Sediment Flushing Research Articles

The Hybrid System of Fluidization and Sediment Flushing for Maintenance Dredging Technique

The Hybrid System of Fluidization-sediment flushing is a dredging technique that combines the functions of fluidization and suction in the same fluidization pipe using a perforation pipe. The purpose of this study was to address an easier dredging method using fluidization pipes. 2-dimensional (2D) experimental physical modeling research and multiple linear regression analysis were used to process the test result. The results found that for optimal sediment flushing after the sediment layer was agitated by fluidization, the influence parameter was analyzed must follow the limitations of the experimental result, such as the hole diameter (Df) is not more than 5 mm (Df < 5 mm), the hole distance (ɑ) is less than 5 cm (ɑ/db < 5 cm), the pump head (HP) is small, and the fluidization pipe depth/sediment thickness (db) can be larger. The research findings are presented in the correlation equation which indicates the relationship of dimensionless parameters was Vs/Vw = 1/Df ((ɑ/db), (HP/db), (t.(g×0.5)/(db0.5)), (v/(g.db(S – 1)0.5)) which can be applied to 3-dimensional experiments and field experiments. One of the advantages of the hybrid system of fluidization-flushing sediment is its ease of use and lack of impact on the aquatic environment as a dredging technique. Doi: 10.28991/CEJ-2024-010-07-013 Full Text: PDF

Hydraulic Flushing of Sediment in Reservoirs: Best Practices of Numerical Modeling

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines.

Modeling the total outflow of reservoirs using Wavelet-developed approaches: a case study of the Mahabad Dam reservoir, Iran

Abstract Lack of water reserves in artificial reservoirs poses serious challenges in meeting various human requirements, especially during periods of water scarcity. In the current research, the Total Outflow (TO) of the Mahabad Dam reservoir has been estimated under six scenarios including the Monthly Cumulative Rainfall (MCR), Snow Water Equivalent (SWE), Stream Flow (SF), Mean Temperature (T), Pan Evaporation (Ep), Sediment Flushing Gate Outlet (SFGO), Penstock Outflow (PO), Evaporation Losses (EL), Cumulative Non-Scheduled Discharge (CNSD), Live Storage Volume (LSV), Water Surface Area (WSA), Monthly Water Level (MWL), Total Allocated Water (TAW), and Generated Power (GP) variables for the 2001–2021 period. Estimation of TO is accomplished via individual and wavelet-developed (W-developed) data-mining approaches, including Artificial Neural Networks (ANNs), wavelet-ANNs (WANNs), adaptive neuro-fuzzy inference system (ANFIS), wavelet-ANFIS (WANFIS), Gene Expression Programming (GEP), and wavelet-GEP (WGEP). The obtained values of RMSE for WGEP1–WGEP6 models account for 5.917, 2.319, 4.289, 8.329, 10.713, and 9.789 million cubic meters (MCM), respectively, based on the following scenarios: reservoir inlet elements, reservoir outlet elements, consumption, storage characteristic, climate, and energy. This research revealed that combining the wavelet theory (WT) with individual models can be a powerful method to improve the modeling performance in the TO estimation.

Experimental Investigation on Reservoir Sediment Flushing through a Bottom Tunnel with an Initially Covered Intake

Reservoir sedimentation is of worldwide concern, involving not only reservoir benefits, but environmental and ecological issues. Sediment flushing is one of the most common and effective methods for alleviating sedimentation and its negative impacts. To date, however, it has remained unknown whether sediment flushing can be accomplished through a bottom tunnel once its intake has been covered by sediment deposits. Here, a total of 65 runs of flume experiments were conducted to investigate the threshold conditions for occurrence of sediment flushing. The results demonstrate that higher water level, smaller cover layer thickness, shorter tunnel length, and steeper tunnel slope favor the occurrence of sediment flushing. Physically, as the gate located at the tunnel intake is opened, the sediment deposits immediately upstream of the intake collapse and enter the tunnel, entraining water. A mass of hyperconcentrated water-sediment mixture is generated, in which the amount of sediment depends on the cover layer thickness. If the water level is sufficiently high, the cover layer thickness is low, the tunnel slope is steep, or the tunnel is short, the pressure difference between the inlet and outlet of the tunnel suffices to drive the water-sediment mixture to move down to the outlet, overcoming the resistance due to the tunnel boundary. This way, sediment flushing is accomplished. Based on dimensional analysis of the observed data, a threshold condition is proposed for the occurrence of sediment flushing. It is also shown that an equilibrium scour hole is formed immediately upstream of the tunnel intake, and an empirical model for the scour hole geometry is proposed. The present findings can be exploited to improve sediment-rich reservoir planning, design, and operation for benefit maximization and eco-environmental wellbeing.

