Navigation Channel Research Articles

Field Measurements of Bridge Pier Scour in a Curved Channel

Pier scour is the most common cause of bridge failures, so the problem for the erosion of soil surrounding a bridge foundation has attracted extensive attention. The Jiaxing-Shaoxing Bridge (JSB) is located in Jianshan bend of the Qiantang River Estuary (QRE). The special flow structure and bed morphology of the bend makes the scouring characteristics of the piers particularly complex. Based on the results of Multibeam Echosounders for topographic surveying in recent six years, the scouring characteristics of pier foundation of a main navigation channel of the JSB are analysed in this paper. The results show that with the implementation of the reclamation project in the QRE area, the river channel has been gradually narrowed, coupled with the sharp reduction of the sediment entering the sea of the Yangtze River, the river regime swing in the QRE has changed significantly compared with that in the original design stage of the JSB. Under adverse river regime hydrological conditions, the riverbed erosional depth near the bridge is remarkable, and the local scouring depth of the pier is superimposed, which significantly will reduce the minimum elevation of the bed around the pier.

Sedimentation processes in the navigation channel of Patos Lagoon Estuary, southern Brazil

The morphology of estuarine navigation channels varies in time and space. Siltation occurs in areas where flow conditions enable sediment trapping and it limits navigability in most cases, requiring periodic dredging. Identifying sedimentation patterns is fundamental to designing ports to reduce siltation. The Port of Rio Grande, located in the Patos Lagoon estuary, holds strategic significance and it is a key example for understanding the evolution of large estuarine access channels. We used 19 bathymetric surveys from April 2001 to February 2018 to generate Digital Elevation Models and evaluate the evolution in time of bed morphology in the Porto Novo basin and its access channel (located in Port of Rio Grande). Also, we considered hydrological data available from September 2005 to December 2011. Major siltation rates were observed in the northwestern portion of the basin and the convex margin of the access channel, whereas other locations exhibited stable conditions. Channel configuration and position were determinants to define spatial variations of sedimentation processes. Hydrological conditions, mainly when discharge exceeds 4,000 m3/s over long periods, strongly controlled siltation magnitude in the Porto Novo basin and its access channel.

Evaluation of Cua Lo Estuary’s Morpho-Dynamic Evolution and Its Impact on Port Planning

Coastal erosion and accretion along the Quang Nam coast in Vietnam have been increasing in recent years, causing negative impacts on the inhabitants and local ecology. The Cua Lo estuary in Nui Thanh district has a complex hydrodynamic regime owing to its connection with two estuaries and three different tributaries. Therefore, a detailed study of the mechanisms and processes of these phenomena is crucial to understand the potential impact of a proposed 50,000-ton cargo port. In this study, the Delft3D model is employed to evaluate the morpho-dynamic changes in the area of Cua Lo under monsoon wave climate, storm, and flood conditions both before and after port and navigation channel construction. Results indicate that in the absence of the port, tidal currents and waves during monsoon storms cause significant erosion on the south bank and accretion on the north bank. Furthermore, the GenCade model is utilized to predict the future shoreline changes after the construction of two jetties. The model reveals that after 50 years of operation, the shoreline modifications will extend 449 m towards the sea, in comparison to natural conditions. However, the design of the northern jetty will ensure safe and proper operation without impacting the navigation channel. This study offers valuable insights into the morphological changes in the Cua Lo area and their potential implications, which can aid in the development of sustainable coastal management strategies for the region.

