Multibeam Sonar Research Articles

The value of multibeam bathymetry in marine spatial planning in South Africa: A review

Given a growing global population and shift to embrace the blue economy, a need for marine spatial planning (MSP) has emerged in South Africa to sustainably resolve the rising conflicts over the use of marine and seabed resources and services. A well-developed marine spatial plan yields numerous ecological, social and economic benefits. These are achieved through mediating between spatially conflicting economic drivers’ interests (e.g. commercial fishing, tourism, mining), preventing their activities from compromising thresholds of an environment’s sustainability. Within the MSP framework, high-resolution geospatial datasets are required to document and describe the seabed in the highest possible detail. At any scale, integrated analysis of seabed geomorphology and habitats is anticipated to greatly improve the understanding of ecosystem functioning from a multidisciplinary perspective, whilst improving MSP procedures and management of marine space. South Africa is the first of few African countries to have an approved and implemented MSP framework, but is still somewhat behind globally in implementing large-scale regional hydroacoustic surveys to cover the country’s vast offshore territory. The deficiency of hydroacoustic surveys is perhaps due to a relative lack of funds and poor communication about the value of multibeam echo-sounder (MBES) derived data, whilst marine geoscience remains a scarce skill in the country. This review paper presents a geological perspective of MSP and explores (1) the value that seabed mapping offers MSP specifically and (2) the need to increase seabed mapping with MBES, using a recently initiated project from the South African east coast as a case study. Significance: The collected MBES data (our case study) provides unprecedented seabed detail of the complex reef habitat and adjacent areas within specific management zones of the uThukela Banks Marine Protected Area. We reveal seabed features and their spatial distribution at a scale not possible using earlier (singlebeam) seabed mapping techniques. These high-resolution data will enable a better understanding of east coast marine habitats whilst contributing to improved spatial management of areas within and around the uThukela Banks Marine Protected Area.

Acoustic estimation of ferromanganese crust exposure and sediment cover in a Northwest Pacific seamount using statistical analyses of shipboard multibeam acoustic data

The estimation of the distribution of ferromanganese crusts (FMCs) is determined using the threshold of backscatter intensity of the multibeam echo sounder in ground-truth data; however, this is not accurate. This study developed a method to quantitatively estimate the distribution of FMCs and thickness of the surface sediment (TSS) by determining the relationship between topographic features, backscatter intensity using statistical analyses. Thus, the exposure of FMCs and TSS was quantitatively evaluated with accuracies of 17% and 2.5 m, respectively. This method can efficiently estimate distributions of FMC and TSS of entire seamounts for the benefit of future mineral explorations.

Submerged reef and inter-reef morphology in the Western South Atlantic, Abrolhos Shelf (Brazil)

Submarine geomorphology is a main environmental driver defining the seascape and associated benthic habitat. In this sense, eustatic sea-level fluctuations plays a major role in shaping the morphology of the seafloor. During the last deglaciation, changes in rates of sea-level rise led to moments of stillstand and rapid rise acceleration, forming and drowning distinct shelf geomorphological features. Here, we present and discuss the morphology and associated habitats related to submerged reefs and inter-reef areas along the southern Abrolhos inner shelf (western South Atlantic, Brazil). Our aim is to discuss the morphological evidence of reef drowning and related sea-level/climate events, and the formation of distinct habitats during the post-Last Glacial Maximum transgression. Multibeam echosounder data and sub-aquatic video footage are the basic datasets. Automatic seabed classification was carried out by combining morphometric analysis, acoustic backscatter and ground-truthing. Results show the presence of two clusters of submerged reefs (14-23 m and 24-35 m deep), associated with longitudinal and transverse bedforms, banks, and shelf-incised valleys. Rhodolith beds comprise the main inter-reef benthic habitat. Distinct reef clusters defined by reef top depths indicate that reef drowning occurred in two different moments. The shallower reefs are likely related to the rapid sea-level rise associated with MWP 1C, while deeper reefs are interpreted as remanent carbonate build-ups. Habitats are strongly influenced by the marine geodiversity forming a mosaic of reef, inter-reef and bedforms classes that seem to be associated with an antecedent paleo landscape marked by shelf-incised valleys and paleochannels. Submarine geomorphology is an environmental component that drives geodiversity and is driven by distinct seafloor processes acting in different time and spatial scales, as well as being able to quantify biogenic phenomena, for example, surrogacy and provide records of sea-level changes.

