Dimensional Analysis of Compound Section in The Regulate Section Channel Model for Maintenance Main Channel

A dimensionless number is used to express the relationship between parameters and is used to describe the research results. Commonly used dimensional analysis methods are the Basic Echelon method, the Buckingham method, the Rayleight method, the Stepwise method and the Langhaar method. The compound section in the regulated section channel model aims to make the section convenient to the flow existing discharge at tidal conditions, in sediment flushing. In this study using the Buckingham’s method of dimensional analysis to determine the weight equation for the flushing sediment (w) and the variables that have been scaled on the flume, W = • (B, B*, h, h*, ⊗h, t, V, Q, g, W,)w,)S), where B is the width of the river (cm), B* is the width of the Flushing section (cm), h is the height of the water level (cm), h* is the height of the flushing section (cm), ®h is the difference in water level (cm), t is the tidal time period (s), V is the flow velocity (cm/s), Q is the water discharge (cm3/s), g is the gravity (cm/s2), )S is the mass density of the sediment (gr/cm3), )w is the density of the water mass (gr/cm3). From the analysis results obtained equations = B * B . h * h . Δ h h . v g t . Q g h 2 t . ρ s h 3 . Where w is the weight of the flushing sediment (gr), B * B is the ratio of the design cross-sectional width to the width of the estuary, h * h is the ratio of the flushing cross-sectional height to the water level, Δ h h is the ratio of the height water level to water depth, v g t is the velocity of falling sediment, Q g h 2 t is the discharge of sediment flushing, ρ s h 3 is the hydrostatic pressure.

Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan

The Unazuki Reservoir is located on the Kurobe River, which is influenced by a catchment with one of the highest sediment yields in Japan. Due to a sufficiently available discharge during flood events, annual sediment flushing with full water-level drawdown (i.e., free-flow sediment flushing) is conducted to preserve the effective storage capacity of the reservoir. Nevertheless, the upstream half of the reservoir (i.e., study segment) suffers from the excessive deposition of coarser sediments. Remobilization of these coarser materials and their transportation further downstream of the reservoir is a priority of reservoir owners for sustainable reservoir functions, such as flood-risk management and hydroelectric energy generation. In this paper, an already conducted sediment-flushing operation in the Unazuki Reservoir is simulated, and its effects on sediment scouring from the study segment of the reservoir together with changes in bed morphodynamics are presented. A fully 3D numerical model using the finite volume approach in combination with a wetting/drying algorithm was utilized to reproduce the hydrodynamics and bed changes using the available onsite data. Afterwards, the effects of discharge adjustment on the morphological bed changes and flushing efficiency were analysed in the study segment using an additional single-discharge pulse supplied from upstream reservoirs. Simulation results showed that an approximately 75% increase in the average discharge during the free-flow stage changed the dominant morphological process from deposition into an erosive mode in the study segment. If the increase in discharge reaches up to 100%, the flushed volume of sediments from the target segment can increase 2.9 times compared with the initiation of the erosive mode.

Evaluation Of Sediment Management Strategies For Large Reservoirs

Multipurpose large dams play a key role in the development of world by providing water for irrigation, flood control and hydropower. Tarbela is one of the world's largest earth and rock fill dam. Being multipurpose dam, it provides vital role for economic stability and social development of Pakistan. Tarbela Reservoir has lost its significant capacity due to sediment deposition. The objective of the study was to evaluate different options for evacuation of deposited sediments and reducing sediment inflows to Tarbela Reservoir through sediment modeling by HEC-RAS. Sediment flushing from existing power tunnels was evaluated in first option and found not feasible due to the downstream constraints and loss of 7848 MW hydropower from Tarbela and Ghazi Barotha. New sediment bypass tunnels were proposed on right bank of the dam to overcome the constraints in second option. Sediment modeling was performed by HEC-RAS to evaluate each scenario of sediment flushing with different parameters. The sediment balance ratio and long term capacity ratio was also checked for each scenario for technical evaluation and also economic analysis was performed. Most technical viable scenario was flushing for 90 days at reservoir drawdown level of 390 m with discharge of 5000m 3 /s. However, this scenario was not economically feasible as net present value was negative, internal rate of return was 3-4 %, and benefit cost ratio was found less than one. The 3 rd option, with under construction multipurpose Diamer Basha Dam on upstream of Tarbela Reservoir, was also evaluated on HEC-RAS. Results depicted that large amount of sediments were trapped in the upstream reservoir which ultimately reduced significantly the inflow of sediments and delta movement in Tarbela Reservoir. This option is recommended because it will enhance the life of Tarbela Reservoir and it will keep on providing multiple benefits for longer time.