Gravel Movement Research Articles

Gravel‐Sand Transition of the Yangtze River: Human Disturbances, Migration Processes, and Controlling Factors

AbstractDespite abundant studies on gravel‐sand transitions (GSTs), GST origin and migration in large alluvial channels characterized by significant variations in width, numerous tributary (or distributary) streams, and frequent human disturbances remain difficult to explain. Here, we take the Yangtze River as an example and use field observations and numerical modeling to make progress toward addressing GST origin and migration. The results show that the Yangtze River exhibits a non‐abrupt GST approximately 60 km long. Within the GST and the adjacent area, there are two dramatic decreases in shear stress; the upstream one induces the settlement of sand from suspension, explaining the emergence of the Yangtze River GST, whereas the downstream one induces general cessation of gravel movement. However, the deposited gravel was mostly overwhelmed by sand. We argue that these changes in shear stress in the Yangtze River depended primarily on the combined effects of width variability and distributary systems. Since 1970, the Jingjiang Meander Cut‐off, the Gezhouba Dam, and the Three Gorges Dam (TGD) have been completed in succession, repeatedly altering the flow‐sediment regime within the GST. However, the GST position remained unchanged until the TGD began operation in 2003. The stability of the GST was primarily ascribed to the sufficient upstream sand supply (grain size <0.5 mm), the resistant lithologies upstream of Zhicheng, and the Jingjiang Great Levees constraints.

The deflectors influence on flow complexity, bed morphology, sediment transport and water quality of urban lotic waters ‐ A laboratory study

AbstractIn this laboratory study different combinations of bed (sand, pebble gravel [gravel], and a mix of sand and gravel) and flow (typical and overtopping) were experimented with to investigate the impact of porous deflectors in flow diversity, water quality, and fish performance in prismatic open channels. Deflectors changed the gradually varied flow to a rapidly varied flow, as a sudden change in the water depth was observed at the deflectors, and this change was large for smooth beds. With the presence of gravel, the scouring near the downstream deflector was almost twice that of the sand bed, and with the scouring at its own upstream deflector, irrespective of whether the flow was typical or overtopping. This behavior was a result of sand mobilization due to shear stress and sand mobilization aided gravel transport. The mixed bed showed less gravel movement compared to the gravel‐only bed. The percentage of sediment washed out was minor for all bed scenarios, indicating that sediment transport was local. Relative to the sand bed without deflectors (representing a typical urban canal), deflectors resulted in reduced and improved water quality (in terms of sediment load) for sand, and mixed bed, respectively. The fishes found refuge and were comfortable in the pool areas created by deflectors unlike in channels without deflectors where they showed exhaustion.

Numerical Simulation of Wave Overtopping of an Ecologically Honeycomb-Type Revetment with Rigid Vegetation

Traditional concrete revetments can destroy the ecological environment and the water landscape. An increasing number of ecological revetment structures have been applied in coastal, lake, and river regulation projects. It has been found that honeycomb-type revetments display a better performance in the attenuation of wave overtopping when compared to experimental data collected using the Eurotop and Muttray’s formula; recording a 40% decrease in the wave run-up in comparison to the latter. To further investigate the wave run-up and overtopping of the ecologically vegetated honeycomb-type revetment, based on OpenFOAM, an open source computational fluid dynamics software, a three-dimensional numerical wave tank was established. The Discrete Particle Method (DPM) was used to simulate gravel movement, and the flexible plant move boundary model was developed to simulate vegetation. The results of wave run-up calculated by the numerical model and those obtained by the experiments were in good agreement, with errors less than 20%. The modeled results of wave overtopping were within the same order of magnitude as those from the experiments; however, critical limitations were noticed due to effects of plant generalization and grid restrictions imposed by DPM methods. The results showed that wave overtopping increased with increasing wave period and wave height. However, with an increase in the wave overtopping, the influence of the wave period on wave overtopping decreased. The increase in vegetation density effectively reduced wave overtopping. Furthermore, an empirical formula for wave overtopping, considering the effects of vegetation density, was proposed.

