Shallow Channel Research Articles

Seismic characterization of a fluid escape structure in the North Sea: the Scanner Pockmark complex area

SUMMARYSubsurface fluid escape structures are geological features which are commonly observed in sedimentary basins worldwide. Their identification and description have implications for various subsurface fluid flow applications, such as assuring integrity of overburden rocks to geological CO2 storage sites. In this study, we applied 3-D first-arrival traveltime tomography to a densely sampled wide-azimuth and wide-angle ocean bottom seismometer (OBS) data set collected over the Scanner Pockmark complex, a site of active gas venting in the North Sea. Seismic reflection data show a chimney structure underlying the Scanner Pockmark. The objective of this study was to characterize this chimney as a representative fluid escape structure in the North Sea. An area of 6$\times $6 km2 down to a depth of 2 km below sea level was investigated using a regularized tomography algorithm. In total, 182 069 manually picked traveltimes from 24 OBS were used. Our final velocity model contains compressional wave velocity perturbations ranging from −125 to +110 ms−1 relative to its average 1-D model and compares favourably with a coincident seismic reflection data set. The tomographic velocity model reveals that the chimney as observed in seismic reflection data is part of a larger complex fluid escape structure, and discriminates the genuine chimney from seismic artefacts. We find that part of the seeping gas migrates from a deep source, accumulates beneath the Crenulate Reflector unconformity at ∼250 m below seafloor (mbsf) before reaching the porous sediments of the Ling Bank and Coal Pit formation at <100 mbsf. In addition, the model shows that the venting gas at Scanner Pockmark is also being fed laterally through a narrow NW–SE shallow channel. Quantitative velocity analysis suggests a patchy gas saturation within the gas-charged sediments of the Ling Bank and the Coal Pit formations. Confined to the well-resolved regions, we estimate a base case average gas saturation of ∼9 per cent and in-situ gas volume of ∼1.64 $\times {10^6}\ {{\rm{m}}^3}$ across the Ling Bank and Coal Pit Fm. that can sustain the observed methane flux rate at the Scanner Pockmark for about 10 to 17 yr.

An investigation of a closed-form solution for non-linear variable-order fractional evolution equations via the fractional Caputo derivative

Determining the non-linear traveling or soliton wave solutions for variable-order fractional evolution equations (VO-FEEs) is very challenging and important tasks in recent research fields. This study aims to discuss the non-linear space–time variable-order fractional shallow water wave equation that represents non-linear dispersive waves in the shallow water channel by using the Khater method in the Caputo fractional derivative (CFD) sense. The transformation equation can be used to get the non-linear integer-order ordinary differential equation (ODE) from the proposed equation. Also, new exact solutions as kink- and periodic-type solutions for non-linear space–time variable-order fractional shallow water wave equations were constructed. This confirms that the non-linear fractional variable-order evolution equations are natural and very attractive in mathematical physics.

Understanding tidal mixing at the Strait of Gibraltar: A high-resolution model approach

