Bathymetry Research Articles

Application of Unmanned Surface Vehicles in Coastal Environments: Bathymetric Survey using a Multibeam Echosounder

Kum, B.-C.; Shin, D.-H.; Jang, S.; Lee, S.Y.; Lee, J.H.; Moh, T.J.; Lim, D.G.; Do, J.-D., and Cho, J.H., 2020. Application of unmanned surface vehicles in coastal environments: Bathymetric survey using a multibeam echosounder. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1152-1156. Coconut Creek (Florida), ISSN 0749-0208.This paper presents the practical application and results of a bathymetric survey carried out in a shallow marine coastal zone (Hujeong beach, located in the East Sea, South Korea) using a multi-functional unmanned surface vehicle (USV) equipped with a multibeam echosounder. Operation of the USV was conducted along the coast in very shallow water [depth ≤ 1.5 m (0.3 m below the transducer)], which is inaccessible to manned research vessels. High-resolution bathymetric data is expected to help with assessment and prediction of rapid changes in the shallow coastal zone. This work supports the applicability of USVs to scientific research and environmental monitoring in very shallow coastal areas. The USV will be the most extensively used technique for observing marine coastal environment.

Video Depth Inversion at a Microtidal Site Exposed to Prevailing Low-energy Short-period Waves and Episodic Severe Storms

Bouvier, C.; Balouin Y.; Castelle B., and Valentini N., 2020. Video depth inversion at a microtidal site exposed to prevailing low-energy short-period waves and episodic severe storms. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1021–1026. Coconut Creek (Florida), ISSN 0749-0208.Over the last decades, a wide range of depth inversion algorithms have been developed, which aim to infer local water depth from remotely-sensed wave parameters based on physical relations. Particularly, the depth inversion algorithm named cBathy (Holman, Plant, and Holland, 2013) showed good results for a range of wave conditions and environments but the method was only applied to beaches exposed to moderate or highly energetic wave climate, with wave peak period often larger than 8 s. This paper applies the cBathy algorithm for the very first time on a Mediterranean Sea beach, Sète, southeast France, a semidiurnal microtidal environment exposed to a moderate-energy modal wave climate and episodic severe storms. The objective of the paper is to assess the ability of the cBathy algorithm to estimate the nearshore bathymetry for waves with large energy spread in both direction and frequency. After a comparison between the remotely sensed bathymetry and a ground truth bathymetric survey, we use a non-linear, depth-averaged morphodynamic model, 2DBeach (Dubarbier et al., 2017), on remotely sensed bathymetries to determine the sensitivity of nearshore waves and horizontal circulations to the estimated morphology. The depth inversion technique estimates the nearshore bathymetry with good accuracy (RMSE = 0.39 m) for a beach area extending respectively 1600 m and 600 m in the longshore and cross-shore directions, respectively, suggesting the technical feasibility of coupling remotely-sensed bathymetry to 2DH numerical model, even at short-waves exposed Mediterranean beaches.

Coupling SWAT and bathymetric data in modelling reservoir catchment hydrology

A physically based model; Soil and Water Assessment Tool (SWAT) and bathymetric data were integrated to simulate and evaluate the water balance of the Brimsu Reservoir from 2002 to 2018. The simulated water balance describes the changes in water storage of the reservoir as a hydrological component that is dependent on inflows (precipitation, runoff) and outflows (evaporation, infiltration, discharge and water consumption). In the absence of storage capacity data, a bathymetric survey was conducted to determine the capacity of the reservoir. The result showed that there has been a reduction of about 27.6% in gross capacity of the reservoir. The SWAT model indicates a satisfactory performance for both calibration (NSE = 0.66, Bias = − 5.0% and R2 = 0.86) and validation (NSE = 0.63, Bias = − 10.4% and R2 = 0.82) periods. The monthly water budget revealed that 30.50% and 69.50% of the total inflow within the catchment constitute direct precipitation and runoff respectively while 32.50%, 12.50%, 34.40% and 20.60% of total outflow represents evaporation, seepage, spillage and water consumed. Though the average final-to initial-volume ratio of 1.15 indicates that the reservoir is not emptying, and water is withdrawn from the reservoir at a sustainable rate, yet water from the reservoir does not yield the treatment plant’s design capacity of 29,500 m/day. Overall, the model demonstrated a good performance by providing quantitative information to serve as a guide for stakeholders to make better decisions in planning and managing the Brimsu Reservoir.

