Shallow Water Depth Research Articles

Generation and Absorption of Periodic Waves Traveling on a Uniform Current in a Fully Nonlinear BEM-based Numerical Wave Tank

Accurate and efficient numerical wave generation and absorption of two-dimensional nonlinear periodic waves traveling on a steady, uniform current were carried out in a potential, fully nonlinear numerical wave tank. The solver is based on the Βoundary Εlement Μethod (ΒΕΜ) with linear singularity distributions and plane elements and on the mixed Eulerian–Lagrangian formulation of the free surface equations. Wave generation is implemented along the inflow boundary by imposing the stream function wave solution, while wave absorption at both end-boundaries is effectively treated by introducing absorbing layers. On the absorbing beach side, the outflow boundary condition is modified to ensure that the solution accurately satisfies the dispersion relation of the generated waves. The modification involves a free-parameter that depends on the mass flux through the domain and is determined through a feedback error-correction loop. The developed method provides accurate time domain wave solutions for shallow, intermediate, and deep water depths of high wave steepness (wave heights up to 80% of the maximum value) that remain stable for 150 wave periods. This also holds in case a coplanar or opposing uniform current of velocity up to 20% of the wave celerity interacts with the wave.

Tectonic, volcanic and hydrothermal features of a nascent rift graben in the southern Okinawa Trough

High-resolution geophysical mapping using an autonomous underwater vehicle (AUV) and surface vessel revealed tectonic, volcanic and hydrothermal features of a nascent rift graben in the southern Okinawa Trough. Ship-based bathymetry identified ENE–WSW trending lineaments at a water depth of 1900–2000 m that form a rift graben, the Ishigaki Rift, which is ~50 km long, ~7 km wide and has relief of ~100 m. Shipboard EM122 multibeam sonar detected acoustic bubble plumes and high-backscatter intensity on the seafloor along the rift. The AUV high-resolution bathymetry (2 m) and sidescan imagery revealed the presence of a ropey texture with high acoustic reflectivity, interpreted to be relatively young lava flows. Evidence of hydrothermal venting was observed at two previously unknown sites along the rift. Steep-sided spires up to 23 m in height and a mound discharging smoke-like acoustic plumes were identified. The AUV temperature sensor observed sharp temperature increases of up to ~0.13 °C around the plumes, even at the vehicle's altitude of ~100 m above the seafloor. The presence of relatively young lava flows and indicators of high-temperature hydrothermal venting and gas bubbles suggest the Ishigaki Rift is magmatically active. Compared with adjacent active back-arc rifts, the Ishigaki Rift has a shorter length, narrower width and lower relief, and occurs at a shallower water depth, suggesting that the rift is relatively young and immature. Considering that the Ishigaki Rift is located near the arc volcanic front and that other mature rifts are typically located farther from the front, it is suggested that a new axial rift system is evolving within the Okinawa Trough and that back-arc rifting processes may be gradually migrating arcward in the trough during the Quaternary.

Shallow Water Bathymetry Based on Inherent Optical Properties Using High Spatial Resolution Multispectral Imagery

Bathymetric surveys are of great importance for submarine topography mapping and coastal construction projects. They are also of great significance for terrain surveys of islands and coastal zones, maritime navigation and marine management planning. Traditional ship-borne water depth measurement methods are costly and time-consuming, therefore, in recent years, passive optical remote sensing technology has become an important means for shallow water depth measurements. In addition, multispectral water depth optical remote sensing has wide application values. Considering the relationship between water depth and the inherent optical characteristics of water column, an inherent optical parameters linear model (IOPLM) is developed to estimate shallow water bathymetry from high spatial resolution multispectral images. Experiments were carried out in the shallow waters (≤20 m) around Dongdao Island in China’s Paracel Islands and Saipan Island in the Northern Mariana Islands. Different accuracy evaluation indexes were used to verify the model. The comparisons with the traditional log-linear model and the Stumpf model show that in terms of overall accuracy and accuracy in different water depths, the IOPLM has slightly better results and stronger retrieval capabilities than the other models. The mean absolute error (MAE) of Dongdao Island and Saipan Island reached 1.17 m and 1.92 m, and the root mean square error (RMSE) was 1.49 m and 2.4 m, respectively.

