Shallow Water Depth Research Articles

Numerical modelling of a soil structure interaction for a torpedo base conductor in a petroleum well under an extreme lateral load

This work aims to compare the performance, regarding the soil structure interaction, of a torpedo base conductor and a jetted conductor, considering a drilling rig drift-off scenario. This can be considered an extreme load scenario and the results will be shown for lateral loads coming from the interaction between the wellhead and the drilling rig, drilling riser and BOP.A complete 3D CAD model of the Torpedo Base Conductor was created and the soil was also modelled with 3D elements. Based on previous references, the selected 3D soil element was the Drucker-Prager constitutive model (Costa, 2008, Aysen, 2016 and Sanomia, 2016). Notably, the Drucker-Prager model accounts for non-homogeneous soil, meaning that the material properties vary with depth according to its undrained shear strength profile.The final results show the behavior of soil under lateral loads for both the torpedo base and the jetted conductor, as well as the structural response. The final conclusion is that the torpedo base has a better performance under lateral loads than the jetted conductor and can be considered a good well foundation solution to mitigate problems associated with interventions with dynamic position drilling rigs in shallower water depth.

VALIDATION OF A NONLINEAR WAVE DECOMPOSITION METHOD INCLUDING SHOALING FOR IRREGULAR WAVES

It is important to decompose the signals when performing physical model experiments. In this paper, a nonlinear decomposition method is extended with the effects of a sloping bed. The approach is validated based on synthetic signals and numerical simulations. Verification with linear synthetic signals shows that the effect on the wave height is limited for intermediate water depth, but increases for shallow water depth with an error of up to 4%. Moreover, when not accounted for a sloping bed the wave height at the first wave gauge is overestimated in shallow water and underestimated in deep water. The results from the numerical simulations show that a shoaling coefficient for the bound waves based on the water depth ratio with a power 1 is reasonably accurate for the sub-harmonics but not valid for the higher harmonics. In addition, it is recommended to verify this assumption for a large range of test conditions. When applying both the method without and with the effects of a sloping bed on physical model experiments, the average differences are 1 % with a maximum up to 4 % in terms of the wave height.

Relationships between C/N metabolism and rice growth related indicators under alternating drought and flooding stress

The increasing frequency of drought and flooding events due to climate change exposes rice to intensified alternating drought and flooding stress during different growth stages. To elucidate the impacts of alternating drought and flooding stress on rice growth and carbon (C) and nitrogen (N) metabolism, five irrigation regimes were established: alternating cycle of light drought-flooding-light drought during the tillering stage (T-LD), heavy drought-flooding-heavy drought during the tillering stage (T-HD), light drought-flooding-light drought during the jointing stage (J-LD), heavy drought-flooding-heavy drought during the jointing stage (J-HD), and frequent irrigation with shallow water depth (0–5 cm) for growth stages except for the maturation stage (CK). The results indicated that the tiller numbers, K+ concentrations in leaves, and above-ground biomass subjected to T-HD and T-LD treatments were significantly lower than in CK, J-HD and J-LD. Compared to CK, T-LD enhanced chlorophyll content and nitrate reductase activity (NRA) in rice leaves, leading to elevated photosynthetic rates (Pn) and improved δ13C values. The δ15N values under the CK, T-HD, and T-LD treatments were significantly greater than those under the J-HD and J-LD treatments (p<0.05). Additionally, NRA showed a significant positive correlation with leaf N concentration during the jointing stage. Path analysis indicates that δ13C, leaf water content, tiller number, leaf area, K⁺ concentration, and N concentration were directly related to above-ground biomass, whereas photosynthetic parameters indirectly affected biomass through N-metabolism related indicators. This result offers a theoretical support for the scheduling of irrigation and drainage practices in the field.

