The effect of tetrahedron framed permeable weirs on river bed stability in a mountainous area under clear water conditions

Abstract

A flexible riverbed protection called tetrahedron framed permeable weirs (TFPW) is proposed to protect riverbeds in mountainous areas from scouring. Under clear water conditions, a series of laboratory flume experiments were performed to study the effects of TFPW with different layout types on the stability of riverbeds. The objectives of this paper were to advance understanding of the role that TFPW play in the erosion process of river beds and to optimize the TFPW design for reducing velocity, promoting sediment deposition and good structural stability. Data on velocity distribution and variation, equilibrium bathymetry, flow resistance, bed form characteristics and structural stability were collected and analyzed. The results indicate that (1) with good structural stability, all the TFPW with different layout types had significant effects on the stabilization of the riverbed by reducing velocity, raising the water level, increasing the roughness coefficient, protecting the riverbed from degradation and promoting deposition; and (2) the random Double TFPW with large rates of deceleration, large deposition ranges, and good structural stability, and the paved Single TFPW with small rates of deceleration but large deposition ranges and perfect structural stability, were suitable and optimal for riverbed protection in a clear water channel.

Bed Morphology around Various Solid and Flexible Grade Control Structures in an Unstable Gravel-Bed River

“…Therefore, the TFPW could remarkably decelerate the flow velocity. The similar change regulations were observed by Wang et al (2017), both the mean velocity and dimensionless near-bed velocity downstream from the TFPW were decreased by TFPW [39].…”

“…A series of experiments were carried out under different structural conditions, including no GCSs, bed sills, and TFPW with different layouts. It has been investigated experimentally that the random Double TFPW and the paved Single TFPW were suitable and optimal for riverbed protection in mountainous rivers [39]. Further, the bed morphology under the protection of random Single TFPW (TFPW I), random Double TFPW (TFPW II) and the paved Single TFPW (TFPW III) in a piedmont river were observed in this study.…”

“…Because of high water permeability, the water over the TFPW was hardly obstructed, where the water surface stayed almost horizontal with no jets or turbulence (Figure 10b). The water-depth variation around a TFPW used for riverbed stability in a mountainous channel was observed experimentally (in a narrow flume with a width of 1.0 m and a slope of 10 , and the bed was paved as mountainous river morphology in each test) [39], where the water level changed slightly upstream from the TFPW, followed by a significant water level rise over the structures, and finally maintained a stable level. In this study, in a gentler and wider piedmont river, the water level varied less pronouncedly.…”

“…In this study, solid bricks were arranged as the model bed sills (11.5 cm wide, 5.3 cm above the bed and 5.3 cm below the bed level, respectively). Geometric similarity was followed when choosing the frame models, also with a proportional similarity of 1:20 [39]. The tetrahedron frame model consisted of six identical bars (the length was 5.0 cm).…”

“…Tetrahedron frames retard the flow and reduce the boundary shear stress, thus reducing the probability of sediment entrainment and even inducing sediment deposition [38]. With high permeability but also retarded flow, TFPW were proposed as a new kind of flexible riverbed protection structure in a mountainous river [39], and they had a significant effect on riverbed stabilization. In detail, TFPW can reduce the velocity, increase the water level, augment the roughness coefficient, protect the bed from degradation and promote sediment deposition.…”