Numerical investigation on the dynamic responses of three integrated concepts of offshore wind and wave energy converter

To achieve a better utilization of ocean space and energy, three integrated concepts of column-type wind turbine and heave-type wave energy converter (WEC) have been proposed for deep, intermediate and shallow water depth conditions, respectively. The WECs are installed on the wind turbine columns, then wave energy can be absorbed by power-take off (PTO) system through the relative heave motions between wind turbine column and the WEC. The spar-type floating wind turbines with long and short floaters are considered for deep and intermediate water depth conditions whereas a fixed-type wind turbine is considered for the shallow water depth condition. On the other hand, the WECs are torus-shaped heave-type devices, with dimensions and configurations the same for the three concepts. Numerical models are established for all the three concepts. The combined systems are subjected to various wind and wave conditions. The dynamic response analysis is carried out, and the responses including motions, forces and power, are compared among them. The results show that significantly different dynamic responses of the three concepts under environmental actions are observed.

Lack of methane hotspot in the upstream dam: Case study in a tributary of the Three Gorges Reservoir, China

River damming has seen a growing trend in demand worldwide and the impounded reaches are considered hotspots of greenhouse gas emissions. However, it remains unclear how the spatial distribution of C-gas in sediments and methane (CH4) emissions of dammed tributary changes under different operation periods of the Three Gorges reservoir (TGR). We measured CH4 and carbon dioxide (CO2) concentrations in sediment and CH4 emissions from a dammed river of the TGR, and evaluated the effect of damming on the spatial variability of carbon in the sediment and on CH4 flux. It was found that damming led to a distinct spatial pattern of total organic carbon (TOC) in the sediment, which resulted in higher CH4 and CO2 in upstream sediment compared to the downstream. During the TGR impounding period, the upstream CH4 diffusive flux (0.253–0.427 mg m−2 h−1) across the water-air interface was higher than in the downstream (0.093 mg m−2 h−1), which was consistent with the spatial variation of CH4 in the sediments. However, the CH4 emission was predominantly by ebullition and the flux in the downstream (169.173 mg m−2 h−1) was significantly higher than upstream (12.23–123.05 mg m−2 h−1) in the discharging period. This can be attributed to a sharp increase in TOC in downstream sediment due to riparian zone soil erosion on both banks, which was caused by periodic large fluctuation in the water level, and a shallow water depth in the downstream. This study adds to our understanding of effects of the TGR's operation on CH4 emissions from a dammed tributary and suggests that the water level fluctuation of tributaries which has direct influence on ebullition and methane oxidation caused by manipulation of the TGR should not be overlooked.

Enhanced Vertical Mixing in Coastal Upwelling Systems Driven by Diurnal‐Inertial Resonance: Numerical Experiments

AbstractThe land‐sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30°N/S. 1‐D vertical numerical experiments were undertaken to study the key drivers of enhanced diapycnal mixing in coastal upwelling systems driven by diurnal‐inertial resonance near the critical latitude. The effect of the land boundary was implicitly included in the model through the “Craig approximation” for first‐order cross‐shore surface elevation gradient response. The model indicates that for shallow water depths (<∼100 m), bottom shear stresses must be accounted for in the formulation of the “Craig approximation,” as they serve to enhance the cross‐shore surface elevation gradient response, while reducing shear and mixing at the thermocline. The model was able to predict the observed temperature and current features during an upwelling/mixing event in 60 m water depth in St Helena Bay (∼32.5°S, southern Benguela), indicating that the locally forced response to the land‐sea breeze is a key driver of diapycnal mixing over the event. Alignment of the subinertial Ekman transport with the surface inertial oscillation produces shear spikes at the diurnal‐inertial frequency; however their impact on mixing is secondary when compared with the diurnal‐inertial resonance phenomenon. The amplitude of the diurnal anticyclonic rotary component of the wind stress represents a good diagnostic for the prediction of diapycnal mixing due to diurnal‐inertial resonance. The local enhancement of this quantity over St Helena Bay provides strong evidence for the importance of the land‐sea breeze in contributing to primary production in this region through nutrient enrichment of the surface layer.

