Effects of Spur Dyke’s Orientation on Bed Variation in Channel Bend

Spur dykes also known as Groynes are often used to either divert or attract the flow from the main structure to safeguard their life. Those structures may be bridge piers, abutments or any similar hydraulics structures. Spur dykes are also used to save the cutting of banks on concave side of stream. Lots of work have been done in recent past on spur dykes by many investigators in which various hydraulic and geometrical parameters of spur dykes such as discharge, sediment size, flow velocity, shear stress, spur dykes shape, size and submergence etc. are studied in detail. But mostly all the studies were pointed out in straight open channels. Very few studies were done in curved channel and only their similar effects were studied. In present thesis main emphasis is given to study the effect of orientation and location of spur dykes in meandering channel on the bed of downstream side. In the present study experimental work has been carried out in 80° bend and constant discharge (Q = 4.5 l/s) is allowed to pass in channel without spur dyke. It is found that maximum scouring occurs at angular displacement θ = 60° to 80° in the vicinity of outer bank. To minimize this scouring, spur dyke has been installed at angular displacement θ = 20°, 40° & 60° by changing the dyke angle α = 60°, 90° & 120° respectively. It is found that scouring at θ = 60° is reduced by installing spur dyke at angular displacement θ = 40° which is oriented at α = 60° and scouring at θ = 80° is reduced by installing spur dyke at angular displacement θ = 60° which is oriented at α = 60°.

Enhancing scour protection in river bends: a novel slotted bank-attached vane

One of the most effective approaches for bank control erosion is using bank-attached vanes. In spite of the superiority of the bank-attached vanes to spur dikes, the vanes' tips are still vulnerable to local scour caused by flow–structure interaction. In this study, slotted bank-attached vanes are proposed to reduce local scour at the tip of the triangular submerged vane. For this, a rectangular slot is created parallel to the chord of the vane with an area of ten percent of the effective area of the vane surface. Two types of conventional vanes and slotted vanes were installed at different angles of attack of 23, 30, 40 and 60 degrees in an arch flume. Experiments were carried out in clear water conditions with different flow regimes with Froude numbers of Fr = 0.287, 0.304 and 0.322. The results show that the slotted vane outperforms the conventional vane by reducing maximum scour depth by about 70, 20, 17 and 54 percent for different angles of attack of 23, 30, 40 and 60 degrees, respectively. The proposed slotted vane also resulted in reduction of scour hole volume around the vane and formed the scour hole away from the outer bank.

Numerical study of flow pattern around lateral intake in a curved channel

This paper deals with numerical study of flow field in a channel bend in presence of a lateral intake using three-dimensional numerical model SSIIM2. The effects of bend on the structure of the flow around the intake are investigated and compared with the experimental data. The tests are carried out in a U-shaped channel bend with a lateral intake. The intake is located at the outer bank of an 180∘ bend at position 115∘ with 45∘ diversion angle and the experimental data can be used to calibrate and validate numerical models. The results show that both the center-region and outer-bank cross-stream circulations are observed in the experiments while only the former is captured by the numerical model due to the limitations of the turbulence model. In the curved channel after the intake, both experimental and numerical results show another type of bi-cellular circulations in which clockwise center-region circulations and counterclockwise circulations near the inner bank and the free surface (inner-bank circulations) are captured. The study shows that the numerical model very satisfactorily predicts streamlines, velocity field and flow pattern in the channel and in vicinity of the intake. Investigation of flow pattern around lateral intake in channel bends shows that contrary to the case of flow diversion in straight channels, the width of the dividing stream surface near water surface level is greater than that of near bed level. Finally, the effects of position and diversion angle of the lateral intake, discharge ratio and upstream Froude number on the flow pattern are investigated.

Investigation of Shear Stress Distribution in a 90 Degree Channel Bend

Shear stress is a key parameter that plays an important role in sediment transport mechanisms; therefore, understanding shear stress distribution in rivers, and especially in river bends, is necessary to predict erosion, deposition mechanisms and lateral channel migration. The aim of this study is to analyze the shear stress distribution near a river bed at 90-degree channel bend using a depth-average method based on experimental measurement data. Bed shear stress distribution is calculated using the depth-averaged method based on velocity components data has been collected from a 3D-ADV device (three-dimensional acoustic doppler velocity) at different locations of a meandering channel. Laboratory experiments have been made at the hydraulic laboratory of the RCRFIDF (Research Center for River Flow Impingement and Debris Flow), Gangneung-Wonju National University, South Korea to provide data for simulating the incipient motion of the riverbed materials and then predicting the river morphological changes in the curved rivers. The calculated results show that the maximum value of shear stress distribution near the riverbed in the different cross sections of the surveyed channel occurs in a 70-degree cross section and occurs near the outer bank. From the beginning of a 40-degree curved channel section, the maximum value of the shear stress occurs near the outer bank at the end of the channel.