The Enigmatic Pockmarks of the Sandy Southeastern North Sea

AbstractNatural seafloor depressions, known as pockmarks, are common subaqueous geomorphological features found from the deep ocean trenches to shallow lakes. Pockmarks can form rapidly or over millions of years and have a large variety of shapes created and maintained by a large variety of mechanisms. In the sandy sediments of the southeastern North Sea, abundant shallow pockmarks are ubiquitous and occur at shallow water depths (&lt;50 m). Their formation has previously been linked to methane seepage from the seafloor. Here, we characterize over 50,000 pockmarks based on their morphology, geochemical signature, and the subsurface pre‐conditions using a new integrated geoscientific data set, combining geophysical and sedimentological data with geochemical porewater and oceanographic analysis. We test whether the methane seepage is indeed responsible for pockmark formation. However, our data suggest that neither the seepage of light hydrocarbons nor groundwater is driving pockmark formation. Because of this lack of evidence for fluid seepage, we favor the previously suggested biotic formation but also discuss positive feedback mechanisms in ocean bottom currents as a formation process. Based on a comparison of pockmarks to the central and southeastern North Sea, we find that local lithology significantly affects pockmark morphology. Muddy lithologies favor the formation of larger, long‐lived structures, while sandy lithologies lead to short‐lived, small‐scale structures that are large in area but with shallow incision depth. We conclude that pockmarks in sandy environments might have been overlooked globally due to their shallow incision depth and recommend reevaluating the role of hydrocarbon ebullition in pockmark formation.

An adaptive internal mass source wave-maker for short wave generation

The mass source wave-maker is commonly employed for generating water waves in numerical simulations, during which a correct amount of mass is introduced or subtracted from the internal flow region to produce target waves. The method has proven to be effective in producing waves in shallow and intermediate water depths, while its efficiency is declined for short wave generation. The main reason for this efficiency declination is that the internal mass source in deeper water region is not effective to generate short waves with their motions primarily on water surface. In order to overcome this shortcoming, many of the previous numerical treatments have introduced various enhancement factors into the source functions, which are empirically obtained and also violate the law of mass conservation. In this study, we develop a new adaptive internal wave-maker model that can be self-adjusted to suit different wave conditions. The line source starts from the bottom and extends to the computational cell right beneath free surface at each time step. The depth dependent weighting coefficient is introduced to the source function based on the linear wave theory for each wave component. No empirical coefficients are necessary, and the mass conservation is strictly and explicitly enforced. In principle, the method can be applied to all types of linear waves in the entire range of kh. The numerical experiments show that the present method can produce very good results for linear waves with kh up to 16.11, adequate for most of wave conditions in coastal engineering. For generation of fifth-order Stokes waves, the method can be extended straightforwardly for each of five wave components. For irregular waves composed of many linear wave components, different weighting coefficients can be readily calculated for each of them, respectively. As a result, the new model can generate irregular waves with overall better performance of reproducing wave spectrum, whose high-frequency part has been underestimated by previous methods. The numerical experiments also show that the new model can produce better results for focused waves where many linear waves of different frequencies start from the same point with specific phase angles, due to its capability of generating shorter wave components.

Possible Indication of the Impact of the Storegga Slide Tsunami on the German North Sea Coast around 8150 cal BP

