Underwater Sediment Research Articles

Kehancuran dan Harapan Baru: Gempa, Tsunami dan Likuifaksi di Palu Sulawesi Tengah 2018

Natural disasters are events that require significant attention, and it is imperative to protect nature and remain submissive to the Creator. The purpose of this research is to express the author's concern regarding the tragedy that occurred in the city of Palu, Central Sulawesi, on September 28, 2018. In this study, the researcher employed a literature review method, sourcing references from journals, books, and information related to the Palu tragedy at that time. The findings of this research indicate that on September 28, 2018, at 18:42 WITA, a natural disaster occurred in the form of a 7.4 magnitude earthquake, followed by a tsunami and liquefaction. This was triggered by underwater sediment landslides. Mythical aspects related to this tragedy are issues that have not been scientifically validated. The Nomoni Festival, which includes the Balia Dance, is considered by some community members to be contrary to their religious beliefs. Some people believe that such practices invite divine wrath, manifesting as natural disasters. However, scientific explanations for the disaster indicate that the earthquake and tsunami were the result of tectonic activity, which can be geologically explained. It is essential to combine scientific understanding with respect for local beliefs to enhance disaster preparedness and mitigation in the future. This research aims not only to reveal the scientific facts behind the Palu tragedy but also to raise awareness about the importance of maintaining ecological balance and gaining a deeper understanding of natural phenomena.

Interference of Echo-Signals from Two Buried Spherical Targets

A numerically efficient technique is presented for computing the backscattered fields from two spherical targets embedded in an underwater sediment. The bottom is assumed to be a homogeneous liquid attenuating half-space. The transmitter/receiver is located in a homogeneous water half-space. The distances between the transmitter/receiver and objects of interest are supposed to be large compared to the acoustic wavelengths in water and seabed. In simulations, the spherical scatterers of the same radius are assumed to be acoustically rigid. The interactions between two spheres are not taken into account because of the strong attenuation in the bottom. The scattering from one sphere in a wide frequency range is determined using the Hackman and Sammelmann’s general approach. The arising scattering coefficients of the sphere are evaluated using the steepest descent method. The obtained asymptotic expressions for the scattering coefficients essentially allowed to decrease a number of summands in the formula for the form-function of the backscattered acoustic field.

The dredger

ABSTRACT The dredging of navigable waterways is a critical but often overlooked precondition for global trade. Focusing on the figure of “the dredger”—which can refer to a machine that excavates underwater sediment or a person who does that work—this short article links the modern maritime industry, colonial expansion, and terracentric anthropological thought. I argue that the figure of the dredger is useful for understanding the collective geological agency of humanity.

Underwater Sediment Layers analysis using Convnet with Adam Optimiser and mapping its reflection coefficient parameter with the Particle Size

Underwater Sediment Layers analysis using Convnet with Adam Optimiser and mapping its reflection coefficient parameter with the Particle Size

Research on Sedimentary Microfacies of an Oil Layer in a Block of Songliao Basin

This topic uses debris, core log, core description data, combines regional research results, determine that the oil layer in a block of the Songliao Basin is the most developed in the front subfacies and prodelta subfacies of delta underwater sediment. Microfacies include underwater distributary channels, underwater natural levees, distributary bays, estuary dams, distal bars, sheet sand, and prodelta mud. The contiguous distribution of dam sand is the main feature of this area. On the basis of single-well facies research, it is the first time that this topic has studied the features of the plane and profile distribution of the reservoir sedimentary facies belt in the study area, and finally builds the sedimentary facies model, and provides a solid geological basis for fine reservoir description and favorable area prediction.

New horizons for dredging research: The ecology and politics of harbor deepening in the southeastern United States