Monitoring and Modelling of Sediment Flushing : A Review

With ever decreasing potential for suitable new dam sites, sustainable use of existing water reservoirs is of paramount importance. In absence of appropriate measures, reservoir storage is continually reduced due to sedimentation. One option to remove sediment deposits is hydraulic flushing. During the flushing operation, bottom outlets are open and water and sediment released. Whether flushing successfully removes sediment depends on a number of factors, such as bottom outlets capacity, reservoir shape and water availability. Modelling is often used to assess viability of flushing for sediment management in the reservoir, as well as to design the operations and optimize their scheduling. One-dimensional numerical models are preferred for long term simulations, assessments on of a large number of scenarios, and optimization studies. Two- and three-dimensional numerical models and physical models can be used, each on their own or in combination as hybrid models, to understand local scouring near the gates and other details of operation. Monitoring of flushing operations can help improving their efficiency while at the same time limit downstream impacts. General monitoring of the reservoir and its catchment can help understanding the sedimentation problem and thus facilitate preparation of efficient sediment management strategies. Live monitoring of sediment concentrations is possible with modern equipment though not without challenges, and reservoir survey can be performed faster. Earth observation techniques are also an attractive option, allowing to monitor large areas and areas of difficult access, as well as to provide historical information going back several decades. This paper reviews monitoring and modelling approaches published in the literature, as well as presents some previously unpublished analyses.

Preliminary Experiment on Reservoir Sediment Flushing

Prediction of reservoir sediment flushing requires a large amount of sample data obtained from long-term field measurements. Before running the complete laboratory experiments to understand the flushing mechanism, preliminary experiments using an acrylic tank and a simple piping system were carried out. The acrylic model consists of a constant head tank and a reservoir model. The constant head tank is a model that ensures a continuous and consistent flow rate contribution to the next model component, namely the reservoir model. The Reservoir model is a component for modeling the sediment flushing process, where the sediment deposits have been prepared. The reservoir sediment flushing experiment used a bottom outlet with a circular hole connected by a pipe to a valve to release sediment. The valve is assumed to be a sluice gate that can be opened and closed for sediment flushing. Preliminary experiments show that the model can simulate the flow of reservoir sediment flushing through the bottom outlet with stable reservoir water depth, operation of sluice gates, and the presence of scour cones in the sediment.

Numerical Investigation of Sediment Flushing and Morphological Changes in Tamsui River Estuary through Monsoons and Typhoons

The removal of reservoir silt and the restoration of existing reservoir capacities through land excavation and hydraulic sediment flushing have become necessary. Hydraulic sediment flushing discharge changes flow and sediment conditions of the downstream river channel. In the Tamsui River estuary in Taiwan, sediment flushing from the Shihmen reservoir upstream has potential impacts on the morphology of the navigation channels and the adjacent coasts. This study employed a validated coastal and estuarine processes model to investigate: (1) the influence of sediment flushing and tidal levels on morphological changes during flood and flushing-discharge operations of the reservoir, and (2) the differences in morphological changes on the estuary between monsoon and typhoon seasons. The prediction of the morphological changes was carried out by simulating hydrodynamic and morphodynamic processes under multi-year synthetic conditions combined by northeast monsoon and three historical typhoon events. The simulation results reveal that during the operation of sediment flushing when the peak discharge of river flood flow reaches the estuary section at ebb tides, more sediment can be transported to the open sea than that at flood tides. Additionally, the nature reserve area on the left bank of the estuary is eroded during monsoon and silted in typhoon seasons.