KARAKTERISTIK ALIRAN PADA BELOKAN SALURAN TERBUKA

Studi tentang Saluran berbelok cukup penting, karena saluran berbelok mempunyai karakteristik yang unik dengan tingkat rawan yang cukup tinggi terhadap daya rusak air bila dibandingkan dengan saluran lurus. Melalui penelitian ini diharapkan dapat memberikan informasi tambahan pada pemanfaatan air bersedimen yang lebih efisien yakni mengenai wilayah mana akumulasi partikel-partikel sedimen suspensi berada dan juga sebagai referensi untuk pendeteksian awal terjadinya banjir serta sebagai referensi dalam menganalisa distribusi kecepatan dan sedimen pada belokan saluran yang bervariatif atau saluran berbentuk kelokan berlanjut (meandering) atau kelokan tunggal (curvature bend profile). Dari hasil analisis terhadap pengukuran kecepatan aliran dan konsentrasi sedimen suspensi yang dilakukan pada tiga lokasi dengan sudut dan jari-jari belokan yang bervariasi, menunjukkan bahwa untuk trend kecepatan minimum terjadi di dekat dasar dan bertambah besar ke arah permukaan aliran. Kecepatan aliran mengalami percepatan dan perlambatan ketika melalui belokan, dimana kecepatan aliran meningkat di sisi dalam belokan (inner bank) ketika melewati awal belokan dan kecepatan menurun saat melewati akhir belokan dan sebaliknya kecepatan menurun di sisi luar belokan (outer bank) ketika melewati awal belokan dan mengalami peningkatan di sisi dalam belokan saat melewati akhir belokan. Adapun konsentrasi sedimen suspensi mempunyai trend yang hampir sama untuk seluruh tampang, yaitu konsentrasi sedimen suspensi meningkat ke arah dasar saluran dan mengalami penurunan ke arah permukaan air dengan trend distribusinya semakin tegak dengan nilai yang semakin seragam ke arah permukaan air. Pada arah transversal, konsentrasi sedimen suspensi cenderung meningkat ke arah sisi dalam belokan ketika melewati awal belokan, lalu menurun ke arah sisi dalam belokan saat melewati pertengahan belokan dan kembali meningkat ke arah sisi dalam belokan saat melewati akhir belokan yang mengakibatkan terjadinya deposition di sisi dalam belokan (inner bank) dan erosion di sisi luar belokan (outer bank) pada dasar saluran. Untuk analisis konsentrasi sedimen suspensi hasil pengukuran lapangan yang dibandingkan dengan analisis dari persamaan Rouse dan persamaan Tanaka-Sugimoto menunjukkan bahwa cukup dapat memprediksi data pengukuran konsentrasi sedimen suspensi pada belokan, meskipun sudut dan jari-jari belokan bervariasi. Data hasil pengukuran sedimen suspensi nilainya mendekati data hasil analisis Rouse dan Tanaka-Sugimoto. Adapun hasil analisis Tanaka-Sugimoto bisa memberikan hasil lebih baik dari analisis Rouse.

ANALISIS DISTRIBUSI KECEPATAN DAN SEDIMEN PADA TIKUNGAN 55° SALURAN TERBUKA TAMPANG SEGI EMPAT

Predicting the behavior of the flow in the channel bend quite important, because the channel bend a fairly high degree of cartilage against the destructive force of water when compared to a straight channel. Phenomena that may occur and cause detriment is the phenomenon of sediment transport that passes through the channel bend. The phenomenon that occurs in the channel bend can be detected by measuring the field directly. For a case study of the Irrigation Mataram, research done by the measurement of the concentration profiles of sediment transport using devices Opcon. The study was conducted at a locations with the curves that have angles, α = 55° with Radius = 50 m. From the analysis of the measurement of velocity flow and sediment concentration suspensions were performed at the curves that have angles, α = 55° with Radius = 50 m, indicating that the minimum velocity for trend occurs near the base and the increase in size towards the surface of the stream. Flow velocity acceleration and deceleration experienced when through the turn, which increases the velocity flow in the bend side (inner bank) when passing the initial curves and velocity decreases as it passes through the opposite end of the turn and descent speed on the outside of the bend (outer bank) when passing through curves and initial experience increase in the inside of the turn as it passes through the end of the turn. The concentration of sediment suspensions have almost the same trend for the entire face, the concentration of sediment suspension increases towards the base line and decreased with the trend towards the surface of the water distribution more upright with a more uniform rate towards the surface of the water. In the transverse direction, the concentration of sediment suspension tends to increase towards the inner side of the bend when passing through the initial turn, and then decreases towards the inner side of the bend as it passes through the middle of the turn and increased again towards the inside of the turn as it passes through the final turn which resulted in deposition on the inside of the turn (inner bank) and erosion on the outside of the bend (outer bank) at the base of the channel. For analysis of the consentration of sediment suspension field measurement results are compared with the analysis of the Rouse equation and equation-Sugimoto Tanaka showed that the measurement data can reasonably predict the consentration of sediment suspension on curves, although the angle and bend radius varies. Measurement data of suspended sediment consentration approaching the value of data analysis results Rouse and Tanaka-Sugimoto.

Self-Adjustment Process of Flow Pathway in a Narrow Curved Channel

This study focuses on river bed fluctuation of the curved channel with channel width narrowing, where is located in the inlet of the old meandering river with 30 (m) width from straightened one with 80 (m) in the Kushiro Wetland. From field survey, in response to change in water and sediment discharges, significant streamwise variation in water flow width in the curved channel adjusts in order to establish the dynamic equilibrium. Along the outer bank of curved channel, the secular bed deposit beside the outer bank is increasing, and as a result, the main streamline flows into the old river along the inner bank as left bank. Moreover, this narrowing curved channel easily leads to overspill some flood water including rich suspended sediment and to deposit some fine sand near channel side flood plain. We intend to explain above significant bed variations by using movable bed experiments with the distorted model. As a result, we suggest, though qualitatively, that the existence of the sandbar upstream of the curved channel causes the autonomous specification of the flow path width in the curved channel with a narrowing width, and that this flow path is formed.