GEOGRAPHICALLY WEIGHTED REGRESSION APPROACH FOR SHALLOW WATER DEPTH ESTIMATION USING MULTISPECTRAL SATELLITE IMAGERIES

Abstract. Shallow water depth is essential for coastal planning, monitoring, and research. Bathymetry data is mostly produced from hydrographic survey using echosounder. The generic result from those measurements is discrete values while the desired output is a continuous depth model. To fill the gaps in the sounding data, we use Satellite Derived Bathymetry (SDB) approach with Geographically Weighted Regression (GWR). This study aims to investigate the feasibility of GWR to model bathymetry of shallow water in the eastern part of Indonesia. We explore the correlation between the number of training data and the predicted result. Two different satellites images are used, namely: Sentinel-2A and Landsat 8 OLI/TIRS with 10 and 30 m resolutions respectively. For the experiment, in-situ data are set into training and validation in three different ratios. The model is developed using adaptive GWR approach in which the parameter of regression would adapt the local data set within different kernel sizes. Finally, we compute RMSE (Root Mean Square Error), R2, and TVU (Total Vertical Uncertainty) to assess the quality of our model. In general, Sentinel-2A produces more detailed information due to higher resolution than Landsat 8 OLI/TIRS. Sentinel-2A also obtains more accurate results based on RMSE values. The percentage number of the estimated depth that fulfils TVU requirements is up to 83%. These assessment quality results give us an insight that the SDB approach using GWR is promising. Thus, the GWR method may be able to provide an estimate of bathymetry for many coastal areas in Indonesia.

The feasibility of assessing swell-based bathymetry using SAR imagery from orbiting satellites

Remote sensing instruments, especially synthetic aperture radar (SAR), have become valuable tools for monitoring coastal bathymetry in both space and time. In this study, we investigate the viability of using data from spaceborne SAR satellites to detect shallow water depths from swell patterns. Using data from four Sentinel-1A SAR images, we employed numerical simulations to quantify the sensitivity of the bathymetry results to different initial input parameters such as wavelength, swell period, and initial water depth. Our sensitivity experiments indicate that the swell period is most sensitive to the water depth, while the initial water depth has the lowest impact on the shallow water depth estimation. Once we quantified the sensitivity of the estimated water depth to these parameters, we calculated the minimum and maximum detectable shallow water depth ranges of six SAR orbiting satellites (L-band: ALOS-2, C-band: GF-3, RADARSAT-2 and Sentinel-1, X-band: TerraSAR-X and COSMO-SkyMed). Because of its single-polarization SAR data, the TerraSAR-X satellite is ultimately the best source of SAR data for swell-based bathymetry analyses. With an incidence angle of 20° and significant wave height of 0.6 m, the TerraSAR-X satellite has the largest theoretical depth detection range (with a minimum detectable depth of less than 2 m, and a maximum detectable depth of more than 200 m) for swell waves with a period of 15 s. The results of this study demonstrate that for low to moderate wave height, satellites with lower slant range to platform velocity ratios (RRV) can be successfully applied to the task of large-scale bathymetric mapping at shallow depths where there are weak tidal currents or where no recent or accurate ground truth data is available. Based on these results, we can make recommendations that will enable future users to get reliable, robust bathymetry information from their SAR data sets.

Fully nonlinear investigations on performance of an OWSC (oscillating wave surge converter) in 3D (three-dimensional) open water

The hydrodynamic behavior of a hinged Oscillating Wave Surge Converter (OWSC) device in open water, including motion response, extracted power and capture efficiency, is numerically investigated through a developed three-dimensional (3D) fully nonlinear higher-order boundary element method (HOBEM) model. In this time-domain mode, an image Green function is adopted in the whole circular domain with radiation condition at far field to avoid re-reflection from the lateral walls and resonance of the transverse standing waves which both occur in 3D numerical wave tank. The calculated surface elevation and the structural response are compared well with the existing measured and numerical results. It can be proved from present results that wave nonlinearity would change the flap’s natural frequency and break the limit of highest possible efficiency 50%. An OWSC with thinner thickness and wider width becomes more efficient for extending the applicable extent of wave frequency for performance improvement. In addition, when the OWSC device is installed at the shallow water depth, the energy extraction can be magnified due to shoaling effect. The time series further reveal that the larger wave amplitude leads to the motion response dominated simultaneously by difference frequency, fundamental frequency and higher-order frequencies.

