Spatial variation of coherent turbulent flow structure inside ingoing multi-bend river meander

In this paper the effect of different curvatures on spatial variation of coherent flow structure and bursting events inside two multi-bend meanders models with the strong and mild curved are investigated. Two models with three sequential meanders were built and three dimensional flow velocities at five cross sections were measured using Micro-ADV. Based on orthogonal analysis of three dimensional flow velocity, bursting events are classified into two classes and eight zones. The results indicated that the effect of curvature in sequential bends is obvious in model 1. In two models, the occurrence probabilities of sweep and ejection events are higher than outward and inward interactions. The minimum contribution probability is found for zone III-B. The above results can be useful to find meandering pattern inside the rivers and also for river training works

Study of coherent turbulent flow over the ripples using Particle Image Velocimetry

The structure of turbulent flow over ripples is important to understand initiation of sediment entrainment and transport. The focus of this study is the measurement and analysis of the dominant bursting events and the flow structure over the ripples in the bed of a channel. One type of ripple with sinusoidal form was tested in this study. The velocities of flow over the ripples were measured in three dimensions using Particle Image Velocimetry (PIV). These velocities were measured at different points within the flow depth from the bed and at different longitudinal positions along the flume. It was found that upstream of the ripple crest, transition probability of stable organization (P44) were dominant when compared to other 15 transition probabilities. This can be interpreted as an expectation that entrainment should occur at this location. However, downstream of the ripple crest, transition probability of zone 2 to zone 3 (P23) and transition probability of zone 3 to 4 (P34) were more dominant than others. Therefore would be expected sedimentation to occur at this location

Dynamic mechanism of turbulent flow in meandering channels: considerations for deflection angle

To find turbulent flow structure inside meandering channels, three physical models of river meanders representing strongly curved bend, mild bend and elongated symmetrical meander loop were tested in this paper. Instantaneous velocity data in three dime

An optimised water intake with the presence of submerged vanes in irrigation canals

One of the problems at most water intakes is accumulation of sediment at the entrance and changing of flow talweg path at the water intake. Submerged vanes are small hydraulic structures that are used for flow and sediment control on the bed of rivers. The submerged vanes may be installed individually or in a group with different arrangements. In this study, a group of submerged vanes are installed at the entrance of a rounded edge 558 water intake with parallel and zigzag arrangements. The vanesâ installation angles were selected to be 10, 20, 30 and 408 to the flow direction. The sedimentation pattern at the entrance of the water intake and the amount of sediment entering into the lateral channel were measured after experimental tests. From the experimental study, the optimum vane angle for the above-specified water intake was found to be 308. Also the parallel arrangement was found to be the best arrangement for the submerged vane

PIV measurements of coherent turbulent flow structure and bursting process around a scour hole

The results of a series of experimental tests related to the flow characteristics in a scouring hole are presented in this paper. The experimental tests were carried out for five different stages of development of a scour hole. These stages are defined on the basis of experimental observation. The mechanisms of the development of the scour hole and flow characteristics were investigated in this study. The flow velocities were measured using Particle Image Velocimetry to characterize the mean velocity field and turbulent characteristics of flow in the scour hole. The measurements reveal a good understanding of the flow characteristics and bursting process and a strong recirculation in the hole. The results showed that upstream of the orifice, the transition probabilities of the stable events were higher than other transition probabilities. Therefore, the events of P11, P22, P33 and P44 were dominant when compared to others. This can be interpreted as an expectation that entrainment should occur at this location. These expectations are consistent with scour hole development and were confirmed by measuring scour hole depth upstream of the orifice

Effect of rounded-edge entrance on discharge coefficient of side weir in rectangular channels

Side weirs are flow diversion devices that are widely used in irrigation and drainage networks and urban sewage systems. They are usually built with a squared-edge entrance. The present study focuses on the effect of rounded-edge entrance shape on the discharge coefficient of a side weir under subcritical flow condition in rectangular channels. In this study, 90 laboratory tests were conducted and the results were analyzed to find the influence of non-dimensional hydraulic parameters on the discharge coefficient. From the results, it was found that under subcritical flow condition the side weir with rounded-edge entrance discharges 10% more flow rate than the squared edge entrance. As a result, for equal flow rate, the rounded-edge entrance side weir with small dimensions can be designed for use in practical applications