Frequency of river gravel mobility

Size-selective bedload transport is well established in channels dominated by gravel. This study investigates the mobility of gravel-sized clasts in a channel dominated by sand to quantify the annual frequency of gravel movement. A Helley-Smith bedload sampler was deployed at three locations in the low-gradient, sand-dominated San Antonio River. The smallest flow in which a given gravel fraction was captured defines the mobilizing discharge from which an annual frequency of occurrence was derived using flow duration analysis. Results document that smaller gravel fractions (2–4 mm) move between 54 and 96% of the year. Larger gravels are less mobile at all sites, but grain diameters between 16 and 32 mm mobilize every year on average, depending on river location. Comparison to mobilizing flows established for 10 rivers with different bed material textures documents the higher annual gravel mobility in sand-dominated channels. These results shed light on the extent of gravel mobility in the distal portion of watersheds, and help explain patterns in the gravel-sand transition in riverbed material.

Investigating threshold wind velocity for movement of sparsely distributed gravels in a wind tunnel: Effect of surface coarseness

In this study, wind tunnel experiments were conducted to determine the relationship between the texture of road surfaces and the threshold wind velocity that causes the movement of sparsely distributed gravels. We proposed a method that uses analogous particles having lower densities compared to actual gravel, considering the threshold velocity for gravel is too large to imitate in a typical wind tunnel. We first conducted a preliminary experiment, which confirmed that the threshold velocity for denser prototype particles can be estimated from the density ratios of the analogous and prototype particles. Furthermore, a main experiment was conducted to analyze different road surface textures using pumice stones, as their particle density is less than that of gravels. The results showed that coarser road surfaces exhibited larger threshold velocities for the gravel movement. Quantitatively, the coarsest asphalt concrete exhibited a threshold velocity that was 2.5 times larger than that of the smoothest surface (cement concrete). However, surface coarseness was dependent on the particle size, whereas the effect of particles trapped by the gaps in surfaces was more dominant than the fluid force acting on the particles of a relatively coarse surface. This force balance is reversed for a smooth surface, which indicates the possibility of determining threshold friction velocity from the particle size and surface texture coarseness.

Do brown trout (Salmo trutta L.) move streambed substrate?—Implications for durability and maintenance of artificial spawning habitat

AbstractArtificial spawning habitat has been used to mitigate for lost habitat and to increase the abundance of salmonids, but the endurance and potential need of maintenance of these habitat improvements have not been well studied. We studied the movement of gravel, attributed to spawning activity of brown trout in a third‐order stream in northern Sweden by deploying PIT‐tagged grains of gravel on artificially constructed gravel patches. The results suggest that gravel movement was substantial and most prevalent at the central parts of the patches. As 76% of the tagged gravel was mobilized during a single spawning season, maintenance of this habitat improvement may be necessary in order to guarantee its functionality over time. This study provides a first step in guiding managers tasked with identifying factors degrading restored spawning habitat and maintenance needed.

Typhoon Impact on a Pure Gravel Beach as Assessed through Gravel Movement and Topographic Change at Yeocha Beach, South Coast of Korea

ABSTRACT Han, M.; Yang, D.Y.; Yu, J., and Kim, J.W., 2017. Typhoon impact on a pure gravel beach as assessed through gravel movement and topographic change at Yeocha Beach, south coast of Korea. This study investigated sediment movement and topographic change using radio frequency identifier (RFID) tracers and real-time kinematic (RTK)–global positioning system (GPS) data to examine the response of a gravel beach under typhoon conditions. Yeocha Beach, the study site and a pure gravel beach, was affected by strong wind and waves produced by Typhoon Goni on 24–26 August 2015. On 26 August, the main direction of the tracer movement was toward the upper part of the beach and toward the west relative to the onshore-offshore and alongshore directions. The average movement distance of the tracers differed according to the insertion points. The tracers inserted in the beach face showed a longer average movement distance of 12.07 m compared with 1.89 m for those inserted in the storm berm. In addition, the tracer...

