Development of a Numerical Model to Analyze the Formation and Development Process of River Mouth Bars

An integrated sediment management approach that includes the recovery of the amount of declined sediment supply is effective as a fundamental solution to coastal erosion. During planning, it is essential to analyze the transfer mechanism of the sediments generated from estuaries (the junction between a river and sea) to assess the amount and rate of sediment discharge (from the river to sea) supplied back to the coast. Although numerical models that interpret the tidal sand bar flushing process during flooding have been studied, thus far, there has been no study focusing on the formation and development processes of tidal sand bars. Therefore, this study aims to construct wave deformation, flow regime calculation, and topographic change analysis models to assess the amount of recovered sediment discharge and reproduce the tidal sand bar formation process through numerical analysis for integrated littoral drift management. The tidal sand bar formation process was simulated, and the wave energy and duration of action concepts were implemented to predict the long-term littoral movement. The river flux and wave conditions during winter when tidal sand bars dominantly develop were considered as the external force conditions required for calculation. The initial condition of the topographic data directly after the Maeupcheon tidal sand bar flushing during flooding was set as the initial topography. Consequently, the tidal sand bar formation and development due to nearshore currents dependent on the incident wave direction were reproduced. Approximately 66 h after the initial topography, a sand bar formation was observed at the Maengbang estuary.

Pedaro formation, equivalent of Plover sandstone at Savu Island, Outer Banda Arc

Plover Sandstone have been widely known as a good quality of oil and gas reservoir in NW Australia. As the continuity of NW Australia margin, outer Banda Arc become the distribution area of the equivalent of Plover Sandstone units. Therefore, a clear distinction and characterization of equivalent of Plover Sandstones distributed in this area is needed. Thick unit of quartz rich sandstone is scrap out in south Savu Island. Refers to the location where the lithology is found widely distributed, the unit is suggested to be called as Pedaro Formation. The characteristic of the lithology is determined through detailed measured section from two trajectories and laboratory analysis, including fourteen samples of petrography analysis, eight samples of Scanning Electron Microscope (SEM) analysis, and three samples of X-Ray Difraction (XRD) analysis. The lower part of the unit is initiated by braided fluvial conglomerates which gradually become tidal sand flat association of shale layers, coal seams and sandstone insertion. While the upper part of the unit is consisting of thick bedded quartz sandstone with thin siltstone insertion, deposited in the shoreface environment. Those facies association developed at transgressive conditions in the estuarine environment. The characteristic of the sandstone unit of Pedaro Formation is thickly bedded quartz wacke to quartz arenite, white to light grey in color, moderately to very well sorted, mostly mature sand. Pedaro Formation is identified to be deposited at Early Jurassic in interior craton tectonic setting. The characterization of sandstone unit of Pedaro Formation is showing that the unit can be correlate to the equivalent of Plover Sandstone found in Timor. Sandstone unit of Pedaro Formation can play a role as reservoir candidate in petroleum system of Savu and surrounding area.

Modelling the Past and Future Evolution of Tidal Sand Waves

This study focuses on the hindcasting and forecasting of observed offshore tidal sand waves by using a state-of-the-art numerical morphodynamic model. The sand waves, having heights of several meters, evolve on timescales of years. Following earlier work, the model has a 2DV configuration (one horizontal and one vertical direction). First, the skill of the model is assessed by performing hindcasts at four transects in the North Sea where sand wave data are available of multiple surveys that are at least 10 years apart. The first transect is used for calibration and this calibrated model is applied to the other three transects. It is found that the calibrated model performs well: the Brier Skill Score is ’excellent’ at the first two transects and ’good’ at the last two. The root mean square error of calculated bed levels is smaller than the uncertainty in the measurements, except at the last transect, where the M2 is more elliptical than at the other three transects. The calibrated model is subsequently used to make forecasts of the sand waves along the two transects with the best skill scores.