Downdrift Port Siltation Adjacent to a River Mouth: Effects of Mesotidal Conditions and Typhoon

The Zhuoshui River has one of the highest sediment yields in the world. The riverine sediment may have been transported away from the river mouth by strong tidal currents and deposited in a navigational channel and a harbor basin south of the Zhuoshui River. This study describes the dispersal of riverine sediments in mesotidal conditions, including transport processes of sediments via river plumes, initial deposition, resuspension, and long-term net accumulation. Our results revealed that the distribution of suspended sediment concentration (SSC) and the transport process of the river plume was markedly modulated by tidal currents in a north–south direction. Under high-discharge conditions, energetic winds and ocean currents interrupted the offshore propagation of the sediment-laden river plume with a high SSC to the ocean. The plume, induced by typhoon floods, was either propagated northward due to the Coriolis effect or was deposited near the river mouth. The sediments deposited within the inner shelf were resuspended by intensive tidal currents and transported through southward residual circulations to the navigation channel south of the river mouth.

ФОРМИРОВАНИЕ СТРУКТУРНОЙ СХЕМЫ РАДИООБМЕНА С ПРИМЕНЕНИЕМ ПСП

The structure of the radio exchange demonstrates the interconnection pattern of the drones with the control center. To protect against unauthorized access to control and navigation channels it is necessary to hide such data and increase their noise immunity. The aim of the work is to use signals with a pseudorandom sequence and duplicate control and navigation blocks in the information channel of a small-scale aerial vehicle. Thus, at the beginning of the paper, a general structural diagram of radio communication between the unmanned aerial vehicle and the control center is presented. The model of 2-element antenna array consisting of two non-directional antenna elements is considered. On the basis of which it is possible to conclude about the signal arrival with a phase shift, taking into account which it is possible to determine the output signal of the array. An important factor is the synchronization and encryption of the signal. Data synchronization can be used by synchronous signal transmission between the drone and the control center. To reduce the probability of interception of the synchronous signal, the data packets containing it are transmitted in a pseudo-random sequence. Synchronization is achieved by using a micronavigation system through continuous radio transmissions from a ground source and simultaneous reception and recording of the signal on the drone. A one-time encryption or scrambler with a reversible symmetric transformation of the encoded information can be used as an encryption or scrambler. A random number generator is used to generate a sequence of random data, from which an array of key information tied to a specific period of use is created. The phase method can be used to process the signal. By measuring the phase shift with a phase detector, you can determine the location of the radio source with respect to the base normal. Measurements can be made with a digital receiving antenna array. Signal processing with digital receiving antenna array is performed by the diagramming device and the adaptive processor unit. As a result, all data using this approach is entered into the information block with the use of a pseudo-random coding change scheme, pseudo-random permutation of the navigation and control blocks.

Analysis of Sediment Dynamics in Ports: A Case Study from Umm Qasr-Basra for Sustainable Sediment Management

Sedimentation processes are complex and interact with many Coupled Human and Natural Systems (CHANS). In ports, intensive commercial activities result in complicated sediment transport and accumulation processes. Therefore, it is crucial to investigate and analyze the sedimentation factors that may impact shipping activities within commercial ports. A case study has been conducted to investigate these factors in the northern port of Umm Qasr, Basra Governorate in Iraq. The results indicate that several factors increase erosion and sedimentation processes within the study site, including natural factors (climate, river, and tidal processes), and anthropogenic factors (ship movements). These factors have different influences in terms of the intensity of their impact, the amount and composition of sediment within the navigation channel, and the temporal variation in the activity of these factors. Precipitation in the surrounding region causes erosion of soft-fine-sediment that is carried in suspension toward the ports through tributary creeks and temporary rivers. Sediment distribution in the port has been worsened by human activities and tidal processes in the navigation channel. Consequently, the General Company of Ports in Iraq had to implement annual sediment control procedures to maintain the operational standards of the navigation channel. Although these measures are effective, they are greatly lacking efficiency due to high costs and execution difficulties. Therefore, studies are necessary and encouraged to further understand sediment dynamics in the port of Umm Qasr and to create the basis for establishing sustainable sediment management.

