Riverbed Research Articles

The Seismic Surface Rupture Zone in the Western Segment of the Northern Margin Fault of the Hami Basin and Its Causal Interpretation, Eastern Tianshan

The Eastern Tianshan region, influenced by the far-field effect of northward compression and expansion of the Qinghai-Xizang block, features highly developed Late Quaternary active faults that exhibit significant neotectonic activity. Historically, the Barkol-Yiwu Basin, located to the north of the Eastern Tianshan, experienced two major earthquakes in 1842 and 1914, each with a magnitude of M71/2. In contrast, the Hami Basin on the southern margin of the Eastern Tianshan has no historical records of any major earthquakes, and its seismic potential, mechanisms, and future earthquake hazards remain unclear. Based on satellite image interpretation and field surveys, this study identified a relatively recent and well-preserved seismic surface rupture zone with good continuity in the Liushugou area of the western segment of the Northern Margin Fault of the Hami Basin (HMNF), which is the seismogenic structure responsible for the rupture. The surface rupture zone originates at Kekejin in the east, extends intermittently westward through Daipuseke Bulake and Liushugou, and terminates at Wuzun Bulake, with a total length of approximately 21 km. The rupture zone traverses the youngest geomorphic surface units, such as river beds or floodplains and first-order terraces (platforms), and is characterized by a series of single or multiple reverse fault scarps. The morphology of fault scarps is clear, presenting a light soil color with heights ranging from 0.15 m to 2.13 m and an average displacement of 0.56 m, suggesting that this surface rupture zone likely represents the most recent seismic event. Comparison with historical earthquake records in the Eastern Tianshan region suggests that the rupture zone may have been formed simultaneously with the Xiongkuer rupture zone by the 1842 M71/2 earthquake along the boundary faults on both sides of the Barkol Mountains, exhibiting a flower-like structural pattern. Alternatively, it might represent a separate, unrecorded seismic event occurring shortly after the 1842 earthquake. The estimated magnitude of the associated earthquake is about 6.6~6.9. Given that surface-rupturing earthquakes have already occurred in the western segment, the study indicates that the Erdaogou–Nanshankou section of the HMNF has surpassed the average recurrence interval for major earthquakes, indicating a potential future earthquake hazard.

Influence of particle density on turbulence characteristics over a rough surface

The objective of the study is to use a 3D Acoustic Doppler Velocimeter (ADV) to gauge the typical flow and turbulence characteristics within a non-uniform open channel. The findings of experimental examinations of the subcritical flow along the channel are presented in this work. The behavior of sand grains in turbulent open channel flow across porous and rough bed surfaces was examined in laboratory research, and the results were obtained. The properties of turbulent flow, i.e., turbulence intensity, turbulent kinetic energy, and Reynolds shear stresses, are determined from ADV data. The continuity equation and the Reynolds equation of open-channel flow have been used to build theoretical formulations for the velocity distribution and Reynolds stress distribution in the vertical direction. Measured profiles of vertical velocity and Reynolds stress are compared to the derived expressions. The impact of the size of particles on the distribution of mean flow characteristics is discussed. This work provides a novel origin for the profile and analyzes the behavior of the vertical velocity distribution in the region where fully formed turbulence is dominating in open channels using the Navier–Stokes equations. In comparison to other sand roughness, Chopan sand bed (with greater density) exhibits the strongest turbulence intensities in both vertical and streamwise direction just next to the bed when away from the channel boundary. In contrast to flow across a rough surface, the variance ranges between 150 and 250% concerning the channel bed’s roughness type, impacting the velocity triple products that signifies transfer of turbulent kinetic energy.

Forces and grain–grain contacts in bidisperse beds sheared by viscous fluids

In a recent paper [Gonzalez et al., “Bidisperse beds sheared by viscous fluids: Grain segregation and bed hardening,” Phys. Fluids 35, 103326 (2023)], we investigated the motion of grains within a granular bed sheared by a viscous fluid and showed how segregation and hardening occur in the fluid- (bedload) and solid-like (creep) regions. In this paper, we inquire further into the mechanisms leading to grain segregation in a bidisperse bed, and how the forces are distributed. For that, we carried out numerical simulations at the grain scale by using computational fluid dynamics–discrete element method, with which we were able to track the positions, velocities, forces, and solid contacts underwent by each grain. We show that during the upward motion of large grains the direct action of fluid forces is significant in the middle and upper parts of the bedload layer, while only contact forces are significant in the creep layer and lower part of the bedload layer. We also show that in all cases the particles experience a moment about a −45° contact point (with respect to the horizontal plane) when migrating upward, whether entrained by other contacts or directly by the fluid. In addition, we show the variations in the average solid–solid contacts, and how forces caused either by solid–solid contacts or directly by the fluid are distributed within the bed. Our results provide the relationship between force propagation and reorganization of grains in sheared beds, explaining mechanisms found, for example, in river beds and landslides.