Lateral bearing behaviour of vibro‐ and impact‐driven large‐diameter piles in dense sand

AbstractMonopiles are the preferred foundation solution for offshore wind turbines in sandy soils below shallow and moderate water depths. The piles are commonly installed using impact driving. A severe disadvantage of this installation method is that high noise levels occur in the water, which are a risk to animals living in the sea. Approval authorities are known to impose statutory requirements to mitigate this risk, placing a financial burden on installation. Vibratory driving is an alternative installation method that reduces noise emission levels significantly. However, the effect of vibro‐driving on the bearing behaviour of piles under lateral loading is largely unknown. Full‐scale load tests were conducted in predominantly dense, non‐cohesive, saturated soil to investigate the differences between impact‐driven piles and vibrated piles regarding their lateral bedding behaviour. CPTs and pile head load‐displacement curves were recorded and evaluated. In general, it was determined that the bearing behaviour of vibro‐driven piles is heavily dependent on the parameters of the installation process. For the installation parameters used in the test campaign, two vibro‐driven piles showed a weaker bedding reaction in comparison to the impact‐driven piles, although one vibrated pile installed with unintentionally different parameters showed an only slightly weaker behaviour under primary loading and even increased unloading and reloading stiffness. Furthermore, it was observed that an indication regarding the differences in the bedding resistance can be obtained via CPT measurements before and after installation, since the installation procedure considerably affects the relative density of the soil around the pile.

Satellite-derived bathymetry using the ICESat-2 lidar and Sentinel-2 imagery datasets

Accurate bathymetric data is essential for marine, coastal ecosystems, and related studies. In the past decades, a lot of studies were investigated to obtain bathymetric data in shallow waters using satellite remotely sensed data. Satellite multispectral imagery has been widely used to estimate shallow water depths based on empirical models and physics-based models. However, the in-situ water depth information is essential (as the priori) to use the empirical model in a specific area, which limits its application, especially for remote reefs. In this study, the bathymetric maps in shallow waters were produced based on empirical models with only satellite remotely sensed data (i.e., the new ICESat-2 bathymetric points and Sentinel-2 multispectral imagery). The bathymetric points from the spaceborne ICESat-2 lidar were used in place of the in-situ auxiliary bathymetric points to train the classical empirical models (i.e., the linear model and the band ratio model). The bathymetric points were firstly extracted from noisy ICESat-2 raw data photons by an improved point cloud processing algorithm, and then were corrected for bathymetric errors (which were caused by the refraction effect in the water column, the refraction effect on the water surface, and the fluctuation effect on the water surface). With the trained empirical models and Sentinel-2 multispectral images, the bathymetric maps were produced for Yongle Atoll, in the South China Sea and the lagoon near Acklins Island and Long Cay, to the southeast of Bahama with four-date Sentinel-2 images. The bathymetry performance (including the accuracy and consistency of multi-date data) was evaluated and compared with the in-situ measurements. The results indicate that the bathymetric accuracy is well, and the RMSE is lower or close to 10% of the maximum depth for the two models with four-date images in two study areas. The consistency of multi-date data is well with the mean R2 of 0.97. The main novelties of this study are that the accuracy bathymetric points can be obtained from the ICESat-2 raw data using the proposed signal processing and error correction method, and using the ICESat-2 bathymetric points, the satellite multispectral imagery based on empirical models is no longer limited by local priori measurements, which were essential in previous studies. Hence, In the future, with the help of free and open-access satellite data (i.e., ICESat-2 data and Sentinel-2 imagery), this approach can be extended to a larger scale to obtain bathymetric maps in the shallow water of coastal areas, surroundings of islands and reefs, and inland waters.