The Strait of Gibraltar is a narrow and shallow channel that controls the Mediterranean Sea thermohaline and biogeochemical balances. Strong tidal currents significantly modulate exchanges across this strait and induce an intense vertical mixing, impacting both the Mediterranean Sea and the Atlantic Ocean on a climatic scale. However, the turbulent processes controlling the tidal mixing location, timing, and magnitude remain unclear. To fill this gap, we investigate tidal mixing at the Strait of Gibraltar in yearly twin tidal and non-tidal simulations from a regional configuration of the three-dimensional numerical model MITgcm, using a high spatial resolution around the Strait of Gibraltar (1/200°, 100 vertical levels). More specifically, we investigate the model turbulence closure scheme, based on a turbulent kinetic energy budget, and illustrate that vertical buoyancy fluxes should be preferred to diapycnal diffusivities as mixing indicators. In agreement with previous literature, we find that tides strongly intensify vertical mixing and motions within the Strait of Gibraltar. We then demonstrate that tidal mixing relies on two main ingredients: a sustained vertical shear of horizontal velocities and a local weakening of stratification. In the Mediterranean layer, the former drives diapycnal mixing near the seafloor and the latter in shallower areas above the prominent sills of the strait. We also evidence the frequent but irregular occurrences of static instabilities in the vicinity of these sills. In the Atlantic layer, both vertical shear and stratification are involved in diapycnal mixing that develops along the trail of the eastward internal bore released at the Camarinal sill. At high frequency, the local weakening of stratification results from convergence and divergence patterns in the vicinity of the Camarinal and Espartel sills, feeding recirculation cells between the Atlantic and Mediterranean layers. In addition, we highlight that diapycnal mixing mainly develops during the westward tidal phase in the Mediterranean layer and the eastward tidal phase in the Atlantic layer. We conclude by proposing a revised conceptual view of tidal mixing at the Strait of Gibraltar, where tidally-induced recirculation cells play an instrumental role in transforming the exchanged water masses. Overall, this study emphasizes the relevance of a realistic representation of both tides and abrupt topography to simulate the exchanges through the Strait of Gibraltar and argues for the use of a specific tidal mixing parameterization otherwise.

Seismic geomorphological analysis of channel types: a case study from the Miocene Malay Basin

Abstract Imaging the subsurface is a major challenge due to many aspects; the most notable is the resolution of the data, which often leads to misinterpretation of reservoir behaviour and depositional environment. Even with the robust tools available to precisely model the subsurface reservoir and depositional architecture, a precise result is still incorrect if derived from an inaccurate subsurface description. Recent advances in 3D seismic geomorphology analytical methods, particularly the application of root mean square (RMS) and frequency decomposition analysis, have enabled detailed imaging, description and classification of subsurface channel networks. Typically, it is easier to image shallow subsurface channels (<500 m depth), but it gets increasingly challenging to recognize channel features at subsurface depths ≥1.5 km. This paper presents the characterization of channel features imaged from such depths within the Miocene section of the Malay Basin, offshore Peninsular Malaysia. An integrated dataset from a selected area in the central region of the Malay Basin was used for this study, including a high-quality 3D seismic cube (1563 km2) and data from one well penetrating the Miocene section of the Malay Basin. We have identified five seismic geobody groups and 10 channel types from both planform and cross-section views. The dimensions, shapes, sinuosities and thicknesses of these channel types vary. Additionally, they display various seismic characteristics in cross-section and planform views. Variability in channel geometries is related to the complex interplay between fluvial and marine processes.

Non-residual unrestricted pruned ultra-faster line detection for edge devices

Line detection with deep learning is a popular visual task that focuses mostly on lane detection. It requires quicker inference speed and lower consumption, especially for high-speed edge device applications. Based on the UFAST, we propose the Non-Residual Unrestricted Pruned Ultra-faster (NRUPU) line detection via a novel model compression method including non-interference structural reconstruction (NISR), shallow channel priority reservation (SCPR) pruning and non-residual equivalent transformation (NRET). NISR is a structure reconstruction scheme allocating residual branches into each layer to solve the cross-layer channel interference in ResNet-18. SCPR pruning directly uses the factors of BN layers to build channel importance evaluation for backbone and designs channel selection method for head based on data distribution consistency, reducing the parameters of each layer independently. Then NRET losslessly converts the multi-branch model to a single-branch one containing only convolution, linear, and relu, which reduces implementation complexity on edge devices. These designs follow the theoretical foundations: the data distribution transformation trend and effect of gradient back-propagation on model learning ability. Compared with previous pruning methods, our method optimizes not only the parameters of the model but also the structure of the model. We train NRUPU in RTX2080Ti and deploy tests on edge devices NVIDIA Jetson Xavier NX (NJXN) and Atlas 200 DK (A2DK). Extensive experiments are conducted on the dataset TuSimple, CULane and our belt dataset with 11,894 data. Results show that NRUPU achieves over 96% speed increase and over 66% parameter reduction on all datasets within 0.7% accuracy loss. The FPS can reach 749, 665 and 783 on RTX2080Ti, 133, 117 and 143 on NJNX, 178, 161 and 183 on A2DK respectively. The code is released at https://anonymous.4open.science/r/NRUPU-29B0.