Volume Variations of Small Inland Water Bodies from a Combination of Satellite Altimetry and Optical Imagery

In this study, a new approach for estimating volume variations of lakes and reservoirs using water levels from satellite altimetry and surface areas from optical imagery is presented. Both input data sets, namely water level time series and surface area time series, are provided by the Database of Hydrological Time Series of Inland Waters (DAHITI), developed and maintained by the Deutsches Geodätisches Forschungsinsitut der Technischen Universität München (DGFI-TUM). The approach is divided into three parts. In the first part, a hypsometry model based on the new modified Strahler approach is computed by combining water levels and surface areas. The hypsometry model describes the dependency between water levels and surface areas of lakes and reservoirs. In the second part, a bathymetry between minimum and maximum surface area is computed. For this purpose, DAHITI land-water masks are stacked using water levels derived from the hypsometry model. Finally, water levels and surface areas are intersected with the bathymetry to estimate a time series of volume variations in relation to the minimum observed surface area. The results are validated with volume time series derived from in-situ water levels in combination with bathymetric surveys. In this study, 28 lakes and reservoirs located in Texas are investigated. The absolute volumes of the investigated lakes and reservoirs vary between 0.062 km 3 and 6.041 km 3 . The correlation coefficients of the resulting volume variation time series with validation data vary between 0.80 and 0.99. Overall, the relative errors with respect to volume variations vary between 2.8% and 14.9% with an average of 8.3% for all 28 investigated lakes and reservoirs. When comparing the resulting RMSE with absolute volumes, the absolute errors vary between 1.5% and 6.4% with an average of 3.1%. This study shows that volume variations can be calculated with a high accuracy which depends essentially on the quality of the used water levels and surface areas. In addition, this study provides a hypsometry model, high-resolution bathymetry and water level time series derived from surface areas based on the hypsometry model. All data sets are publicly available on the Database of Hydrological Time Series of Inland Waters.

How do deep-water volcanoes grow?

Deep-water volcanoes are emplaced in water depths >1.0 km and are widespread along continental margins and in ocean basins. Whilst the external morphology of deep-water volcanoes can be mapped using bathymetric surveys, their internal structure and true volume remain enigmatic. It is thus difficult to determine how deep-water volcanoes grow. We investigate 13 Late Miocene-to-Quaternary, deep-water volcanoes that are imaged in 3D by seismic reflection data from the northern South China Sea, which allow us to quantify their external morphology and examine their internal structure. These deep-water volcanoes were emplaced in water depths >1.5 km, are relatively small (<3.0 km diameter, <0.56 km tall, and <0.92 km3 in volume), and have steep slopes (up to 42°). Most of the volcanoes have erosional, ‘crater-like’ bases, infilled with sub-horizontal seismic reflections. These crater-like bases are overlain by downward-converging, conical seismic reflections delineating the classical volcano morphology. We suggest the crater-like bases formed by excavation of cold, wet, and poorly consolidated near-seabed sediment during expulsion of hydrothermal fluid, and not by explosive magmatic eruptions or gravitational subsidence. Erupted igneous material infilled the precursor craters with the observed sub-horizontal layers, likely comprising hyaloclastites. After this initial phase of volcanism, the buildup of volcanic material produced layers that are now represented by the flank-parallel or downward-converging, conical seismic reflections. We suggest high hydrostatic pressures of >15 MPa, which are typical of water depths >1.5 km, inhibited degassing and fragmentation of ascending magma and thus erupted lava. This lack of degassing and fragmentation permitted effusive eruptions during the latter stages of volcanism. Our models for volcano growth in the deep submarine realm demonstrate the power of using 3D seismic data when investigating the internal structure and total volume of deep-water volcanoes.