Long-term effects of Abay River flow regulation at Lake Tana on the geomorphic and ecological responses of the downstream river channels, Upper Blue Nile basin, Ethiopia

Alluvial rivers adjust their geometry in response to environmental and anthropogenic disturbances. Flow regulation results in a new geomorphic condition that affects the aquatic ecosystem and its nature. This paper examines the long-term effects of flow regulation on the geomorphic and ecological responses of the downstream river channels of the Abay River, which is the only natural outflow of Lake Tana, Ethiopia. Since 1996, the river’s discharge regime has been affected by constructing a head-rise weir (Chara Chara) at its natural outlet for hydropower production and dam construction on the Lake Tana tributary rivers. Hydrologic data collected at the outlet of the river, SPOT, and Google Earth images were used for the study. River banks and bed topography were extracted via ArcGIS for selected study periods. The study revealed that existing water resource development on the tributary rivers of Lake Tana modified (decreased) the outflow discharge on the Abay River, and resulted a changed morphological and moderate level ecological impact on the river system. Future ongoing and planned water resource developments will exacerbate the pressure on the lake. Without careful management, these changes are likely to have severe morphological, ecological and social consequences.

Identifying the origin, recharge, and salinity sources of the Romqan saline spring, causing intense salinization of the Shirinrud River in southern Iran

Salinization of originally freshwater rivers by saline springs is a growing threat to availability of water resources in the semiarid region of southern Iran. The problem is further complicated by persistent drought of recent years, which has resulted in prolonged periods of reduced streamflow. This issue has prompted research on possibility of finding practical techniques for flow stoppage of saline springs by investigating their recharge and salinization mechanisms as well as emergence time. To this end, the Shirinrud river in southern Iran is selected as a case study. While this river contains freshwater flow, it is intensively salinized due to annual discharge of ∼110000 tons salt from the Romqan saline spring. Study area streamflow gauges, water sampling, plus field observations and measurements have been used to provide the required data and information. Data analyses included evaluation of temperature variations of study area groundwaters, long-term salinity of the Shirinrud River, and isotopic and hydrochemical compositions of water samples. Results of thermal, isotopic, and hydrochemical tracing methods together with hydrogeological evidences in the Romqan spring site indicated that although the Romqan saline spring is recharging from a fresh groundwater flow, it becomes intensely salinized due to passage of ∼1.7 km of its recharging water pass inside the Romqan salt diapir. Furthermore, sudden drying of a freshwater spring at border of Romqan salt diapir just after the 1999 earthquake in spring site area, resulted in redirection of the fresh groundwater flow of the dried spring into the Romqan salt diapir, followed by emergence of the Romqan saline spring in the Shirinrud River bed. For flow stoppage of the Romqan saline spring, an interceptor drainage system is suggested, which would divert the spring fresh recharging groundwater flow at border of Romqan salt diapir and finally desalinize the Shirinrud River from Romqan saline spring.

Hypermobility of a Catastrophic Earthquake-Induced Loess Landslide

Landslide mobility refers to how far and fast a landslide can move downslope. It controls landslide impact areas and damage power. Highly mobile landslides are often initiated on slopes steeper than 30°. However, on 18 December 2023, an earthquake-induced landslide (35°52′54″N, 102°51′10″E) exhibited extraordinary mobility, with an overall travel angle of 1.5°, breaking an on-land landslide record. The landslide originated on a gentle slope (3.6°), eroded an earth dam along its travel path, and finally destroyed 51 houses and claimed 20 lives. Remote sensing and field surveys were conducted to provide morphological characteristics of the hazard chain. A numerical program, EDDA (Erosion–Deposition Debris Flow Analysis), was employed to reproduce the flow dynamics and investigate the causes of hypermobility. The findings reveal three primary causes of hypermobility: (1) liquefaction of the saturated silty loess stratum due to the combined effects of irrigation activity and seismic loading, (2) the loose and macro-pore structure of loess, and (3) confined topography and icy channel bed. The mechanisms revealed have broad implications for understanding fluidized mass movements on gentle slopes in seismically active regions.

