Sediment-laden River Research Articles

Morphodynamics of the erosional phase of crevasse-splay evolution and implications for river sediment diversion function

Despite being a primarily depositional landform, a crevasse splay experiences an initial evolutionary phase that is primarily erosional as sediment-laden river water spills from a main river channel and incises a new route through the river banks and levee into an interdistributary basin or floodplain. This phase sets the dimensions and the conveyance properties of the crevasse, which, in turn, influences the continued expansion or closure of the crevasse channel. However, little is known about the controlling morphodynamics or how the erosional processes transition to depositional processes during this phase. The objective of this study is to investigate these phenomena at the West Bay sediment diversion (Louisiana, USA) using coupled field observations and numerical modeling. The West Bay diversion was cut into a lower Mississippi River levee to mimic the function of a crevasse-splay, i.e., to divert river water and sediment to an adjacent receiving basin for land-building purposes. Bathymetric measurements show that the diversion channel experienced significant natural morphologic evolution during the initial decade (2004–2014). Hydrodynamic and sediment transport modeling suggests that this evolution initially increased the discharge of flow and sediment through the crevasse as the channel became wider and deeper and altered its orientation relative to the main river flow direction. After 5years, the model results predict that further evolution led to monotonically reduced diversion discharges. During this time, natural and engineered sediment deposition in the receiving basin decreased predicted basin-flow velocities and promoted a backwater effect that reduced the sediment transport capacity of the diversion channel. Observations during the final 2years show that much of the initial erosion around the diversion had abated indicating that diversion morphology may have stabilized. A modeling sensitivity analysis confirmed that the observed changes to channel geometry and orientation likely promoted flows of water and sediment through the diversion while increases in basin-bed elevation would have had a contrary effect. The morphodynamic evolution of the West Bay diversion documented in this study presents a model indicative of the erosional phase of crevasse-splay evolution in a deltaic distributary fluvial network. Study results offer an analogue on how an engineered river sediment diversion constructed for coastal restoration may function during its first years of operation and suggest that the desired land-building processes may take time to become established.

Monitoring the river plume induced by heavy rainfall events in large, shallow, Lake Taihu using MODIS 250m imagery

Abstract Knowledge of stormwater river plume dynamics is important for the management of lake water quality because river discharge associated with rainstorms can be a major source of pollutants for lake waters. Total suspended matter (TSM) derived from the discharge of sediment-laden rivers is highly variable over a wide range of time and space scales. In the present study, the first use of remote sensing to monitor the river TSM plume was conducted to investigate the effects of heavy rainfall events on Lake Taihu by the largest inflowing river (Tiaoxi River) based on a calibrated and validated model using daily 250 m MODIS imagery in band 1 (620–670 nm). From 2004 to 2013, 48 MODIS images of 20 heavy rainfall events were obtained, showing that the area of the TSM plume significantly increased in the waters adjacent to the inflowing river, reflecting runoff input. The TSM concentration of the river plume after heavy rainfall was significantly higher than that before rainfall (ANOVA, p ˂ 0.001). A significantly positive correlation between the TSM plume area and the rainfall amount in heavy rainfall events ( p ˂ 0.01) was also observed. The heaviest rainfall event, in October 2013, caused a river plume with an area of 302.8 km 2 , which lasted for more than 10 days. The significant increase in the frequency and rainfall amount of rainstorms and large rain in the past 50 years (1965–2014) in Lake Taihu under global warming indicated an important role of remote sensing in monitoring the river plume resulting from heavy precipitation. The present study demonstrates that remote sensing tools can be valuable instruments in the detection and tracking of the effect of heavy rainfall events on the distribution and diffusion of the TSM concentration in the lake. The results obtained from the present study are valuable for further hydrological research on the Tiaoxi River, particularly for the immediate assessment of flood impacts on soil erosion of the catchment.