Effects of sand content on initial gravel motion in gravel‐bed rivers

AbstractWhen fine sediments are present in gravel streambeds (gravel‐framework beds), the gravel can be more easily removed from its original position, compared with gravel in a streambed without fine sediment but otherwise under the same hydraulic conditions. In this study, the effect of the presence of sand on the initiation of gravel motion in gravel riverbeds was investigated using flume experiments. The relationship between the critical Shields stress for gravel motion initiation and the fraction of sand in the bed was determined experimentally. The results can be summarized as follows. (1) When the fraction of sand in the bed is smaller than about 0.4, the critical Shields stress for the initiation of gravel motion decreases with increasing fraction of sand. The critical Shields stress increases, however, with increasing fraction of sand when it is larger than about 0.4. (2) The difference between the value of the critical Shields stress predicted by the Egiazaroff equation and the value obtained from the experimental data becomes maximum at about 0.4 of the fraction of sand. Here an empirical relation between the critical Shields stress and the fraction of sand is proposed so as to consider the effects of the ratio of the characteristic gravel size to the mean size of the bed material on the critical Shields stress. (3) Gravel in armored beds can be more easily mobilized by supplying sand as part of a sediment augmentation scheme. The sand fraction in the subsurface layer of the bed appears to reduce the friction angle of exposed particles. Sediment augmentation using sand has been recently demonstrated to be a viable alternative for mobilizing gravel for the restoration of gravel‐bed rivers downstream of dams. The quantitative evaluation obtained through the experiments reported here may be useful for the design of augmentation schemes. Copyright © 2017 John Wiley & Sons, Ltd.

Incipient motion of coarse uniform gravel

ABSTRACTThe influence of several parameters on the incipient motion of gravels has been carefully examined from theoretical and experimental standpoints. The effect of the longitudinal bed slope is significant and well described with existing methods. This analysis shows that the effects of the grain Reynolds number and relative submergence are negligible for turbulent flows over hydraulically rough boundaries. Laboratory experiments for homogeneous gravels on a plane bed provided detailed measurements of both mean flow velocity and velocity fluctuations for the analysis of the lift and drag coefficients. This analysis of the lift and drag coefficients enables a better evaluation of the Shields parameter for incipient motion as a function of the angle of repose . The theoretical developments presented in this paper are corroborated by the results of our laboratory experiments as well as many others available in the literature.

Effects of invasive crayfish on fine sediment accumulation, gravel movement, and macroinvertebrate communities

AbstractCrayfish are one of the most prolific freshwater invaders, yet the role of crayfish as ecosystem engineers that structure benthic substrates in their nonnative habitat is rarely studied. We used an in situ experimental manipulation to document changes in sediment dynamics and macroinvertebrate density and richness caused by the presence or absence of invasive rusty crayfish (Orconectes rusticus). Rusty crayfish reduced fine-sediment accumulation and increased pit and mound structures in the river bed by moving gravels at the bed surface. We predicted that this omnivorous species would directly reduce macroinvertebrate density and richness, but we found that macroinvertebrate density was higher in treatments with rusty crayfish present and that macroinvertebrate richness did not differ between treatments with and without crayfish. Our findings suggest that rusty crayfish, which are spreading throughout the northeast USA, are probably important engineers of physical habitat structure in stream ecosy...

RFIDを用いた砂礫混合海浜における礫の移動機構の解明

RFIDを用いた砂礫混合海浜における礫の移動機構の解明

Incipient motion of gravel in a bottomless arch culvert

Incipient motion was investigated for four gravel substrate materials in a bottomless arch culvert and a rectangular flume. Different methods for calculating Shields parameter at incipient motion (θ c ) based upon local flow parameters were explored. An incipient motion region for bottomless arch culverts in fully turbulent flow was defined with two bounding curves on Shields diagram. The variation of θ c as a function of relative roughness was examined. Also, a method that utilizes measured flow velocities to determine stable substrate particle diameters for bottomless arched culverts is presented as an alternative to the Shields diagram.