The Storegga slide tsunami (SST) at ca. 8100 ± 100–250 cal BP is known to be the largest tsunami that affected the North Sea during the entire Holocene. Geological traces of tsunami landfall were discovered along the coasts of Norway, Scotland, England, Denmark, the Faroes and Shetland Islands. So far, the German North Sea coast has been considered as being well protected due to the wide continental shelf and predominant shallow water depths, both assumed to dissipate tsunami wave energy significantly, thus hindering SST propagation dynamics. The objective of our research was to clarify if the SST reached the German Bight and if corresponding sediment markers can be found. Our research was based on the in-depth investigation of a 5 m long section of the research core Garding-2 from Eiderstedt Peninsula near Garding in North Frisia known from a previous study. For this, we newly recovered sediment core Garding-2A at exactly the same coring location as core Garding-2. Additionally, high-resolution Direct Push sensing data were collected to gain undisturbed stratigraphic information. Multi-proxy analyses of sediment material (grain size, geochemical, geochronological and microfaunal data) were carried out to reconstruct palaeoenvironmental and palaeogeographical conditions. We identified a high-energy event layer with sedimentological (e.g., erosional unconformity, rip-up clasts, fining-upward), microfaunal (e.g., strongly mixed foraminiferal assemblage) and other features typical of tsunami influence and identical in age with the SST, dated to ca. 8.15 ka cal BP. The event layer was deposited at or maximum ca. 1–1.5 m below the local contemporary relative sea level and several tens of kilometers inland from the coastline within the palaeo-Eider estuarine system beyond the reach of storm surges. Tsunami facies and geochronological data correspond well with SST signatures identified on the nearby island of Rømø. SST candidate deposits identified at Garding represent the southernmost indications of this event in the southeastern North Sea. They give evidence, for the first time, of high-energy tsunami landfall along the German North Sea coast and tsunami impact related to the Storegga slide. SST deposits seem to have been subsequently reworked and redeposited over centuries until the site was affected by the Holocene marine transgression around 7 ka cal BP (7.3–6.5 ka cal BP). Moreover, the transgression initiated energetically and ecologically stable shallow marine conditions within an Eider-related tidal channel, lasting several millennia. It is suggested that the SST was not essentially weakened across the shallow continental shelf of the North Sea, but rather caused tsunami run-up of several meters (Rømø Island) or largely intruded estuarine systems tens of kilometers inland (North Frisia, this study). We, therefore, assume that the southern North Sea coast was generally affected by the SST but sedimentary signals have not yet been identified or have been misinterpreted. Our findings suggest that the German North Sea coast is not protected from tsunami events, as assumed so far, but that tsunamis are also a phenomenon in this region.

Flow Evolution and Vertical Accelerations in Wave‐Swash Interactions

AbstractWe report on a laboratory study of wave‐swash interactions, which occur in the very nearshore environment of a beach when the shallow swash flow of a breaking wave interacts with a subsequent wave. Wave‐swash interactions have been observed in the field, hypothesized to be important for nearshore transport processes, and categorized into different qualitative types, but quantitative descriptions of their dynamics have remained elusive. Using consecutive solitary waves with different wave heights and separations, we generate a wide variety of wave‐swash interactions with large flow velocities and vertical accelerations. We find that wave‐swash interactions can be quantitatively characterized in terms of two dimensionless parameters. The first of them corresponds to the wave height ratio for consecutive waves, and the second is a dimensionless measure of the time separation between consecutive wave crests. Using measurements of bed pressure and free‐surface displacement, we estimate the total vertical accelerations and focus on the peak upward‐directed acceleration. We find that wave‐swash interactions can generate vertical accelerations that can easily exceed gravity, despite occurring in very shallow water depths. The large vertical accelerations are upward‐directed and are quickly followed by onshore‐directed horizontal velocities. Together, our findings suggest that wave‐swash interactions are capable of inducing large material suspension events of sediment or solutes in sediment pores, and transporting them onshore. While the data are from a single location making it difficult to generalize the findings across the swash zone, the results clearly demonstrate the importance of large vertical accelerations in wave‐swash interactions.

Ecosystem links: Anthropogenic activities, environmental variables, and macrophytes structure snail preferences in man-made waterbodies