Estimating the Bulk Refractive Index and Related Particulate Properties of Natural Waters From Remote-Sensing Data

A proof-of-concept method is developed to estimate bulk refractive index ( ${{{\eta }}_{{\bm {bp}}}}$ ) of particles for deriving information on their composition and optical properties of natural waters using satellite ocean color data. It estimates ${{{\eta }}_{{\bm {bp}}}}$ as a function of the backscattering ratio ( ${{\bm {B}}_{\bm {p}}}$ ), hyperbolic slope of the particle size distribution ( ${{\xi }}$ derived from the beam attenuation slope ${{\beta }}$ ), and apparent density of particles ( ${{{\rho }}_{\bm {a}}}$ ) as described in our previous inversion model. For deriving these parameters from remote-sensing data, large in situ measurement data of the remote-sensing reflectance ( ${{\bm {R}}_{{\bm {rs}}}}$ ), particulate scattering ( ${{\bm {b}}_{\bm {p}}}$ ), backscattering ( ${{\bm {b}}_{{\bm {bp}}}}$ ) beam attenuation ( ${{\bm {c}}_{\bm {p}}}$ ), and seawater constituents’ concentrations are used to establish the required relationships and derive the model parameters (i.e., ${{{\eta }}_{{\bm {bp}}}} \leftarrow {{\bm {B}}_{\bm {p}}}$ , ${{\xi }}$ , ${{{\rho }}_{\bm {a}}}$ ; ${{\bm {B}}_{\bm {p}}} \leftarrow {{\bm {R}}_{{\bm {rs}}}}$ ; ${{\xi }} \leftarrow {{\beta }} \leftarrow {{\bm {c}}_{\bm {p}}} \leftarrow {\bf Turbidity}$ ; ${\bf Turbidity} \leftarrow {{\bm {R}}_{{\bm {rs}}}}$ ; and ${{{\rho }}_{\bm {a}}} \leftarrow {{\bm {c}}_{\bm {p}}}$ ). When validated with those derived from in situ data spanning the large dynamic range in water optical properties and relevant water constituents impacting the remote-sensing signal, the derived model parameters and bulk refractive index had errors of a few percent which falls well within the benchmark for a validated uncertainty of ${\rm \pm }{\bf 35}\% $ endorsed for the remote-sensing retrieval of chlorophyll- $a$ in oceanic waters. The model was applied to regional and global images of satellite ocean color observations provided by the MODIS-Aqua sensor. Global images of seasonal climatology over a decade of MODIS-Aqua ocean color observations provided interesting insights into the seasonal variability of ${{{\eta }}_{{\bm {bp}}}}$ in coastal and open ocean waters. To further investigate the bulk particulate assemblages in some regional waters, several MODIS-Aqua imageries from different regional waters dominated by sediment-laden river plumes and phytoplankton blooms were analyzed. Satellite retrievals of the ${{{\eta }}_{{\bm {bp}}}}$ varied from 1.035 to 1.05 for clear oceanic waters, 1.045–1.07 for phytoplankton-dominated waters (higher water content), 1.05–1.15 for floating algal blooms and Cocolithophore blooms, 1.07–1.10 for coastal waters dominated by detrital particles, and 1.10–1.28 for river plume and sediment-laden coastal waters (lower water content). These results were consistent with those expected for the waters examined, being in excellent agreement with the previous reports and estimates based on the laboratory/ in situ measurements and modeling studies. Given the fact that there is currently no satellite-based method to differentiate between bulk particulate compositions, the new method provides a valuable tool for estimating ${{{\eta }}_{{\bm {bp}}}}$ values as a proxy for the apparent density and composition of particles and such information when derived from satellite ocean color data provides new tools for improving our current understanding of particle dynamics of pelagic ecosystems, advancing biogeochemical modeling, assessing the global ocean ecosystem, and elucidating the coastal processes.

