Acoustic Doppler Current Profiler Research Articles

Field based estimates of wave power at a nearshore Mediterranean locale for sustainable wave energy harnessing

Measurements from two Nortek/AWAC acoustic Doppler current profilers deployed for over three years at three sites were used to estimate the nearshore wave energy resource of the Gulf of Chania, in the island of Crete, Greece. Similar to other Mediterranean nearshore locations, low maximum and mean wave power values were observed, i.e., 133 and 2.57 kW/m at ∼20 m depth, respectively. Even though the study sites were in close proximity, considerable differences were observed, highlighting the nearshore effects of shoaling, refraction, and focusing on wave power estimates, and the need for long-term measurements. Short-duration storms (lasting a few days) with high wave power potentials were observed. During summer, the sea was much calmer. The nearshore wave power resource was found unsteady, with coefficients of variation well above 2, while the capacity factors of Pelamis and Oyster wave energy converters were 3.65% and 9.57%, respectively. As a result, existing technology is currently commercially unattractive for the Mediterranean nearshore. Marine renewable energy can play an important role in EU’s Blue Growth strategy and assist in meeting the 2050 carbon neutrality target. For this reason, research should focus on downscaling and redesigning wave energy technology to enable sustainable deployment in the Mediterranean nearshore.

Towards affordable 3D physics-based river flow rating: application over the Luangwa River basin

Abstract. Uncrewed aerial vehicles (UAVs), affordable precise global navigation satellite system hardware, multi-beam echo sounders, open-source 3D hydrodynamic modelling software, and freely available satellite data have opened up opportunities for a robust, affordable, physics-based approach to monitoring river flows. Traditional methods of river discharge estimation are based on point measurements, and heterogeneity of the river geometry is not contemplated. In contrast, a UAV-based system which makes use of geotagged images captured and merged through photogrammetry in order to generate a high-resolution digital elevation model (DEM) provides an alternative. This UAV system can capture the spatial variability in the channel shape for the purposes of input to a hydraulic model and hence probably a more accurate flow discharge. In short, the system can be used to produce the river geometry at greater resolution so as to improve the accuracy in discharge estimations. Three-dimensional hydrodynamic modelling offers a framework to establish relationships between river flow and state variables such as width and depth, while satellite images with surface water detection methods or altimetry records can be used to operationally monitor flows through the established rating curve. Uncertainties in the data acquisition may propagate into uncertainties in the relationships found between discharge and state variables. Variations in acquired geometry emanate from the different ground control point (GCP) densities and distributions used during photogrammetry-based terrain reconstruction. In this study, we develop a rating curve using affordable data collection methods and basic principles of physics. The basic principal involves merging a photogrammetry-based dry bathymetry and wet bathymetry measured using an acoustic Doppler current profiler (ADCP). The output is a seamless bathymetry which is fed into the hydraulic model so as to estimate discharge. The impact of uncertainties in the geometry on discharge estimation is investigated. The impact of uncertainties in satellite observation of depth and width is also analysed. The study shows comparable results between the 3D and traditional river rating discharge estimations. The rating curve derived on the basis of 3D hydraulic modelling was within a 95 % confidence interval of the traditional gauging-based rating curve. The 3D-hydraulic-model-based estimation requires determination of the roughness coefficient within the stable bed and the floodplain using field observation at the end of both the dry and wet season. Furthermore, the study demonstrates that variations in the density of GCPs beyond an optimal number have no significant influence on the resultant rating relationships. Finally, the study observes that which state variable approximation (water level and river width) is more accurate depends on the magnitude of the flow. Combining stage-appropriate proxies (water level when the floodplain is entirely filled and width when the floodplain is filling) in data-limited environments yields more accurate discharge estimations. The study was able to successfully apply advanced UAV and real-time kinematic positioning (RTK) technologies for accurate river monitoring through hydraulic modelling. This system may not be cheaper than in situ monitoring; however, it is notably more affordable than other systems such as crewed aircraft with lidar. In this study the calibration of the hydraulic model is based on surface velocity and the water depth. The validation is based on visual inspection of an RTK-based waterline. In future studies, a larger number of in situ gauge readings may be considered so as to optimize the validation process.