Simulation of Sediment Flushing in Paonia Reservoir of Colorado

AbstractA one-dimensional sediment transport model (SRH-1D) was updated to simulate a sediment sluicing and flushing plan for the Paonia Reservoir, located on Muddy Creek in western Colorado. The P...

Application of Godunov Type 2D Model for Simulating Sediment Flushing in a Reservoir

Worldwide large dams are being discouraged on environmental, social or political grounds. Small-to-medium-sized cascade reservoirs with the hydropower projects are being preferred. However, the flushing of sediments by drawing down the reservoir is of immense interest to increase the useful life of a reservoir. In our research, we applied a depth-averaged, Godunov type model to simulate the 2D flushing. The solution technique employed possesses shock-capturing property and is especially suitable to dam-break accompanied by intense sediment transport phenomenon. The retrogressive erosion and flushing out a large volume of sediment in a very small time interval with creation of transitory flow conditions was tackled by this technique. We applied the model to two experiments; the first was a physical model study, while the second case pertained to a laboratory flume. The model validation was made through the bed topography change and the computation of the flushing efficiency. The model was in good agreement with the bed changes demonstrating its suitability to reproduce the phenomenon of retrogressive channel as well as lateral erosion. The accompanying sensitivity analysis focused on evaluating the influence of a number of parameters critical to a successful flushing simulation exercise.

Sediment Flushing of Reservoirs under Environmental Considerations

Freshwater reservoirs are under threat because of huge amounts of sediments deposited annually. Sediment flushing seems to be effective to preserve reservoir storage, but it may have negative environmental impacts on downstream ecosystems such as fish mortality. Therefore, providing a suitable flushing strategy that could be compatible with the river ecosystem downstream is of great importance. Two numerical models were developed in this paper to predict the suspended sediment concentration (SSC) on the reservoir-river system and effects of different flushing scenarios on aquatic life. Developed models were applied to the Dez Resevoir system in the southwest of Iran which has suffered from the sediment problems in two last decades. The suitable values for flushing time, concentration limits, and flushing discharge have been recommended in this research by use of the existing information and previous flushing records, as well as field measurement and modeling. Based on social, environmental and technical limitations, March is the appropriate time for flushing. After hydraulic simulation of different flushing scenarios and sediment routing along the river, flushing with 1275 and 800 cubic meter per second with 30 and 20 g per lit concentration in dry and wet season respectively are feasible and have minimum environmental impacts.

Simulation of Reservoir Sediment Flushing of the Three Gorges Reservoir Using an Artificial Neural Network

Reservoir sedimentation and its effect on the environment are the most serious world-wide problems in water resources development and utilization today. As one of the largest water conservancy projects, the Three Gorges Reservoir (TGR) has been controversial since its demonstration period, and sedimentation is the major concern. Due to the complex physical mechanisms of water and sediment transport, this study adopts the Error Back Propagation Training Artificial Neural Network (BP-ANN) to analyze the relationship between the sediment flushing efficiency of the TGR and its influencing factors. The factors are determined by the analysis on 1D unsteady flow and sediment mathematical model, mainly including reservoir inflow, incoming sediment concentration, reservoir water level, and reservoir release. Considering the distinguishing features of reservoir sediment delivery in different seasons, the monthly average data from 2003, when the TGR was put into operation, to 2011 are used to train, validate, and test the BP-ANN model. The results indicate that, although the sample space is quite limited, the whole sediment delivery process can be schematized by the established BP-ANN model, which can be used to help sediment flushing and thus decrease the reservoir sedimentation.