Estuarine response to storm surge and sea-level rise associated with channel deepening: a flood vulnerability assessment of southwest Louisiana, USA

This study investigates the sensitivity of the Calcasieu Lake estuarine region to channel deepening in southwest Louisiana in the USA. We test the hypothesis that the depth increase in a navigational channel in an estuarine region results in the amplification of the inland penetration of storm surge, thereby increasing the flood vulnerability of the region. We run numerical experiments using the Delft3D modeling suite (validated with observational data) with different historic channel depth scenarios. Model results show that channel deepening facilitates increased water movement into the lake–estuary system during a storm surge event. The inland peak water level increases by 37% in the presence of the deepest channel. Moreover, the peak volumetric flow rate increases by 291.6% along the navigational channel. Furthermore, the tidal prism and the volume of surge prism passing through the channel inlet increase by 487% and 153.3%, respectively. In our study, the presence of the deepest channel results in extra 56.72 km2 of flooded area (approximately 12% increase) which is an indication that channel deepening over the years has rendered the region more vulnerable to hurricane-induced flooding. The study also analyzes the impact of channel deepening on storm surge in estuaries under different future sea-level rise (SLR) scenarios. Simulations suggest that even the most conservative scenario of SLR will cause an approximately 51% increase in flooded area in the presence of the deepest ship channel, thereby suggesting that rising sea level will cause increased surge penetration and increased flood risk.

Application of Geotextile Tubes to Coastal Silt Mitigation: A Case Study in Niaoyu Fishing Harbor

Pengpeng Beach, near Niaoyu Fishing Harbor, is an offshore sandbar that formed on the west side of Niaoyu Island in Penghu County, Taiwan, in 1995. Due to siltation, Pengpeng Beach also forms a sandbar tail that stretches toward the Niaoyu Fishing Harbor, meaning the Niaoyu Fishing Harbor and its navigation channel are facing serious siltation problems. This study aimed to find a solution for the siltation problem of the area by utilizing geotextile tubes, which are an economical material in terms of their material and construction cost, as well as being ecologically friendly in terms of their carbon emissions during production and transportation. Based on numerical simulations, location candidates for placing silt trap facilities were tested, selected, and modified to develop alternative mitigation plans. Evaluation of the mitigation plans was based on (1) the silt mitigation effect; (2) engineering cost; (3) public acceptance; and (4) impact on the surrounding landscape. The results showed that the proposed silt mitigation plan would be effective, and the plan was accepted by the local residents and government.

A practical pCO2 estimation and carbonate dynamics at an event of hypoxic water upwelling in Tokyo Bay

Urban bays have been considered to have a high CO2 absorption function due to the high nutrient load and resultant primary production. It is expected to enhance the function by promoting a blue carbon policy co-beneficial with strengthening ecosystem services such as fisheries. Estimates of CO2 absorption in urban bays have been based mostly on fragmentary information from shipboard observations, and an evaluation based on continuous observation of water quality is necessary considering the large spatiotemporal variability of such bay environment. In particular, Tokyo Bay has a specific feature of water pollution problem of hypoxia and anoxia leading to emitting high CO2. Bottom hypoxic and anoxic waters develop from early summer to autumn in the central part of the bay and enclosed areas such as navigation channels and borrow pits. It is known that pCO2 becomes very high in these waters, and their upwelling (called blue tide in the bay from the discoloration of the sea surface) is thought to cause high CO2 emissions; however, the actual situation is unknown. We developed a practical method for continuous estimation of pCO2 by appropriately combining continuous observation of water quality using sensors and measurements of carbonate parameters by water sampling. The results show that a highly reproducible and practical method for continuous estimation of pCO2 was possible by combining in situ salinity and pH meters and the total alkalinity and calc. pH measured by a total alkalinity titrator for water samples. This method was then applied to the duration of blue tide that occurred in the head of the bay in the summer and autumn of 2021. The pCO2 in the surface water was found to increase significantly and exceed 2000 µatm due to the upwelling of anoxic bottom water containing high pCO2. Mean CO2 emissions of approximately +2150 and +1540 µmol m-2 h-1 were observed at two stations during the upwelling period. The mean values rose to +2390 and +2190 µmol m-2h-1 with the blue tide and lowered to +810 and +1120 µmol m-2 h-1 without it, suggesting that high CO2 emissions may occur due to upwelling, especially with blue tides.

