Sediment Flushing Research Articles

Reservoir Operation for Simultaneously Meeting Water Demand and Sediment Flushing: Stochastic Dynamic Programming Approach with Two Uncertainties

AbstractRiver bed materials are commonly removed and conveyed downstream. In this process, some sediments are deposited in reservoirs, causing a decrease in reservoir active storage capacity and thus its ability to meet water demand. Flushing is a sediment-release method operated from the bottom outlet gates that releases stored water to flush sediments. As a result, water shortages may occur after the flushing operation. Thus, it is important to develop a reservoir operation policy for time and volume release of sediment that meets water demand. Uncertainties in water and sediment inflows to the reservoir are also important issues that add to the complexity of such policies. This paper presents a stochastic dynamic programming (SDP) model with two uncertainties to determine the simultaneous optimal operation policies for meeting water demand and sediment flushing. To evaluate the capability of the SDP model with two uncertainties, four other operation policies are developed, and all five scenarios are ev...

Compatibility of Reservoir Sediment Flushing and River Protection

In this paper, we propose a system of numerical models for the compatibility assessment of reservoir sediment flushing and protection of downstream river environments. The model system is made up of two simulation models. The first model simulates soil erosion in watershed slopes and sediment transport in the tributary of the reservoir by means of a weighted essentially nonoscillatory (WENO) method, which is conservative and fourth-order accurate in space and time. The second model simulates velocity and suspended solid concentration fields in the reservoirs. This model is based on the three-dimensional (3D) numerical integration of motion and concentration equations, expressed in contravariant form on a generalized boundary-conforming curvilinear coordinate system by using a conservative and higher-order accurate numerical scheme. The proposed system of models is applied to the Pieve di Cadore (Veneto, Italy) reservoir and to its catchment area. By comparing suspended solid concentrations that are discha...

Planning Theory toward the Assessment of Impact Due to Sediment Flushing from Dam Reservoir

Planning Theory toward the Assessment of Impact Due to Sediment Flushing from Dam Reservoir

Performances of Hydraulics and Bedload Sediment Flushing in Rigid Channel Using Surge Flows

This paper presents an investigation of the performance of the hydraulic and sediment removal of a flushing system in a detention basin. A hydraulic criterion for the design of the flushing system is proposed. An equation for the maximum height of the flushing wave front as a function of the distance from the gate, the initial water depth in the chamber, and the chamber length is proposed. The Lauber and Hager equation for the maximum velocity of a flushing wave is also verified. Effective removal of sediment particles on the bed is a direct function of the bed shear stress generated by the flushing flow. This study reveals that the bed shear stress on the channel bed induced by the flushing flow can be attributed to the hydrostatic pressure, the flow acceleration, and the convection-induced momentum. The shear stress associated with fluid distortion and the turbulent viscosity may be neglected. Significant error would occur if the hydrostatic pressure component were used as an estimate of the bed shear stress on a mild slope channel. The energy slope method may provide an overestimate of the bed shear stress. Finally, an appropriate equation to evaluate the maximum bed shear stress is proposed.

Discussion of “Gate and Vacuum Flushing of Sewer Sediment: Laboratory Testing” by Qizhong Guo, Chi-Yuan Fan, Ramjee Raghaven, and Richard Field

Discussion of “Gate and Vacuum Flushing of Sewer Sediment: Laboratory Testing” by Qizhong Guo, Chi-Yuan Fan, Ramjee Raghaven, and Richard Field

Closure to “Gate and Vacuum Flushing of Sewer Sediment: Laboratory Testing” by Qizhong Guo, Chi-Yuan Fan, Ramjee Raghaven, and Richard Field

Closure to “Gate and Vacuum Flushing of Sewer Sediment: Laboratory Testing” by Qizhong Guo, Chi-Yuan Fan, Ramjee Raghaven, and Richard Field

HYDRAULIC MODEL STUDIES FOR A DUAL PURPOSE SPILLWAY WITH 21 M DEPTH OF OVERFLOW—A CASE STUDY

ABSTRACT The perennial Himalayan rivers provide potential for large scale power generation. Excessive sediment load especially during monsoon is a typical characteristic of such rivers. Flushing of sediment through spillway is an effective technique to control sedimentation. In order to achieve this, spillways with very low crest and very high depth of overflow of the order of 21 m and associated energy dissipation arrangement are envisaged. The present paper describes the hydraulic model studies conducted for Chamera H.E. Project, Stage—II, Himachal Pradesh, to evolve a spillway crest profile free of sub-atmospheric pressure, a stilling basin at the toe of the spillway and power intake alignment to ensure smooth entry of water to the head race system.

Technical Feasibility Study of Sediment Flushing in Reservoirs Using the RESCON Model

Technical Feasibility Study of Sediment Flushing in Reservoirs Using the RESCON Model

Prediction of Concerted Sediment Flushing

A proprietary one-dimensional numerical model was developed for predicting the amounts of sediment flushed and deposited in the reservoirs in series, the bed evolutions, and variations of the suspended solids concentrations along a river during the concerted sediment flushing events. The model consists of a flow movement module and sediment transport module in which the bed material load is taken as sediment mixture. The nonuniform property of the bed material load is modeled by the introduction of a mixing layer, transition layer, and deposition strata. The model was calibrated on the basis of the field data at Dashidaira and Unazuki reservoirs on the Kurobe River in Japan. The calculated results are in good agreement with the measurements. For the reservoirs out of Japan, the Ashida and Michiue bed load formula used in the model should be verified or replaced by other formulas.