Effect of Sand Erosion on Turbine Components: A Case Study of Kali Gandaki “A” Hydroelectric Project (144 MW), Nepal

In high sediment laden river projects or silt affected power stations, the frequency of repair and maintenance of underwater parts is comparatively higher which leads to increase the overall forced outages per year for repair The extent of the major maintenance will depend on the operating condition such as suspended sediment load passing through the turbine and how the machine was loaded during the operation. This paper illustrates the analysis of sediments, effect of sand erosion and maintenance of turbine of Kali Gandaki “A” Hydroelectric Plant (144 MW). The paper also describes the repair methods used for different turbine components to minimize the effects induced by sediment erosion. HYDRO Nepal JournalJournal of Water, Energy and EnvironmentIssue: 17, July 2015

Experiment Study on Sediment Control and Sediment Discharge of Lake-Type Reservoir on Sediment-Laden River

Taking Derisubaoleng Reservoir as an example, the experiment is mainly based on physical model and numerical simulation to study the effect of sediment control and discharge of the sediment retaining weir. With the help of the reservoir terrain a sediment retaining weir is built to form a“ deputy reservoir” ,which makes the sediment passing road more narrow, As a result, the ability of sluicing sediment is stronger than before. The purpose of this paper is to search a new idea to solve sediment problem in lake-type reservoir on sediment-laden river. The study result indicates that the sediment retaining weir both can prevent sediment being deposited in north “deputy reservoir” and can enhance the ability of sediment discharge in south “main reservoir” . Thus ,the sediment retaining weir is a effective engineering measure to solve sediment problem in lake-type reservoir.

A Novel “FlocDrifter” Platform for Observing Flocculation and Turbulence Processes in a Lagrangian Frame of Reference

AbstractA novel drifter platform was used to measure the properties of aggregated particles called flocs—a key component of sediment transport in muddy environments. Also concurrently measured were turbulence, suspended sediment concentration (SSC), velocity, and salinity in both Lagrangian and Eulerian frames of reference. In Lagrangian mode the system performed well in a heavily sediment-laden river, providing measurements over a large spatial scale. The platform navigated itself through a complex geometry encompassing many bends and significant depth changes. Observed velocities relative to the drifter and salinities indicated that the drifter motion was almost Lagrangian with minimal slippage between the drifter and the water motion. The small amount of slippage that did occur was sufficient to ensure that the drifter oriented itself into the oncoming flow.High-quality in situ images of flocs were collected using a high-magnification floc camera (FlocCam). An automatic image analysis routine was developed to identify and characterize flocs within each FlocCam image, employing an artificial neural network (ANN) to ensure that only in-focus particles were included in the analyses. The results indicated that the FlocCam system had an upper working SSC limit of around 350–400 mg L−1.The SSC estimates show that the drifters encountered considerable variability as they were advected downstream; however, concentrations predominantly remained under the image processing threshold of 350–400 mg L−1. The system captured the evolution of floc characteristics over short spatial scales (hundreds of meters). The median floc size (d50) was found to be positively correlated with SSC (r2 = 0.5). A comparison between Eulerian and Lagrangian floc histories can then be used to evaluate the role of antecedent conditions within the flocculation process.

Large-scale dam removal on the Elwha River, Washington, USA: Fluvial sediment load

The Elwha River restoration project, in Washington State, includes the largest dam-removal project in United States history to date. Starting September 2011, two nearly century-old dams that collectively contained 21±3millionm3 of sediment were removed over the course of three years with a top-down deconstruction strategy designed to meter the release of a portion of the dam-trapped sediment. Gauging with sediment-surrogate technologies during the first two years downstream from the project measured 8,200,000±3,400,000tonnes of transported sediment, with 1,100,000 and 7,100,000t moving in years 1 and 2, respectively, representing 3 and 20 times the Elwha River annual sediment load of 340,000±80,000t/y. During the study period, the discharge in the Elwha River was greater than normal (107% in year 1 and 108% in year 2); however, the magnitudes of the peak-flow events during the study period were relatively benign with the largest discharge of 292m3/s (73% of the 2-year annual peak-flow event) early in the project when both extant reservoirs still retained sediment. Despite the muted peak flows, sediment transport was large, with measured suspended-sediment concentrations during the study period ranging from 44 to 16,300mg/L and gauged bedload transport as large as 24,700t/d. Five distinct sediment-release periods were identified when sediment loads were notably increased (when lateral erosion in the former reservoirs was active) or reduced (when reservoir retention or seasonal low flows and cessation of lateral erosion reduced sediment transport). Total suspended-sediment load was 930,000t in year 1 and 5,400,000t in year 2. Of the total 6,300,000±3,200,000t of suspended-sediment load, 3,400,000t consisted of silt and clay and 2,900,000t was sand. Gauged bedload on the lower Elwha River in year 2 of the project was 450,000±360,000t. Bedload was not quantified in year 1, but qualitative observations using bedload-surrogate instruments indicated detectable bedload starting just after full removal of the downstream dam. Using comparative studies from other sediment-laden rivers, the total ungauged fraction of <2-mm bedload was estimated to be on the order of 1.5Mt.