Validation of Actuator Line Modeling and Large Eddy Simulations of Kite-Borne Tidal Stream Turbines against ADCP Observations

The representation of tidal energy in future renewable energy systems is growing. Most of the current tidal turbine designs are limited by the minimum current velocity required for efficient operation. The Deep Green (DG) is a kite-borne tidal power plant designed to sustain efficient operation in tidal current velocities as low as 1.2 ms−1. This could increase the geographical areas suitable for large-scale tidal power arrays. Numerical modeling of the Deep Green was carried out in a previous study using large eddy simulations and the actuator line method. This numerical model is compared with acoustic Doppler current profiler (ADCP) measurements taken in the wake of a DG operating in a tidal flow under similar conditions. To be comparable, and since the ADCP measures current velocities using averages of beam components, the numerical model data were resampled using a virtual ADCP in the domain. The sensitivity of the wake observations to ADCP parameters such as pulse length, bin length, and orientation of the beams is studied using this virtual ADCP. After resampling with this virtual ADCP, the numerical model showed good agreement with the observations. Overall, the LES/ALM model predicted the flow features well compared to the observations, although the turbulence levels were underpredicted for an undisturbed tidal flow and overestimated in the DG wake 70 m downstream. The velocity deficit in the DG wake was weaker in the observations compared to the LES. The ALM/LES modeling of kite-borne tidal stream turbines is suitable for further studies of array optimization and wake propagation, etc.

The Iceland–Faroe warm-water flow towards the Arctic estimated from satellite altimetry and in situ observations

Abstract. The inflow of warm and saline Atlantic water to the Arctic Mediterranean (Nordic Seas and Arctic Ocean) between Iceland and the Faroes (IF inflow) is the strongest Atlantic inflow branch in terms of volume transport and is associated with a large transport of heat towards the Arctic. The IF inflow is monitored in a section east of the Iceland–Faroe Ridge (IFR) by use of sea level anomaly (SLA) data from satellite altimetry, a method that has been calibrated by in situ observations gathered over 2 decades. Monthly averaged surface velocity anomalies calculated from SLA data were strongly correlated with anomalies measured by moored acoustic Doppler current profilers (ADCPs) with consistently higher correlations when using the reprocessed SLA data released in December 2021 rather than the earlier version. In contrast to the earlier version, the reprocessed data also had the correct conversion factor between sea level slope and surface velocity required by geostrophy. Our results show that the IF inflow crosses the IFR in two separate branches. The Icelandic branch is a jet over the Icelandic slope with average surface speed exceeding 20 cm s−1, but it is narrow and shallow with an average volume transport of less than 1 Sv (106 m3 s−1). Most of the Atlantic water crosses the IFR close to its southernmost end in the Faroese branch. Between these two branches, water from the Icelandic branch turns back onto the ridge in a retroflection with a recirculation over the northernmost bank on the IFR. Combining multi-sensor in situ observations with satellite SLA data, monthly mean volume transport of the IF inflow has been determined from January 1993 to December 2021. The IF inflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which is expected to weaken under continued global warming. Our results show no weakening of the IF inflow. Annually averaged volume transport of Atlantic water through the monitoring section had a statistically significant (95 % confidence level) increasing trend of (0.12±0.10) Sv per decade. Combined with increasing temperature, this caused an increase of 13 % in the heat transport, relative to 0 ∘C, towards the Arctic of the IF inflow over the 29 years of monitoring. The near-bottom layer over most of the IFR is dominated by cold water of Arctic origin that may contribute to the overflow across the ridge. Our observations confirm a dynamic link between the overflow and the Atlantic water flow above. The results also provide support for a previously posed hypothesis that this link may explain the difficulties in reproducing observed transport variations in the IF inflow in numerical ocean models, with consequences for its predictability under climate change.