Gate and Vacuum Flushing of Sewer Sediment: Laboratory Testing

The objective of this study was to test the performance of a traditional gate-flushing device and a newly designed vacuum-flushing device in removing sediment from combined sewers and CSO storage tanks. A laboratory hydraulic flume was used to simulate a reach of sewer or storage tank. The flushing device was fabricated and installed at upstream end of the flume. The removed sediment was collected at downstream end of the flume and weighed. The test results indicate that the weight of flushed sediment increases with increasing initial water depth in the flushing device; the weight of flushed sediment decreases with increasing initial water depth in the flume; the weight of flushed sediment only changes slightly with changing height of flushing device opening for water release and does not necessarily increase with increasing opening height. Water is held up by vacuum and is released upon dissipation of the vacuum in the vacuum-flushing device rather than through closing and opening of a mechanical gate in the gate-flushing device. The test results indicate that sediment removal efficiency of the vacuum-flushing device is practically the same as the gate-flushing device.

AN EVALUATION METHOD OF THE IMPACTS ON CHAR OF TURBID WATER BY SEDIMENT FLUSHING FROM DAMS

In this study, we discuss about the impacts on fish of sediment flushing from dams by points of turbid water. The aims of this study are to make a model for evaluation for the impacts of the increase of suspended solids concentration on Char (Salvelinus leucomaenis) and to check the feature of the model. Firstly, we haveexamined the variations of concentrations of dissolved oxygen and suspended solids of the three sites where sediment flushes were done. Secondly, we have made the model. We have thought that if suspended solidsconcentration increased, the uptake volume of oxygen by fish decreased by the adhesion of the sediment on the gills. By using the model, if we know the time variation of concentrations of suspended solids and dissolved oxygen, we can calculate the time variation of the rate of dead fish or fish in asphyxia and the adhesion area of sediment on the gills, and can evaluate no impact time on chars, and have found that if dissolved oxygen concentration decreased, more chars died earlier.

Effects of flow regulation and sediment flushing on instream habitat and benthic invertebrates in a New Zealand river influenced by a volcanic eruption

AbstractI sampled five sites above and below a dam in the central North Island of New Zealand on five to six occasions to examine the effects on benthic substrates, periphyton and invertebrate communities of (i) degree of flow regulation and (ii) flushing of sediment stored behind a dam. A series of volcanic eruptions during the course of this study provided the opportunity to investigate the effects of a period of high sediment delivery on this regulated river. The operation of the dam prior to sluicing of stored sediment appeared to have little impact on substrate size distribution or fine suspendable sediment levels. Periphyton biomass was markedly higher below than above the dam when sampling was preceded by a period of stable baseflow, but over all sampling dates biomass and inorganic content of periphyton did not appear to be related to degree of flow regulation. The taxonomic richness, biomass and density of invertebrate communities were lowest directly below, rather than above, the dam on most dates, and the site below the dam differed significantly from some of the downstream sites. However, changes in invertebrate abundance and diversity generally did not follow the expected gradient of flow regulation impacts except for the mayfly Deleatidium. Multiple regression analyses implicated substrate size and the biomass and inorganic content of periphyton as significant predictor variables for invertebrate density, biomass and taxonomic richness on sampling dates not influenced by recent sediment flushes, whereas degree of flow regulation was a significant predictor for densities of the dominant chironomid Cricotopus. The volcanic eruption led to deposition of fine silt that had passed through the dam with the residual flow and coarser sediments released during subsequent dam flushes. Flushing of stored sediment during large floods increased levels of sand and gravel directly below the dam and upstream of a large island in the middle reaches of the river, and also appeared to increase scouring of periphyton and associated invertebrates downstream. Overall, invertebrate communities in the study reach appeared to be structured more by periphyton accrual patterns, changes in substrate composition, the occurrence of large floods and natural longitudinal gradients than degree of flow regulation. These findings suggest that site‐specific and large‐scale factors can obscure generalized reach‐scale patterns expected along regulated rivers. Copyright © 2002 John Wiley & Sons, Ltd.

Analytical Study on Sediment Flushing in the Reservoirs

The sedimentation in the reservoirs is a natural phenomenon, but its progression causes serious problems for reservoir operations and controls. Because it raises water levels, blocks water ways, and reduces the reservoir's capacity, etc. As a countermeasure, mechanical dredging has been applied to its removal from the reservoirs, but sediment flushing has to be available as well. This paper is based on the field survey and its data which derived from the sediment flushing carried out at the TAKI reservoir in 1991. It presents the numerical analysis on river bed formation after the sediment flushing in the reservoir and points out several matters which should be taken into account in the implementation of such a plan.

Sediment Flushing after Dredging in Tidal Bays

A one-dimensional dispersion model for tidal flushing of suspended material has been formulated. It is suggested that this model can be used to predict the escape of suspended material from an astuarine dredging area out into the adjacent waters. The dispersion model includes a sedimentation function to reproduce the effect of resedimentation. Calibration of the model was carried out in a restoration area by means of in-situ tracer tests and salinity measurements to establish the dispersive properties of the water body. The settling characteristics of the upper sediment layer were established by sedimentation analysis of bottom samples from the dredging area, divided into an organic (polluted) top layer and the underlying inorganic sediment.