Geophysical and Geochemical Exploration of the Pockmark Field in the Gulf of Patras: New Insights on Formation, Growth and Activity

The Patras Gulf Pockmark field is located in shallow waters offshore Patras City (Greece) and is considered one of the most spectacular and best-documented fluid seepage activities in the Ionian Sea. The field has been under investigation since 1996, though surveying was partially sparse and fragmentary. This paper provides a complete mapping of the field and generates new knowledge regarding the fluid escape structures, the fluid pathways, their origin and the link with seismic activity. For this, data sets were acquired utilising high-resolution marine remote sensing techniques, including multibeam echosounders, side-scan sonars, sub-bottom profilers and remotely operated vehicles, and laboratory techniques focusing on the chemical composition of the escaping fluids. The examined morphometric parameters and spatial distribution patterns of the pockmarks are directly linked to tectonic structures. Acoustic anomalies related to the presence of gas in sediments and in the water column document the activity of the field at present and in the past. Methane is the main component of the fluids and is of microbial origin. Regional and local tectonism, together with the Holocene sedimentary deposits, appear to be the main contributors to the growth of the field. The field preserves evidence that earthquake activity prompts the activation of the field.

Method of Time Estimation for the Bathymetric Surveys Conducted with a Multi-Beam Echosounder System

Exact and complete preparation of a hydrographic survey project allows for the avoidance or reduction of additional costs and unexpected delays and, at the same time, increases the efficiency of the survey. One of the essential requirements at the survey planning stage is a calculation of time necessary for performing bathymetric measurements with a multi-beam echosounder. Based on these calculations, many decisions related to the costs and methodology are made. The article presents the method of time estimation for the hydrographic surveys and takes into account many variables that directly affect the final duration of the project. The paper demonstrates the influence of water depth, multi-beam echosounder swath angle, and other planning parameters related to the scheme of survey lines on the total time of stay at sea. The main findings are based on the author’s over twenty years of experience aboard the Polish Navy hydrographic ship Arctowski and include thorough analysis of specialist literature, publications, manuals, and international standards.

Effect of the structural complexity of a coral reef on wave propagation: A case study from Komaka Island, Japan

The structural complexity of coral reefs has an essential impact on coastal wave propagation. Nevertheless, bathymetry data, from which complex structures of several meters in size can be ascertained, have yet to be used for numerical modelling. To investigate the effects of coral reef structural complexity on coastal wave propagation, we first obtained 1-m resolution bathymetry data from a multibeam echosounder on Komaka Island, Japan. Then we conducted numerical simulations of storm waves over the obtained bathymetry. The simulation results using fine topographic resolution demonstrate that vorticity over the reef slope is significant due to the structural complexity of coral reefs, including spurs and grooves. This implies that complex features of several meters over the reef slope induce wave-driven currents, which is often a pathway for nutrient transport. However, the calculated wave energy densities over the reef flat are mostly the same, even when coarse bathymetry resolution is used. Thus, the overall reef slope, edge, and flat account for most of the dissipation process of storm waves, whereas complex structures of several meters in size have little impact. In contrast, the coral structures several meters in size contribute to the ecosystem by facilitating seawater rather than dissipating extreme waves.

Marine Habitat Mapping using Multibeam Echosounder Survey and Underwater Video Observations: A Case Study from Tioman Marine Park

In recent years, there has been an increasing trend of utilizing high-resolution multibeam echosounder (MBES) datasets and supervised classification via machine learning to create marine habitat maps. The purpose of current study was threefold: (1) to extract bathymetric and backscatter derivatives from a multibeam dataset, (2) to measure the correlation between bathymetric and backscatter derivatives, and (3) to generate a marine habitat map using the Random Forest (RF). Tioman Marine Park (TMP), which is situated Southeast China Sea. MBES surveyed area are encompassed an area of 406 km² and served as the location for the study. Based on results and analysis, fourteen (14) derivative were derived from bathymetry map and backscatter mosaic. The second step involved integrating variables and a total of 152 of habitat ground-truth data were used, derived from underwater imageries, and sediment samples, into an RF model to generate a map of the marine habitat. Based on marine habitat map, six habitat classes including sand, rock, gravel and sand, coral rubble, coral and rock, and coral were classified. The distribution of coral habitat was found to be correlated with the depth of the bathymetry in the shallow water region. Therefore, the study has reached the conclusion that the integration between MBES derivatives, ground-truth data, and RF machine learning algorithm is an effective in classifying the distribution of marine habitats, specifically the coral habitat.