Field Observation of Foreshore Changes around Sand Bags on Oiso Coast

Three sand bags were experimentally installed on the Oiso coast in December 2010 to investigate the effect of short groins for controlling gravel movement on the foreshore. The foreshore changes around these sand bags were measured using a portable laser scanner. During the observation, storm waves with a significant wave height of 4.1 m occurred and significant beach changes were observed around sand bags. Sand bags were effective for depositing gravel around the sand bags.

Gravel Addition as a Habitat Restoration Technique for Tailwaters

AbstractWe assessed the efficacy of passive gravel addition at forming catostomid spawning habitat under various flow regimes in the Cheoah River, a high‐gradient tailwater river in North Carolina. The purpose was to provide a case study that included recommendations for future applications. A total of 76.3 m3 (162 tons) of washed gravel (10–50 mm) was passively dumped down the streambank and into the channel in four locations. Gravel sites differed in terms of average reach slope, bank slope, and the initial volume of gravel added, which could have influenced gravel entrainment. Maps of gravel movement under various flows suggested that large‐magnitude discharges (≥113 m3/s) caused extensive migration; however, less obvious, smaller discharges (∼28 m3/s) still caused substantial shifting, which may influence the stability of catostomid spawning substrates. Following gravel addition, the proportion of gravel in the streambed was significantly higher at all gravel sites. However, comparisons of sites to reference stream reaches suggested that sand, gravel, and cobble were still extremely deficient. Additionally, the volume of gravel was inadequate to create gravel depths that provided suitable habitat for catostomid spawning. Although periodic, passive gravel additions may take years to provide suitable spawning habitat for some fish species, we found that river chub Nocomis micropogon utilized the newly added gravel for spawning.

Flood wash-out conditions of an exotic and invasive plant, Eragrostis curvula, in Arakawa River, Japan

The effect of an exotic and invasive plant, Eragrostis curvula, on the threshold of gravel movement and wash-out conditions of the plant due to flood was investigated in the midstream Arakawa River, Japan. Under various hydraulic conditions (grain diameter, bed slope, and water depth) and plant growth characteristics (clump diameter and plant density), the Shields parameter of the gravel in the plant-vegetated area was estimated using the drag characteristics of the plant measured directly in field and wind tunnel experiments, and the plant's effect on friction velocity was evaluated. The removal threshold of E. curvula could be defined when the friction velocity around the plants was equal to the critical friction velocity of d 84 grain diameter at which 84% volume passed through the sieve. The threshold condition was found to be well expressed by the relationship between the bed slope direction component of the water weight and the drag characteristics due to the plant MD c 1.5, where M is the plant density and D c the clump diameter of E. curvula.

Controlling Diffusion of Gravel in Foreshore Nourishment Using Groins and Detached Breakwaters

Method controlling the diffusion of gravel in foreshore nourishment using short groins and small-scale detached breakwaters were investigated, taking into consideration the fact that the gravel movement concentrates on the foreshore. When beach material composed of mixed grain sizes is nourished on the foreshore, the discharge of the gravel component may be reduced when these structures are installed, while supplying fine sediment to downcoast. The mechanism was investigated using the contour-line-change model considering the change in grain size under the conditions beach nourishment is carried out on a dynamically equilibrium beach with a constant longshore sand transport.

Development and Movement of Sand Body on Shizuoka Coast and Prediction of Fine Sand Movement in Offshore Zone

On the Shizuoka coast, many detached breakwaters have been constructed since 1970 as a measure against beach erosion. After their construction, sand movement as a sand body which is mainly composed of gravel and has a movement velocity of 260 m/yr was observed in the zone shoreward of these detached breakwaters. Due to the analysis of bathymetric survey data, fine sand movement was also found in the zone offshore of the detached breakwaters apart from the gravel movement near the shoreline. In this study, a model for predicting both the movement of a sand body and fine sand movement in the zone off the detached breakwaters is proposed.