On the status and mechanisms of coastal erosion in Marawila Beach, Sri Lanka

Coastal erosion remains a problem in many developing countries because of a limited understating of erosion mechanisms and management. Sri Lanka is one of the countries that recognized coastal erosion management as a governmental responsibility, in 1984. Nevertheless, erosion mechanisms have not yet been fully understood. We investigate the status and mechanisms of coastal erosion using empirically collected data and various techniques, such as Geographic Information System analysis of satellite images, drone mapping, bathymetric surveys, hindcasting of wind-induced wave climate, questionnaires, and semi-structured interview surveys. We identified wave climate change, reduction in river sand supply, interruptions from previous erosion management measures, and offshore sand mining as potential causes of erosion considering sediment flux and rates of erosion. Erosion of Marawila Beach began during 2005–2010 and has been continuing ever since, due to a lack of integration in the beach and the entire sediment system. It is necessary to identify the long-term, large-scale changes in the sediment system through data collection. This study highlights the importance of an integrated coastal erosion management plan and could facilitate better coastal erosion management in Sri Lanka, as well as in other developing countries.

A high-resolution bathymetry dataset for global reservoirs using multi-source satellite imagery and altimetry

Although accurate 3-D reservoir bathymetry is a key input for multiple applications (such as global hydrological models, local water resources related studies, and others), such information is only available for very few locations. To fill this knowledge gap, we generated a 30 m resolution bathymetry dataset for 347 global reservoirs, representing a total volume of 3123 km3 (50% of the global reservoir capacity). First, Area–Elevation (A–E) relationships for the identified reservoirs were derived by combining altimetry data from multiple satellites with Landsat imagery data. Next, the resulting A–E relationships were applied to the Surface Water Occurrence (SWO) data from the JRC Global Surface Water (GSW) dataset to obtain bathymetry values for the dynamic areas of the reservoirs. Lastly, an extrapolation method was adopted to help achieve the full bathymetry dataset. The remotely sensed bathymetry results were primarily validated against the following: (1) They were validated against Area–Elevation (A–E) and Elevation–Volume (E-V) relationships derived from the in situ elevations and volumes for 16 reservoirs, with root-mean-square error (RMSE) values of elevation from 0.06 m to 1.99 m, and normalized RMSE values of storage from 0.56% to 4.40%. (2) They were also validated against survey bathymetric maps for four reservoirs, with R2 values from 0.82 to 0.99 and RMSE values from 0.13 m to 2.31 m. The projected portions have relatively large errors and uncertainties (compared to the remotely sensed portions) because the extrapolated elevations cannot fully capture the underwater topography. Overall, this approach performs better for reservoirs with a large dynamic area fractions. It can also be applied to small reservoirs (e.g., reservoirs with surface areas of a few square kilometers or less), where ICESat observations are available, and to large natural lakes. With the contribution of ICESat-2, this dataset has the potential to be expanded to thousands of reservoirs and lakes in the future.