Effect of water depth and waterway obstructions on the divergence and confluence areas of Dongting Lake and the Yangtze River after the operation of the Three Gorges Project

AbstractClimate change and human activities have profoundly changed the evolutionary processes and developmental trends of the hydrology and geomorphology of rivers and lakes. Such changes have affected the evolution of bars and channels at the intersections of rivers and lakes and the utilization of water depth resources in waterways, which, in turn, have affected the sustainable development of waterways, such as the “Golden Waterway” of the Yangtze River. Considering the confluence of Dongting Lake and the Yangtze River as the present study area, we analyzed the effect of the hydrology of Dongting Lake and the evolution of bars and channels in the Jingjiang reach of the Yangtze River on the depth of the waterways. Our results indicated that from before the operation of the Three Gorges Project (1960–2002) to after its operation (2003–2021), the flow and sediment volume of the three inlets of Dongting Lake demonstrated a continuous decreasing trend. Furthermore, the relative increase in the runoff of the Jingjiang reach increased channel erosion. Channel erosion at the river–lake confluence from 2003 to 2021 created favorable conditions for increasing the dimensions of the waterways. The total length of the river–lake confluence that did not meet the requirements for safe navigation [4.5 × 200 m (water depth × width)] was 12.6 km, accounting for 68.35% of the total length of the Jingjiang reach with obstructed navigation. We observed that a decrease in the low‐water level and “steep slope and rapid flow” were the major factors hindering the navigation of the reach (from Zhicheng to Dabujie) affected by the Songzikou diversion of Dongting Lake. This was mostly reflected by the width of the 4.5 m waterway being less than 200 m. A declining water level, shrinking sandbanks and tidal flats, and alternating branches that destabilize the low‐water route were the major factors hindering navigation in the reach (from Taipingkou) affected by the Taipingkou diversion of Dongting Lake. Consequently, alternative waterways were implemented during low‐water periods with the water depth decreasing below 4.5 m. The obvious collapse of sandbanks and tidal flats and their erosion and migration were the major factors hindering navigation of the Ouchikou diversion of Dongting Lake. In addition, the scattered submerged shoals in the navigation channel restricted the width of the 4.5 m channel to less than 200 m. The reach affected by the Dongting Lake confluence (from Xiongjiazhou–Chenglingji reach) was subject to the erosion and silting of bends and the jacking effect of lake outflow, causing shoals with a water depth of less than 4.5 m in the channel. However, the jacking effect slowed the current, thereby assisting in improving channel conditions.

Large-scale morphological changes and sediment budget of the Western Scheldt estuary 1955–2020: the impact of large-scale sediment management

Abstract In the Western Scheldt estuary, like in many estuaries, safe navigation, flood protection, and ecological targets require a balanced and sustainable sediment management. A thorough understanding of the morphodynamic functioning of the estuary and its response to changes in hydrodynamics (natural sediment transport) and large-scale interventions is imperative. This paper presents a detailed overview of over 65 years of morphological changes and a comprehensive sediment budget of the Western Scheldt estuary that is based on analysis of a unique series of frequent bathymetric surveys and historical data on human–sediment interactions of dredging, dredge disposal and sand mining. Solving the sediment budget reveals an annual sediment import of 2.2 million m3. The highest sediment imports occurred between 1980–1994 and 2005–2020 (2.9 and 3.7 million m3/year). A 1.3 million m3/year net export prevailed between 1994 and 2005. Natural variations in the hydrodynamics (e.g., tidal asymmetry and amplification) and sediment transports cannot explain the derived temporal variations in sediment import rates. Anthropogenic activities play a dominant role. Capital dredging of the main navigation channel has led to channel deepening and significantly increased dredge and disposal volumes. Disposal on tidal flats and in the secondary channel leads to a long-term storage of sand and, consequently, a local increase in bed level and a sand deficit in the remainder of the system that results in increased sediment imports. Large-scale disposal in the western part of the estuary can (temporarily) reverse the sediment exchange between the estuary and its mouth area, as observed between 1994 and 2005. Apparently, large-scale anthropogenic reallocation of sediment by dredging and/or disposal as part of navigation channel improvement, sand mining or nourishment essentially influences the morphological development of the Western Scheldt estuary. This reveals responsibilities as well as opportunities of sediment management for the Western Scheldt and similar estuaries worldwide.

