رويين ممقانيه

The implementation of nature-based solutions to address environmental challenges, has received wide attention in recent years. Engineered logjams (ELJs) are among the aforementioned solutions, employed in order to control flooding, prevent excessive erosion an‎d sedimentation, rehabilitate fluvial ecosystems, an‎d increase the resiliency of forested catchments to wildfires. However, due to relative novelty of this technology, the current knowledge on morphodynamical response of river corridors to ELJs, is still limited. To fill this research gap, the present study was conducted with the main objective of investigating the interaction between ELJ structures an‎d erodible river beds. In order to achieve this objective, a channel-spanning ELJ model was subjected to flow in a laboratory flume with san‎d bed, until the scouring process attained an equilibrium state. Subsequently, three-dimensional, instantaneous, velocity components were collected at upstream an‎d downstream of the ELJ model, by utilizing the acoustic Doppler velocimetry (ADV) technique. Our results revealed that: • Channel-spanning ELJs can significantly impact geomorphic features of the channel, even at far downstream distances. •As the scour hole beneath the structure evolved, the upstream backwater rise became less an‎d less pronounced until the end of the test, when no noticeable difference was observed between upstream an‎d downstream flow depths. Thus, for channel-spanning ELJs, installed with the aim of generating backwater rise, the bed erosion beneath the structure may lead to a loss of functionality for the structure. •Upstream of the logjams, flow diverted toward the lower gap, creating a primary wall-jet exiting underneath the structure. •The velocity distribution in the wake region of the logjam exhibited a two-layer configuration, with the jet layer situated beneath the reverse flow layer. Due to the porose nature of the logjam, a portion of the flow was able to seep through the structure, which subsequently led to the formation of secondary offset jets in the upper wake layer. These jets had a direct interaction with the reverse flow layer. •Presence of bedforms led to the occurrence of adverse an‎d favorable pressure gradients in the upstream an‎d downstream of the structure, respectively. This directly influenced the wall-jet from the perspectives of similarity, growth of the length scales, an‎d decay of the velocity an‎d turbulence parameters scales. •Distributions of Reynolds shear stresses an‎d root mean square values of instantaneous velocities, showed that the peak mixing intensity occurs at the vertical location of the boundary between lower an‎d upper wake layers. Our study expan‎ds the current knowledge of the wood, flow, sediment interaction an‎d highlights potential implications for river engineering applications.

انباشته‌هاي چوبي مهندسي شده , آب‌شستگي موضعي , موانع تراوا , راه‌حل‌هاي طبيعت محور , احياي رودخانه

Engineered Logjams , Local Scour , Leaky Barriers , Nature-Based Solutions , River Rehabilitation

Ruyin Mamaghaniyeh

Hossein Afzalimehr