SAR Imaging Features of Shallow Water Bathymetry

Purpose. The aim of the article is to study manifestations of the underwater topography features in the northern part of the White Sea in the images made by the spaceborn synthetic aperture radars (SAR) Sentinel-1A, Sentinel-1B. Methods and Results. In the SAR images, the bottom features are revealed as bright and dark brightness anomalies. The anomalies were observed at the wind speed ranging from 2.6 to 10.8 m/s, and became reverse (bright anomalies turned dark and vice versa), when a tidal current changed its direction. It is shown that the observed SAR imagery contrasts correlate to divergence of a current formed by interaction of a tidal flow with the bottom topography inhomogeneities. The simulated SAR contrasts agree with the observations, and confirm the relation between the observed SAR contrasts and the current divergence. Together with modeling the SAR contrasts, the contribution of different mechanisms to formation of the observed modulations of the normalized radar cross section was qualitatively estimated. The wave breaking effect was especially accentuated. The method for retrieving the underwater bottom topography based on the relationship between the bottom gradient and the SAR imagery contrasts is proposed. Conclusions. Location of the bottom inhomogeneities in the shallow water region on the whole coincides with that of the tidal current divergence and convergence zones, which are observed as brightness anomalies in the SAR images. Breaking of surface waves is the main contributor to the observed SAR contrasts. The bottom topography reconstructed from the SAR contrasts, and the actual one resulted from the bathymetry maps are in good agreement. Some discrepancies are interpreted as possible changes in depth and shape of the bottom topography features induced by action of strong currents and waves.

Accumulation of organic carbon in a large canyon reservoir in Karstic area, Southwest China.

Artificial reservoirs play an important role in intercepting organic carbon (OC), which affects the carbon cycle of inland waters. However, limited by the methods of field observations, studies on the potential carbon sink of sediment in reservoirs are not accurate enough. In this study, we investigated OC accumulation in the Wujiangdu Reservoir (WJDR), a canyon reservoir located in a karst area of Southwest China, by coupling seismic survey data with physicochemical data of sediment cores. The results showed that irregular underwater topography resulted in spatial heterogeneity of the sediment deposition. The mean OC accumulation rate in the WJDR was 579.2gCm-2year-1, and the OC accumulation flux of the WJDR was 1.4 × 1010gCyear-1. δ13C values coupled with a mixing model indicated that the autochthonous OC ranged from 14.2 to 97.0% of the total OC in the sediment, with an average of 48.4%. The significantly positive relationship between autochthonous OC and TN indicated that the autochthonous OC generated in the reservoir was associated with nutrient input. The autochthonous OC accumulation flux was 6.6 × 109gCyear-1, which was equal to 2.3 times the carbon emission from the reservoir surface to the atmosphere as CO2-C, indicating that the autochthonous OC produced within the reservoir is a large carbon sink.

Connection between macrotidal estuaries along the southeastern Amazon coast and its role in coastal progradation

Sediment transport in the southeastern Amazon coastal zone (SACZ) is substantially affected by tidal asymmetry, seasonal variation of the wind and wave regime and especially rainfall (i.e., river discharge). The regional climate and geological configuration have resulted in numerous estuaries and large mangrove-covered coastal plains that partially divide the estuarine basins, which are connected by tidal channels. Based on the investigation of the Furo Grande tidal channel, we assess the relevance of connectivity on the sediment transport and evolution of the ~8000 km2 SACZ mangrove belt. Extensive sedimentologic and bathymetric surveys, as well as hydrodynamic measurements including water level, water and sediment flow, and physical-chemical characteristics of the water, were undertaken at different seasonal periods. Water-level variation along the channel shows that sediment-transport convergence (STC) tends to be formed within the connecting channel, as the tide propagates from both ends. Morphologic and sedimentologic results show the accumulation trend of fine sediments within the STC zone, and this is relevant for mud retention and further delivery to the mangrove plains, which may eventually lead to channel-connection closure. Despite the STC, results also show that there is an important net flux of suspended sediments between estuaries through the studied channel. However, the connected estuaries of Taperaçu and Caeté have substantial differences regarding riverine discharge, and thus estuarine processes, tidal propagation and sediment transport. Bottom sediments and morphology reflect long-term trends and show STC migration towards the Taperaçu as a result of substantially smaller fluvial discharge in that estuary, and therefore higher sediment accumulation rates, compared to the Caeté estuary. The migration of the STC prevents the closure of the connection, and its maintenance preserves these channels as sediment-flow conduits between estuaries. The connectivity is a key process to redistribute mainly muddy sediments along this coastal sector, which helps to explain the evolution and maintenance of the relatively homogeneous and widespread progradation of mangroves along the SACZ, with uneven mud supply.