Lateral Shear Stress Calculation Model Based on Flow Velocity Field Distribution from Experimental Debris Flows

AbstractDebris flows continuously erode the channel downward and sideways during formation and development, which changes channel topography, enlarges debris flow extent, and increases the potential for downstream damage. Previous studies have focused on debris flow channel bed erosion, with relatively little research on lateral erosion, which greatly limits understanding of flow generation mechanisms and compromises calibration of engineering parameters for prevention and control. Sidewall resistance and sidewall shear stress are key to the study of lateral erosion, and the distribution of the flow field directly reflects sidewall resistance characteristics. Therefore, this study has focused on three aspects: flow field distribution, sidewall resistance, and sidewall shear stress. First, the flow velocity distribution and sidewall resistance were characterized using laboratory debris flow experiments, then a debris flow velocity distribution model was established, and a method for calculating sidewall resistance was developed based on models of flow velocity distribution and rheology. A calculation method for the sidewall shear stress of debris flow was then developed using the quantitative relationship between sidewall shear stress and sidewall resistance. Finally, the experiment was validated and supplemented through numerical simulations, enhancing the reliability and scientific validity of the research results. The study provides a theoretical basis for the calculation of the lateral erosion rate of debris flows.

Numerical Simulations of Impact River Morphology Evolution Mechanism Under the Influence of Floodplain Vegetation

Shallow floodplains play a crucial role in river basins by providing essential ecological, hydrological, and geomorphic functions. During floods, intricate hydrodynamic conditions arise as flow exits and re-enters the river channel, interacting with the shallow vegetation. The influence and mechanism of shoal vegetation on channel hydrodynamics, bed topography, and sediment transport remain poorly understood. This study employs numerical simulations to address this gap, focusing on the Xiaolangdi–Taochengpu river section downstream of the Yellow River. Sinusoidal-derived curves are applied to represent the meandering river channel to simulate the river’s evolutionary process at a true scale. The study simulated the conditions of bare and vegetated shallow areas using rigid water-supported vegetation with the same diameter but varying spacing. The riverbed substrate was composed of non-cohesive sand and gravel. The analysis examined alterations in in-channel sediments, bed morphology, and bed heterogeneity in relation to variations in vegetation density. Findings indicated a positive correlation between vegetation density and bed heterogeneity, implying that the ecological complexity of river habitats can be enhanced under natural hydrological conditions in shallow plain vegetation and riparian diffuse flow. Therefore, for biological river restoration, vegetation planting in shallow plain regions can provide greater effectiveness.

Experimental investigation of dissolved oxygen improving aeration efficiency by hydraulic jumps

The dissolved oxygen (DO) level in water is vital for water quality and supporting aquatic life. Hydraulic jumps involve rapid flow changes from super-critical to sub-critical, visible at abrupt bed slope shifts, like at spillway bases in rivers or canals. The hydraulic jump efficiently mixes oxygen from air into water and offers a cost-effective method of aeration by entraining air bubbles in the stream to improve oxygen transfer compared to traditional systems. The objective of this experimental research is to investigate the aeration performance with hydraulic jump parameters and establish correlations crucial to measuring aeration (or transfer) efficiency. Relationships between transfer efficiency, jump height, jump length, sequent depth ratio, discharge, inlet Froude number, and channel bed slope were determined. To investigate the nature of such relationships, a series of experiments were conducted in a rectangular tilt flume to test the aeration performance of forced submerged hydraulic jumps with five different discharges and five different smooth bed slopes. The inlet Froude number before the jump varied from 2.18 to 8.23. Experimental observation confirms a positive relationship between transfer efficiency and jump control parameters. During experimentation, transfer efficiency was found to vary between 9.4 % and 34 %. This research includes estimating the optimal transfer efficiency due to hydraulic jumps, which can help hydraulic engineers in building structures that can revitalize any degraded stream.