Impact of dynamic factors on the exchange flow between two neighboring bays with contrasting topography during summer: A numerical study

A high-resolution, three-dimensional numerical ocean model was employed to understand the exchange flow through Noryang Channel, which connects Gwangyang Bay and Jinju Bay. These two bays exhibit contrasting topographies, with Gwangyang Bay connected to the open ocean through a broad and deep channel, whereas Jinju Bay is relatively isolated from the open ocean by a narrow and shallow channel. Numerical experiments were conducted to determine the contribution of river discharge, wind stress, surface heat flux, and tides to the exchange flow between the two bays during summer. The results suggested that river discharge was the dominant factor affecting the exchange flow along Noryang Channel. Particularly, a high river discharge during summer increased the sea level in Jinju Bay, creating a barotropic flow toward Gwangyang Bay. However, the dense water entering Gwangyang Bay through the wide and deep channel generated a baroclinic flow toward Jinju Bay along the lower layer of Noryang Channel. An analytical model supported the conclusion that river discharge is the main driver of the exchange flow in Noryang Channel.

MVCNN: A Deep Learning-Based Ocean–Land Waveform Classification Network for Single-Wavelength LiDAR Bathymetry

Ocean–land waveform classification (OLWC) is crucial in airborne LiDAR bathymetry (ALB) data processing and can be used for ocean–land discrimination and waterline extraction. However, the accuracy of OLWC for single-wavelength ALB systems is low given the nature of the green laser waveform in complex environments. Thus, in this article, a deep learning-based OLWC method called the multichannel voting convolutional neural network (MVCNN) is proposed based on the comprehensive utilization of multichannel green laser waveforms. First, multiple green laser waveforms collected in deep and shallow channels are input into a multichannel input module. Second, a one-dimensional (1-D) convolutional neural network (CNN) structure is proposed to handle each green channel waveform. Finally, a multichannel voting module is introduced to perform majority voting on the predicted categories derived by each 1-D CNN model and output the final waveform category (i.e., ocean or land waveforms). The proposed MVCNN is evaluated using the raw green laser waveforms collected by Optech coastal zone mapping and imaging LiDAR (CZMIL). Results show that the overall accuracy, kappa coefficient, and standard deviation of the overall accuracy for the OLWC utilizing green laser waveforms based on MVCNN can reach 99.41%, 0.9800, and 0.03%, respectively. Results further show that the classification accuracy of the MVCNN is improved gradually with the increase in the number of laser channels. The multichannel voting module can select the correct waveform category from the deep and shallow channels. The proposed MVCNN is highly accurate and robust, and it is slightly affected by aquaculture rafts and the merging effect of green laser waveform in very shallow waters. Thus, the use of MVCNN in OLWC for single-wavelength ALB systems is recommended. In addition, this article explores the relationships between green deep and shallow channel waveforms based on the analysis of CZMIL waveform data.

Analysis of the bed forms simulated using the three-dimensional model SSIIM, case of a natural shallow water channel

El objetivo de este trabajo se enfoca en analizar las dimensiones dominantes de las formas de fondo simuladas mediante un modelo hidrodinámico tridimensional acoplado con procesos de transporte de partículas y metodologías numéricas de utilidad para estimar los cambios en la morfología de flujos con superficie libre. En este sentido, se aplicaron técnicas de estadística descriptiva y espectral a las geometrías de fondo simuladas, obteniendo una discretización espacial y temporal de las dimensiones dominantes en el dominio de estudio del río Tercero en su paso por la ciudad de Villa María, Argentina. Las características del tramo seleccionado corresponden a las de un río de aguas poco profundas y con pendiente de fondo acorde con la de un cauce de planicie.

An optical nanofibre-enabled on-chip single-nanoparticle sensor.