Estimating turbulent kinetic energy with an acoustic Doppler current profiler

A new method for estimating turbulent kinetic energy (TKE) from acoustic Doppler current profiler (ADCP) measurements is presented. Current methods of estimating TKE from ADCP measurements require assumptions regarding the flow being measured. Combining the geometric orientation of ADCP sampling beams and the relative contributions of root mean square (RMS) velocities to the total TKE results in a formula that can be written for any ADCP. Data from a direct numerical simulation (DNS) are used with a virtual ADCP to assess the success of this method, and laboratory experiments are used to test the new method in a physical setting. The proposed approach measures TKE with an average RMS error of 15.2%, which is less than that from previous methods. Error caused by the ADCP sampling in different spatial locations contributes most to overall error; commercially available ADCPs typically sample at a high enough frequency and fine enough resolution to measure the RMS velocities needed to calculate TKE. Guidelines for measuring TKE with an ADCP are proposed, and published data on rivers are used to estimate the applicability of this method in practice.

Evaluating the estuarine tidal discharge through water stage component analysis and in-situ measurement — Case study Mandovi–Zuari estuary of Goa, India

Determining tidal reach and long-term monitoring of tidal discharge are vital in an estuarine system due to their potential use in water resource management and inland navigation. The upstream river discharge contributes to the nonstationary and nonlinear features of estuarine discharge. The tidal reach of an estuary can be identified based on the tidal influence on its water stage components. In the present study, a novel approach based on the Hilbert–Huang transform (HHT) and complete ensemble empirical mode decomposition with adaptive noise (CEEMDN), is used to decompose water stages into several Intrinsic mode functions (IMF). Those IMFs with different amplitudes and periodicities represent those factors that influence the water stages in an estuary. The efficiency of the present method is analyzed with the measured water level data from the estuary of Mandovi–Zuari in Goa, India. Principal ocean lunar semidiurnal constituent M2 is found to be the major tidal constituent, which is consistent in the coastal region. Subsequently, the high-frequency discharge is computed and validated with direct discharge measured by Rio Grande Acoustic Doppler Current Profiler (ADCP). Post-monsoonal discharge is computed using pre-monsoonal calibration coefficients, and a strong correlation is found between post-monsoonal measured and computed discharge. The proposed study will be helpful to estimate reliable estuarine tidal discharge with minimum operational maintenance.

Application of Acoustic Doppler Current Profile (ADCP) to Estimate Suspended Solid Concentration (SSC) During the Tidal Phase, Case Study: Donggala, Palu.

Understanding various types of kite material, known as suspended solid concentration (SSC), affects the strength of the reflected acoustic signal. SSC is a concentrate that floats in a body of water, the character of the increase in concentration is strongly influenced by the transport medium, namely ocean currents and tides. The use of the Acoustic Doppler Current Profile (ADCP) in this study was developed to estimate the SSC at each elevation change in the tidal phase. This study aims to identify the relationship between the intensity of scattering values to estimate SSC, and to compare SSC temporally in the tidal phase. ADCP measurement is implemented at Donggala, Palu Waters to collected tidal behavior and strength signal during 30 days measurement, with 8 layers profile. Data analysis by classifying the relative acoustic backscatter value. The conversion of the scattering value obtained has a range between 20 - 150 db. The classification of scattering is as follows 70-77 db, 65-69 db, and 60-64 db respectively near the bottom, middle and surface waters. The results of the linear echo intensity (db) relationship with SSC observation (10log) have a strong relationship with an accuracy of R values 0.936. The characteristics of SSC at neap tide and ebb current elevation were relatively higher, with concentration values ranging from 80 – 82 mg l-1, while other conditions were 77 – 79 mg l-1. This study concludes that the intensity relationship can estimate SSC with an error of 2.61% with average layer difference concentration 0.59 mg/l.

Eddy Tracking From In Situ and Satellite Observations

AbstractMesoscale eddies are a dominant source of spatial variability in the surface ocean and play a major role in the biological marine carbon cycle. Satellite altimetry is often used to locate and track eddies, but this approach is rarely validated against in situ observations. Here we compare measurements of a small (under 25 km radius) mode water anticyclonic eddy over the Porcupine Abyssal Plain in the northeastern Atlantic Ocean using CTD and Acoustic Doppler Current Profiler (ADCP) measurements from three ships, two gliders, two profiling floats, and one Lagrangian float with those derived from sea level anomaly (SLA). In situ estimates of the eddy center were estimated from maps of the thickness of its central isopycnal layer, from ADCP velocities at a reference depth, and from the trajectory of the Lagrangian float. These were compared to three methods using altimetric SLA: one based on maximizing geostrophic rotation, one based on a constant SLA contour, and one which maximizes geostrophic velocity speed along the eddy boundary. All algorithms were used to select CTD profiles that were within the eddy. The in‐situ metrics agreed to 97%. The altimetry metrics showed only a small loss of accuracy, giving >90% agreement with the in situ results. This suggests that current satellite altimetry is adequate for understanding the spatial representation of even relatively small mesoscale eddies.