Bedforms on the submarine flanks of insular volcanoes: New insights gained from high resolution seafloor surveys

AbstractA comparative analysis of bedform fields along the submarine flanks of insular volcanoes, characterized by different morpho‐structural settings, volcanic and meteo‐marine regimes (Vanuatu, Kermadec, Bismark, Madeira and Aeolian archipelagos), is presented here to provide insights on the size distribution, morpho‐dynamic and genesis of such bedforms. Two main types of bedforms are recognized according to their size, location and preconditioning/triggering processes. Small‐scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres. Because of their small‐size, they are typically not recognizable at water depths greater than 400 m from vessel‐mounted bathymetric surveys. Few examples of small‐scale bedforms are reported from upper volcanic flanks, where steep gradients commonly hinder their formation. Their recognition is mostly limited to the thalweg of shallow and flat‐bottomed channels that carve the insular shelf on slope gradients &lt;15°. Small‐scale bedforms are mostly related to erosional–depositional processes due to sedimentary gravity flows that are often the result of a cascading effect between volcanic and non‐volcanic processes (for example, flood discharges and retrogressive landslides). Large‐scale bedforms occur at all water depths, having wavelengths of hundreds/thousands of metres and wave heights up to few hundreds of metres. The origin of large bedforms is more difficult to ascertain, especially if only bathymetric data are available. Some diagnostic criteria are presented to distinguish between bedforms associated with landslide deposits and those associated with density currents. In this latter case, relevant sediment sources and slope gradients (&lt;8°) are key factors for bedform development. Erosional–depositional bedforms are typically related to eruption‐fed density flows formed during large caldera collapses or to large turbidity flows. Bedforms generated by turbidity flows are often observed in the lower volcanic flanks, where an abrupt decrease of gradients is present, often matching a change from confined to unconfined settings. In summary, this study provides insights to interpret bedforms in modern and ancient marine volcaniclastic settings elsewhere.

Surface waves in a channel with thin tunnels and wells at the bottom: Non-reflecting underwater topography

We consider the propagation of surface water waves in a straight planar channel perturbed at the bottom by several thin curved tunnels and wells. We propose a method to construct non reflecting underwater topographies of this type at an arbitrary prescribed wave number. To proceed, we compute asymptotic expansions of the diffraction solutions with respect to the small parameter of the geometry taking into account the existence of boundary layer phenomena. We establish error estimates to validate the expansions using advances techniques of weighted spaces with detached asymptotics. In the process, we show the absence of trapped surface waves for perturbations small enough. This analysis furnishes asymptotic formulas for the scattering matrix and we use them to determine underwater topographies which are non-reflecting. Theoretical and numerical examples are given.

Determining Bathymetry of Shallow and Ephemeral Desert Lakes Using Satellite Imagery and Altimetry

AbstractWater volume estimates of shallow desert lakes are the basis for water balance calculations, important both for water resource management and paleohydrology/climatology. Water volumes are typically inferred from bathymetry mapping; however, being shallow, ephemeral, and remote, bathymetric surveys are scarce in such lakes. We propose a new, remote‐sensing‐based, method to derive the bathymetry of such lakes using the relation between water occurrence, during &gt;30 year of optical satellite data, and accurate elevation measurements from the new Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2). We demonstrate our method at three locations where we map bathymetries with ~0.3 m error. This method complements other remotely sensed, bathymetry‐mapping methods as it can be applied to: (a) complex lake systems with subbasins, (b) remote lakes with no in‐situ records, and (c) flooded lakes. The proposed method can be easily implemented in other shallow lakes as it builds on publically accessible global data sets.