Single-nanoparticle detection has received tremendous interest due to its significance in fundamental physics and biological applications. Here, we demonstrate an optical nanofibre-enabled microfluidic sensor for the detection and sizing of nanoparticles. Benefitting from the strong evanescent field outside the nanofibre, a nanoparticle close to the nanofibre can scatter a portion of the field energy to the environment, resulting in a decrease in the transmitted intensity of the nanofibre. On the other hand, the narrow and shallow microfluidic channel provides a femtoliter-scale detection region, making nanoparticles flow through the detection region one by one. By real-time monitoring of the transmitted intensity of the nanofibre, the detection of a single polystyrene (PS) nanoparticle as small as 100 nm in diameter and exosomes in solution is realised. Based on a statistical analysis, the mean scattering signal is related to the size of the nanoparticle. Experimentally, a mixture of nanoparticles of different diameters (200, 500, and 1000 nm) in solution is identified. To demonstrate its potential in biological applications, high-throughput counting of yeasts using a pair of microchannels and dual-wavelength detection of fluorescently labelled nanoparticles are realised. We believe that the developed nanoparticle sensor holds great potential for the multiplexed and rapid sensing of diverse viruses.

An analysis of the effects of urbanization on urban drainage systems in Ankpa, Dekina and Oguma Towns of Kogi State in North Central Nigeria

Managing complex environmental problems such as flood disaster require up to date technology. Much of these disasters can be prevented and reduced through the use of technology such as Geographic Information Systems (GIS) and remote sensing as well as questionnaire administration. The spatial analytic capacity of GIS is employed to carryout hydrological analysis such as drainage network, DEM, Slope, flow direction and accumulation, stream order. Also land use and land cover analysis was done to examine the changes in land cover pattern across the study area. Different datasets were extracted from satellite imagery (landsat TM and OLI) of the Study area. ArcGIS 10.8 and Idrisi Terrset were used for the land cover change spatial analyses. The results from image analysis revealed that built-up area have been increasing significantly in the area due to increasing population pressure, it increases from 11.70%, 9.74% and 13.15% in 1990 to 18.12%, 16.05% and 19.37% in 2021 for Ankpa, Bassa and Oguma (Dekina) respectively. The flood risk vulnerability map reveals that about 15.44% (835.73 km2) and 15.81% (856.25 km2) of the study area have very high and high susceptibility to flooding inundation, respectively. The vulnerable zones are located on the lowest part of the plain which is responsible for the high flood vulnerability experienced in this area. It can be deduced that the magnitude of the flood hazard of a given area is a function of both the distance to the river and the elevation of the area in question. The result of the questionnaire analysis indicates that 67.55%,65.96% and 61.48% strongly agreed that shallow drainage channels in Ankpa, Dekina and Oguma are the major drainage challenges in the study area while 65.70%, 56.73% and 56.46%, strongly agree that several homes are destroyed when drainage fail and 56.20%, 63.32%, and 57.26% strongly agree that availability of social services is responsible for the increase population upsurge to urban centers. It is believed that the result of this research can be used as a means of regulating development along the plain and also serve as a decision support when making policies relating to drainage and flood management around urban centres.

Moving Targets Detection for Video SAR Surveillance Using Multilevel Attention Network Based on Shallow Feature Module

In this article, a novel method for the moving target detection through multilevel spatial and channelwise attention network based on shallow feature channel module (MSCA-SFCM) is presented, and the circular spotlight (CSL) video synthetic aperture radar ground moving target indication (Video-SAR-GMTI) mode of the Nanjing University of Aeronautics and Astronautics miniature SAR (NUAA MiniSAR) system is introduced. However, due to the lack of moving target samples, MSCA-SFCM cannot be directly applied to the CSL Video-SAR-GMTI mode in the real system. To this end, this article proposes a training sample library construction scheme for moving targets of high verisimilitude. In this scheme, based on the radar system parameters, after the traversal of moving target parameters and SAR imaging, the scattering line characteristic of all possible moving targets under the current system parameters is simulated and then used for MSCA-SFCM network training. Afterward, the properly trained network can be used for moving target detection in real radar data. The effectiveness of the proposed method is verified by the NUAA MiniSAR system.

