Available online at www.CivileJournal.org Civil Engineering Journal (E-ISSN: 2476-3055; ISSN: 2676-6957) Vol. 9, No. 06, June, 2023 1356 River Mobile Armor Layer Induced by Flood Arlendenovega S. Negara 1* , Cahyono Ikhsan 2 , RR. Rintis Hadiani 2 , Yusep M. Purwana 2 1 Doctoral Program in Civil Engineering, Faculty of Engineering, Universitas Sebelas Maret, Surakarta, Jawa Tengah, Indonesia. 2 Department of Civil Engineering, Faculty of Engineering, Universitas Sebelas Maret, Surakarta, Jawa Tengah, Indonesia. Received 03 March 2023; Revised 10 May 2023; Accepted 19 May 2023; Published 01 June 2023 Abstract The armored layer is crucial for protecting the riverbed. The bed layer of the river is a movable material that protects the material below the surface layer. This study aimed to develop formulas to estimate the thickness of a mobile armor layer with noncohesive materials and establish a correlation between the flow velocity and shear stress under conditions of erosion and sedimentation. The research methods included field measurements, laboratory tests, and numerical simulations. The primary data included grain size gradation profiles, river topography, and flood discharge. The results demonstrated consistency in the behavior of the riverbed under various flood discharge conditions. The fundamental variables affecting the mobile armor thickness included the gradation coefficient (v) and the dimensionless shear stress (0/c). The fundamental novelty of this study is the derivation of the mobile armor layer thickness, which is influenced by grain size and shear stress. The present findings significantly contribute to the design of more efficient and environmentally friendly riverbed protection rather than rigid structures. These results indicated that erosion and sedimentation were primarily influenced by the flow velocity and the applied shear stress above the riverbed. Keywords: Armor Layer; Shear Stress; Grain Size; Bed Load; River. 1. Introduction The research delves into the high frequency of erosion and sedimentation phenomena in rivers and irrigation canals, which incurs high costs for maintaining and constructing canals. This phenomenon has forced policymakers to construct rigid river structures, which are more expensive than unlined channels. Thus, riverbed control work utilizing natural materials is essential for innovating lower river maintenance costs, greater efficiency, and more environmentally friendly river maintenance work. As such, riverbed variations occur naturally in rivers and can affect their environment and hydraulic structures. The variations in riverbed elevation are influenced by the flow velocity [1] and bedload of the sediment transport [2, 3]. Based on the characteristics of the riverbed armor, it can be divided into two types: static and mobile [4, 5]. Although previous research on armor layers should provide a formula for determining the thickness of the armor developed under certain flow conditions, only a few studies have calculated the thickness of the armor layer. For example, Ikhsan et al. [6] evaluated the thickness of the armor under stationary conditions, and Marion & Fraccarollo [5] presented the formation of mobile armor under steady flow conditions. To date, no study has attempted to derive the thickness of the mobile armor under flood conditions. This research gap inspired us to develop a numerical simulation of mobile armor under flood hydrograph conditions for deriving a formula for the thickness of the mobile armor. In principle, we defined the thickness of the mobile armor as the average thickness of the riverbed alterations in * Corresponding author: satrianegara@student.uns.ac.id; satrianegara@gmail.com http://dx.doi.org/10.28991/CEJ-2023-09-06-05 © 2023 by the authors. Licensee C.E.J, Tehran, Iran. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).