Characteristics of Loose Rough Boundary Streams at Near-Threshold

Laboratory experimental results on the turbulent flow characteristics, measured by an acoustic Doppler velocimeter, over loose rough boundaries at the near-threshold of motion are reported. The primary endeavor was to investigate the response of the turbulent flow field, having zero-pressure gradient, to the uniform gravel beds at the near-threshold of motion with reasonably wide range of relative roughness ε∕h (0.02<ε∕h<0.15; where ε=Nikuradse’s equivalent roughness and h=flow depth). Five uniform gravel sizes, ranging from 4.1to14.25mm, were used in the experiments. The vertical distributions of time-averaged velocity, turbulence intensities and the Reynolds stress were measured and analyzed. The variation of the mixing-length is considerably linear with the depth within the inner layer, whose thickness is 0.23 times the boundary layer thickness δ, and the von Kármán constant is obtained as 0.35. The boundary shear stresses were determined by three independent methods, such as using the logarithmic law (the Clauser method), Reynolds stress profiles and bed slope. It is observed that in the inner layer, the logarithmic law of wall for the time-averaged streamwise velocity holds with the von Kármán constant 0.35 and a constant of integration 7.8; whereas in the outer layer, the law of the wake defines the velocity profiles with average value of the Coles’ wake parameter 0.11. Alternatively, velocity profiles based on 1∕nth power law are also put forward, where n is expressed as a function of ε∕δ. The equation of the friction factor f is obtained from the depth averaging of the velocity profile; and the collapse of the estimated f and the measured data (experimental and field) is reasonable. The turbulence intensities being non-isotropic can be defined by an exponential law; whereas the Reynolds stress varies almost linearly with the depth. The values of the Shields parameter for the threshold of gravel motion obtained experimentally correspond closely with the curve obtained from the modified model of Dey considering the present logarithmic law of velocity. For all the aforementioned parameters, thorough statistical and error analyses of the experimental data are done to ascertain the adequacy of the proposed equations.

EFFECTS OF FLOOD DISTURBANCE ON THE MORPHOLOGY, PRODUCTIVITY AND RUNNER-EXPANSION OF Phragmites japonica

he effect of flood disturbance on the morphology of runners, plant productivity and runner-expansion characteristics of Pharagmites japonica was investigated at midstream of the Arakawa River. The dynamic growth model of P. japonica was developed considering the effect of disturbance, i. e., the difference of runner morphology and shoot productivity in the parent colony. The aboveground biomass distribution along the distance from the parent colony was well represented by the model. For analyzing the effect of flood disturbance interval, maximum water levels at three flood events were calculated and evaluated whether the habitat of P. japonica were inundated or not. In addition, the threshold friction velocity of the average grain diameter was compared with the friction velocity at the flood event. Although the gravel movement possibility has a little different tendency with the damaged situation of P. japonica, the clear relationship between the flood interval and the productivity in each habitat is found. The analysis indicates the possibility to calculate the plant productivity under the effect of flood disturbance.

THRESHOLD OF GRAVEL MOVEMENT IN Eragrostis curvula VEGETATED ZONE AND ITS REMOVAL CONDITION BY FLOOD IN RELATION TO THE PLANT'S DENSITY AND GROWTH STAGE

Field observation was conducted to elucidate the effect of Eragrostis curvula on the threshold of gravel movement at midstream of the Arakawa River. Under various hydraulic conditions (particle diameter, bed slope and water depth) and growth conditions (colony diameter and density of the plant), Shields parameter of the gravel in the plant-vegetated area was estimated using the drag characteristics of the plant and calculated friction velocity affected by the plant. Threshold of gravel movement of median grain size (d50) and d84 (84% of the grain weight) around the plants was evaluated by comparing friction velocity of the flow condition with the critical friction velocity of the diameter. The removal threshold of Eragrostis curvula was defined at which the friction velocity affected by the plant's drag is equal to the critical friction velocity of d84. The threshold condition related to HI (H: water depth, I: bed slope) and the drag by plant was validated for a flood in the Arakawa River and for two floods in the Yoshino River.