An Integrated Approach to an Assessment of Bottlenecks for Navigation on Riverine Waterways

Water transport, both sea and inland, is the cheapest, least invasive, and safest option for non-standard loads; hence, it is important to increase the percentage share of inland waterway transport on the rivers of Central and Eastern Europe. Transporting cargo is particularly difficult on shallow waterways because rivers overloaded with sediment determine the vertical parameters on inland waterways. A ship’s safe manoeuvrability depends on the available water depth of the navigational area concerning the vessel’s draught. The draught is related to channel depth and sediments. The paper presents a model assessment of a new tool for studying limitations for ships carrying oversized cargo and the shallow channel bed inland waterways. Our analysis was carried out on the Vistula River lowland reach for the winter hydrological conditions. The Lower Vistula River in Poland is a clear example of a sedimentation problem. This waterway is also a zone of active sediment transport of sandy material; a massive volume of sediment reaches 1 million cubic meters per year. The results of this research could be helpful for inland transport management, risk assessment of ships entering waterways with shallow channel beds such as the Vistula River, and analysis for a new waterway project.

Enhanced pinch flow fractionation using inertial streamline crossing

In this work, we study the influence of inertia on the dynamics of neutrally buoyant spherical microbeads of varying diameter in a pinch flow fractionation device. To that aim, we monitor their trajectory over an unprecedented wide range of flow rates and flow rate ratios. Our experimental results are supplemented by a depth-averaged 2D-model where the flow is described using the Navier-Stokes equation coupled with the shallow channel approximation and where particles trajectories are computed from Newton’s second law of motion with a particle tracing model. Above a certain flow rate, we show that particles inertia enables them to cross streamlines in response to an abrupt change of direction. These streamline crossing events combined with the increasing effect of the inertial lift forces drive particles to deviate from the inertialess trajectory. The amplitude of the resulting inertial deviation increases both with the particles diameter and the total flow rate before reaching a plateau. Consequently, based on our numerical and experimental results, we determine the optimal flow conditions to shift the particles distribution in order to significantly enhance their size-based separation.

Reconstructing late Miocene depositional environments in the central High Plains, USA: Lithofacies and architectural elements of the Ogallala Formation

The late Miocene Ogallala Formation hosts much of the High Plains aquifer of North America, though it is poorly studied in the central High Plains region where only a small fraction of its total thickness is exposed. One exception is in western Kansas, where up to 40 m of the Ogallala Formation crop out along the bluffs of Ladder Creek Canyon. These deposits consist of stacked and laterally extensive, multistory channel bodies dominated by sandy bedforms with little or no intervening floodplain mudstone. We interpret each ~2–4 m-thick story as a sandstone bed that formed during a single depositional episode and infilled a broad and relatively shallow braided river channel. Each story preserves elements suggesting high discharge conditions, followed by low discharge or the complete abandonment of the river channel after active streamflow either migrated away from the study area or ceased regionally for a relatively long period of time. High discharge conditions are characterized by channel-filling, current-formed transverse bars, gravel-rich longitudinal bars, and sand sheets deposited while the channel was largely flooded and nearly the entire riverbed mobilized. Low discharge conditions are indicated by lens-shaped, trough cross-stratified channels scoured into previously deposited bars. Channel-fill deposits were formed when the remaining flow was confined to one or more narrow streams that braided across the exposed channel belt. Persistent low discharge conditions are suggested by channel-belt-wide subaerial exposure of bar surfaces for a period of time sufficient to promote colonization by soil-burrowing organisms and moderate soil development. Abandonment of the broader channel belt is indicated by advanced calcretization within a story and the presence of aerially restricted and fossiliferous mud-filled channel pools where the final repositories of surface water attracted local paleofauna before infilling or drying completely. The depositional environment of the Ogallala Formation in the study area is most similar to “Platte type” fluvial systems characterized as shallow, perennial, and sand-dominated braided rivers. Comparisons with previously studied localities in the northern and southern High Plains reveal differences in fluvial style, sediment source areas, cut-and-fill geometries, and eolian input.