A comparative analysis of the robustness of multimodal comprehensive transportation network considering mode transfer: A case study

<abstract> <p>China has built a nationwide transportation network, but there needs to be a smooth connection and transfer between different modes. Five networks are constructed to explore the characteristics of a multimodal comprehensive transportation network (CNet) in Jiangsu Province based on the optimized modeling method and multisource data. Statistical and robustness characteristics are analyzed for CNet and other single-mode networks including the highway, railway, navigation channel and airway networks (HNet, RNet, NNet and ANet, respectively). The research results show following: (ⅰ) In Jiangsu, CNet, HNet, RNet and NNet are not scale-free networks and do not have small-world properties. However, ANet is the opposite. (ⅱ) The five networks in Jiangsu are robust to the random attack and their robustness changes during the attack. However, their robustness is different under different calculated attacks. For all attack strategies, CNet is the most robust. (ⅲ) In Jiangsu, the three optimized methods enhance the robustness significantly. The network failure is delayed by 12.34, 2.79 and 2.44%, respectively. The average connectivity degree is improved by 265.69, 52.95 and 32.54%, respectively. The more hubs there are with powerful transfer capacity, the stronger the network robustness. The results reveal the key points of the construction of a multimodal comprehensive transportation system and can guide the design and optimization of it.</p> </abstract>

Evolution process and mechanism of mid-channel bars composed of different bed materials in the Upper Jingjiang Reach after the Three Gorges Project operation

三峡及上游梯级水库群运用后,大坝下游江心洲以冲刷为主,直接影响分汊河段河势条件及航道边界的稳定性。本文采用卫星遥感影像、实测水沙及固定断面床沙级配等资料,分析上荆江枝江、沙市河段中不同河床组成江心洲的演变过程及其机理。结果表明:①三峡水库蓄水后(2003-2019年),沙市段沙质江心洲较枝江段卵石夹沙质江心洲萎缩更为显著,出露面积的减幅分别达31%和24%。②以关洲和金城洲分别代表卵石夹沙质和沙质江心洲,三峡工程运用后关洲洲头形态较为稳定,受无序采砂的影响其沙质组成的洲尾面积显著减小,而金城洲面积萎缩程度更大。③床沙组成对江心洲冲刷程度差异具有重要影响,关洲洲头较金城洲抗冲性更强,与其床沙在年内达到起动条件的数量更少、时长更短有关;建立了江心洲面积与水流冲刷强度及相对水深的定量关系,该关系能综合考虑水沙变化与床沙组成调整的影响,能更好地反演近期江心洲的面积变化特点。;After the operation of the Three Gorges cascade reservoirs (TGP), the mid-channel bars (MCBs) downstream of the dam were generally scoured and shrank, which directly affects the river regime in ana-branching reaches and the stability of the navigation channel boundaries. The morphological evolution processes and mechanisms of MCBs in the Zhijiang (ZJ) and Shashi (SS) sub-reaches of the Upper Jingjiang Reach were analyzed, using the remote sensing images, the hydrological data and the measured riverbed compositions. The results indicate that: (i) During the post-TGP period (2003-2019), the sandy MCBs in the SS subreach shrank more significantly than the one in the ZJ subreach. The total exposed area of the former decreased by 31%, while the latter decreased by 24%; (ii) Guanzhou (GZ) and Jinchengzhou (JCZ) were taken as the representative sandy-gravel and sandy MCBs, respectively. During the post-TGP period, the head zone of the GZ MCB was relatively stable, and the reduced area was mainly in the bar-tail zone due to the illegal sand mining, while the JCZ MCB had a more obvious erosion trend; (iii) The bed-material composition had an important influence on the erosion degree of MCBs. The GZ MCB had a stronger anti-erosion capacity than the JCZ MCB, which was related to the less amount and duration of bed material that can reach the incipient condition in a hydrological year. Moreover, different empirical relationships were developed between the exposed area of MCB, fluvial scour intensity, and relative water depth. It is found that comprehensive consideration of the effects of flow-sediment condition and bed-material composition adjustment can better explain the recent variations in the exposed areas of MCBs.