Effect of different meander curvatures on spatial variation of coherent turbulent flow structure inside ingoing multi-bend river meanders

In this paper, the effect of different curvatures on the spatial variation of coherent flow structure inside two physical models with both strongly curved and mild multibend meanders is investigated. Three dimensional flow velocities at three sequential meanders were measured using an Acoustic Doppler Velocity meter (Micro-ADV). Three dimensions of flow velocity are classified into two major classes and eight different bursting events. The contribution probability and transition probability of each zone is calculated from experimental data. The results indicated that the effect of curvature in sequential bends was important particularly for strongly curved bends. The contribution probability of the events for strongly curved meanders with relative curvature (Rc/B) of 2.6 were found to be higher than for mild curved meanders with relative curvature (Rc/B) of 4.43. The minimum contribution probability was found in external inward interaction event. In addition, analysis of bursting events showed that the highest values of transition probabilities occurred in the stable organizations for both models. The influences of different curvatures on distributions of the Reynolds shear stress, the turbulent kinetic energy, the streamwise velocity and the vertical velocity were also shown to be in good agreement with eroded bed. The above results can be useful for finding meandering patterns inside rivers and also in river training works

How far must trees be cultivated from the edge of the flood plain to provide best river bank protection?

In this study, to find the best location to cultivate the trees for river bank protection, some experimental tests were performed. One row of trees were cultivated at five different distances from the main channel/floodplain interface in a rectangular compound open channel. In experimental model for simulating the trees, some cylindrical wood rods were attached to the bed of flood plain. The three-dimensional flow velocity of flow in a cross-section between the trees were measured in 149 nodal points using Micro-acoustic Doppler velocimeter (ADV) velocity meter. At each nodal point, 6000 velocity data for each direction were stored in a computer. From the analysis of the experimental data, it was concluded that upon cultivating trees at 10% distance of flood plain width from the edge of main channel, the minimum streamwise velocity occurred near main channel/floodplain interface, while the maximum streamwise velocity occurred far from the edge of floodplain. Therefore, the best location for cultivating the trees was found to be at 10% of floodplain width and it is suggested for river bank protection in practical applications

Prediction of riverine suspended sediment discharge using fuzzy logic algorithms, and some implications for estuarine settings

The ability of fuzzy logic algorithms to model relationships between stream flow and suspended sediment discharge was investigated using daily measurements of stream flow and suspended sediment discharge for the Escanaba River mouth station, situated on the shore of Lake Michigan and operated by the US Geological Survey. Three different configurations of inputs were applied, whereby the inputs were fuzzified into fuzzy subsets of variables by means of triangular membership functions. The relationships between inputs and suspended sediment discharge (output) were represented by a set of fuzzy rule expressed in IFâTHEN format. The weighted average method served for defuzzification. The commonly used sediment rating curve was also applied to the data, and its performance compared with that of the three models by means of statistical analyses. For all three models, suspended sediment discharge predicted by the fuzzy logic algorithm was in satisfactory agreement with observations. Furthermore, the fuzzy logic algorithms performed better than the sediment rating curve, particularly at higher rates of suspended sediment discharge (in this study, more than 50Ã106g/day). Considered collectively, the use of fuzzy logic algorithms is suggested as a simple and effective approach for better prediction of suspended sediment discharge, also for estuaries

Study of near bed stochastic turbulence and sediment entrainment over the ripples at the bed of open channel using image processing technique

In this study, the coherent structure in near bed bursting events over the ripples and mechanism of sediment bed load transport were investigated experimentally. The experiments in this study were carried out in the laboratory flume, in two parts; fixed bed ripple and mobile bed ripple. Tow artificial ripples, were built and used for making both fixed and mobile bed. For the fixed bed part, velocity fluctuations were measured using an Acoustic Doppler Velocimeter. In order to apply bursting analysis for obtained data, a computer programwas written in visual basic language. Then, variation of turbulence shear stress associated with different bed form geometries was determined and mechanism of sediment transport by ripple shape at the bed of open channel was investigated. For the mobile bed part, artificial ripples were used as mould to make ripples. An image processing technique was used to record amount of sediment particles which are entrained and deposited over the same selected points at the fixed bed part. Results of mobile bed part, confirmed the results of shear stress analysis of fixed bed part