Freshwater snails act as obligate intermediate hosts for trematode parasites that cause trematodiases threatening public and veterinary health, and biodiversity conservation. While interest in snail control for trematodiases has re-emerged, their ecology remains poorly understood. We examined the relationship between ecosystem indicators – such as environmental variables, macroinvertebrates, macrophytes, and land use – and their correlation with snail abundance, diversity, and infection prevalence in 19 man-made ponds in eastern Zimbabwe. In total, 926 freshwater snails from 10 species were collected, with 547 individuals belonging to five schistosome-competent species: Bulinus tropicus, Bulinus truncatus, Bulinus globosus, Bulinus forskalii, and Biomphalaria pfeifferi. The remaining 379 snails comprised Radix natalensis, Gyraulus sp., and the exotic invasive species Melanoides tuberculata, Pseudosuccinea columella, and Physella acuta. Six cercarial types – mammalian schistosomes, avian schistosomes, longifurcate pharyngeates, echinostomes, amphistomes, and xiphidiocercariae – were isolated from 104 out of 926 snails (11.2 %). PCR revealed a significantly higher infection rate, with 70.2 % of snails testing positive for trematodes. Snail taxon diversity and infection rate significantly varied across land use types, with the lowest values observed in the commercial tobacco farm section, highlighting the potential adverse effects of agriculture on biodiversity. Ponds with extensive Lagarosiphon major (oxygen weed) coverage appeared to facilitate the presence and abundance of P. acuta and P. columella. Schistosome-competent snails such as B. truncatus and B. tropicus seemed to favor shallow water depths and more eutrophic sites characterized by high levels of nitrates, phytoplankton biomass, turbidity, and phycocyanin. These ponds were predominantly associated with the emergent macrophyte Cladium mariscus, revealing a potential association with important intermediate snail hosts. In conclusion, our study emphasizes the complex interplay among environmental factors, macrophyte composition, land use, and the abundance, diversity, and infection prevalence of freshwater snails, offering insights into potential strategies for targeted snail control and disease management in man-made waterbodies.

Seismic Imaging of the Arctic Subsea Permafrost Using a Least-Squares Reverse Time Migration Method

High-resolution seismic imaging allows for the better interpretation of subsurface geological structures. In this study, we employ least-squares reverse time migration (LSRTM) as a seismic imaging method to delineate the subsurface geological structures from the field dataset for understanding the status of Arctic subsea permafrost structures, which is pertinent to global warming issues. The subsea permafrost structures in the Arctic continental shelf, located just below the seafloor at a shallow water depth, have an abnormally high P-wave velocity. These structural conditions create internal multiples and noise in seismic data, making it challenging to perform seismic imaging and construct a seismic P-wave velocity model using conventional methods. LSRTM offers a promising approach by addressing these challenges through linearized inverse problems, aiming to achieve high-resolution, subsurface imaging by optimizing the misfit between the predicted and the observed seismic data. Synthetic experiments, encompassing various subsea permafrost structures and seismic survey configurations, were conducted to investigate the feasibility of LSRTM for imaging the Arctic subsea permafrost from the acquired seismic field dataset, and the possibility of the seismic imaging of the subsea permafrost was confirmed through these synthetic numerical experiments. Furthermore, we applied the LSRTM method to the seismic data acquired in the Canadian Beaufort Sea (CBS) and generated a seismic image depicting the subsea permafrost structures in the Arctic region.

One-year monitoring of grass-type architectural waterscapes with long-term operation: Water quality and microorganism

Grass-type architectural waterscapes (GAWs) utilize submerged plants to enhance self-purification ability and maintain a clear-water state. However, knowledge about their long-term water quality and microbial community dynamics remains limited. This study monitored the water quality, microbial community composition, and networks in two GAWs. GAW1 consisted solely Hydrilla verticillata with a water depth of 0.70 m, while GAW2 primarily contained Vallisneria natans, Microsorum pteropus, and Aquarius grisebachii with a water depth of 0.30 m. Results show that both water depth and submerged plant species play crucial roles in GAW establishment. The water depth of 0.7 m enabled Hydrilla verticillata to thrive underwater despite temperature variations, which demonstrated excellent nutrient uptake capacity. Thus, GAW1 exhibited superior self-purification ability, consistently meeting Class III standard for surface water in China. In contrast, GAW2 had a shallow water depth and contained ornamental plants, only meeting Class V standard. Furthermore, microbial communities were shaped by water quality, with distinct enriched genera serving as potential “microbial indicators”. Enrichment of the hgcI clade and Sporichthyaceae_unclassified indicated superior water quality in GAW1, while prevalence of Comamonadaceae_unclassified, Flavobacterium, Rhodoluna, and Pseudarcicella suggested poor water quality in GAW2. Additionally, highly complex and connected microbial networks suggested elevated pollutant levels in GAWs. This study emphasized the significance of submerged plant species and water depth in GAWs construction and highlighted microbial communities and networks as potential indicators of water quality.