Misinterpretation of velocity pull‐ups caused by high‐velocity infill of tunnel valleys in the southern Baltic Sea

ABSTRACTIn this study, we undertake a renewed investigation of up‐bent reflections seen in seismic time sections from the Baltic Sea, Bay of Kiel. These warped reflections stretch over the entire vertical extent of the sections, from Permian to Quaternary strata, and underlie tunnel valleys. Previous studies interpreted these structures as anticlines, explaining them together with adjacent faults and disrupted strata as the consequence of ice‐load‐induced salt tectonics. This conclusion would have influenced theories on how tunnel valleys formed. However, well data from tunnel valleys in other regions supported the interpretation of the up‐bent reflections as imaging artefacts (pull‐ups). A newly acquired long‐offset, multichannel seismic data set images all strata from Base Zechstein up to the seafloor. Owing to the length of the streamer and a shallow water depth, the data display significant moveout and refracted waves, allowing the application of different quantitative methods to investigate velocities. By generating partial‐offset sections, we reveal an offset dependence in the imaging of the up‐bent structures caused by a local, near‐surface high‐velocity zone. This also explains a smoothing of the up‐bending with depth in the seismic image. A velocity model gained by a travel‐time tomography shows positive velocity anomalies in the upper strata correlating with tunnel valleys resolved in the reflection images. A pre‐stack depth migration performed with a velocity model containing a high‐velocity zone results in a seismic image almost free of the observed up‐bent reflections. High‐frequency reflection seismic data confirm this result as it shows a detailed image of a tunnel valley with a phase‐reversed bottom reflection caused by the velocity inversion at the base of the high‐velocity valley fill deposits. Hence, there is consistent evidence that all up‐bent reflections in the Bay of Kiel are imaging artefacts (pull‐ups) that formed beneath tunnel valleys. A salt tectonic control on tunnel valley evolution is, consequently, not likely. This study is the first purely seismic data‐driven study that proves high‐velocity valley fill deposits. Our findings imply that extra care must be taken when interpreting reflection undulations as tectonic features where glacial deposits are present.

Development and analysis of a numerical model for a two-oscillating-body wave energy converter in shallow water

The Energy Double System (EDS) is a two-degree-of-freedom (2DOF), nearshore, point absorber wave energy converter (WEC). It is composed of a heaving float and a surging paddle, which are interconnected and each one has its own Power Take-Off (PTO). In this work, a numerical model of the EDS was developed on the basis of the existent laboratory model, which had already been the object of several studies at the Politecnico di Milano. Firstly, a general mechanical scheme of the EDS was developed, which is simplified with respect to the laboratory model. This is a mass-spring-damper 2DOF system, described by a couple of equations linearized around the equilibrium position. Once that the mechanical equivalence with the laboratory model was established, the simplified EDS geometry was set in a Computational Fluid Dynamics (CFD) model, together with the experimental boundary conditions: the EDS is placed in shallow water depth along a sloping beach, undergoing regular waves. Numerical results fairly agree with the experimental ones, although slightly overestimate the energy absorption of the float (+20%) and the paddle (+10%). Finally, new cases were simulated: different values of PTO damping and random waves were tested.

Numerical investigation of local scour around USAF with different hydraulic conditions under currents and waves

An umbrella suction anchor foundation (USAF) is a new foundation type used for offshore wind turbines. In this paper, a three-dimensional numerical model was established in FLOW-3D to study the local scour characteristics under the coupled effects of waves and currents. RANS equations, closed with an RNG k-ε turbulence model, were established for simulating the flow field around pile groups. The simulation results were compared with a 1:40 model test and showed good agreement. Then, the effects of different hydraulic conditions and dimensionless parameters such as water depth, wave height, velocity, Keulegan-Carpenter number (KC) and the ratio of relative wave-current velocity (Ucw) on the maximum scour depth were considered in detail, and compared with the results of other scholars. This study found that the local scour shape of a USAF is different from that of a monopile foundation. Its maximum scour depth appears downstream behind the USAF, and the anchoring structure effectively blocks the scour in front of the USAF. The shallower water depth, the higher wave height and the faster flow velocity result in a more intense scour. When KC < 7 and Ucw <0.7, the maximum scour depth of the USAF increases with increasing KC number and Ucw.

