Experimental investigation of effect of the apron installation on local scour at the downstream of block ramp

Document Type : Research Paper

Authors

1 Department of water engineering, Faculty of Agriculture Science, University of Guilan, Rasht

2 Department of Water Engineering, Faculty of Agriculture Science, University of Guilan, Rasht, Iran; Department of Water and Environmental Engineering, Caspian Sea Basin Research Center, University of Guilan, Rasht, Iran

3 Department of water Engineering, Faculty of Agriculture Science, University of Guilan, Rasht

4 IA.ING, Lecce, Italy

Abstract

Control of the degradation of river beds is a critical issue that river engineers encounter today. Block ramps are grade control structures that implement as a countermeasure to overcome erosion in rivers bed and have suitable environmental conditions in terms of aquatic migration to upstream reaches and also increase the dissolved oxygen in the water. One of the important issues in the design and safety of these structures is to predict and reduce the magnitude of scour depth in the downstream pool. In the present study, the effect of the installation of the apron on reduction of scour in the downstream of the block rams under smooth and rough the surface of the structure was investigated experimentally. The experiments were performed for slopes of 1:3 and 1:5, the ratio of the critical depth to the height of the structure 0.2-0.14 cm, roughness height of 1.15-5.2 cm and different arrangements; as well as apron with equal and half of height of the structure at the hydraulic and physical hydraulic lab of university of Guilan in 2020 and 2021. The comparison of the results of all slopes of the structure showed that the apron installation is directly related to the reduction of the maximum scour depth, so that by installing apron of length equal to the height of the structure, the maximum scour depth for slopes 1:3 and 1:5 reduced by an average of 58 and 43%, respectively, compared to the the smooth block ramp. By increasing the roughness height, the maximum scour depth h over range of minimum and maximum flow discharges and the structures slopes reduced by an average of 39 to 62 % compared to the corresponding smooth block ramp.

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