AbstractHarbor deepening projects in the southeastern United States illuminate a global phenomenon: navigable rivers and coastal estuaries have been dredged to new depths as port authorities and governments compete to accommodate and benefit from new generations of massive oceangoing ships. This urbanized region has dozens of ports situated in estuaries and deltas where major rivers meet the Atlantic Ocean and Gulf of Mexico. It is also home to the majority of U.S. inland federal waterways, significant cargo traffic, and remarkable cultural and ecological diversity. Moving enormous volumes of underwater sediment is as much a social, economic, and political phenomenon as an intervention in hydrological and geomorphological processes. Therefore, dredging demands an analytical framework that bridges disciplines and spatial scales. Putting dredging research into conversation with scholarship on global shipping, logistics, and port development, we call for an analytical framework that draws upon political ecology and geosocial theory. We use this framework to examine large harbor deepening projects near Savannah, Jacksonville, Mobile, and New Orleans. Each project has been rationalized in terms of accommodating the megaships transiting an expanded Panama Canal and, more generally, linking local and regional economic development to global supply chains. An expanded and comparative framework reveals the geographical scale and variegated politics that characterize navigation dredging today.This article is categorized under: Human Water > Methods

Experimenting with Underwater Sediment Slides

Sediment-laden currents caused by breaching flow slides are hazardous to flood defenses and seabed infrastructure. New research shows that these phenomena must be accounted for in erosion simulations.

Chemical weapons dumped after WWII are polluting the Baltic Sea

Mustard gas and other dumped after World War II are polluting the Baltic Sea’s underwater sediment. Researchers found traces of arsenic-containing agents and mustard gas products in sediment and fi...

Uncommon southwest swells trigger sea urchin disease outbreaks in Eastern Atlantic archipelagos.

Recurrent sea urchin mass mortality has recently affected eastern Atlantic populations of the barren‐forming sea urchin Diadema africanum. This new episode of die‐off affords the opportunity to determine common meteorological and oceanographic conditions that may promote disease outbreaks. The population dynamics of this sea urchin species are well known—urchin barrens have persisted for many decades along most of the coastlines off the archipelagos of Madeira, Selvages, and the Canary Islands, where they limit macroalgae biomass growth. However, this new and explosive mortality event decimated the sea urchin population by 93% on Tenerife and La Palma Islands. Two severe episodes of southwestern rough sea that led to winter storms, in February 2010 (Xynthia) and February 2018 (Emma), preceded both mass mortality events. The autumn and winter months of those years were anomalous and characterized by swells with an average wave height above 2 m that hit the south and southwest sides of the islands. The amoeba Paramoeba brachiphila was the only pathogen isolated this time from the moribund and dead sea urchins, suggesting that the amoeba was the primary cause of the mortality. This new sea urchin die‐off event supports the “killer‐storm” hypothesis that has been already described for western Atlantic coasts. These anomalous southwest storms during winters generate pronounced underwater sediment movement and large‐scale vertical mixing, detected in local tide gauge, which may promote paramoebiasis. This study presents valuable insights about climate‐mediated changes in disease frequency and its impacts on the future of coastal marine ecosystems in the Atlantic.

High-resolution single-camera photogrammetry: incorporation of refraction at a fluid interface

Photogrammetry uses images of a three-dimensional structure to derive information about its shape and position. In this work, a photogrammetric technique is implemented with a single camera and a digital projector to measure changes in an underwater sediment bed. This implementation incorporates refraction at an interface allowing for measurements through a deformed or changing water surface. The digital projector provides flexibility in choosing projected patterns and has a high frame rate, which allows to easily increase the spatial and temporal resolution of the measurements. The technique requires first for both the camera and the projector to be calibrated using triangulation. With the calibration, we construct lines in three-dimensional space that originate from the projector and the camera, and intersect on the surface to be measured. To correctly incorporate refraction due to a change of medium, each line in space is recalculated from its intersection with the interface using Snell’s law. This has the benefit that only one calibration for measurements is needed if the location and shape of the interface are known. The technique is validated by measuring a submerged undulated surface, plastic objects and a sediment bed. In particular, the undulated plate is reconstructed under a flat and a parabolic water surface. Finally, the technique is used in combination with particle image velocimetry to dynamically measure a changing sediment bed under an oscillating flow and the flow velocity at the free surface.Graphic abstract