Species of Wadicosa (Araneae, Lycosidae): a new species from the southeastern Arabian Peninsula

Wadicosa arabica sp. nov. is described from material of both sexes collected in Oman and the United Arab Emirates. The species belongs to the W. fidelis group and differs from its congroupers, inter alia, by the shape of the tegular apophysis and the embolus in the male. The occurrence of W. arabica sp. nov. is restricted to the gravel, pebble and cobble beds of ephemeral and intermittent streams (wadis) in the mountains of the eastern United Arab Emirates and northern Oman (the Hajar Mountains sensu lato). There it is often common and conspicuous alongside areas of surface waters. Notes on its courtship behaviour are given.

Research on sedimentation characteristics of the end bend water extraction project of cascade reservoir backwater

Abstract The operation mode of upstream and downstream cascade power stations significantly impacts the river bed in the water intake section, leading to complex sediment deposition characteristics in the curved river section at the reservoir’s end. In this research, a standard physical model for bed load and suspended load at a scale of λl=λh=100 was conducted, combined with the operation mode of upstream and downstream power stations, to investigate the sediment deposition patterns in the intake section and to study the sediment deposition characteristics in the intake area. The experimental results reveal that bed load sediment predominantly accumulates on the right bank (convex bank) of the river, with no bed load sediment accumulation at the mushroom head layout of the water intake project on the left bank (concave bank). When the operation of upstream and downstream power stations is uncoordinated, suspended sediment settles in the water intake section, with no sediment accumulation in the local area of the mushroom head of the intake due to the disturbance effect. Safety sensitivity analysis indicates that the safety of the water intake project can be ensured.

Features of protection and use of biological features of protection and use of biological resources in the territory of the lower Amudarya reserve of the republic of Karakalpakstan

Abstract The Republic of Karakalpakstan is the focus of this article’s conservation and environmental management issues. The authors emphasize the unique characteristics of environmental management in this region in relation to the drying out of the Aral Sea and the low water level of the Amudarya River bed. Despite these environmental disasters, our country preserves the biodiversity of flora and fauna in the Badai-Tugai Nature Reserve.

An Update on the Conservation Status Assessment of two Endangered Freshwater Mussel Species in Bavaria, Germany

ABSTRACTThe two highly endangered European mussel species Margaritifera margaritifera and Unio crassus are target species of conservation. Based on a recently completed systematic state‐wide monitoring of each 22 M. margaritifera and 22 U. crassus streams in Bavaria, Germany, we present an update on population trends, conservation status, habitat quality and threats for both species. Populations status and habitat quality varied strongly between M. margaritifera and U. crassus streams, but there was also great variability within each of those groups. The population decline of M. margaritifera has continued, albeit higher proportions of juveniles originating from artificial breeding programmes have been established in some streams. Habitat quality often did not match known requirements as evident from poor stream bed quality, lack of hosts and elevated nutrient levels. In contrast, U. crassus populations showed a better status, with an increase in population size over all sampled streams. Successful recruitment was indicated by high proportions of juveniles. However, no mussels older than 16 years were found, probably due to predation and structural stream maintenance measures. Climate change effects, such as extreme droughts, affected both species. This study demonstrates different needs in conservation management for both species. Although mitigation of drought effects is commonly needed for both species, tackling host fish management and direct threats such as predation should be prioritized in U. crassus, whereas restoration of prime habitat quality and intact catchments is key to enable natural recruitment and sustainable populations of M. margaritifera.

Impact of dyke and vegetation on fluid force and moment reduction under sub and supercritical flow conditions

Flooding is the most common natural disaster throughout the world and requires efficient management. Therefore, the current investigation aimed to explore the impact of a composite defense system comprising dyke and vegetation on flow dynamics and velocity reduction. Experiments were conducted in an open channel setup with an adjustable bed slope and transparent sidewalls, and the vegetation model was replicated as real trees such as Eucalyptus trees. The study involved calculating several parameters, including flow velocity, reduction of fluid force index (RFI%), reduction in moment index (RMI%), and hydrostatic and hydrodynamic forces. These calculations were done by changing the channel bed slope and keeping the flow rate (discharge) constant while considering both subcritical and supercritical flow conditions. Moreover, regression analysis was performed for the prediction of RFI% and RMI% under various flow conditions. Also, statistical analyses were performed to assess the effectiveness of the defense system in reducing fluid force and moment indices. The result of the current investigation indicates that the highest values of RFI% and RMI% under subcritical flow conditions were 79% and 88%, while under supercritical flow conditions they were 94% and 78%, respectively. Moreover, a velocity reduction of 69% was observed under subcritical flow, while 84% was observed under supercritical flow conditions. Under subcritical flow conditions, RFI% and RMI% enhanced by enhancing Froude number (Fr) because of an increase in velocity reduction and hydraulic jump formation. Similar trends were observed under supercritical flow conditions, with effective mitigation of high-velocity flows by the composite system. The finding of current research helps in providing effective techniques for flood management.

