustrates the deficiency of the current hybrid 2D/one-line approach when applied to hindcast shoreline change from 2014 to 2016 along a sandy coast with fringing reefs in Puerto Rico. Results show that the hybrid approach is unable to predict observed shoreline change (Brier Skill Score = 0) as a result of the one-line theory assumption of a spatially constant closure depth, which defines the offshore extent of significant cross-shore sediment transport. To address this, a new hybrid approach is developed for application in complex morphologies that accounts for alongshore variations in the closure depth. In the new hybrid approach, the coast is divided into segments according to the alongshore distribution of fringing reef substrate with each segment having a different closure depth specified based on their underlying bed morphology. Results show that this new hybrid approach enables a more realistic simulation (Brier Skill Score = 0.4) of observed shoreline change. This finding explicitly demonstrates that the closure depth is an important variable in shoreline evolution models. It also implicitly indicates that we are likely to better simulate shoreline evolution in complex morphologies over timescales of concern in coastal management by allowing the closure depth to vary alongshore in hybrid models

Multimodal harbor wave climate characterization based on wave agitation spectral types

A new numerical methodology reaching an improved characterization of the historical harbor wave agitation climate is presented in this work. A detailed frequency-direction wave spectrum definition of wave agitation patterns within harbor basins is achieved, providing an in-depth description of the whole multidirectional and multireflective wave patterns occurring as a natural harbor response. This constitutes an advance from the monoparametric/aggregated wave height parameter-based approaches, traditionally used for wave agitation characterization, to a multivariate and disaggregated representation of in-port waves and the multiple wave transformation processes within harbor basins. In addition, the wave agitation spectral type concept is proposed, whereby the wave agitation spectral shapes are classified into representative clusters of the historical wave agitation response in a harbor. A detailed multiannual analysis of the wave agitation response, based on the different in-port spectral wave components, their relation with the outer-harbor forcing waves, and their interactions with the harbor structures, can be achieved with the proposed methodology. This improved harbor wave climate characterization can be especially relevant for port operability and downtime analyses. The methodology is applied and validated in Africa basin (Las Palmas Port, Spain).This work was supported by a FPU (Formación de Profesorado Universitario) grant from the Spanish Ministry of Science, Innovation and Universities to the first author (FPU18/03046). This work was also partially funded under the State R&D Program Oriented to the Challenges of the Society (PID2020-118285RB-I00) of the Spanish Ministry of Science, Innovation and Universities