Video Sensing of Nearshore Bathymetry Evolution with Error Estimate

Although coastal morphology results essentially from underwater sediment transports, the evolution of underwater beach profiles along the diverse coastlines of the world is still poorly documented. Bathymetry inversion from shore-based video cameras set forth a more systematic evaluation and is becoming more commonly used. However, there are limitations to this profiling method that are insufficiently assessed, undermining confidence in operational applications. In this paper, we investigate the daily evolution of a low tide terrace (LTT) in Nha Trang beach, Vietnam, under strong seasonal forcing: from weak wind waves during summer monsoon to moderate waves during winter monsoon. A new error estimation for depth inversion is presented based on tidal evaluation. The method compares video-based estimate and direct measurement of tidal amplitudes to provide a quality criterion. It reveals three types of errors, the main one being a deep water error associated with physical limits—loss of celerity-bathymetry relationship in deep water. This error is dependent on wave period and thus has a strong seasonal pattern in Vietnam. It is generally detrimental to depth inversion where wind waves are dominant (in summer here). On the contrary, the second error type is larger for larger waves and is located at breakpoint, altering wave detection. The last error type is due to nonlinear effects and wave setup in shallow water. After removing the faulty data, we finally present the first reliable three-year time-series of a beach profile in Nha Trang, Vietnam. A main result is the overall stability demonstrated for the LTT beach, with rapid exchange of sediment between the terrace and the upper beach during typhoons, monsoon events or seasonal cycles. These tropical environments may provide faster beach recovery compared with mid-latitude configurations.

Optical wide-field tomography of sediment resuspension.

We present a wide-field imaging approach to optically sense underwater sediment resuspension events. It uses wide-field multi-directional views and diffuse backlight. Our approach algorithmically quantifies the amount of material resuspended and its spatiotemporal distribution. The suspended particles affect the radiation that reaches the cameras, hence the captured images. By measuring the radiance during and prior to resuspension, we extract the optical depth on the line of sight per pixel. Using computed tomography (CT) principles, the optical depths yield estimation of the extinction coefficient of the suspension, per voxel. The suspended density is then derived from the reconstructed extinction coefficient.

THE RESEARCH OF CORRELATION OF WATER SURFACE SPECTRAL AND SEDIMENT PARAMETERS

Abstract. In the method of survey underwater topography using remote sensing, and the water surface spectral reflectance R, which remote sensing inversion results were closely related to affects by the water and underwater sediment and other aspects, especially in shallow nearshore coastal waters, different sediment types significantly affected the reflectance changes. Therefore, it was of great significance of improving retrieval accuracy to explore the relation of sediment and water surface spectral reflectance. In this study, in order to explore relationship, we used intertidal sediment sand samples in Sheyang estuary, and in the laboratory measured and calculated the chroma indicators, and the water surface spectral reflectance. We found that water surface spectral reflectance had a high correlation with the chroma indicators; research result stated that the color of the sediment had an very important impact on the water surface spectral, especially in Red-Green chroma a*. Also, the research determined the sensitive spectrum bands of the Red-Green chroma a*, which were 636–617 nm, 716–747 nm and 770–792 nm.

Characteristics and risk assessment of organochlorine pesticide residues in surface sediments collected at the Qingshitan Reservoir

ABSTRACTAn ultrasonic extraction – gas chromatography – electron capture detector analytical method was used to measure the concentration and types of organochlorine (OC) pesticides in sediment to obtain a better understanding of the characteristics and hidden ecological risks associated with OC pesticide exposure in surface sediment of the Qingshitan Reservoir. Fifteen types of OC pesticides were detected in the sediment, and the sum concentration of these chemicals was in the 149.32–490.19 ng/g range (mean value: 319.39 ng/g). The concentrations of detected OC pesticides occurred in the following order: hexachlorohexanes (HCHs) (mean value: 200.17 ng/g) > DDTs (mean value: 36.92 ng/g) > heptachlors (mean value: 32.74 ng/g) > methoxychlor (mean value: 24.13 ng/g). There was a 100% detection rate for HCH isomers, and their concentrations occurred in the following order: β-HCH > δ-HCH > γ-HCH > α-HCH. β-HCH was the main component of HCHs. Ratios between α-HCH/γ-HCH and β-/(α+γ)-HCH were used to investigate the sources of pollution. Most of the surveyed areas were polluted by lindane, which originated from past pesticide residue usage, and no new inputs of HCHs were found. DDT was the major component of the DDTs, and accounted for 52%–87% of the DDTs. The ratios of (DDE+DDD)/DDT at all sample collection points were less than 1, indicating that degradation rate of DDTs in sediment was low and there was a new input of DDTs in these surveyed areas. The ratio of DDD/DDE was less than 1 at most of the sample collection points, indicating that the degradation of DDT in the sediments primarily took place under aerobic conditions. Comparison of OC pesticide residual levels in the underwater sediment collected at the Qingshitan Reservoir to other states and countries showed the pollution level of these chemicals of the Qingshitan Reservoir was relatively high. The ecological risk was assessed based on guideline values of effects range-low (ERL) and effects range-medium (ERM). The results showed that DDD, DDE, DDTs and endrin residues in the sediment posed a moderate ecological risk, but DDT and γ-HCH showed high ecological risk. These OC pesticides might adversely affect biological systems, and need to be addressed.