Influence of flood events on the response of steep and coarse-grained channels to base-level lowering in an arid setting

The Dead Sea level has been undergoing a continuous and rapid lowering, presently ∼ 1.1 m/yr, providing a real time laboratory to examine the response of drainage systems to base level drop. There is a gap of knowledge concerning the impact of floods on the fluvial system in an environment of continuous base level lowering. Such knowledge is of pronounced importance due to the world-wide reduction of natural water recourses caused by human and climate impacts. We relate the effects of flash floods on morphological changes in small, steep and coarse-grained alluvial channels as a response to a rapid base level fall. We studied the steep (7–9 %) David and Qedem channels draining to the Dead Sea by (i) monitoring flow events using depth transducers and (ii) topographic changes by repeat drone-based photogrammetric surveys to quantify fluvio-morphological dynamics, and (iii) analyzed boulder-related bedforms and their distance from the thalweg. Altogether 15 monitored flow events of varying magnitude led to a wide range of fluvio-morphological changes. Considerable erosion occurred as expressed by bank collapse and channel bed incision. Small events displayed incision with morphological changes limited to the downstream reach, while larger events caused morphological changes throughout the entire channel. Substantial deposition at the outlet occurred together with local mechanisms of deposition upstream. The extents of erosion and net volumes of change highly correlated with event peak-discharge and event water volume. Frequent thalweg deflections occurred, some of which were related to the interaction with boulders. Boulder ribs displayed processes of formation/destruction in multiple phases, often occurring in larger events. The examined aspects illustrate the unique dynamics of a continuously unstable fluvial system under a flash-flood hydrological regime and its impact on fan delta incision and sediment transport processes.

Palaeolithic investigations at Morpani, Central Narmada Basin, India

Morpani is a recently discovered Palaeolithic complex in the central Narmada Basin (Madhya Pradesh, India), discovered during the course of field investigations carried out by the Narmada Basin Palaeoanthropology Project. This site is situated in a region of the Gondwana Supergroup formations, south of the Narmada River. Regions to the north of the river, dominated by rock outcrops of the Vindhyan Supergroup formation present a multitude of Palaeolithic sites, in stark contrast to the southern region, dominated by the Gondwana Supergroup and Deccan Trap formations. This site is one of the few Palaeolithic sites in this southern region, and this paper reports on the recent Palaeolithic investigations undertaken at the site and the results of the lithic analyses of the recovered lithic assemblage. These investigations were carried out to qualify the nature of the Palaeolithic occupation in this region, as well as probe into the possible factors for the underrepresentation of the archaeological record here, especially when juxtaposed to the rich archaeological context noted to the north of the river. Lithic analyses indicates that Morpani represents an expedient lithic assemblage, located along the banks and bed of an ephemeral stream channel, and in regions where suitable raw material clasts are available. More work and collections are needed to securely characterise and attribute the technological features of this Palaeolithic site.

Measurements of frazil ice flocs in rivers

Abstract. Frazil floc sizes and concentrations have been investigated in a small number of laboratory studies, but no detailed field measurements have been reported previously. In this study, a submersible camera system was deployed a total of 11 times during the principal and residual supercooling phases in the North Saskatchewan, Peace, and Kananaskis rivers to capture time-series images of frazil ice particles and flocs. Images were processed to accurately identify flocs and to calculate their sizes and concentrations. Key hydraulic and meteorological measurements were collected, and air–water heat fluxes were estimated to investigate their influence on floc properties. A lognormal distribution was found to be a good fit for the floc size distribution. The mean floc size ranged from 1.19 to 5.64 mm and the overall mean floc size was 3.80 mm. The mean floc size decreased linearly as the local Reynolds number increased. The average floc number concentration ranged from 1.80×10-4 to 1.15×10-1 cm−3. The average floc volumetric concentration ranged from 2.05×10-7 to 4.56×10-3 and was found to correlate strongly with the fractional height above the river bed. No significant correlations were found between the air–water heat flux and floc properties. Time series analysis showed that during the principal supercooling phase, floc number concentration and mean size increased significantly just prior to peak supercooling and reached a maximum near the end of principal supercooling. During the residual supercooling phase, the mean floc size did not typically vary significantly even 2.5 h after the residual phase had ended and the water temperature had increased above 0 °C.