Quality control in welding repair of Pelton runner

Turbine material is heavily eroded when operated in sediment-laden rivers. Erosion reduces the efficiency and increases operational risk. Therefore, welding repair is chosen in Nepal due to low cost to build up the eroded surface. Welding repair of hydraulic turbine does not impair the material property but, it can be catastrophic when carried out improperly. Such problem has been observed in Khimti Hydro-Power (KHP) in Nepal. The Pelton runner at KHP had operated without any major defects for 22,000 h before repair. But, root cracks extending up to 110 mm deep was revealed during inspection of welding repaired runner after 11,000 h of operation. Therefore, quality control during repair of runner is essential to achieve the desired properties and avoid catastrophic failures. Various factors like quality of weld deposit, preheating and post weld heat treatment conditions, and design changes during repair cause failure. The paper presents the possible causes of failure of Runner 1, 3 and 4 with reference to the operation and maintenance history, and quality control measures used in repair of Runner 7 of KHP.

Study on Evolvement of High Beach and Deep Channel of Reservoir in the Sediment-Laden Rivers

According to datas of Sanmenxia Reservoir and physical model test of Xiaolangdi Reservoir during later sediment retaining period, the paper study evolvement of high beach and deep channel of reservoir in the sediment-laden rivers. The results show that: 1The evolution of high beach and deep channel is as follows, firstly, beach and channel increase synchronously , and then scour happens in channel. Channel scour and scour amount is crucial to form high beach and deep channel. 2It is found that tributaries were equivalent to the horizontal extension of mainstream riverbed. The deposition process of tributary is closely related to many factors of natural topographic condition, deposition morphology of mainstream at the confluence area of mainstream and tributary and so on. The cross-section of tributary kept uplift horizontally, and sand bar has formed in some tributary estuary. 3Rainfall erosion formed in flood period is beneficial to forming hyper-concentrated flow, to a certain extent; it can recover channel storage capacity, and play an important role on utilizing long-term comprehensive benefits. Studying evolvement of high beach and deep channel can supply some technical supports for regulating operational mode of Xiaolangdi Reservoir during later sediment retaining period and prolonging service life.

Problems on Sediment Treatment and Utilization on Sediment-Laden River

The study of the beginning of the sediment treatment and utilization is to build the levee of the river and used for construction. The problems for treatment and utilization are among the two problems. One is the money, and the other is the amount for used is much less than the sediment from above. So the plan for the utilization is important.

Boundary shear stress in asymmetric rectangular compound channels

A series of nine experiments was performed in a physical model of an asymmetric compound channel to quantify the boundary shear stress at the interface of the bed of a main channel and floodplain. Commonly used equations of shear stress distributions across the bottoms of the main channel and floodplain interfaces were analyzed and tested for various types of asymmetric compound channels and their flow conditions. The lateral momentum transfer between the deep main channel and the adjoining shallow floodplains was found to greatly affect the shear stress distribution at the bottoms of the main channel and the flood plain subsections. Different dimensionless ratios of shear stress distributions were obtained and related to the relevant parameters. Some important results concerning the uniformity of the shear stress distribution, which is significant in sediment-laden rivers to state the possible locations of erosion and deposition, are presented.

Advances and Prospects of Reservoir Sedimentation Problem on Sediment-Laden River

Reservoir sediment problem on sediment-laden river is the main puzzle problem in reservoir operation. Reservoir sedimentation, reservoir operation, reservoir sediment treatment and utilization and simulation of reservoir are analyzed in the paper. Difficulty is also provided during the research process. And reservoir sediment research on Yellow River is prospected. The paper can be helpful to provide the basis for reservoir sediment problem on sediment-laden river, and also point out the direction of reservoir sediment research on Yellow River.