A Comparative Assessment of Floating and Submerged Sensor Network Deployments for Monitoring Underwater Sediment Transport Processes

Wireless Sensor Networks (WSNs) are a pioneering technology in many environmental monitoring applications owing to their ability to be deployed for long periods of time in locations that cannot be reached manually. One such use-case is the monitoring of underwater sediment transport, a process that plays a significant role in coastal erosion. Previous examples of WSNs deployed for this purpose have been in the form of underwater sensor networks (UWSNs), which have a number of shortcomings from both a practical and technical viewpoint. As such, this paper provides a comparative assessment of UWSNs and an alternative deployment approach of floating echo- sounding sensor networks for the purpose of monitoring underwater sediment transport.

Long-lost relatives found at bottom of Arctic Ocean

An entirely new group of organisms discovered at the bottom of the Arctic Ocean are human's closest simple-celled relatives ever found. Approximately 2 billion years ago, complex eukaryotic cells, which make up animals, plants and fungi, split from smaller, simpler cells called prokaryotes. Researchers have now identified human's closest relatives from before this split. Thijs Ettema at Uppsala University, Sweden, and his team discovered the new organisms when they analyzed DNA extracted from underwater sediment near Loki's Castle, a region of hydrothermal vents along the Arctic mid-ocean ridge.

Determining the radon exhalation rate from a gold mine tailings dump by measuring the gamma radiation

The mining activities taking place in Gauteng province, South Africa have caused millions of tons of rocks to be taken from underground to be milled and processed to extract gold. The uranium bearing tailings are placed in an estimated 250 dumps covering a total area of about 7000 ha. These tailings dumps contain considerable amounts of radium and have therefore been identified as large sources of radon. The size of these dumps make traditional radon exhalation measurements time consuming and it is difficult to get representative measurements for the whole dump.In this work radon exhalation measurements from the non-operational Kloof mine dump have been performed by measuring the gamma radiation from the dump fairly accurately over an area of more than 1 km2. Radon exhalation from the mine dump have been inferred from this by laboratory-based and in-situ gamma measurements. Thirty four soil samples were collected at depths of 30 cm and 50 cm. The weighted average activity concentrations in the soil samples were 308 ± 7 Bq kg−1, 255 ± 5 Bq kg−1 and 18 ± 1 Bq kg−1 for 238U, 40K and 232Th, respectively. The MEDUSA (Multi-Element Detector for Underwater Sediment Activity) γ-ray detection system was used for field measurements.The radium concentrations were then used with soil parameters to obtain the radon flux using different approaches such as the IAEA (International Atomic Energy Agency) formula. Another technique the MEDUSA Laboratory Technique (MELT) was developed to map radon exhalation based on (1) recognising that radon exhalation does not affect 40K and 232Th activity concentrations and (2) that the ratio of the activity concentration of the field (MEDUSA) to the laboratory (HPGe) for 238U and 40K or 238U and 232Th will give a measure of the radon exhalation at a particular location in the dump. The average, normalised radon flux was found to be 0.12 ± 0.02 Bq m−2 s−1 for the mine dump.

