mohsen sajjadi

Physical properties of tree species determine their reaction to external loads as a result of water flow. The greater the trees ability to withstand water load, the greater the amount of water energy absorption, generation of water eddies, and the acceleration of turbulence in vegetation canopies. This will increase water flow energy lost. In general, physical properties of trees include leaf density, shape, and overall flexibility of their species. In this study, an index is proposed to characterize physical properties of tree species. This will enable the application of a single momentum (or energy) equation to determine overall reaction of variety of tree species in a community. The index is derived based on the resonance frequency of the first mode of vibration of trees and a fundamental relationship for the homogeneous beams. The derived indexes for four species of coniferous trees were used in a mathematical model to estimate the drag and energy coefficients as representatives for tree reaction to water flow, and could account for the differences due to the leaf density, shape, and rigidity of the tree species.

The high flow velocity downstream of weirs and gates can cause the destruction of erosive beds in rivers or even non-erosive channels. To reduce the flow's kinetic energy, structures are needed to consume this energy. Expansion basins are often used downstream of structures such as weirs, gates, and chutes to increase energy dissipation in hydraulic jumps. Various methods are used to stabilize asymmetric hydraulic jumps in abrupt expanding channels. In this study, the interaction of multiple submerged water jet injection systems with S-type hydraulic jump for stabilizing and stabilizing the hydraulic jump was investigated. The different configurations of the jet system were tested with Froude numbers 7.4, 8.7, and 9.5, and finally, three optimal configurations were selected as configurations 1, 2, and 3. In order to investigate the performance of the jet injection system under other hydraulic boundary conditions, flow velocities downstream of the jet system were measured for three optimal configurations with different depths of the tailwater. Comparison of the results of using a water jet injection system with S-type hydraulic jump showed that the energy and momentum correction coefficients in all different configurations were significantly reduced. The highest relative energy loss was observed in configuration 3, equal to 68.42%. The results showed a good performance of the jet injection system in stabilizing the asymmetric hydraulic jump S and reducing the length of the stilling basin.