Environmental controls at multiple scales for the western Pacific: An Okinawan case study

In this study, the principal controls on the coastal environment around the Pacific island of Okinawa, typical of the many mountainous islands of the sub-tropical and tropical northwest Pacific in the arc from Melanesia to the Ryukyu Islands, are investigated. Two principal satellite remote sensing data products were used to observe properties at regional-scale and in the Okinawan coastal zone: (1) AVHRR sea surface temperature (SST) for 1985–2006 and (2) a SeaWiFS ocean colour variable to estimate combined sediment and chlorophyll-a loadings for 1998–2006, along with direct observations (e.g. climatological data, river discharge, suspended sediment and typhoon tracks). Analysis suggested that coastal SST is strongly influenced by the outer ocean SST, indicating a regional control. However, the local winds, with associated summer rainfall and copious sediment-laden run-off, had a significant secondary impact. Typhoons are also an important factor leading to ocean colour variation. Along the western coastal zone of Okinawa, the winter East Asian Monsoon causes significant upwelling and seafloor sediment removal, while terrestrial impact is a significant secondary control in summer on ocean colour variability via sediment-laden river run-off. Previously noted changes in the magnitude of extreme rainfall events in the area suggest that sediment delivery to the coastal zones of islands in the region has been increasing in recent decades, providing a combined climate and terrestrial impact on the coastal environment. Although typhoons and heavy rainfall are episodic events, appropriate land management on the many hilly and mountainous islands of the sub-tropical northwestern Pacific is needed if such events are not to lead to deterioration, and decrease of resilience, of coastal ecosystems.

Spatial Change of Grading Pattern of Subaqueous Flood Deposits In Lake Shinji, Japan

Abstract We acquired three geo-slicer cores along a longitudinal profile on the subaqueous portion of the Hii River delta built since the 1630s in Lake Shinji, western Japan. Grading patterns of 26 individual sand beds in the cores vary spatially. We interpret these sand beds as subaqueous flood deposits from their sedimentary structures, the geomorphology of the delta lobe, and the absence of hydrodynamic influences other than river floods entering the lake. Most sand beds at shallow depths (< 4 m below the water surface) display triple stacks of inverse-to-normal grading. Single inverse-to-normal grading appears between 4 and 5 m depth, and normal grading dominates in deeper beds. Inverse and normal grading could reflect the waxing and waning of the parent flow, respectively. We explain the occurrence of triple stacks of inverse-to-normal grading in shallower horizons and single inverse-to-normal grading in deeper horizons as consequences of lateral movement of the plunge point of flood plumes during the course of flood events. Spatially decelerating sediment-laden river plumes steeply increase their velocity after they plunge beneath the water surface. In depth-limited proximal areas of a subaqueous delta, back-and-forth translation of the plunge point over a fixed point due to the waxing and waning of river discharge leads to three cycles of waxing and waning of flow velocity, and the resulting deposits at the fixed point would have triple stacks of inverse-to-normal grading. In the distal parts of the delta, velocity of fully plunged hyperpycnal flow increases and then decreases, reflecting directly the waxing and waning of river discharge, and the resulting deposits would be composed of single inversely-to-normally graded beds. In the most distal parts, the slower initial part of the hyperpycnal flow may be overtaken by the succeeding faster part to yield a monotonically waning flow at a fixed point. This process may have resulted in sand beds with uniformly normal grading in lower (distal) horizons. Assuming that flood hydrographs for the Hii River have not changed since the 17th century, these findings mean that the momentum of river flow during floods propagates to the outflow differently at different distances from the river mouth. Our results show that in parts of the delta-front slope, the outflow of river floods accounts for the inverse-to-normal grading considered to be an important basis for identifying hyperpycnal flow turbidites. However, in other parts of this environment, grading patterns of flood deposits do not necessary reflect the flood hydrograph. Overdependence on inverse-to-normal grading in identifying hyperpycnal flow deposits may lead to inaccurate estimations of their frequency in the sedimentary record. On the other hand, special care is needed for the reconstruction of paleo-flood hydrographs using sedimentary records.