Effectiveness of Sediment Flushing by Using By-Pass Flush Canal

The objective of this study was to analyze the effectiveness of sediment flushing system of BY PASS channel with 1 door, 2 door and 3 door at a floodway. To determine which was the most effective, empirical model of effectiveness of each channel of sediment flushing were built. The object model of this study was the Floodway Sedayu Lawas, located in Lamongan, East Java Province. This study uses Hydraulic Physical Model Test. Built and test the model conductedin the Laboratory of River, in Surakarta, Cental of Java. The variables of this study were sediment weight (W), water depth(H), sediment mass density (ρs), sediment diameter (ds), waterflow rate (Q), and floodway wide (Bo)

The Effect of Water Level on The Effectiveness of Sediment Flushing

This research is focused on determining the effective flushing water level in pressure flushing activity at storage sedimen based on the hydraulic physical model test in the laboratory. The effective water level is the elevation of water level in sediment flushing which result in the highest concentration of sediment scours. Effective flushing water level is the elevation of water level near the top layer of sediment deposit which can trigger the erosion of the top layer of sediment so that it creates a maximum scours. That elevation is known as Effective Flushing Water Level (EFWL). This research was conducted in the laboratory using Wonogiri Reservoir prototype, with scale model of 1:66.67. The model operated without inflow, started from control water level (CWL) .and lowered gradually by operating the flushing gates. The gates were operated of a = 2.50 cm. The flushing implementation was repeated with variation of sediment thickness Hs=1.50; 3.00; 3.75 and 4.50 cm. The water level, sediment concentration, flushing discharge, and the flow velocity in the upstream of the gates were observed every 1.50 cm lowered of water level. Coal dust was used in this research to substitute sediment material. The result of this research is expected to be used as an initial consideration of effective sediment flushing in Wonogiri reservoir protoype in order to reduce the capacity loss of the reservoir due to sedimentation , or in other words to extend the life time plan of reservoir.

Multi-Objective Reservoir Operation with Sediment Flushing; Case Study of Sefidrud Reservoir

In this study, the non-dominated sorting genetic algorithm (NSGA-II) is used for the multi-objective optimization of the Sefidrud reservoir in Northern Iran. The main objectives include water supply, hydropower generation and sediment flushing. In addition to some physical constraints such as the reservoir storage and the outlet flow, maximum flushing outflow and non-flushing in irrigation seasons, the environmental constraints as fish migration and spawning are taken into an account. After obtaining the Pareto optimal solutions by means of the weighted objective functions and non-symmetric Nash bargaining, various scenarios are defined. Then these scenarios are analyzed by introducing a new sustainability index. Furthermore, the different percentages of downstream water demand are considered in order to achieve a better evaluation of the scenarios. The results of study indicate that the optimal solutions are more sustainable than those of the current operation of Sefidrud reservoir, which increase the sediment flushing by 37 million tons compared to the current operation, with the same hydroelectric energy and downstream water supply. The proposed methodology could be used successfully in other reservoir operations including the sediment flushing.

Downstream Ecological Impacts of Controlled Sediment Flushing in an Alpine Valley River: A Case Study

AbstractSediment flushing may be effective to tackle the loss of reservoir storage as a result of siltation. When operationally possible, the impact of this practice on the downstream aquatic environment can be mitigated by limiting the sediment concentration of the discharged waters (controlled sediment flushing). However, this topic is poorly documented, and concerns arise when limits are discussed. We present the results of a 3‐year field investigation concerning the controlled sediment flushing of a small reservoir on the Adda River, the main tributary of Lake Como—Italy. Two limits for suspended solid concentration (SSC) were adopted: 1.5 g L−1, as average value throughout the whole working day, and 3.0 g L−1, as alert threshold to adjust the ongoing activity. These constraints were essentially fulfilled in the course of the documented operations. The first year sediment flushing was more significant than the following year: 25 000 tons of fines below 2 mm in diameter were flushed in six non‐consecutive days in summer 2010, while, one year earlier, 75 000 tons were flushed in 16 non‐consecutive days. In the third year of investigation (2011), no sediment evacuation took place. The benthic macroinvertebrate and the fish communities were surveyed a short distance below the reservoir, that is, in the potentially more affected river reach. Clear pieces of evidence of environmental quality degradation were not detected; the adopted strategies can therefore be considered to be appropriate when planning sediment flushing management in comparable contexts. Copyright © 2014 John Wiley & Sons, Ltd.

