The continuous movement of riverbed particles due to turbulent flow determines the stability of non-cohesive riverbeds and banks during riverbed and bank erosion and sedimentation. This study emulated the stable channel design by deriving the low maintenance cost of the channel through bed protection by an armor layer. The study investigated the effects of shear stress and grain size uniformity to determine the minimum non-cohesive armor layer thickness for the stability of riverbeds under steady uniform flow conditions. Experiments were conducted with four different discharges, five armor material gradations, and five bed-slope variations in a full-scale flume. We observed and recorded the behaviors of the five gradations of armor materials for given discharges and bed slopes. Eighty data points were recorded and analyzed. The hydraulic analysis of the flow along with the soil mechanics analysis of the armor materials was done. The soil mechanic analysis was particularly focused on the uniformity coefficient of the armor layer, Cu, to derive the armor layer equation. However, for the manageability of the study, we set the limit of the Cu between 3.0 and 6.0. From the viewpoint of non-erodibility, a wider Cu value indicated a thinner armor layer. Variables that govern the armor layer thickness and the layer thickness itself were derived and proposed. The variables, namely Cu, shear stress (t0 and tc), and mean diameter of the bed load and armor materials (Db50 and Da50). Our results show that these variables governed the thickness of the armor layer, and this is expected to contribute to the design of stable natural channels, which can minimize the cost of irrigation canal maintenance and development. Doi: 10.28991/CEJ-2022-08-06-01 Full Text: PDF

Armoring is forming an armor layer of the riverbed which is preceded by the transportation of bed sediment. Mobile armor occurs when the riverbed reaches equilibrium, then eroded, and the surface of the riverbed recovers. Therefore, protection is formed by moving riverbed material. This research used a simulation model generated through HEC RAS software version 6.1. The model input location was Krasak River, Sleman, Yogyakarta. The data for model input were the topography of the Krasak River from upstream to the point of view, flood discharge hydrograph, and grain size gradations. The simulation combination consisted of three locations with the riverbed material of each location sampled tested for grain size distribution. The running simulations combined the flood discharge at return periods of 2, 5, 10, 25, 50, and 100 years. There were three variations of grain size distribution used as input data. Meanwhile, variations of sediment transport methods used the Meyer-Peter Muller and Wilcock-Crowe methods. Overall, the simulation results show that the shear stress and the proportion of sand-to-grain material affect the armoring process and riverbed changes.

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 (sv) and the dimensionless shear stress (t0/tc). 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. Doi: 10.28991/CEJ-2023-09-06-05 Full Text: PDF