Mouth bars’ development along the West Pearl River main course

River mouth bars’ formation is a key process of the delta development and river bifurcation, but details of the long-term developmental history of mouth bars and their role in the delta evolution are substantially less well documented. To characterize deltaic mouth bars’ development, this study investigated the Sixianjiao, Jun’an, Da’aosha and Denglongsha mouth bars formed successively along the main course of the West Pearl River. The detailed lithological analyses of sediment cores indicate that the mouth bar sediment is characterized by its sandy nature with mud laminations or lenses and poorly preserved foraminifera. The onset of mouth bar sedimentation is affected by water depth. The Sixianjiao and Jun’an mouth bars initiated at shallower water depth (8.0 m and 11.0 m, respectively) due to the restrictions of higher basement landforms. In an area where water is deeper, the mouth bar development would begin only with the site being elevated up to about 16.0 m water depth, such as a case in Da’aosha. The duration between their onset and end of vertical growth varies between 2000 and 2800 years, which is inversely related to their sedimentation rates between 2.7 and 5.7 mm/a, indicating the importance of sediment supply. In addition, the locations of the four mouth bars were to some extent determined by the antecedent landscapes. Finally, the ages of these four mouth bars show a chronological order from land to sea, reflecting seaward delta progradation, contrary to previous morpho-dynamical numerical model’s predictions. Our reconstruction of the West Pearl River mouth bars’ developmental history provides a new insight into the geomorphological evolution of the Pearl River delta, a special delta developed within a complex estuarine bay.

Distribution of methane in the upper water layer of the northern Black Sea: Seasonal and daily trends and seawater-air emissions

We report on methane (CH4) concentration measurements in the northern Black Sea area conducted during 6 cruises with R/V Professor Vodyanitsky from 2017 to 2019. Our work is a multi-season study at a uniform station grid covering an area of 88 × 103 km2 and including three latitudinal transects that comprises both surface and vertical profile water-column measurements. The main goal of the work was to assess the seasonal patterns of vertical CH4 structure in the aerobic water column (upper 100 m) and its emission to the atmosphere.In surface waters, the mean dissolved CH4 concentration ranged from 2.6 nmol L−1 detected in November 2018 to 11.5 nmol L−1 measured in June–July 2018, respectively. Calculated CH4 seawater-air fluxes and saturations were mostly positive (i.e. net flux to atmosphere), and winter fluxes (2.6 μmol m−2 d−1) were higher than summer fluxes (1.6 μmol m−2 d−1) due to the higher wind speed. The integral CH4 flux from the whole study area (88 × 103 km2) ranged from 84 to 235 kM day−1.It was shown that, on average, the methane concentration in the upper layer for deep-water stations where the seabed is located at depths >160 m (σt >16.2) was lower compared to stations at shallow water depths (28–140 m, σt <16.2). The most distinct difference was obtained for the summer season (June–July 2018) and a less significant difference – for spring (April–May 2019) and winter season (November–December 2018). During these seasons the water column was also considerably less saturated in CH4 compared to the entire monitoring period. We observed subsurface maxima, which were generally located at the base of the thermocline and exceeded 100 nmol L−1 at some stations. Exceptions were observed in October 2019 (cruise 110), when vertical CH4 distributions were characterized by two-peaks at ∼20 and ∼50 m depth. The strong influence of the thermohaline structure on the water column CH4 distribution has also been shown in studies of daily dynamics of CH4 vertical profiles in the shallow water region. Despite the high variability of CH4 concentrations, significant similarities in vertical distributions of CH4 and chlorophyll-a for which sub-surface maxima coincided at some stations, are shown. Extremely high concentrations of CH4 (up to 351 nmol L−1) in the near-bottom water layer were revealed during all seasons at the station near the Dnieper paleo-channel at the northwestern edge of the study area. This enrichment is assumed to be caused by methane emissions from gas seeps densely located in this region.