Experimental study on the effect of flow channel parameters on the durability of PEMFC stack and analysis of hydrogen crossover mechanism

Polymer electrolyte membrane fuel cell (PEMFC) is a leading technology with a bright future in the field of transportation. The bipolar plate structure has a profound impact on the mass and heat transfer of PEMFC. In this study, the durability tests of two stacks with different channel depths are carried out for 1000 h respectively on the 1 kW fuel cell stack test platform. We detect the overall performance change of the stack and characterize the membrane electrode assembly at the end of the test. Based on the first principle calculation, the mechanism of membrane degradation and hydrogen crossover is analyzed, and some durability experimental results are explained. The results show that the durability of the PEMFC with a shallow flow channel is worse, the voltage drops significantly, and the hydrogen crossover increases significantly after 500 h. The first principle calculation results reveal that the chemical structure change of the membrane is caused by the free radical attack. Hydrogen crossover promotes ∙H to attack carbon-fluorine bonds. This paper reveals the mechanism of hydrogen crossover and its influence on the catalyst layer, which is helpful to improve the durability of PEMFC.

Nanosecond Laser-Textured Copper Surfaces Hydrophobized with Self-Assembled Monolayers for Enhanced Pool Boiling Heat Transfer.

Increased cooling requirements of many compact systems involving high heat fluxes demand the development of high-performance cooling techniques including immersion cooling utilizing pool boiling. This study presents the functionalization of copper surfaces to create interfaces for enhanced pool boiling heat transfer. Three types of surface structures including a crosshatch pattern, shallow channels and deep channels were developed using nanosecond laser texturing to modify the surface micro- and nanomorphology. Each type of surface structure was tested in the as-prepared superhydrophilic state and superhydrophobic state following hydrophobization, achieved through the application of a nanoscale self-assembled monolayer of a fluorinated silane. Boiling performance evaluation was conducted through three consecutive runs under saturated conditions at atmospheric pressure utilizing water as the coolant. All functionalized surfaces exhibited enhanced boiling heat transfer performance in comparison with an untreated reference. The highest critical heat flux of 1697 kW m-2 was achieved on the hydrophobized surface with shallow channels. The highest heat transfer coefficient of 291.4 kW m-2 K-1 was recorded on the hydrophobized surface with deep channels at CHF incipience, which represents a 775% enhancement over the highest values recorded on the untreated reference. Surface microstructure was identified as the key reason for enhanced heat transfer parameters. Despite large differences in surface wettability, hydrophobized surfaces exhibited comparable (or even higher) CHF values in comparison with their hydrophilic counterparts, which are traditionally considered as more favorable for achieving high CHF values. A significant reduction in bubble departure diameter was observed on the hydrophobized surface with deep channels and is attributed to effective vapor entrapment, which is pointed out as a major contributing reason behind the observed extreme boiling heat transfer performance.

Flume experiment study of the formation process and sedimentary characteristics of a shallow‐water delta

This paper investigates the influence of water level oscillation and sediment supply volume on shallow‐water delta development by means of a flume experiment. The experiment simulated the natural water level by dividing a cycle of sediment period into four parts: the draught period, the flood period (FP), the interflood period in a falling limb (IPF) and the interflood period in a rising limb (IPR). During the FP, flooding broke former channels and a large amount of sediments were evenly unloaded at the surface of lobes. Erosion often appeared at the beginning of the IPF and was dominant at low stand. Most sediments were concentrated in incised valleys and unloaded at the channel mouth to form a new lobe during the falling limb. Erosional channels and lobes were broken at the IPR. Sediments homogeneously covered the surface of lobes and few new lobes appeared during the period. Different sediment supplies influenced the characteristics of incised valley and channel style. Low sediment supply to the delta was strongly influenced by water level change, while high sediment supply was mainly affected by fluvial processes. Based on the flow sand content of water, channels can be classified into four types: (a) narrow and deep multiple channels, (b) narrow and shallow branch channels, (c) broad and shallow main channels, and (d) broad and deep stable channels. Their width‐to‐depth ratios are 1.1–3.5, 5.1–12.9, 7.3–20.2, 2.6–4.6, respectively. Most mouth bars were initially formed but then broken by water level oscillation and channel bifurcation. The preserved mouth bars were well preserved at the far end of lobes, where they entered the low‐energy environment.