Nonlinear dynamics of sand waves in sediment scarce environments

<p>Field observations in the Dover Strait (Le Bot and Trentesaux, 2004) show sandy bed patterns in an environment where sand is scarce. Their morphological features closely resemble tidal sand waves, however, these type of bed forms are characterized by a crest-to-crest spacing which is larger than the wavelength of sand waves in the same surveyed area where sand is abundant. Based on stability theory, Porcile et al (2017) developed a morphodynamic model that was able to explain these features. They found that where the motionless substratum is exposed due to the growth of dunes, the lack of sand affects sediment transport, and consequently the morphology of the bed patterns. Their results also showed that the continuous growth leads to a lengthening of the dunes, and an increasing irregularity of the spacing. The found that their results were supported by the field observations.</p><p>Since the model by Porcile et al (2017) is partly based on the perturbation principle, the results are only valid for small amplitude patterns. To further understand the nonlinear behaviour of these sand starved dunes (e.g. shape, height), we here apply the fully numerical sand wave model by Damveld et al (2020). We extend this model by accounting for the presence of a hard substrate just below a thin layer of sand. Moreover, we start with a randomly perturbed bed pattern to give the morphodynamic system the freedom of self-organization.</p><p>Preliminary results show that the numerical model is able to reproduce the results found by Porcile et al (2017). In situations where sand is less abundant, wavelengths increase, and so does the spacing irregularity. Moreover, it is found that the average height of the sandy dunes is becoming increasingly smaller with decreasing sand availability. Further analysis should reveal dependencies to different environmental parameters, such as grain size, depth and tidal current strength.</p><p>Le Bot, S., & Trentesaux, A. (2004). Types of internal structure and external morphology of submarine dunes under the influence of tide- and wind-driven processes (Dover Strait, northern France). Marine Geology, 211(1), 143-168. doi:10.1016/j.margeo.2004.07.002</p><p>Damveld, J. H., Borsje, B. W., Roos, P. C., & Hulscher, S. J. M. H. (2020). Horizontal and Vertical Sediment Sorting in Tidal Sand Waves: Modeling the Finite-Amplitude Stage. Journal of Geophysical Research: Earth Surface, 125(10), e2019JF005430. doi:https://doi.org/10.1029/2019JF005430</p><p>Porcile, G., Blondeaux, P., & Vittori, G. (2017). On the formation of periodic sandy mounds. Continental Shelf Research, 145(Supplement C), 68-79. doi:10.1016/j.csr.2017.07.011</p>

FASIES DAN LINGKUNGAN PENGENDAPAN FORMASI KANIKEH, CEKUNGAN BULA, MALUKU

Batuan silisiklastik berumur Trias yaitu Formasi Kanikeh, tersebar di Pulau Seram hingga Pulau Kesui dan Teor dari Maluku hingga Maluku Tenggara. Formasi Kanikeh telah lama dikenal memiliki karakteristik batuan induk yang baik. Pemahaman tentang Formasi Kanikeh masih minim, interpretasi lingkungan pengendapan dan korelasi stratigrafi masih ada perbedaan. Tujuan penelitian ini adalah mendapatkan hasil interpretasi lingkungan pengendapan berdasarkan data terbaru. Metode yang digunakan dalam penelitian ini adalah pengukuran penampang stratigrafi pada empat lintasan pengamatan di daerah Seram Bagian Timur dengan menggunakan pendekatan analisis litofasies dan asosiasi fasies. Hasil dari penelitian ini menunjukkan adanya 9 litofasies, yaitu: Litofasies Batupasir Konglomeratan (Sg); Litofasies Batupasir Lapisan Silangsiur Mangkok (Sp); Litofasies Batupasir Bioturbasi (Sb); Litofasies Batupasir Karbonan (Sc); Litofasies Batupasir Bergelombang (Sw); Litofasies Batupasir Flasser (Sf); Litofasies Batupasir Laminasi Sejajar (Sh); Litofasies Batulumpur Lenticular (Fl); Litofasies Batulumpur Berlapis (Fsc). Deskripsi litofasies tersebut termasuk ke dalam suatu sistem pengendapan pasang-surut (intertidal) yaitu tidal channel, tidal sand flat, tidal sand-mud mixed flat, dan tidal mudflat. Formasi Kanikeh terendapkan dengan sistem pengendapan batuan silisiklastik yang dipengaruhi oleh arus pasang-surut pada lingkungan pengendapan transisi. ABSTRACT - Facies and depositional environment of Kanikeh Formation, Bula Basin, Maluku. The Triassic siliciclastic rocks, Kanikeh Formation are spread across Seram, Kesui, and Teor Island from Molucca to Southeast Molucca. The Kanikeh formation has been known as an excellent source rock. However, its interpretation of the depositional environment and stratigraphic correlation are still poorly understood. This study aims to give a better understanding of the depositional environment. This study consists of Lithofacies descriptions and facies associations of four stratigraphy measuring sections in Eastern Seram Island. The results of this study indicate that there are 9 lithofacies, including conglomeratic sandstone (Sc); Through cross bed sandstone (Sp); Bioturbated sandstone (Sb); Carboniferous sandstone (Sc); Wavy Sandstone (Sw); Flasser Sandstone (Sf); parallel laminated sandstone (Sh); lenticular mudstone (Fl); dan laminated mudstone (Fsc). The lithofacies description is included in four facies associations which are included in a tidal deposition system (intertidal) there are tidal channels, tidal sand flat, tidal sand-mud mixed flat, dan tidal mudflat. Based on the results Kanikeh Formation is deposited with a siliciclastic deposition system influenced by tidal currents within transition deposition environments.