Modelling shear stress distribution in ice-covered streams

Abstract Distribution of bed shear stress is the critical factor in regulating the meandering of single-thread rivers. However, the impact of ice cover on bed shear stress is largely unknown. In this study, we develop a theoretical model of cross-stream momentum balance to examine the distribution of bed shear stresses in ice-covered meandering rivers. To validate the theoretical model, field surveys were carried out in a river reach of the Red River in Fargo, North Dakota. Data monitoring was completed using an Acoustic Doppler Current Profiler to obtain time-averaged velocity profiles. Our theoretical model indicates that an ice covering develops high-shear zones near both the inner and outer banks, which might exacerbate sediment transport and enhance bank erosion. Velocity measurements confirm the results of the proposed model and demonstrate a clear impact of meandering river banks on velocity profiles and secondary flow patterns under ice cover. Based on our results, we hypothesize that ice cover increases turbulent stresses near banks, which in turn lead to the enhancement of the bed shear stress. Our work provides new insights into the impact of ice cover on bed shear stress distribution, which could play an important role in driving sediment-transport processes and the long-term morphodynamic evolution of meandering rivers seasonally covered by ice.

Model and method to predict the turbulent kinetic energy induced by tidal currents, application to the wave-induced turbulence

A prediction model for the turbulent kinetic energy (TKE) induced by tidal-currents is proposed as a function of the barotropic velocity only, along with a robust method evaluating the different parameters involved using Acoustic Doppler Current Profiler (ADCP) measurements from Alderney Race. We find that the model is able to reproduce correctly the TKE profiles with coefficients of correlation on average higher than 0.90 and normalised root-mean-square errors (NRMSE) less than 14%. Different profiles are also tested for the mean velocity, no satisfactory prediction model is found but we are able to have decent estimates of the velocity shear and friction velocity. Two applications are then carried out. First the turbulent budget terms are estimated and discussed. We identify the turbulent production and dissipation of TKE as the most important mechanisms, then we discuss the validity of several theoretical results derived for isotropic turbulence for this application. A strong departure for the estimation of the turbulent dissipation is notably found and explained by the turbulent anisotropy. At last the prediction model for the TKE is used to infer the wave-induced TKE. We show the importance of removing the tidal component, waves can have a strong influence down to mid-depth.

Analysis of the riverbed backscattered signal registered by ADCPs in different bedload transport conditions – field application

Acoustic Doppler current profilers (ADCP) were deployed to investigate the backscattering (BS) signal in three navigable rivers, in different bedload transport conditions. This study aims to demonstrate that the BS strength, as an additional variable to the apparent bedload velocity, improves the characterization of the bedload transport using ADCPs. The M9 –3 MHz and the vertical beam M9 – 0.5 MHz showed decline of the BS strength as the bedload intensity increased, whereas the RDI –1.2 MHz was relatively insensitive. The correlation between the median grain size and the BS strength for the 0.5 MHz was linear, for the 3 MHz the BS strength was attenuated in the active layer, and for 1.2 MHz, it revealed a parabolic distribution. Moreover, the analyses of the ADCP measured variables, using wavelet transformations and unsupervised machine learning, highlighted the importance of the spatial and temporal variance and transient nature of the bedload transport.