Primary productivity recovery and shallow-water oxygenation during the Sturtian deglaciation in South China

The Cryogenian Period (ca. 720–635 Ma) marks a key node in Earth's history, characterized by two global glaciations when the paleo-tropical regions were covered by glaciers, namely the Sturtian and Marinoan Snowball Earth events. Within the Cryogenian, the evolution of primary producers persisted, evidenced by the worldwide discovery of diverse microfossils and the proliferation of algae in the interglacial oceans. The Cryogenian radiation of algae facilitated the emergence and evolution of early eumetazoan animals. However, the paleoredox reconstruction of the interglacial Cryogenian presents more challenges. The open oceans were predominantly and permanently ferruginous throughout the Cryogenian Period, and persistently euxinic conditions developed in restricted basins, such as the Nanhua Basin. Some of the studies suggested a possible fully‑oxygenated interval in the aftermath of the Sturtian glaciation. Therefore, a knowledge gap lies between the biological prosperity and severe habitability in the interglacial oceans. In order to fill this gap, we report a newly discovered interglacial deposition – the Datangpo Formation – of shallow water depth from the Guitouwan section, Shennongjia area, South China. A combination of iron speciation, total organic matter (TOC), and pyrite sulfur isotopes (δ34Spy) analyses are conducted, along with numerical simulations, for reconstructions of paleoredox conditions and paleoproductivity level. Additionally, we collected Fe chemistry, TOC, and pyrite sulfur data from multiple successions of the Datangpo Formation in South China to reconstruct the paleoredox landscape. The spatial TOC comparison suggests that the interglacial interval is marked by a TOC increase at the base, and the Guitouwan succession represents the early deposition during the wake of Sturtian deglaciation. Fe speciation suggests locally (dys)oxic-ferruginous condition in the Shennongjia area, while the δ34Spy systematics indicate a transition from ferruginous to euxinic condition and a sharp increase in primary productivity during the Sturtian deglaciation. With respect to the high δ34Spy values, the observed discrepancy suggests that the iron proxy might be inapplicable during fast environmental changes, especially during the deglaciation episodes. The comparison of Fe chemistry and pyrite sulfur isotopes between different water-depth settings informs a redox-stratified ocean in the Nanhua Basin. The newly discovered interglacial deposition fills the blank in understanding the shallow-water oxygenation in the Sturtian glacial aftermath, recording the transition from (dys)oxic-ferruginous to ferruginous-euxinic and from low to high productivity levels. These findings shed new light on the interpretation of Fe chemistry and δ34Spy in the geological past, and provide a novel perspective on investigating productivity levels.

Development of desalination plants within the semi-enclosed Persian Gulf

Although many desalination plants have been built in the countries around the Persian Gulf (PG) over the past decade, there exist crucial water demands in this region. Considering the limited water exchange between PG and the open seas, effluents more than the natural capacity of the PG will increase the sea-water salinity continuously. This excess salinity, in addition to threatening the marine ecosystems, endangers the water supply for many population centers. This study provides a comprehensive numerical analysis of the impact of existing and new desalination plants on the PG’s salinity. In addition, the water residence time and pollutant extension have been investigated in the PG. There exist several concerns, especially in recent years about the probable threat of desalination growth in semi-enclosed seas such as PG. The effect of desalination plants on the mean salinity of PG is one the questions investigated in this research. Results demonstrate that the water residence times in the southern and northwestern regions are more than five years. This time is reduced to nearly 26 to 45 months in the eastern regions near the Strait of Hormuz. Generally, the desalination plants have a negligible effect on the salinity of PG in comparison with the climate conditions such as evaporation and water exchanges. Based on the results, a 50% increase in effluent discharge of existing desalination plants increases the average salinity of the PG by only 0.01 psu. However, the annual volume of net evaporation (that exits the clean water directly) is nearly 36 times more than the effluent discharge from the existing desalination plants. Furthermore, this value is almost 0.2% of the amount of water that enters the PG through the Strait of Hormuz. In spite of these findings, the regional effects can be significant in some parts of the PG. For example, the southern and western coasts of PG are generally more vulnerable to pollution than other areas. The main reason is the shallow water depth in these areas and the water recirculation pattern. Some sensitive local areas have been also addressed in this study. Among the studied regions, the coastlines at the northwest of PG and at the north the Qeshm Island are two susceptible areas. The findings of this study underscore the importance of considering a new integrated viewpoint in developing desalination plants within PG.