Characteristic Analysis of Navigable Flow Conditions and Numerical Simulation of Water Conservancy in Steep Bay Section of the Navigable Tunnel

Compared with traditional low-standard ship locks, large-section navigable tunnels have the advantages of increasing water resources dispatching, increasing ship crossing channels and shipping. It is necessary to explore the characteristics of navigable flow conditions under the condition of navigable tunnel and study effective measures to improve the navigable flow conditions at the entrance of approach channel of navigable tunnel in steep bay section. However, the existing research results neglect the navigation channel layout in the steep bay section, and it’s lack of theoretical research on improving the flow conditions at the entrance of approach channel of navigable tunnel in the steep bay section. For this, this article studies the characteristics of navigation flow conditions and numerical simulation of water conservancy in steep bay section of the tunnel. Firstly, the physical model of tunnel navigation in steep bay section is designed to ensure the geometric similarity, flow movement similarity and dynamic similarity between the model and the actual situation in steep bay section. Then, the numerical simulation of navigation water conservancy in steep bay section of tunnel is carried out, and the continuity equation and momentum equation in the new coordinate system are given. This article explores the navigation scheme of large cross-section navigable tunnel in order to obtain effective measures to improve the navigation conditions of this section. Finally, the corresponding experimental results and analysis are given.

Experimental Study on the Influence of New Permeable Spur Dikes on Local Scour of Navigation Channel

The depths and areas of the scour holes around spur dikes are the most concerning issues regarding spur dike design. In this study, using a moving bed experiment, the influence of traditional rock-fill spur dikes and new permeable spur dikes with different permeabilities on riverbed scour under unsteady flow was studied, and the spatial characteristics of scour holes at dike heads were analyzed. The results show that with increases in the permeability coefficient of the spur dike, the depth and area of the scour hole at the dike head gradually decreases; however, when the permeability coefficient is more than 17.6%, the depth and area of the scour hole downstream of the dike body increases with an increase in the permeability coefficient. According to comprehensive evaluation, when the water permeability is 17.6%, the stability of the spur dike is at its best. The maximum depth of the scour hole at the dike head is affected by factors such as the spur dike permeability coefficient, effective scouring time, and width bottom protection structure. On this basis, a new formula for calculating the maximum depth of the scour hole at a dike head is proposed. These research results will be beneficial to the reliability of spur dikes and the sustainability of navigation channels.