Effect of silt erosion on Francis turbine: a case study of Maneri Bhali Stage-II, Uttarakhand, India

Some of the most attractive hydro power plants are severely affected by silt erosion at certain times of the year, particularly during monsoons. Erosion of hydro-turbine components through sediment-laden river water is one of the most challenging problems in the Himalayan region. Detailed analysis of sediments, erosion of runner blades, guide vanes and labyrinth of a 304-MW hydro power plant has been reported. The efficiency of a desilting chamber in removal of particles of size greater than the threshold particle size (0.15 mm) has been verified for a hydro power plant in Uttarakhand, India. Finally, weight loss of turbine and subsequent reduction in the turbine's efficiency due to silt erosion were also investigated.

Numerical Modeling of Plane Two-Dimensional Flow-Sediment Movement in Inland and Heavy Sediment-Carrying Rivers

The mathematical model of plane two-dimensional flow-sediment in continental sediment-laden river is established in this paper. The two-dimensional model equation is discreted with finite element method and coefficient matrix of ordinary differential equation is approximately dealt with mass-concentration principle, then solve the set of ordinary differential equations with the difference scheme which is first prediction, then correctness and iteration, the stability of this calculation process is better and the efficiency of calculation is comparatively high. The two-dimensional model is applied in numerical modeling of the flow-sediment movement of Yerqiang river middle courses, compared the numerical results with the measured data, which indicates that the numerical results are in good agreement with the measured data, which also prove the reliability and adaptability of the model and calculated method.

Simulation of wave damping during a cold front over the muddy Atchafalaya shelf

The Atchafalaya Shelf off the Louisiana coast in the United States is characterized by fine grained sediments dispersing into the shelf from the lower Atchafalaya River and Wax Lake outlets. Rapid seaward flushing of the sediment-laden river plumes, due to water level set-down during cold front passages forms a fluid mud layer close to the bottom, which effectively dampens the wave energy. In this study, the performance of a phase-averaged spectral wave model was skill assessed based on the wave data recorded close to the southern periphery of the mud zone during several days in March 2009. Separation of wave spectra into sea and swell partitions showed that the wave model overestimated the sea waves generated by northerly wind during the cold front passage. A non-stationary scheme was needed to solve the wave action balance equation to include the wind dynamics during the cold front passages over the study area. A recently developed mud-induced dissipation term was improved by modifying its algorithm for solving the implicit dispersion equation. The modified model became efficient enough to be used for non-stationary calculations. The thickness, density, kinematic viscosity of the mud layer, and its offshore extent were determined by trial and error. The mud-induced energy dissipation term enabled the model to reproduce the energy attenuation of short waves by the fluid mud. A high value of mud viscosity (0.01–0.1m2/s) was required to obtain good agreement with in situ measurements when the maximum wave height occurred. However, the model using lower values of mud viscosity (0.001–0.01m2/s) was more successful in reproducing the measured wave spectra from a few hours after the maximum wave activity. The simulation results also showed that presence of fluid mud with high value of mud viscosity hindered the wave growth in shallow water due to suppression of high frequency waves.

The High Efficient Sediment-Transport Water Volume in the Lower Yellow River

Analyzed the sediment-transport process in high sediment-laden river, the new concept and calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Meanwhile, relations between them and influencing factors are confirmed to calculate efficient sediment-transport water volume after construction of the Xiaolangdi reservoir. Results gained from these functions are consistent well with the facts of real water-sediment regulation in LYR.

High Efficient Sediment-Transport Water Volume in High Sediment-Laden River

Analyzed the sediment-transport process in high sediment-laden river, the new concept and calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Meanwhile, relations between them and influencing factors are confirmed to calculate efficient sediment-transport water volume after construction of the Xiaolangdi reservoir.

The concept and calculating method for efficient sedimenttransport water volume in high sediment-laden river

The concept and calculating method for efficient sedimenttransport water volume in high sediment-laden river