Spatial ecology and population dynamics of brown trout Salmo trutta L. in reservoirs and headwater tributaries.

This investigation compared the spatial ecology and population dynamics of brown trout Salmo trutta L. between reservoirs with (impact; Langsett Reservoir) and without (control; Grimwith Reservoir) barriers to fish movements into headwater tributaries, and the effectiveness of a fish pass intended to remediate connectivity. Passive integrated transponder (PIT) telemetry revealed that fish that emigrated from Langsett and Grimwith tributaries were 1-3 and 0-2 years old, respectively, and predominantly did so in spring and autumn-early winterin both systems. Weirs at Langsett Reservoir appeared to thwart emigration rate (26%) relative to Grimwith Reservoir (85%). Acoustic telemetry (two-dimensional positions) in the impacted reservoir revealed thatthe largest home range was in October-December (95% monthly activity space S.D. up to 26.9 ± 6.69 ha in November), activity was influenced by both month and time of day, and fish occupied shallow water depths (relative to reservoir depth), especially at night. Brown trout tagged in Grimwith and Langsett Reservoirs (42.9% and 64.1%, respectively) and fish tagged in the tributariesthat emigrated (37.2% and 27.7%, respectively) were detected immigrating into tributaries throughout the year. At both reservoirs, peak immigration for ≥3-year-old trout occurred primarily in autumn-early winter. Overall passage efficiency went from 3% prior to remediation to 14% after and there was no significant increase in fish densities following the construction of the fish pass. Fish were attracted towards and entered the fish pass under a wide range of river levels, but only succeeded in passing upstream during low levels, which are uncommon druing the main migration period. Overall, this investigation significantly furthers our understanding of brown trout spatial ecology and population dynamics in reservoirs and headwater tributaries.

Sediment distribution and transport pattern in the nearshore region, southeast coast of India

The present paper aimed to assess the sediment distribution pattern, mode of transport, and its interaction with hydrodynamic and topographic conditions at different depths and regions along the east coast of India. About 900 surficial sediment samples were collected and analysed on a monthly basis for the Chennai coastal region at 32 stations from 2013 to 2015. The study region is classified into four types, such as beach, inlet, 5 m, and 10 m depth. Sediment textural and grain size trend analyses were conducted to achieve the objectives. Sediment characteristics for the region were recorded as sandy, equally dominated by unimodal and bimodal at the beach, while unimodal at shallow depths (5 and 15 m). The sediments were medium sand to coarse sand at the beach, mostly fine followed by medium at 5 and 15 m depths. The sediment sorting is dominated by moderately well-sorted sediments; the skewness of beach sediments was negative, while nearshore sediments were found positive; average kurtosis values of sediments were noticed to be mesokurtic. The CM plot depicts that the sediments were mostly derived by tractive current, and the modes of transport are “bottom suspension and rolling” and “graded suspension no rolling” at beach locations and shallow water depths, respectively. The GSTA analysis reveals the annual average sediment transport pattern is northerly. The numerical hydrodynamic study confirms the GSTA and CM plot analysis. The study reveals a stable sedimentary environment south of the Chennai port and instability in the northern part. The study includes large spatiotemporal nearshore sediment data with hydrodynamic conditions, immensely helpful to coastal stakeholders and researchers.