Observed Structure of an Internal Tide Beam Over the Mid‐Atlantic Ridge

AbstractInternal tides are key players in ocean dynamics above mid‐ocean ridges. The generation and propagation of internal tides over the Mid‐Atlantic Ridge (MAR) have been studied through theoretical and numerical models, as well as through moored, that is, one‐dimensional, observations. Yet, observations remain sparse and often restricted to the vertical direction. Here we report on the first two‐dimensional in situ observation of an internal tide beam sampled by a shipboard acoustic Doppler current profiler through a vertical section over the MAR. The beam is generated by the interaction of the barotropic tidal current with a supercritical abyssal hill that sits in the rift valley of the MAR. A vertical mode decomposition is carried out to characterize the spatio‐temporal variability of the beam. Although the modal content of the velocity field is dominated by modes 1 to 3, higher modes display localized and not persistent bursts of energy. The use of an analytical theory for linear internal waves allows us to rationalize the observed velocity field and interpret it as the superposition of modal waves generated on the hill and propagating in the same direction. The observed beam is qualitatively reconstructed as the superposition of waves of modes 2 to 6. The velocity field was sampled seven times across the same section and displayed qualitatively different patterns, unveiling the complexity of the dynamics above the MAR. A ray tracing of modal waves shows that the refraction by mesoscale currents could explain the observed variability of the tidal beam.

The role of the low-salinity, high-nitrate layer as a novel lateral mechanism for nutrient supply into the San Jorge Gulf (Patagonian Shelf) during mid-summer

The San Jorge Gulf (Patagonian Shelf) is productive in the surface layer mainly in three regions during summer associated with small-scale coastal fronts controlled by interaction with islands to the NE, with coastal upwelling to the SW due to the wind, and with the dynamics of the Southern Tidal Front at the gulf mouth. In early February 2014, a time series of the water column characteristics were performed with a Conductivity-Temperature-Depth (CTD)/rosette package and a vessel hull-mounted acoustic Doppler current profiler (ADCP) over two complete semidiurnal cycles in a quasi-fixed location of the San Jorge Gulf mouth in order to evaluate interaction mechanisms between the surface mixed layer and interior layers that condition the distribution of properties. The pycnocline thickness defined by 24.90 kg m−3<σ0< 25.50 kg m−3 is driven by the semidiurnal tide, with a mean modulation of 32.7 m amplitude during a 2.75 m sea-level oscillation (R2 = 0.75). Patchy cores of minimum salinity (SP∼33.10) with high nitrate concentrations (9.9 mmol m−3, on average) were found at the pycnocline centre (38.0 m ± 4.5 m) during the flood as pulses of sub-surface water between consecutive high tides. Also, a high correlation (R2 = 0.88) was found between the thickness of the low-salinity layer (SP< 33.20) and the pycnocline thickness. A clear mode-1 internal tide of semidiurnal frequency was identified during the time series with some non-linear features in the first tidal cycle. As a consequence, a difference in the reversal of the internal tide was seen during both tidal cycles. The water column decreases its stratification when the low-salinity water enters the gulf due to a widening of the pycnocline thickness. At the same time, moderately high nitrate concentrations are observed in the surface mixed layer, suggesting a novel lateral mechanism to maintain the surface chlorophyll layer observed during mid-summer.

Zonal circulation in the North Atlantic ocean at 52°W from WOCE-WHP and CLIVAR sections: 1997, 2003 and 2012

The A20 line is a meridional hydrographic section located at 52°W that cuts through the western North Atlantic Subtropical Gyre (NASG). It encloses the main paths of the Atlantic Meridional Overturning Circulation (AMOC). Using data from three A20 hydrographic cruises carried out in 1997, 2003 and 2012 together with Acoustic Doppler Current Profiler data and the velocities from an inverse box model, the circulation of the western NASG is estimated. The Gulf Stream is the main poleward path of the AMOC, carrying 155.3 ± 11.1, 102.7 ± 13.5 and 181.1 ± 14.9 Sv in 1997, 2003 and 2012, respectively (1 Sv = 106 m3/s ∼ 109 kg/s). In opposite direction, the Deep Western Boundary Current crosses the section at the northern/southern boundaries with a mass transport of −21.2 ± 8.9/29.0 ± 9.1, −14.4 ± 10.8/14.2 ± 8.1 and −37.9 ± 10.2/44.5 ± 9.8 Sv in 1997, 2003 and 2012, respectively. A net heat exchange from the ocean to the atmosphere is estimated to be −0.7 ± 0.1 PW and −0.6 ± 0.1 PW in 1997 and 2012, respectively, but is negligible in 2003 (0.1 ± 0.1 PW). The freshwater flux is significantly lower in 2003 (0.3 ± 0.1 Sv) than in 1997 (0.6 ± 0.1 Sv) and 2012 (0.6 ± 0.1 Sv). Ocean numerical models such as ECCO, GLORYS and MOM are used to address the interannual variability between the three surveys, but only the GLORYS output roughly agrees with the hydrographic data. GLORYS suggests a heat transport from the ocean to the atmosphere throughout the year and a net freshwater flux supported by precipitation plus river runoff higher than evaporation in all seasons except the spring.