The Impact of Catastrophic Floods on Macroinvertebrate Communities in Low-Order Streams: A Study from the Apennines (Northwest Italy)

Floods are normal components of many river regimes and, as such, they exert a significant influence at the ecosystem level. In recent decades, however, climate change has increased the frequency and intensity of floods, with serious consequences for lotic biota, particularly benthic macroinvertebrates, due to their limited mobility and sensitivity to disturbance. The impact of floods varies according to different biological parameters including the characteristics of the macrobenthic communities (taxonomic composition, morphology, behaviour, and life history traits) on one hand and various nonbiological parameters such as flood intensity, artificialisation of the river bed, the presence of dams, and many other factors on the other. Understanding these dynamics is pivotal to improve the effective management and conservation of aquatic ecosystems in the context of current climate change. The aim of this short communication is to evaluate the impact of a catastrophic flood on the macroinvertebrate community of a low-order Appennine stream (NW Italy). This will provide data regarding the varying impacts on different taxa and the recovery pattern of this significant component of the ecosystem.

Impact and erosion dynamics of inclusion-enriched dry granular flows on rigid barriers with basal clearance: Numerical insights from hybrid MP-DEM simulations

Rigid barriers with basal openings are often installed along predicted flow paths to protect downstream facilities from dry granular flows containing large boulders. However, current design practices do not consider the effects of these inclusions during impact, discharge, overflow, and bed erosion. We conducted hybrid MP-DEM simulations to study the dynamics of dry sand flow with inclusions impacting a rigid barrier with a basal opening. Our findings show that accounting for large inclusions is crucial for barrier design, as they alter dry granular flow regimes, delay dead zone formation, and affect overflow dynamics. Current analytical solutions may overestimate velocity attenuation by up to 60% if inclusions are not considered. A 10% increase in inclusion volume fraction leads to 6%-28% increases in internal energy dissipation during overflow, resulting in an overflow distance 20% lower than existing predictions. Additionally, channel bed erosion due to landing flow with inclusions creates a flow depth up to 3.5 times thicker than at the first barrier location. This suggests that using the initial flow depth for impact force assessment on a second barrier may not be conservative for erodible channel beds and inclusion-enriched flows.

Fluvial fan sedimentary characteristics of distributive fluvial system

The characteristics of fan sediment in the distributive fluvial system are evaluated based on a thorough analysis of modern silt in the Guertu river distributive fluvial system, as well as data obtained from UAV aerial photography and satellite remote sensing. The Guertu River Distributive Fluvial System (DFS) is classified into three stages, namely "proximal," "middle," and "distal," based on the examination of river morphology, sediment variations, sedimentary attributes, and other relevant aspects throughout different sections of its tributaries, from the source to the mouth. At the upstream section of the downstream fining sequence, the slope is the steepest and the hydrodynamic conditions are intense, resulting in the formation of a predominantly big gravel braided river. The river bed section has a morphology resembling a combination of a "V" and a "U" shape. It is characterized by a narrow and deep configuration, with a relatively short breadth. The sediment primarily consists of medium to large-sized gravel with minimal sand content. The gravel exhibits good roundness and displays a considerable degree of orientation. The primary microfacies present are braided channel and flood plain. The slope of the central area is decreased in comparison to the nearby end, primarily due to the presence of extensive braided rivers. The river bed has a greater width, with minor eolian dunes visible in the river channel. The gravel particles are predominantly fine to medium in size, and there is an increased amount of sand present. The predominant microfacies are braided channels, floodplains, and eolian dunes. At the distal end, the slope is minimal, the landscape is level, the braided river transitions into a meandering river, the sediment consists primarily of sand, and the signs of bioturbation are clearly visible. The primary microfacies consist of braided channels, meandering channels, floodplains, eolian dunes, lakes, and swamps.