Field observations of the lethality characteristics of endangered and endemic fish under the stress of total dissolved gas supersaturation

AbstractTotal dissolved gas supersaturation (TDGS) caused by high dam discharge may threaten the survival of fish downstream. This study investigated the TDGS of Dadu River in the first 3 years (2016–2018) after the operation of Dagangshan hydropower station. The effect of TDGS on endemic fish was also evaluated for the first time in this study. Schizothoracin prenanti, Schizothorax davidi and Leptobotia elongata, which are endangered and endemic species in the Dadu River, were selected to evaluate the adverse effects of supersaturation on fish. We found that the supersaturation level varied from 115% to 127% in 2016, from 111% to 121% in 2017, and from 103% to 112% in 2018. The average water levels in these 3 years were 2.99, 2.34 and 1.14 m, respectively. The mortality of fish was positively correlated with TDGS and negatively correlated with water depth. The mortality of juvenile fish was highest in 2016, and increased TDGS had a greater contribution to fish mortality than the other factors. The highest mortality of adults occurred in 2017, and inadequate water depth was an important factor that caused fish mortality. The lowest mortality of both adults and juveniles occurred in 2018, and gas bubble disease in fish was almost never found. Even at shallow water depths, low TDGS (103%–112%) did not cause fish mortality.

The effect of a parallel free surface upon a submerged shallow synthetic jet

The interaction of a submerged shallow synthetic jet with a parallel free surface has gathered substantial interest, owing to its relevance to the operation of marine vehicles viz. ships that move close to the water surface. However, despite exhaustive research on the perturbation on a free surface, very few studies have experimentally investigated the effect of unconfined water surface height on the evolution and propagation of a submerged synthetic jet. This study experimentally investigates a synthetic jet submerged in a quiescent flow at shallow depths ejecting parallel to the free surface, through qualitative analysis and quantitative measurements. The qualitative study includes the visualization of the flow using plane laser induced fluorescence (PLIF) technique, whereas the velocity measurements are carried out by a five-beam laser Doppler velocimetry (LDV) probe. The primary objective of these analysis and measurements is to gain a physical insight into the characteristics of vortex ring in a synthetic jet ejected from a fixed orifice at different water depths and at varying Reynolds number. Our studies indicate that the behavior of the vortex rings drastically changes as the depth of the jet crosses a certain threshold. Although no significant change in the path of synthetic jet is observed beyond a threshold depth in our experiments, the jet trajectory shows an interesting dependence on the Reynolds number based on circulation for shallow water depths. It has been found that at the shallow depths, the vortex ring drifts upwards and interacts with the free surface at lower Reynolds number, whereas for larger Reynolds number, the vortex ring rebounds near the free surface and moves downward. Based on our observations, it can be concluded that the phenomenon of upward/downward flection of vortex rings depends both upon its circulation and ejection depth.

Fine-scale velocity distribution revealed by datuming of very-high-resolution deep-towed seismic data: Example of a shallow-gas system from the western Black Sea

Very-high-resolution (VHR) marine seismic reflection helps to identify and characterize potential geohazards occurring in the upper part (300 m) of the subseafloor. Although the lateral and vertical resolutions achieved in shallow water depths ([Formula: see text]) using conventional surface-towed technology are adequate, these resolutions quickly deteriorate at greater water depths. The SYstème SIsmique de Fond (SYSIF), a multichannel deep-towed seismic system, has been designed to acquire VHR data (frequency bandwidth [220–1050 Hz] and vertical resolution of 0.6 m) at great water depths. However, the processing of deep-towed multichannel data is challenging because the source and the receivers are constantly moving with respect to each other according to the towing configuration. We have introduced a new workflow that allows the application of conventional processing algorithms to extended deep-towed seismic data sets. First, a relocation of the source and receivers is necessary to obtain a sufficiently accurate acquisition geometry. Variations along the profile in the depth of the deep-towed system result in a complex geometry in which the source and receiver depth vary separately and do not share the same acquisition datum. We have designed a dedicated datuming algorithm to shift the source and receivers to the same datum. Thus, the procedure allows the application of conventional processing algorithms to perform velocity analysis and depth imaging and therefore allows access to the full potential of the seismic system. We have successfully applied this methodology to deep-towed multichannel data from the western Black Sea. In particular, the derived velocity model highlights shallow gas charged anticline structures with unrivaled resolution.