Effectiveness of vertical error budget model for portable multi-beam echo-sounder in shallow water bathymetric survey

With the increasing availability of portable survey equipment and platforms, hydrographic data acquisition now offers a diverse range of device options and installation methods. Tailoring the mounting and installation of hydrographic survey devices to fit the boat or platform dimensions has become common practice. The use of portable equipment is essential, given the wide selection of combined options available in the market. Consequently, sensor offsets and device performance differ for each survey conducted, necessitating the constant verification of accuracy performance.This paper examines the capabilities of portable multibeam echosounder (MBES) deployments on various types of survey boats. The investigation focuses on error budget modeling and field tests. A model is developed to estimate the propagated uncertainty resulting from different sources of measurement uncertainties. The model primarily considers vertical sources of error in MBES surveys, as they have the most significant impact on hydrographic data quality. To validate the model, field tests are conducted at two different locations using different boat and device configurations. The results demonstrate that the modeled uncertainties align with the measured standard deviations, particularly in the Pramuka area, where the standard deviation of data acquired at the widest beam angle of ±60° is 0.25m, close to the predicted value of 0.28m. However, in the Patimban area, the model overestimates the uncertainty, predicting 0.27m compared to the measured standard deviation of 0.17m.

Geological and Geophysical, Geomorphological and Hydrophysical Investigations in Barents and Kara Seas during the Cruise 51 of the R/V <i>Akademik Boris Petrov</i> in 2022

Comprehensive geological and geophysical, geomorphological and hydrophysical studies carried out on the R/V Akademik Boris Petrov in the eastern part of the Barents Sea and the western part of the Kara Sea in the fall of 2022. The research included multibeam echo sounding and seismic profiling, hydrological sounding, as well as sampling of water and sediments in the areas of oil and gas fields’ development and along the Northern Sea Route. The expedition studied the structure of the seabed relief and the upper sedimentary strata on the polygons of detailed investigations. The areas of distribution of various glacial landforms and modern geohazards specified during the expedition.

A Novel Cone Model Filtering Method for Outlier Rejection of Multibeam Bathymetric Point Cloud: Principles and Applications.

The utilization of multibeam sonar systems has significantly facilitated the acquisition of underwater bathymetric data. However, efficiently processing vast amounts of multibeam point cloud data remains a challenge, particularly in terms of rejecting massive outliers. This paper proposes a novel solution by implementing a cone model filtering method for multibeam bathymetric point cloud data filtering. Initially, statistical analysis is employed to remove large-scale outliers from the raw point cloud data in order to enhance its resistance to variance for subsequent processing. Subsequently, virtual grids and voxel down-sampling are introduced to determine the angles and vertices of the model within each grid. Finally, the point cloud data was inverted, and the custom parameters were redefined to facilitate bi-directional data filtering. Experimental results demonstrate that compared to the commonly used filtering method the proposed method in this paper effectively removes outliers while minimizing excessive filtering, with minimal differences in standard deviations from human-computer interactive filtering. Furthermore, it yields a 3.57% improvement in accuracy compared to the Combined Uncertainty and Bathymetry Estimator method. These findings suggest that the newly proposed method is comparatively more effective and stable, exhibiting great potential for mitigating excessive filtering in areas with complex terrain.

Mesophotic benthic communities associated with a submerged palaeoshoreline in Western Australia.

Key ecological features (KEFs) are elements of Australia's Commonwealth marine environment considered to be important for biodiversity or ecosystem function, yet many KEFs are poorly researched, which can impede effective decision-making about future development and conservation. This study investigates a KEF positioned over the Last Glacial Maximum (LGM) shoreline on the northwest shelf of Australia (known as the 'Ancient Coastline at ~125m depth contour'; AC125). Seafloor bathymetry, sedimentology and benthic habitats were characterised within five study areas using multibeam sonar, sediment samples and towed video imagery. Direct evidence for the existence of a palaeoshoreline formed during the LGM was not found, however candidate areas to find palaeoshoreline material at or just below the modern seabed were discovered. Approximately 98% of the seabed surveyed was comprised of unconsolidated soft sediment habitat (mud/sand/silt) supporting negligible epibenthic biota. The prevalence of soft sediment suggests that post-glacial sediments have infilled parts of the palaeoshoreline, with cross-shelf, probably tidal currents in the northern section of the study area responsible for some of the sediment mobilisation and southern study areas more influenced by oceanic conditions. Within study areas, total biotic cover ranged from 0.02% to 1.07%. Of the biota encountered, most comprised filter feeder organisms (including gorgonians, sponges, and whip corals) whose distribution was associated with pockets of consolidated hard substrate. Benthic community composition varied with both study area and position in relation to the predicted AC125. In general, consolidated substrate was proportionally higher in water shallower than the AC125 compared to on the AC125 or deeper than the AC125. Spatially continuous maps of predicted benthic habitat classes (pre-determined benthic communities) in each study area were developed to characterise biodiversity. Spatial modelling corroborated depth and large-scale structural complexity of the seafloor as surrogates for predicting likely habitat class. This study provides an important assessment of the AC125 and shows that if a distinct coastline exists in the areas we surveyed, it is now largely buried and as such does not provide a unique hard substrate habitat. However, much work remains to fully locate and map the ancient coastline within the vast region of the AC125 and additional surveys in shallow waters adjacent to the AC125 may identify whether some sections lie outside the currently defined KEF.