A first look at megabenthic community responses to seasonal change using the new Holyrood Subsea Observatory in Conception Bay, NL

Sub-Arctic seafloor communities rely on seasonal phytoplankton blooms for food, revealing a tight benthic-pelagic coupling. To maximize resource availability for offspring, organisms such as snow crabs, sea stars, and sea cucumbers synchronize their reproductive and feeding behaviours with spring blooms. Due to climate change, spring blooms are occurring earlier in sub-Arctic regions, leading to a possible mismatch between timing of resource availability and important life-history behaviours. Here, we utilize high-frequency time-series observations from the Holyrood Subsea Observatory, a new cabled seafloor observatory deployed in Conception Bay, Newfoundland. We use hourly data collected from environmental sensors (Conductivity-Temperature-Depth, Acoustic Doppler Current Profiler, fluorometer), a near-surface mooring (fluorometer), and a video camera to identify and quantify abundance and diversity of benthic megafauna, and to determine how community composition changed from pre-bloom to full bloom conditions. Data analysis revealed striking temporal changes in benthic activity, with the notable emergence of Psolus cf. phantapus sea cucumbers (up to 289.9 indiv./m2) coinciding with increased chlorophyll-a concentration and seawater temperature. At least three dense schools of forage fish, two Atlantic herring (79 and 144 indiv. frame−1) and one capelin (91 indiv. frame−1), were observed during the main bloom between May 5 and June 16. This study provides the first high-frequency in situ observations of benthic community response to seasonal food input in the region. The high temporal resolution made it possible to record the precise timing of the of Psolus cf. phantapus emergence in relation to the timing of food input to the seafloor, which will provide a baseline to monitor phenology as climate change progresses. Changes to the timing of spring blooms have implications for sub-Arctic fisheries productivity and ecosystem functioning, making continuous long-term monitoring of seafloor communities essential.

Comparison of Grain Size Trend Analysis and Multi-Index Pollution Assessment of Marine Sediments of the Gülbahçe Bay, Aegean Sea

In this study, 46 elements plus total carbonate and total organic carbon contents were measured in 48 sea bottom sediments to determine the pollution levels in the study area and their source to understand better the natural and anthropogenic processes in the study area. Also current flows and sediment transport pathways inferred using multidisciplinary methods by interrelation between grain size trend analysis, shallow seismic and acoustic doppler current profiler analysis to unravel the hydro-sedimentary processes in a micro-tidal environment. Four main factors that were affecting the study area were identified as lithogenic factor (50.6%) anthropogenic factor caused by untreated domestic waste (13.2%), anthropogenic factor caused by marine traffic/port activities (9.3%) and anthropogenic factor caused by small-scale industrial activities (with 6.9% of the total variance). The main source of metals in the study area were determined as untreated domestic waste discharges (total organic carbon and sulfur), maritime traffic/harbor activities (copper and zinc), and discharges of other wastes caused by urbanization. The main metal element that poses the most significant risk for benthic organisms was determined as nickel in the study area. All environmental indices showed non to moderate pollution existing in Gülbahçe Bay. It has been observed that most prominent feature of the distribution of elemental concentrations and assessment of pollution indices were that the pollutants carried inwards to Gülbahçe Bay from Izmir Central Bay with inflows, following the sediment transport directions.