Modelling Initiation Stage of Backward Erosion Piping through Analytical Models

Backward erosion piping, which is one of the leading causes of levee and dam failures, is more likely to occur when a flow is concentrated on a defect with an overlying low-permeability layer and a shallow erosion channel forming and progressing towards a seepage source. Two analytical models are presented to allow assessment of the seepage regime on the initiation stage of BEP. The variations between the two models are analysed, indicating that the effects of soil loosening have a major role in the assessment of BEP mechanisms. This paper also describes the reliability of using Xiao’s model in 3D analysis, which includes results and parametric analysis. Although the head in front of the tip of the erosion channel can be predicted by this accepted calculation model, which is essential for laboratory work on this topic, the model also has range and boundary limitations that need to be addressed for general prediction when BEP progresses with channel development.

At‐a‐station hydraulic geometry for reaches with bridge collapse events

AbstractThis study explores the at‐a‐station hydraulic geometry (AHG) for reaches with bridge collapse events. Eighteen reaches in Eastern United States, thirteen reaches in Appalachian Highland, and five reaches in Coastal Plain are examined. The methodology applied for retrieving AHG uses LiDAR (Light detection and ranging) data, and the study results are checked for both hydraulic and geomorphic consistency. The resulting data set is composed of five to thirty‐five measurements of water surface width, mean depth, and mean velocity at each of the 181 cross‐sections. The exponents of the AHG relationships vary considerably. Nonetheless, for most of the cross‐sections, width responds more rapidly to changing discharge, and velocity exponents are less than the width and depth exponents combined. Wide shallow channels with highly erodible beds and/or banks, the ability to transport large bed materials, and the ability to attain a super‐critical condition—are the common profile extracted for most of the cross‐sections across all sites. A definitive AHG configuration is found for the sites with the least human interference. Comparatively low variation of bank‐full geometry is also found for the sites with the least human interference. The prevalence of low flows and/or lower return periods of heavy‐tail flows are also exhibited for most of the sites. The study results suggest that the stream channel instability can be reasonably understood and predicted from AHG particularly if human interference is limited within the watershed. These findings have implications not only for the study of the risk of bridge collapse and bridge design but also to characterize instability in a more rigorous and practical way.

Mesolithic Freshwater Fishing: A Zooarchaeological Case Study

Abstract In this article we investigate the importance of freshwater fishing during the Mesolithic in France, in inland sites where fishing was always associated with big game hunting. We present a review of Mesolithic sites that have yielded freshwater fish remains and focus on a case study from an occupation dated to the eighth millennium BC at Les Cabônes rock shelter, located near the Doubs River, that yielded over 9,300 fish remains. Cyprinid (including bream, roach, and minnow) remains are predominant; other taxa, such as salmonids (probably trout), grayling, burbot, perch, and eel, are represented by only a few remains each. Although small fish (about 15 cm) constitute the majority of the catch, we provide evidence that their accumulation in the shelter is mostly of human origin. These catches constituted a source of food throughout the year, particularly during the lean season. According to the ecological preferences of the fish species identified, it is highly unlikely that they were caught in a single location. The animals were probably caught with passive fishing equipment in shallow banks or side channels where large numbers of specimens could be captured. Fishing appears to have been optimised to maximise yield-to-effort ratios, together with other wetland resources. Finally, we question the presumed causal links between site micro-setting, site occupation, and increased dependence on aquatic resources and reduced group mobility.