Investigation of the changes in the stream sedimentation pattern by creating a loop in the Karun River in the Zargan-Farsyat region

Document Type : Complete scientific research article

Authors

1 Department of Civil Engineering, University of Tabriz.

2 Faculty of civil engineering, University of Tabriz, Tabriz, Iran.

10.22069/jwsc.2024.21528.3662

Abstract

Gibson et al. (2010) modeled the COWLITZ river considering the moving bed and used the HEC-RAS model for simulation. They did the modeling for the last 20 miles of the river because the possibility of flooding due to sedimentation was higher in this area. The purpose of this study was to evaluate the effects of sedimentation on the increase of flood risk in the long term. The Laursen-Copeland relationship was used in the sediment calculations because the sediments ranged from very fine sand to large rubble. They also stated that the ability to add bed particle size in 20 different classes has been added to the HEC-RAS model in version 4.1.
The geographic location of this research is based on the UTM geographic system, around 33'22'32' to 32'45'17 north latitude and 40'22'48' to 48'57'19 east longitude. According to Figure 1, the total length of the studied route is about 75 km between Zargan and Farsiat and includes 155 cross sections, and the approximate length of the meander is 13.4 km. In order to simulate the hydraulic flow and sedimentation of the river by HEC-RAS model, geometric information (cross sections, distance of sections from the downstream control section, Manning's roughness coefficient and opening and narrowing coefficients), hydraulic information (flow information and water level level at the lower station) meteorological (water temperature) and sedimentary (related to flow-sediment discharge and bed sediments granularity) is necessary.
In general, it can be said that after the formation of the loop, the upstream interval (R1) of its sedimentation decreases from upstream to downstream until it undergoes erosion at the bifurcation of the river, and the middle interval (R2) changes from erodible to sedimentary and the interval Downstream of the ring (R3) remains almost unchanged and shows very little tendency to erode. HEC-RAS model is used in this research. When using this software, the continuous flow series is divided into continuous flow segments based on flow and time variables. In general, it can be said that after creating the ring of the upstream interval (R1), its sedimentation decreases from upstream to downstream until it undergoes erosion at the bifurcation of the river, and the middle interval (R2) turns from erodible to sedimentary and the base ring interval (R3) remains almost unchanged and has a very little tendency to be erodible.
The middle section of the Karun River (R2) turns from erodible to sedimentary with the creation of a loop, which is the reason for the tendency of the river to deposit sediments in this section after the creation of the loop, reducing the amount of incoming flow and, as a result, reducing the speed The flow in this section is caused by the division of the flow due to the two branches of the river upstream of this section.

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Journal of Water and Soil Conservation
Volume 30, Issue 4
March 2024
Pages 147-164

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