Pressure Flushing of Cohesive Sediment in Large Dam Reservoirs

AbstractPressure flushing of deposited sediments behind large dam walls causes development of a funnel-shaped crater due to the induced vortex and considerable shear flow around the outlets. Laboratory experiments were conducted to investigate interaction of flow and sediment parameters on the development and final size of the scour cone. The volume of the flushed sediment increases with increase of discharge, and decreases with increase of sediment bulk density and the water level above the sediment. While the water depth over the sediments is the most significant parameter in the collapse of sediments above the intake and the initial development of the cone, sensitivity analysis indicated bulk density of cohesive sediment to be the most effective parameter to determine the final size of the scour cone. Using experimental results, two equations were developed to estimate scour cone volume and length with readily defined and measurable parameters of flow and sediment. The field measurements confirm the ca...

Numerical study on the performance of bulb turbine by using runaway condition to flood discharge and sediment dredging

When the floodwater of the bulb tubular type power station is released, a large number of sediment carried by the flood silts up at outlet of the tube, and has a serious impact on the later normal operation of the power station. In order to solve this problem, this paper presents a method that treats the tube sluice as the energy dissipation facility, use the small opening runaway conditions to carry out a regular and short time sediment flush during discharge, and set the sediment self-flushing corridor in the downstream river to achieve sediment flushing and dredging. Unsteady three-dimensional numerical study which considers free-surface of the Reservoir for different tube sluice conditions is conducted to reveal the flow capacity of the turbine and the flow characteristics in the draft tube. In particular, through analyzing the flow characteristics in the tube, the maximum particle size of the sand that can be washed away can be determined, assuming the outlet velocity of the tube is the starting speed, and then the sediment flushing capability of the turbine can also be estimated. The results show that: using the runaway conditions for flood discharge and dropping the height of the tube sluice to achieve the purpose of energy dissipation not only can improve the flood discharge capacity of the power plant, but also can increase flushing distance at the tailrace, and thus enhance the ability to remove silt. Setting the sediment self-flushing corridor at the downstream river would be a good solution to tailrace siltation problems of the bulb turbine.

Environmental Effects of Storage Preservation Practices: Controlled Flushing of Fine Sediment from a Small Hydropower Reservoir

Sediment flushing may be effective in mitigating loss of reservoir storage due to siltation, but flushing must be controlled to limit the impact on the downstream environment. A reliable prediction of the environmental effects of sediment flushing is hindered by the limited scientific information currently available. Consequently, there may be some controversy as regards to management decisions, planning the work, and monitoring strategies. This paper summarizes the main results of a monitoring campaign on the stream below a small alpine hydropower reservoir subjected to annual flushing between 2006 and 2009. The removed sediment was essentially silt, and the suspended solid concentration (SSC) of the discharged water was controlled to alleviate downstream impact. Control was achieved through hydraulic regulation and mechanical digging, alternating daytime sediment evacuation, and nocturnal clear water release. The four operations lasted about two weeks each and had an average SSC of about 4gL(-1). Maximum values of SSC were generally kept below 10gL(-1). Downstream impact was quantified through sampling of fish fauna (brown trout) and macroinvertebrate in the final reach of the effluent stream. The benthic community was severely impaired by the flushing operations, but recovered to pre-flushing values in a few months. As expected, the impact on brown trout was heavier on juveniles. While data biasing due to fish removal and re-stocking cannot be ruled out, the fish community seems to have reached a state of equilibrium characterized by a lower density than was measured before the flushing operations.

Transport Model of Underground Sediment in Soils

Studies about sediment erosion were mainly concentrated on the river channel sediment, the terrestrial sediment, and the underground sediment. The transport process of underground sediment is studied in the paper. The concept of the flush potential sediment is founded. The transport equation with stable saturated seepage is set up, and the relations between the flush potential sediment and water sediment are discussed. Flushing of underground sediment begins with small particles, and large particles will be taken away later. The pore ratio of the soil increases gradually. The flow ultimately becomes direct water seepage, and the sediment concentration at the same position in the water decreases over time. The concentration of maximal flushing potential sediment decreases along the path. The underground sediment flushing model reflects the flushing mechanism of underground sediment.

The Effect of Water Level on The Effectiveness of Sediment Flushing

The Effect of Water Level on The Effectiveness of Sediment Flushing