Underwater surveys reveal deep-sea corals in newly explored regions of the southwest Atlantic

Deep-sea coral distribution and composition are unknown in much of the global ocean, but repurposing ocean industry surveys can fill that gap. In Santos Basin, southeast Brazil, areas (241–963 m depth) were surveyed during seven Petrobras cruises, mapping bottom topography with multibeam sonar, then collecting video with remotely operated vehicles. Here, we defined deep-sea coral species distribution and richness, using these surveys, correlating them to physical oceanographic properties. Solenosmilia variabilis was the most prevalent colonial species in coral mounds. Overall, 67% of species were Octocorallia. Coral assemblage structure, abundance, and richness varied among sites both within and among depths, with higher density and richness in the northernmost Santos basin. Depth was the strongest predictor for scleractinian coral distribution, with depth ranges varying by species. Assemblage differences corresponded to changes in water mass. Desmophyllum pertusum was more abundant in South Atlantic Central Water and S. variabilis in Antarctic Intermediate Water influenced areas.

Multi resolution appraisal of Cork Harbour estuary: An object based image analysis approach

Lithic sedimentary benthic habitats are often organised by the overlying hydrodynamic regime, generating seabed sedimentary bedforms (SSBs) whose morphology and sediment composition are controlled by the current flow properties including speed, direction, and duration. Furthermore, SSBs can manifest at a variety of spatial scales reflecting different aspects of the hydrodynamic regime that operate at distinct intensities and temporal scales. Acoustic seabed mapping of SSBs permits the quantification of the complex seafloor hydrodynamics without in situ measurements. As such, seabed mapping efforts must determine the minimum spatial resolution required to effectively capture the complete seabed hydrodynamic picture. Here, we provide a semi-automated, object-based image analysis (OBIA) of SSBs occurring over 0.5, 1.0, 1.5, 2.0, and 2.5 m spatial resolutions of multibeam echosounder (MBES) data acquired in Cork Harbour, Ireland, to ascertain the optimum resolution at which to derive current velocity attributes. Estimations of seabed sediment grain size were completed through the angular range analysis (ARA) of co-located 400 kHz multibeam backscatter data. Results show that current flow estimations derived at 0.5, 1.0 and 1.5 m resolutions of MBES bathymetry agree with previous in situ current speed measurements. Moreover, sediment grain size estimations produced during the ARA of the 400 kHz backscatter data displayed a clear pattern of sediment resuspension at each section of the harbour, and this was effectively depicted at 0.5, 1.0, and 1.5 m resolution of MBES bathymetry data. However, current flow estimates derived from 2.0 and 2.5 m resolution failed to portray the short-term current variation induced by the ebb phase of the tide. Therefore, it is recommended that MBES data with a pixel size of >50 % of the wavelength of the SSB observed is insufficient for inclusion in an OBIA workflow.

A Method for Multi-Beam Bathymetric Surveys in Unfamiliar Waters Based on the AUV Constant-Depth Mode

Given the lack of systematic research on bathymetric surveys with multi-beam sonar carried by autonomous underwater vehicles (AUVs) in unfamiliar waters, this paper proposes a method for multi-beam bathymetric surveys based on the constant-depth mode of AUVs, considering equipment safety, operational efficiency, and data quality. Firstly, basic principles for multi-beam bathymetric surveys under the constant-depth mode are proposed based on multi-beam operational standards and AUV constant-depth mode characteristics. Secondly, a vertical effective height model for the vehicle is established, providing vertical constraints and a basis for determining fixed depth in constant-depth missions. Subsequently, according to these basic principles and the vertical effective height model, the operational process for multi-beam bathymetric surveys in unfamiliar waters under the AUV constant-depth mode is outlined. Finally, we validate the proposed method through sea trials in the Xisha Sea of the South China Sea. The test results show that the method proposed in this paper not only ensures the vehicle safety operation and multi-beam data quality, but also improves the operation efficiency by about 68%, demonstrating the reliability of the proposed method and its significant engineering value and guidance implications.