On the triggers, resulting flow types and frequencies of subaqueous sediment density flows in different settings

Turbidity currents, and other types of underwater sediment density flow, are arguably the most important flow process for moving sediment across our planet. Direct monitoring provides the most reliable information on the varied ways in which these flows are triggered, and thus forms the basis for this contribution. Recent advances in flow monitoring make this contribution timely, although monitoring is biased towards more frequent flow types. Submarine deltas fed by bedload dominated rivers can be very active with tens of events each year. Larger events are generated by delta-lip failures, whilst smaller events can be associated with motion of up-slope migrating bedforms. River-fed submarine canyons are flushed every few years by powerful long run-out flows. Flows in river-fed delta and canyon systems tend to occur during months of elevated river discharge. However, many flows do not coincide with flood peaks, or occur where rivers do not reach hyperpycnal concentrations, and are most likely triggered by failure of rapidly deposited sediment. Plunging of hyperpycnal river floodwater commonly triggers dilute and slow moving flows in lakes and reservoirs, and has been shown to produce mm-thick fine-grained deposits. It is proposed here that such thin and fine deposits are typical of flows triggered by hyperpycnal river floods, rather than thicker sand layers with traction structure or displaying inverse-to-normal grading. Oceanographic canyons are detached from rivers mouths and fed by oceanographic processes (wave and tide resuspension, longshore drift, etc.). Most events in these canyons are associated with large wave heights. Up-slope migrating crescentic bedforms are seen, similar to those observed in river-fed deltas. Oceanographic processes tend to infill canyons, which are flushed episodically by much more powerful flows, inferred to result from slope failure. This filling and flushing model is less applicable to river-fed canyons in which flushing events are much more frequent. Oceanographic canyons may result from rapid sea level rise that detaches river mouths from canyon heads, and they can remain active during sea level highstands. Deep-water basin plains are often dominated by infrequent but very large flows triggered by failure of the continental slope. Recurrence intervals of these flows appear almost random, and only weakly (if at all) correlated with sea level change. Turbidites can potentially provide a valuable long-term record of major earthquakes, but widespread slope failure is the only reliable criteria for inferring seismic triggering. However, not all major earthquakes trigger widespread slope failure, so that the record is incomplete in some locations.

An Integrated Approach to Hydrographic Surveying of Large Reservoirs—Application to Tarbela Reservoir in Pakistan

Hydrographic surveying in reservoirs is a key activity in order to collect data for a variety of purposes like estimation of storage capacity, rate and pattern of sediment deposition, movement of underwater sediment delta and reservoir routing, etc. These parameters play a pivotal role in any planning, management and operation activity of the reservoirs. Traditional approaches to perform hydrographic surveying in Indus Basin are time consuming, laborious, comparatively inaccurate and costly. As water resources are under immense pressure due to a variety of factors, such inefficient methods are not acceptable for efficient water management. In this study, an integrated approach for hydrographic surveying is introduced and evaluated in terms of its efficiency in comparison with the traditional methods of hydrographic surveying. The approach develops an integrated environment of hydrographic surveying comprising human, hardware and software. The process of surveying starts from in-house planning using specialized geo-spatial softwares. Then, on site a combination of computer hardware, echosounder, differential global positioning system (DGPS), survey vessel and survey crew is made. Post-processing is performed after conducting a survey in order to improve quality of data by filtering errors and producing the end product like reservoir underwater terrain, development of reservoir stage-area and stage-storage relationships, etc. The study was applied to Tarbela Reservoir, Pakistan.

An inter-comparison of sediment classification methods based on multi-beam echo-sounder backscatter and sediment natural radioactivity data

This contribution presents sediment classification results derived from different sources of data collected at the Dordtse Kil river, the Netherlands. The first source is a multi-beam echo-sounder (MBES). The second source is measurements taken with a gamma-ray scintillation detector, i.e., the Multi-Element Detection System for Underwater Sediment Activity (Medusa), towed over the sediments and measuring sediment natural radioactivity. Two analysis methods are employed for sediment classification based on the MBES data. The first is a Bayesian estimation method that uses the average backscatter data per beam and, therefore, is independent of the quality of the MBES calibration. The second is a model-based method that matches the measured backscatter curves to theoretical curves, predicted by a physics-based model. Medusa provides estimates for the concentrations of potassium, uranium, thorium, and cesium, known to be indicative for sediment properties, viz. mean grain size, silt content, and the presence of organic matter. In addition, a hydrophone attached to the Medusa system provides information regarding the sediment roughness. This paper presents an inter-comparison between the sediment classification results using the above-mentioned methods. It is shown that although originating from completely different sources, the MBES and Medusa provide similar information, revealing the same sediment distribution.