Determination of the Trophic State Index (TSI) using remote sensing, bathymetric survey and empirical data in a tropical reservoir

espanolCopepodos calanoides pertenecientes al genero de diaptomido Eudiaptomus Kiefer, 1932 fueron recolectados en una masa de agua artificial en la isla de Madeira, Portugal. Las identificaciones morfologicas y moleculares de los especimenes recolectados demostraron inequivocamente que pertenecian a la especie aloctona Eudiaptomus gracilis (G. O. Sars, 1863), posiblemente introducida inadvertidamente con introducciones de peces o plantas acuaticas ornamentales. En la localidad muestreada, la especie coexistia con el copepodo ciclopoide no nativo Acanthocyclops americanus (Marsh, 1893) y algunas especies de anomopodos. Esta es la primera cita de la especie para Portugal y para Macaronesia, aunque la posible presencia de E. gracilis en la Peninsula Iberica necesita verificacion EnglishCalanoid copepods belonging to the diaptomid genus Eudiaptomus Kiefer, 1932 were collected in an artificial water body on the island of Madeira, Portugal. The morphological and molecular identification of the collected specimens unequivocally proved that they belong to the allochthonous species Eudiaptomus gracilis (G. O. Sars, 1863), possibly unwarily introduced along with fish stockings or ornamental aquatic plants. In the sampled site, the species co-occurred with the non-native cyclopoid copepod Acanthocyclops americanus (Marsh, 1893) and some anomopod species. This is the first record of the species for Portugal and the whole Macaronesia, whereas the possible presence of E. gracilis in the Iberian Peninsula should be verified.

Hypsobathymetric Models of Ksudach Caldera Complex (Kamchatka)

The Ksudach volcano is one of the most complicated and dynamic volcanic centre of the Russian Far East located on the south of Kamchatka peninsula. Modern cone of the volcano is composite construction with five different size and time calderas, two lakes and recent Shtubel’s cone. Studying of modern terrain dynamics on the volcano can be carried out with by comparison of two digital elevation (hypso- and bathy-) models for state of 80s in the 20 century (created on the data of aerial photographs and the bathymetric surveys) and for modern state (on the data of ArcticDEM and digital echosounding bathymetric survey with synchronized satellite fixation of the profiles). The elevation models like these (for Kamchatka’s volcanes and for different it’s conditions) were created at the first time. Its comparison allowed us to recognize new underwater extrusion dome with extensive underwater gas-hydrothermal outlets. Besides this we got the possibilities for clear bordering of different-time calderas using fractures on the automatic traceabled small river profiles. Comparison of high-resolution different-time DEMs for volcanic research is relatively new and perspective way for understanding volcanic life and development.

Determination of the Trophic State Index (TSI) using remote sensing, bathymetric survey and empirical data in a tropical reservoir