Southern Ocean pinnipeds provide bathymetric insights on the East Antarctic continental shelf

Poor coverage of the Antarctic continental shelf bathymetry impedes understanding the oceanographic processes affecting Antarctica’s role in global climate. Continental shelf bathymetry influences warm modified Circumpolar Deep Water movement onto the shelf, making it an important factor promoting ice shelf melting and influencing the flow of ice shelves into the ocean. Building on previous work using seal dives to redefine bathymetry, our longitudinal study of ocean physics and animal behaviour provided new depth information from over 500,000 individual seal dives on the East Antarctic continental shelf. About 25% of these seal dives were 220 m (sometimes over 1000 m) deeper than the interpolated seafloor from IBCSO V2. Focusing on four well-sampled regions, we show that the bathymetry of 22% to 60% of the sampled area was improved by incorporating seal dive data. This revealed new bathymetric features, including troughs off the Shackleton Ice Shelf and Underwood Glacier and a deep canyon near the Vanderford Glacier. This deep canyon, the Mirounga-Nuyina Canyon, was confirmed by a recent multi-beam echo sounder survey. Further acquisitions of seal data will improve our understanding and modelling of Antarctic coastal ocean processes and ice-sheet dynamics.

A Sub-Bottom Type Adaption-Based Empirical Approach for Coastal Bathymetry Mapping Using Multispectral Satellite Imagery

Accurate bathymetric data in shallow water is of increasing importance for navigation safety, coastal management, and marine transportation. Satellite-derived bathymetry (SDB) is widely accepted as an effective alternative to conventional acoustic measurements in coastal areas, providing high spatial and temporal resolution combined with extensive repetitive coverage. Many previous empirical SDB approaches are unsuitable for precision bathymetry mapping in various scenarios, due to the assumption of homogeneous bottom over the whole region, as well as the neglect of various interfering factors (e.g., turbidity) causing radiation attenuation. Therefore, this study proposes a bottom-type adaption-based SDB approach (BA-SDB). Under the consideration of multiple factors including suspended particulates and phytoplankton, it uses a particle swarm optimization improved LightGBM algorithm (PSO-LightGBM) to derive depth of each pre-segmented bottom type. Based on multispectral images of high spatial resolution and in situ observations of airborne laser bathymetry and multi-beam echo sounder, the proposed approach is applied in shallow water around Yuanzhi Island, and achieves the highest accuracy with an RMSE value of 0.85 m compared to log-ratio, multi-band, and classical machine learning methods. The results of this study show that the introduction of water-environment parameters improves the performance of the machine learning model for bathymetric mapping.

FLUIDOGENIC LANDFORMS WITHIN THE PERMAFROST ZONE ON THE SHELF OF THE PECHORA AND KARA SEAS

The study is based on the results of multibeam echo-sounding and high-frequency seismic profiling during the 2018-2022 cruises of the R/V “Akademik Nikolai Strakhov” and “Akademik Boris Petrov”. Regular changes of morphometric parameters and the internal structure of pingo-like formations of the shelves of the Pechora and Kara seas were revealed. A morphometric analysis of pingo-like formations was carried out, which made it possible to draw conclusions about their relative age, as well as the role of near-bottom currents and slope processes in their modern dynamics. It was found that the density and morphological variety of pingo-like formations depend on the geological and tectonic features of the bottom area, the presence and nature of permafrost, the intensity of degassing, and the time of shelf flooding during the Holocene transgression. Pingo-like formations on the shelf, where the depth exceeds 70-80 m, emerged at the early stages of the Holocene transgression, and by now the permafrost there has largely thawed out. At the same time, pingo-like formations are still prominent in the relief and actively transformed by bottom currents, slope and, possibly, pseudovolcanic processes associated with ongoing degassing. Pingo-like formations are rare within shallow (up to 20-30 m) shelf areas close to the shore, and, apparently, continue their evolution at present. At the same time, the large thickness and continuity of permafrost prevent active fluid flow, acting as a seal. Pingo-like formations in the shallow-water zones are mainly cone-shaped mounds without intensive degassing. The density of pingo-like formations is maximum at the intermediate depths (from 20-30 to 70-80 m), in the presence of insular or discontinuous permafrost, under high fluid flow intensity within the fault zones and oil- and gas-bearing structures. Near-surface sediments in such areas are characterized by a combination of localized processes of heaving and active degassing. It predetermines a wide variety of the morphological types of pingo-like formations.Keywords: Arctic, bottom topography, degassing, pingo-like features, acoustic anomalies, multibeam echo sounding, seismoacoustic profiling

