Consideration of parameters of the dividing stream width ‎and rate of sediment entry into the 90◦ intake in various ‎patterns of sediment control

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
Nowadays, the major concerns to meeting the growing demand for water and the sustainable development goals in the nation are these facts that a relatively large area of the nation is in arid and semi-arid regions and the annual aridness continuously increases. Generally, however, the solution to this concern could be tackled by further research on the river engineering issues and providing appropriate solutions for better use of the river water resources. One of these solutions is to minimize the sediment while diverting water away from its natural path into an intake, as the sediment transport through the intake is a serious problem. However, 3D flow conditions in river divisions makes it difficult to characterizing the flow of water and sediment into the intakes. The results of the most recent studies suggest application some patterns, including Submerged Vanes, Sills and spur dikes, to minimize the sediment transport into the intakes. However, it has been shown that the cut-off of sediment flow into the intakes may not completely occur by applying the above-mentioned technologies, individually.

This study aims to assess the influence of these structures application on the amount of sediment flowing into the intakes, individually and as various layouts, under different hydraulic conditions. Three different variables including ratio of bed sediment transport into intake, volume fraction of sediment deposited within intake and dividing stream-plane were studied to better analyze the sediment volume entering the intake. In this regard, the parameters associated with the dividing near-surface stream Index, dividing near-bed stream Index” and “the ratio of the width of dividing near-bed stream to dividing near- surface width Index” were studied at the up-stream of the main channel, under different hydraulic conditions and sediment control systems.

The results indicate that the simultaneous use of “sill-spur dike”, as well as “sill-spur dike-submerged vanes” has high efficiency in sediment removal at the intake. Furthermore, dividing stream-plane can be significantly influenced by all the sediment control structures used herein, although the effect of spur dike and submerged dikes was noted to be more profound. Generally, it can be concluded that spur dike causes an important decrease in “dividing near-surface stream Index”, “dividing near-bed stream Index” and “the ratio of the width of dividing near-bed stream to dividing near- surface width Index”, thus resulting in significant reduction in the sediment entering the intake. This observation may attribute to the induced flow width reduction in the main channel usually associated with converting the flow direction from the straight line into a curve, thus creating a secondary circulation flow. On the other hand, submerged vanes considerably minimize the amount of sediment flowing into the intake through increasing “dividing near-surface stream Index” and decreasing “dividing near-bed stream Index” and “the ratio of the width of dividing near-bed stream to dividing near- surface width Index”. It may be linked to the powerful secondary flow developed at the intake-entrance.

The results also show that the change in the length and height of the spur dikes and sills respectively can induce significant changes in dividing stream-plane, which in turn causes dramatic changes in the sediment transport into the intake. Additionally, the parameters of dividing stream-plane, ratio of bed sediment transport into intake, and volume fraction of sediment deposited within intake are strongly determined by the amount of discharge rate, in a way that the rise in discharge rate leads to increase of “dividing near-surface stream Index” and “dividing near-bed stream Index”. However, a decreasing trend in dividing flow ratio was observed, in some systems and discharge ratios.

As opposed to the case, where the sediment control systems were not used, a reduction of 80% and a growth of more than 100% were observed in dividing near-bed stream Index and dividing stream-plane, respectively, when some systems were installed in the main channel. It, in turn, decreased the entering sediment down to 90%. In the same manner, a reduction of 50% was found in the ratio of the width of dividing near-bed stream to dividing near- surface width Index when the sediment control structures were mounted, resulting in a decrease of 100% in ratio of bed sediment transport into intake approximately.

Keywords

Subjects

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Modares Civil Engineering journal
Volume 21, Issue 1
March and April 2021
Pages 119-133