Morphology, flow structure, and sediment transport in the Paraná and Piquiri Rivers confluence, Brazil

Confluences are places of complex interaction of flow and sediments coming from different channels. Studies at large confluences have advanced the understanding of these environments on a larger scale. This study is carried out at the confluence formed by the Paraná and Piquiri rivers in the state of Paraná - Brazil. It characterizes the morphology, flow structure and sediment dispersion for these two channels. The methodology consists of: interpoling bathymetric data; analyze the ADCP data – Acoustic Doppler Current Profiler and quantify the suspended and bottom sediments. ADCP data was processed in VMT software and generated the following information: flow direction, sediments load (bed and suspended) and also used to calculate the moment ratio (Mr), discharge ratio (Qr), flow power (Ω), and specific flow power (ꞷ) in both channels. The results reveal the variation of channel depth, and specific morphological areas for the confluence with a sediment accumulation zone, submerged lateal bar and excavation area. The flow dynamics shows an increase in velocity in the Paraná River downstream of the confluence, and a decrease in the flow velocity of the Piquiri River as it approaches the junction. The confluence has flow stagnation zone, acceleration and shear layer. The concentration of suspended sediment is higher in the Piquiri River, on the other hand the Paraná River presents thicker fractions of bed material.

Response of Atlantic salmon in flexible sea cages to waves and currents: Measurements at farm-level and modeling

The shift towards salmon farming in more exposed locations has been an industry-wide trend for the last decade. Moving fish farms to locations with high water currents and waves can improve production by providing more stable temperatures and water quality, as well as reducing the negative environmental impacts of fish farming. This study investigates how waves affect the behavior of salmon from the same group, reared at different locations within a fish farm in standard circular sea cages. Using echosounders, DO (dissolved oxygen), temperature sensors and ADCP (Acoustic Doppler Current Profiler), we show that salmon avoid waves, swim below them and maintain their normal behavior. We also show that salmon behavior is related to the exposure of the cage, in the farm layout, to waves and currents. An integrated numerical model of fish and flexible sea cages is used to simulate the fish behavior under waves and currents and it able to reproduce the observed fish distributions in general.

Integrated path planning and control through proximal policy optimization for a marine current turbine

This paper presents an integrated path planning and tracking control framework for a marine current turbine (MCT), where the MCT is treated as an energy-harvesting autonomous underwater vehicle (AUV). Considering the ocean (space of action) is continuous, the proposed framework employs two modules to address path planning and path tracking enabled by the proximal policy optimization (PPO) algorithm, which is a policy gradient deep reinforcement learning (RL) method. To enable fully autonomous operation in a stochastic oceanic environment, the proposed path planning seeks a primary objective of maximizing the harvested energy; then, the path tracking module is designed to minimize the tracking error and avoid collisions with static and dynamic obstacles. Using field-collected acoustic Doppler current profiler (ADCP) data, the performance of the proposed framework is evaluated. Comparative studies with baseline algorithms in three different scenarios of path planning, path tracking without an obstacle, and path tracking with collision avoidance verify the effectiveness of our proposed approach.

Adaptively monitoring streamflow using a stereo computer vision system

Abstract. The gauging of free surface flows in waterways provides the foundation for monitoring and managing the water resources of built and natural environments. A significant body of literature exists around the techniques and benefits of optical surface velocimetry methods to estimate flows in waterways without intrusive instruments or structures. However, to date, the operational application of these surface velocimetry methods has been limited by site configuration and inherent challenging optical variability across different natural and constructed waterway environments. This work demonstrates a significant advancement in the operationalisation of non-contact stream discharge gauging applied in the computer vision stream gauging (CVSG) system through the use of methods for remotely estimating water levels and adaptively learning discharge ratings over time. A cost-effective stereo camera-based stream gauging device (CVSG device) has been developed for streamlined site deployments and automated data collection. Evaluations between reference state-of-the-art discharge measurement technologies using DischargeLab (using surface structure image velocimetry), Hydro-STIV (using space–time image velocimetry), acoustic Doppler current profilers (ADCPs), and gauging station discharge ratings demonstrated that the optical surface velocimetry methods were capable of estimating discharge within a 5 %–15 % range between these best available measurement approaches. Furthermore, results indicated model machine learning approaches leveraging data to improve performance over a period of months at the study sites produced a marked 5 %–10 % improvement in discharge estimates, despite underlying noise in stereophotogrammetry water level or optical flow measurements. The operationalisation of optical surface velocimetry technology, such as CVSG, offers substantial advantages towards not only improving the overall density and availability of data used in stream gauging, but also providing a safe and non-contact approach for effectively measuring high-flow rates while providing an adaptive solution for gauging streams with non-stationary characteristics.