Harmonizing multi-source backscatter data using bulk shift approaches to generate regional seabed maps: Bay of Fundy, Canada

ABSTRACT Advances in sonar technology have revolutionized our ability to map the seafloor, however, differences between legacy and modern data pose challenges when analysing multi-source datasets. Acoustic backscatter recorded via multibeam echosounder is commonly used to characterize the seafloor, but a lack of standardized calibration often yields relative rather than absolute backscatter measurements, hindering comparison between surveys. ‘Bulk shift’ methods have been developed for harmonizing legacy backscatter datasets using overlapping survey areas for relative statistical calibration. This becomes increasingly difficult, though, given many datasets collected over extensive time periods. Backscatter data were collected in the Bay of Fundy, Canada, using multiple sonar systems and vessels over an 18-year period. Here, we propose a reproduceable strategy for harmonizing this large volume of disparate backscatter data using the bulk shift method. A final, harmonized map is presented for the entire Bay of Fundy and is validated using in situ observations from seafloor imagery.

Mapping offshore anthropogenic infrastructure associated with Cannery Row, Monterey Peninsula, California USA

“Cannery Row” is well known from the novel of the same name written by John Steinbeck in 1945. It historically extends back to the early 1940’s when sardines were being heavily fished in Monterey Bay and an extensive network of canneries were established in Monterey. To support these canneries and the fishing vessels delivering fish to the shore-based processing facilities, an extensive network of seabed infrastructure was developed. Once the fisheries collapsed, the canneries shut down and the “Row” became derelict with the seabed infrastructure left to deteriorate in place. Today the row has been revitalized by an invigorating tourist industry brought to the peninsula with the establishment of the Monterey Bay Aquarium (MBA) nearly 40 years ago. New seabed infrastructure was constructed to support the aquatic exhibits of the MBA but unlike the previous canneries’ infrastructure, this infrastructure was constructed with the conservation of the unique and spectacular nearshore marine environment in mind.Using modern geophysical instrumentations consisting of Multi-Beam Echosounder (MBES) and 3.5 kHz Compressed High Intensity Radar Pulse (CHIRP) sub-bottom profiling systems we mapped the seafloor geology, imaged abandoned and present-day seabed infrastructure, and characterized the benthic habitats. From this mapping effort we were able to assess the artifacts of the seafloor and illustrate how modern seafloor processes such as sediment transport is altering the infrastructure. Much of the abandoned submarine infrastructure provides hard substrate within a dynamic unconsolidated sand bottom that is habitat for encrusting and sessile organisms, contributing to the diversity and complexity of the marine ecosystem of the area. In addition, a prominent granodiorite exposure upon which the dynamic sand onlaps is prime holdfast foundation for kelp that in turn provides habitat for fish. Although not pristine, the impacts of previous industrial disturbances and anthropogenic impacts are now well mitigated with the area set aside as a natural reserve and educational center piece within the Monterey Bay National Marine Sanctuary.

Morphological changes analysis using 3D bathymetric surveys in Chilia Branch - Bystroe Channel bifurcation area

The Bystroe Channel project with transboundary environmental impact in the Danube Delta, area of great ecological significance that has already a strong anthropic footprint, requires close monitoring of water quality parameters in order to determine their tendencies and their impact on the ecosystem components. Riverbed bathymetry surveys using multibeam echo-sounders are of high interest due to the data resolution and coverage capabilities that surpass the single-beam methods. Two riverbed elevation datasets, recorded in consecutive years, have been used to carry out morphological comparative analysis for the area where Chilia branch bifurcates in Bystroe Channel and Old Stambul. The analysis has been performed both on the bathymetry grids as a whole and on 3 longitudinal and 9 transversal river sections, the morphological changes values being in majority included in [-0.5 m;+0.5 m], with a minimum of -2.4 m and a maximum of 2.2 m, showing the bifurcation influence on the erosion/deposition processes results.