Port Management Model in the Industrial Revolution 4.0 Era

Sedimentation is a natural and physical phenomenon that affects port management. If it is further elaborated, the main aspects of port management include planning, design, construction, and maintenance activities. Sedimentation can cause a decrease of depth or silting in navigation channels and port pools which to some extent, are dangerous for the inbound vessels that are calling at the port. The silting process is influenced by how much material and what type of material that settles at the base of the water column. To understand the effect of sedimentation on port management, a comparative study was conducted between the terms of port management which are stated in the regulations that apply in Indonesia and the implementation that has been carried out. realized at patimban port. The data that is compared takes the form of planning data and existing conditions in 2020 to then be reviewed with current regulations to assess its compliance with the said regulation. In order to devise technical recommendations in spatial and temporal aspects, the port authorities must have a thorough understanding of the effect of sedimentation on port management. In its implementation, spatial aspects are related to the maintenance of navigation channels and anchoring locations, while temporal aspects are related to the frequency of monitoring of the sediment deposition and sediment removal to keep the navigation channels safe for calling vessels. The monitoring process must be done in a routine and timely manner, by integrating temporal change data with Industrial Revolution 4.0-based technologies to increase the rate of data renwals, so that the manager of the port can respond to any changes that occur in the port accordingly and effectively in a short period of time.

Characteristics of fluid mud in the Yangtze Estuary: Storm, tide, and slope-triggered sediment dynamics and effects

Fluid mud is widely found in estuarine and coastal areas and significantly affects sediment transport, navigational safety, and ecological functions. The formation mechanisms of fluid mud are not yet fully understood because of their complex dynamics, including the effects of riverine discharge, tides, storms, and gravity-driven flows. In this study, the in situ density of 18 fluid mud events was measured along the deep navigation channel (DNC) of the Yangtze Estuary from 2010 to 2016, along with hydrodynamic factors such as riverine discharge, wind, waves, tidal stratification of salinity and suspended sediments, and channel slope. Our results indicate that the scale of storm-triggered fluid mud events in the DNC was 10–60 km long and 0.5–4 m thick, and tidal residual flow circulation and salinity stratification co-formed fluid mud and determined its structure along the DNC. In addition, the coupled stratification induced by the suspended sediment concentration and salinity affected the thickness of fluid mud, and the strengthened stratification induced by the decreasing tide current affected the thickness of high-density fluid mud. Furthermore, gravity-driven flow induced by the steep slope on both channel banks enhanced the accumulation of fluid mud in the DNC. Finally, fluid mud accounted for 20% of the annual silted sediment in the DNC, and the upper low-yield-stress layer of fluid mud (density <1250 kg/m3) could be utilized as the potential nautical depth during fluid mud events, accounting for 20–75% of the entire thickness of the fluid mud. The results of this study can improve the understanding of fluid mud processes and mechanisms and promote cost-effective dredging activities, particularly in muddy tide-dominated estuaries.

Radiopaque Nanorobots as Magnetically Navigable Contrast Agents for Localized In Vivo Imaging of the Gastrointestinal Tract.

Magnetic nanorobots offer wireless navigation capability in hard-to-reach areas of the human body for targeted therapy and diagnosis. Though in vivo imaging is required for guidance of the magnetic nanorobots toward the target areas, most of the imaging techniques are inadequate to reveal the potential locomotion routes. This work proposes the use of radiopaque magnetic nanorobotsalong with microcomputed tomography (microCT) for localized in vivo imaging applications. The nanorobots consist of a contrast agent, barium sulfate (BaSO4 ), magnetized by the decoration of magnetite (Fe3 O4 ) particles. The magnetic features lead to actuation under rotating magnetic fields and enable precise navigation in a microfluidic channel used to simulate confined spaces of the body. In this channel, the intrinsic radiopacity of the nanorobots also provides the possibility to reveal the internal structures by X-ray contrast. Furthermore, in vitro analysis indicates nontoxicity of the nanorobots. In vivo experiments demonstrate localization of the nanorobots in a specific part of the gastrointestinal (GI) tract upon the influence of the magnetic field, indicating the efficient control even in the presence of natural peristaltic movements. The nanorobots reported here highlight that smart nanorobotic contrast agents can improve the current imaging-based diagnosis techniques by providing untethered controllability in vivo.