Multi-spectral remote sensing bathymetry based on the variation of substrate spectra and empirical linear relationship

The high spatial resolution and wide applicability of multi-spectral remote sensing make it significant for estimating shallow water depth. In areas with mixed substrates, determining the contribution of substrate reflection to the sensor’s received signal can effectively enhance the precision of multi-spectral remote sensing bathymetry. Therefore, this paper proposes a Two Factors constrained Quasi-Analytical Algorithm (TF-QAA). Firstly, the algorithm considers the spectral variation of the mixed substrates. Secondly, a robust correlation between inherent optical parameters and water depth is established in this study, which is used to enforce a linear relationship constraint on the initially estimated water depth. Sentinel-2 image data was used to verify the algorithm in the Antelope Reef area of the South China Sea. The best result from images taken at different times indicates that the TF-QAA method has the average absolute error (MAE) of 0.92 m, the root mean square error (RMSE) of 1.20 m, the average relative error (MRE) of 10.6%, and the correlation coefficient (R2) of 0.97. The results suggest that the algorithm is effective for Case 1 water, providing a novel approach for extensive bathymetric mapping in shallow water areas of islands, with or without LiDAR-measured depth data.

Freak wave generation modulated by high wind and linear shear flow in finite water depth

In finite water depths, the effects of high winds and linear shear flow (LSF), encompassing both uniform flow and constant vorticity shear flow on freak wave generation are explored. A nonlinear Schrödinger equation, adjusted for high wind and LSF conditions, is derived using potential flow theory and the multiscale method. This equation accounts for the modulational instability (MI) of water waves and the evolution of freak wave amplitudes. MI analysis reveals that for waves to maintain MI, high tail winds (moving in the same direction as the wave) require less vorticity and deeper water, while adverse winds (moving in the opposite direction) necessitate more vorticity and shallower water depths compared to conditions without wind. Uniform up-flows (down-flows), positive (negative) vorticity, and high tail (adverse) winds, which inhibit (promote) wave propagation, increase (decrease) the MI growth rate and amplify (diminish) freak wave heights. It is through this MI that the generation of freak waves is either promoted or inhibited.

Exploring the Most Effective Information for Satellite-Derived Bathymetry Models in Different Water Qualities

Satellite-derived bathymetry (SDB) is an effective means of obtaining global shallow water depths. However, the effect of inherent optical properties (IOPs) on the accuracy of SDB under different water quality conditions has not been clearly clarified. To enhance the accuracy of machine learning SDB models, this study aims to assess the performance improvement of integrating the quasi-analytical algorithm (QAA)-derived IOPs using the Sentinel-2 and ICESat-2 datasets. In different water quality experiments, the results indicate that four SDB models (the Gaussian process regression, neural networks, random forests, and support vector regression) incorporating QAA-IOP parameters equal to or outperform those solely based on the remote sensing reflectance (Rrs) datasets, especially in turbid waters. By analyzing information gains in SDB, the most effective inputs are identified and prioritized under different water qualities. The SDB method incorporating QAA-IOP can achieve an accuracy of 0.85 m, 0.48 m, and 0.74 m in three areas (Wenchang, Laizhou Bay, and the Qilian Islands) with different water quality. Also, we find that incorporating an excessive number of redundant bands into machine learning models not only increases the demand of computing resources but also leads to worse accuracy in SDB. In conclusion, the integration of QAA-IOPs offers promising improvements in obtaining bathymetry and the optimal feature selection should be carefully considered in diverse aquatic environments.

Rainfall induced shallow flow water depths on vehicular pavements

This article investigates twenty-five experiments of one-dimensional shallow thin-surface flow on wide carriageway pavements, undertaken as part of wider investigations to avoid aquaplaning. Analysis of their predictive equations for surface water depths are assessed, along with informative background papers. Issues regarding rainfall intensity and the macrotexture structure of pavement materials and their inter-relationship are considered. Current international best-practice guidance is contrasted and observations for the practising highway engineer are provided, as well as recommendations for future research.