Flood plains of rivers play a significant role in the transfer of flood discharge. In this research, the vertical distribution of the longitudinal and transverse flow velocities and the amount of discharge passing through different sections of the main channel in flooded meandering rivers under the effect of the change in floodplain width and relative depth were investigated. Because the fact that the width of the floodplain is constantly changing along the river's path, in this article, from the four meandering compound channels with floodplain widths of 3.3, 4.31, 5.32, and 6.33 meters and three relative depths of 0.26, 0.35 and 0.45 were used. The results of the numerical simulation showed that with the increase in the width of the floodplain, the value of longitudinal and transverse flow velocities decreases and these changes in the transverse and longitudinal flow velocities are more noticeable due to the change in the width of the floodplain in the middle sections and above the overflow depth of the main channel, so that with the increase 92% of the width of the floodplain, the value of the maximum transverse and longitudinal flow velocity in the middle section decreases by 21% and 25%, respectively. Also, according to the results of this research, with a 92% increase in the width of the floodplain, the average flow velocity and discharge through different sections of the main channel will decrease by 24% and 33%, respectively.

Introduction: Prediction of flow field in compound channel is an important task for hydraulic researches because of the threedimensional nature of the flow. In compound channels with prismatic floodplains, the main feature consists of theinteraction effect between the fast moving flow in the main channel and the slow moving flow on the floodplains….

In this research, using FLOW3D software, the flow velocity distribution and shear stress of the bed in meandering compound channels due to the change of floodplain width and relative depth were investigated. For this purpose, four sections of meandering compound channels with floodplain width having 3. 3, 4. 31, 5. 32 and 6. 33 meters and three relative depths of 0. 26, 0. 35 and 0. 45 have been used. The results of numerical simulation show that by increasing the floodplain width, the depth averaged velocity and bed shear stress are reduced. So that with a 92% increase in floodplain width, the maximum flow velocity in the main channel decreases by 24%, and the depth averaged velocity at relative depths 0. 45 and 0. 26 are reduced by 17% and 21%, respectively; and the rate of change of depth averaged velocity is more noticeable due to a change in the width of floodplain for low relative depths. The effect of changing the floodplain width on the bed shear stress has the highest value in the mid-section between two apexes (CS3 section); so that by 92% increase in the floodplain width in the mid-section (CS3), the bed shear stress is reduced by 35%. Also, the amount of boundary shear stress in the inner arch wall in all channels which is higher than the boundary shear stress in the outer arch wall; and the maximum amount of wall shear stress occurs near the bankfull level of the main channel and by increasing the relative depth, the wall shear stress increases.

Plantations may influence soil fauna directly or indirectly. This research was conducted in order to study the influence of species plantations on soil macrofauna. Plantations of eight tree species including nitrogen fixing trees and non-nitrogen fixing trees based on complete randomized block design with 3 replicates were established in 1372 in Dez riverside. Soil macrofauna were studied randomly with two 0.5×0.5 m2 samples from the 0-25 cm top soil in 1385. Earthworm, formicidae, coleoptera, collembola, araneae, chilopoda, isopoda and gastropoda were found. The average of soil macroinvertebrate abundances and biomass were consistently higher in A. salicina plantations than the other, whereas, E. camaldulensis had the lowest abundances and biomass and the highest richness. Comparison of the arthropods abundances and biomass did not show any significant differences between the different plantations. Comparison of macrofauna abundances and biomass in tow plantation groups were not significantly different. Principal component analyze of plantation species based on soil macrofauna also did not separate the two groups, so we could say that the differences under the diverse species do not relate to their nitrogen fixing property. As soil macrofauna is an important factor in regulating litter decomposition, the study on the relation of their abundance and richness to litter decompositiom is recommended.

Geotechnical investigations were carried out to establish the bearing capacity of the geological materials that occur at the site. The investigations involved an analysis of the properties of the materials in the area using soil mass characterization, river depth analysis, geotechnical testing and slope stability analysis. The investigations identified several key stability issues such as the depth to the firm foundation, the bearing capacity of the foundation rock, liability to liquefaction and the stability of the slopes.      

Bridge failures due to scour at bridge abutments clarify importance of scour prediction and scour countermeasures. Most of bridge abutments are located in floodplains. One of common cases in floodplains is the existence of vegetation cover. Scope of this study is investigation on effect of vegetated floodplain on vertical wall abutment scour in compound channels. Results show, for constant abutment length and flow depth, with increasing the vegetation concentration, scour depth decreased with an increasing rate. For constant vegetation concentration and abutment length, with increasing the flow depth, effect of vegetation in reduction of scour depth decreased. In abutment with the lengh of 26 cm and concentration with s=8, with increasing the flow depth from 4.8 to 11.8 cm, percentage reduction in scour depth decreased from 40 to 22 percent. Also, vegetation reduces scour hole dimensions and has effect on downstream topography.

River floodplains are fertilized areas that are most considered by humans, and people always like to develop these areas. Therefore, the conservation and management of this area is most important. In This study for management purposes, the 4.5 Km of Ghezelozan River, was determined as flood hazard zone using HEC-RAS with ArcView and HEC-GeoRAS extension. In order to, do the researches, digital maps in 1:1000 scales was provided and the area of study was classified to 118 cross sections. In the other side the hydrological information determined and the Manning roughness coefficient was estimated using Cawen Method. Finally the flood area and depth maps were provided for 7 different return periods of 2, 5, 10, 25, 50, 100 and 200 years. Results showed that about 86.14% of the flood prone area to flooding under 25y return period for 200 years. The flood depth maps indicated 57.29% from flood depth of 200 yreturn period belonged to the to flooding under 25y return period.