portuguesOs reservatorios sao importantes reservas de agua doce que sofrem com despejos de esgotos domesticos e industriais que causam mudancas quantitativas e qualitativas na sua composicao fisico-quimica, alem de causar impactos na fauna e na flora. Uma das consequencias e a eutrofizacao, processo que se caracteriza pelo aumento na concentracao de nutrientes no ecossistema aquatico, principalmente fosforo e nitrogenio. A concentracao de clorofila-a e de fosforo sao obtidas das amostras da agua para alimentar as equacoes de Indice de Estado Trofico (IET). Os metodos usados no presente trabalho visam determinar o grau de trofia utilizando o sensoriamento remoto orbital (SR), que usa a razao entre as imagens das faixas do infravermelho (IVP) proximo e do vermelho (VERM) para inferir a concentracao de clorofila-a, bem como a variacao do IET, no periodo seco e chuvoso. Este metodo permite uma visao sinoptica que possibilita um suporte para tomada de decisao com baixo custo, especialmente quando um grande volume de dados e disponibilizado e/ou gerado, ampliando assim a qualidade em funcao do desenvolvimento tecnologico. Contudo, e necessario considerar a influencia do fundo dos corpos d’agua quando imagens de satelite sao utilizadas, uma vez que a radiacao emergente da zona eufotica e que da respaldo aos resultados. Desde modo, nos excluimos as areas rasas que pudessem comprometer a resposta espectral das imagens de satelite devido ao efeito do fundo, antes de serem usadas para produzir o Mapa de IET SR. Nos criamos o mapa de IET SR (observado) e entao o validamos pelo Mapa de IET Empirico (esperado), obtido por meio de analises quimicas realizadas na agua em 28 pontos georreferenciados ao longo do gradiente lacustre-fluvial, ambos para o periodo seco e chuvoso. Nos realizamos o teste chi-quadrado que apresenta quanta diferenca existe entre o observado e o esperado. Ambos periodos apresentaram x2 = 1, gl = 27, com valores criticos (0.005) de 49.64. Desse modo, nao encontramos diferencas entre o observado e o esperado. Nossos resultados reforcam a potencialidade do SR na obtencao do IET, favorecendo a identificacao de areas eutroficas em sistemas de aguas continentais que apresentam baixa turbidez. EnglishThe reservoirs are important freshwater reserves that suffer with domestic and industrial wastes, causing qualitative and quantitative changes in their physicochemical composition, as well as causing fauna and flora impacts. One of the consequences is eutrophication, a process characterized by increased concentration of nutrients in aquatic ecosystems, mainly phosphorus and nitrogen. In order to classify waterbodies according to their trophic degrees, chlorophyll-a and phosphorus concentration data are usually obtained in water samples, feeding an equation to obtain the Trophic State Index (TSI). The method used at the present work aim to determine the TSI based on remote sensing (RS), by using the ratio between the near-infrared (NIR) and red (RED) images to infer the chlorophyll-a concentration in wet and dry seasons. This method allows a synoptic vision of the reservoir, providing support for decision-making process at low cost, especially when a large amount of data is available and/or generated, increasing quality in consonance with technological development. However, we need to consider the influence of the bottom of shallow areas when using orbital images to evaluate the waterbodies conditions, since the emerging radiation of the euphotic zone is responsible for the results reliability. Thus, it is necessary the exclusion of shallow areas, which may compromise the spectral response of the satellite images due to the bottom effects, before the development of the TSI RS Map. We created the TSI RS Maps (observed) and then we validated it with the Empirical TSI Maps (expected), obtained in 28 geo-coded points along the riverine-transition-lacustrine gradient, both for wet and dry season. We performed the chi-square test that shows how much difference exists between the observed and the expected. Both seasons presented x2 = 1, df = 27, with critical value (0.005) of 49.64. Therefore, we found no differences between the observed and the expected. Our results reinforce the potentiality of the RS to perform the TSI favoring the identification of eutrophic areas in inland water systems with low turbidity

Qualitative Evaluation of Geophysical Aeromagnetic Data For River Anticline Around The River Niger Area In Koton-Karfi, Southern Bida Basin, Nigeria

&#x0D; &#x0D; &#x0D; In this paper a qualitative evaluation of aeromagnetic data maps has been used to preliminarily support the formation of river anticlines beneath major rivers due to isostatic rebound as a result of deep river incision of surface and sub-surface overlying rocks. The regional gradients of digital high resolution aeromagnetic data were removed by polynomial fitting. This involved fitting a plane surface to the reduction to pole map of the aeromagnetic data by using multi-regression least square analysis of the Oasis Montaj 6.4 program. The regional field values from the plane surface are subtracted from the observed data to obtain the residual anomaly values. Power spectrum plots of aeromagnetic data of the study area produced a basement depth contour map. The basement depths of the south-western part of the study area revealed basement uplift with a depth range of 1.8 to 2.5km which lies beneath the Niger River area, SW of the study area, and depicts a river anticline.&#x0D; &#x0D; &#x0D;

Use of bathymetry and clay mineralogy of reservoir sediment to reconstruct the recent changes in sediment yields from a mountain catchment in the Western High Atlas region, Morocco