Interactions between water depth, velocity and body size on fish swimming performance: Implications for culvert hydrodynamics

Understanding how fish traverse man-made barriers (e.g. road-crossings and culverts) ensures that engineering and design guidelines achieve positive outcomes for fish communities. Water velocity, depth and fish body size are interrelated factors that influence fish passage through culverts. Velocity barriers have been a major focus of culvert remediation efforts to improve fish passage, however wide culvert designs that aim to limit high water velocities, often create shallow depths in the culvert barrel that can potentially impede fish passage. Here, we quantified how water velocity, depth and body size interact to affect fish swimming performance and their ability to traverse a 12 m culvert-scale swimming channel. Juveniles and sub-adults of three large-bodied native Australian fish species, silver perch (Bidyanus bidyanus), Murray cod (Maccullochella peelii) and eel-tail catfish (Tandanus tandanus), were chosen to represent a range of body shapes, swimming styles and capabilities. Each species was swum in nine treatments, consisting of three velocities at three water depths, with their time to fatigue and traverse success rates over 8 m of flume length quantified. We found that B. bidyanus had an exceptional probability of traverse success, with larger individuals traversing faster than smaller sized fish, but they were physically hindered by shallow water depths. The interaction between velocity and depth was non-linear and highly affected the swimming performance and traverse success of M. peelii and T. tandanus, particularly for fish >250 mm and < 100 mm. Our results demonstrate the importance of considering size class and species-specific swimming capabilities in culvert design criteria.

Influence of auxiliary cylinders on the dynamics of overland flow upstream of the main cylinder based on particle image velocimetry

The position of auxiliary cylinders in flow experiments noticeably affects soil erosion and pollutant transportation processes by altering the dynamic flow field in front of the main cylinder. However, few studies have been conducted for overland flow due to the shallow flow depth and limited observation technology. In this study, we conducted fixed-bed flume experiments and developed a high-resolution and high-frequency particle image velocimetry system to investigate the two-dimensional dynamic field of overflow using a symmetrical surface (i.e., the vertical plane passing through the axis of the main cylinder in the flow direction) upstream of the main cylinder as the observation area. Two auxiliary cylinders in each position were placed upstream, parallel, and downstream (i.e., pre-column condition, parallel condition, and post-column condition, respectively). Results showed that: For a given flow discharge, the ranking of the cylinder configurations in terms of the stability of the hydrodynamic conditions (velocity, turbulent energy, shear force, and Reynolds stress) was pre-column condition < parallel condition < post-column condition. The number of horseshoe vortices and the rotation intensity of the main horseshoe vortex were similar for the three configurations. The position of the main horseshoe vortex was closest to the main cylinder in the pre-column condition, causing substantial soil erosion around the main cylinder. For different flow rates, the water depth and turbulent intensity showed monotonic increasing trends as the flow discharge increased, whereas the shear force and Reynolds stress exhibited a single peak. As the Reynolds number of the cylinder increased, the flow separation point moved upstream, and the rotation intensity of the main horseshoe vortex was negatively correlated with the water depth. Therefore, a shallower water depth corresponded to significantly greater erosion damage by the horseshoe vortex. Overall, the configuration of the auxiliary cylinders downstream of the main cylinder resulted in the optimum water flow control. The findings of this study provide theoretical support for designing vegetation management strategies that minimize soil erosion and protect water resources.

Assessment of Wind and Vegetation Interactions in Constructed Wetlands

Meteorological data from vegetated and un-vegetated wetlands during wet and dry seasons, were collected and analyzed to evaluate the role of wind and vegetation on wetlands’ hydrology. Wind speed diminished by as much as 40%, accompanied by a measurable change in wind directions in the vegetated compared to the open water site. Wind speed and direction means were significantly different (p &lt; 0.001 and &lt;0.01), for vegetated and non-vegetated wetland, respectively. Cattails (Typha sp.) and open water estimates of wind drag coefficients using the log wind profile, were 0.016 and 0.009 for dry season, and 0.012 and 0.005 for wet season, respectively. Wind set up near the wetland outlet was more pronounced at shallow water depth (&lt;20 cm). Measured velocity profile during inflow discharge event with a wind speed of 0.53 ms−1, showed two-layer flows; wind-generated surface water flow opposite to a sub-surface inflow. This opposing surface flow increases hydraulic residence time and improve nutrient uptake. Conversely, wind-generated flows aligned with inflow discharges, accelerates water flow towards the outlet, reduce the duration of water-biotic interactions, and decrease nutrient uptake.