Study of the effect of the various layout of sediment control on bed ‎topography at the 90◦ lateral intake ‎

Document Type : Original Research

Authors
A. ATTARZADEH 1
M. Ghodsian 2
1 ‎Assistant professor of Hydraulic Engineering, Department of Civil Engineering, Qom University of ‎Technology, Qom, Iran ‎
2 ‎Professor of Hydraulic Engineering, Faculty of Civil & Environmental Engineering, Tarbiat Modares ‎University, Tehran, Iran ‎
Abstract
Two main goals of water diversion away from rivers are sediment control and water supply with minimum sediment. These goals are commonly accomplished by using some hydraulic structures such as: sills, spur dikes and submerged vanes. These structures make changes in the pattern of flow and consequently the bed topography that lead to control of sediment entry into an intake. Despite their important role in sediment control, the results of previously published works indicate that in some cases these structures can cause substantial scour near the bank at the downstream of the intake on the main channel that may seriously jeopardize the stability of the bank in this area.

Using six layouts this report presents the results of an experimental study on the individual and combined effects of these structures (with different dimensions) on the bed topography at the upstream to downstream of main channel and the intake entrance. Furthermore, by measuring the length, width, depth and area, the scour region near the bank at the downstream of the intake on the main channel was qualitatively/quantitatively evaluated. Experiments were performed in a direct flume equipped with a recirculating sediment having a 90° lateral diversion channel at three discharge ratios of 0.12, 0.15 and 0.18 and in six sediment control systems.

The results show that both individual structures (in particular, spur dikes and submerged vanes), and their combination, have significant effects on the bed topography at the upstream/downstream of the main channel, the intake entrance, and particularly at the bank connected to the intake that thus affect the amount of sediment entry into the intake. In fact, submerged vanes, by creating a secondary flow, generate a helical motion near the bank connected to the intake causing important changes in the bed topography in an area at the intake. The spur dikes, by flow deviation to the reservoir and also increase in the flow velocity, create a general scour along the flow path from upstream to downstream of the intake on the main channel. Additionally, they, by creating fluid flow in a curved path and thus a helical motion, cause local scour around the bank connected to the intake on the main channel.

The results also indicate that these structures and their combination play an important role on the size and area of the scour region near the bank at downstream of the intake on the main channel, but their response varies with discharge ratio. It was also observed that in many conditions sill causes a decrease in the size and area of the scour region at the downstream of intake. Similarly, although submerged vanes cause significant scouring at the upstream and downstream of the intake, in some conditions, they reduce the size and area of the scour region at the downstream of the intake. Last but not least, although spur dike causes a rise in the area of the scour region throughout the main channel as well as the intake entrance, its combination with sill and submerged vanes in some conditions reduces the area of the scour region at the intake downstream.

Keywords

Subjects

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Modares Civil Engineering journal
Volume 20, Issue 3
September and October 2020
Pages 117-128