The dam of Takerkoust, located at the outlet side of N'fis Basin (Western High Atlas of Morocco), is one of the strategic reservoirs in Morocco facing a serious problem of siltation due to soil erosion. A paleo-hydrology approach combining chronological and sedimentological analyses is conducted to understand the evolution of the depositional sediment history of the Takerkoust reservoir between 1988 and 2016. First, a series of 8 bathymetric surveys in the Takerkoust reservoir was used to determine the chronology of flood event deposits. Second, grain size distribution, clay mineralogy (XRD) and organic matter content were analyzed in 2 cores drilled in the Takerkoust reservoir and the newly build Ouirgane reservoir in upstream (from which 46 samples were taken). Third, Soils samples collected from the uppermost soil horizons (First 5 cm) of different localities of the N’fis watershed were also analyzed to identify sediments origins. Eleven couplets with different textures and thickness are identified in the Takerkoust reservoir corresponding to the period 1988–2016. The highest correlation is observed between instantaneous maximum flow and thickness of the sandy component of the couplets. The variation of the siltation rate allows highlighting two distinct periods: the oldest period (1988–1999) characterized by a high sediment yield SY (908.6 t·km−2·yr−1) and a youngest one (1999–2016) characterized by a low SY (203.9 t·km−2·yr−1). The newly built Ouirgane dam, seems to be responsible for the decreasing siltation rate and change of the clay assemblages of the sedimentary series in Takerkoust reservoir.

Overview of statewide geophysical surveys for ecosystem restoration in Louisiana

The System Wide Assessment and Monitoring Program (SWAMP) was implemented by the Louisiana Coastal Protection and Restoration Authority (CPRA) to develop an Adaptive Management Implementation Plan (AMIP). SWAMP ensures that a comprehensive network of coastal data collection/monitoring activities is in place to support the development and implementation of Louisiana’s coastal protection and restoration program. Monitoring of physical terrain is an important parameter of SWAMP. For the first time a systematic approach was adopted to undertake a geophysical (bathymetric, side-scan sonar, sub-bottom profile, and magnetometer) survey along more than 5,000 nautical miles (nm) (excluding the 1,559 nm currently being surveyed from west of Terrebonne Bay to Sabine Lake) of track-line in almost all of the bays and lakes from Chandeleur Sound in the east to Terrebonne Bay in the west. This data collection effort complements the regional bathymetric survey undertaken under the Barrier Island Comprehensive Monitoring (BICM) Program in the adjacent offshore areas. This paper describes how a study of this magnitude was conceptualized, planned, and executed along the entire Louisiana coast. It is important to note that the initial intent was to collect bathymetric data only for numerical modelling for ecosystem restoration and storm surge prediction. Geophysical data were added for oyster identification and delineation. These first-order data also help comprehend the regional subsurface geology essential for sediment exploration to support Louisiana’s marsh and barrier island restoration projects.

Applicability of a Recreational-Grade Interferometric Sonar for the Bathymetric Survey and Monitoring of the Drava River

Sonar survey of shallow water bodies has challenged scientists for a long time. Although these water courses are small, still they have an increasing ecological, touristic and economical role. As maritime sonars are non-ideal tools for shallow waters, the bathymetric survey of these rivers has been taken with cross-sectional methods. Due to recent developments, interferometric surveying technology have also burst into the market of recreational-grade fish-finders. The objective of the current study was the development of a novel, complex and integrated surveying technique which is affordable, robust and applicable even at low water levels. A recreational-grade sonar system was assembled and mounted on a double-hull vessel and connected with a geodetic Global Navigation Satellite System (GNSS) device. We have developed a novel software which enables the bridging between a closed sonar file format and the commonly used Geographic Information System (GIS) datasets. As a result, the several month-long conventional bathymetric survey of the 146 km-long reach of the Drava River was reduced to 20 days and provided channel bathymetry of many orders of magnitude higher than the classical methods. Additionally, a large number of spatial derivatives were generated which enables the analysis of channel morphology, textural variation of channel sediments and the accurate delineation of navigational routes.