STUDYING POLYNYA OCCURRENCE TERMS AND DURATION ON THE SHIPPING ROUTES IN THE LAPTEV SEA

The dynamics of the development of the Lena polynya formed on the shipping routes of the Northern Sea Route in the Laptev Sea and its influence on the conditions of navigation in the Arctic are studied. During the period of winter-spring navigation in the Laptev Sea, the Great Siberian polynya, which is located near the fast ice border and creates good opportunities for winter navigation on the Northern Sea Route, is formed. This problem is important to ensure year-round navigation in the Eastern Sector of the Northern Sea Route. The hypothesis that the terms of a polynya occurrence can significantly affect the average rate of its growth is tested in the study. When checking, the results of the GLORYS12v1 global reanalysis and standard methods of mathematical statistics are used. On the example of the polynya section located on the estuary seashore of the largest navigable channel of the Lena River Delta - Bykovskaya, the validity of the hypothesis is confirmed. Steady trends in the change in the polynya formation terms towards earlier dates in the modern period are revealed. A high probability of improving the conditions of navigation in this region in 2020-2040 is noted. At the same time, with further warming of the Siberian climate, the opposite process, namely, the freezing of a polynya that formed too early, which will lead to a cooling of the climate in the region and a deterioration in navigation conditions, is possible. Comparing the results obtained with other studies that are devoted to the construction of general routes for ships in various ice conditions, it is possible to identify trends that the actual routes during independent navigation pass along the forming polynyas, regardless of the physical principle of their formation, then the choice of general routes for ships in the areas of polynya distribution will be promote more intensive and safe shipping. What requires accurate forecasts of its size and position. The relevance of the research results for forecasting year-round navigation, both for independent navigation of ships with a high ice class, and in the development of plans for using icebreaking escort of ships, is noted.

The forgotten ones of ports: The filter feeders at the heart of siltation processes

Siltation is a major concern in dynamic and complex ecosystems, such as ports. The mud must be regularly dredged to avoid disturbing the navigation channels. Sediments are carried by the waters entering the port and are partially trapped by harbour structures. Numerous studies have been conducted on the physical factors influencing siltation in port areas, whereas, few have focused on the role of biotic factors in mud formation. However, research in other contexts has shown that organisms that are abundant in pontoons, such as bivalves and tunicates, play an important role in this siltation process. All of these organisms belong to the filter feeder group. The sediments sucked in by the filter feeders are excreted in the form of faeces or mucus-bound pseudo-faeces. These waste materials, called bioproducts, settle efficiently and are involved in the composition of the mud. This study aimed to highlight the role of filter feeders in the siltation process in port areas and to determine the factors that influence the production of bioproducts by filter feeders. To investigate the role of filter feeders in the siltation processes, an experimental analysis was conducted in the largest marina in Europe (La Rochelle, France). It is divided into four basins with distinct filter feeder communities and environmental conditions, allowing for a detailed study of the environmental factors that influence the production of bioproducts. This analysis consisted of recovering and studying the bioproducts generated by the filter feeders using sediment traps fixed under pontoons. To explore the evolution of this biological production, 16 campaigns were conducted from January to March 2020 and May to July 2020. The total amount of dry matter produced was constant between seasons at approximately 130 g/m2/d; marina-wide, this amount represents a total daily production of 3.2 tons. However, the production amount varies spatially and temporally in relation to marine hydrodynamics and the organisms involved. Bioproduction was taxon-dependent: areas abundant in oysters and mussels were the areas with the most pronounced bioproduction, whereas there was no significant relationship between bioproduction and the presence of tunicates or scallops. If we consider bioproduction on a seasonal scale, we can see that the campaigns with the greatest production correspond to the periods when the sediment supply was the highest, i.e. when the tidal range was the highest. The quality of the bioproducts (organic matter content) differed between seasons, which can be explained by both environmental and metabolic changes. Understanding the role of filter feeders in siltation processes appears to be essential in port environments that need to be regularly dredged to ensure safe navigation.