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.

Meanders are among the important characteristics of some rivers that flow in semi-arid regions. Swift displacement along the river's flow, change in the location of the central ridge and bank erosion leateral erosion are resulted from making meander in the river's flow. Meanders in river courses on North East slopes of Sahand (Located in 46o 43’ to 47o 15’ E and from 36o 05’ to 37o 20’N) are very typical. These meanders and their movements are the main cause of lateral erosion and result in the collapse of materials into flood plains and also the creation of these geomorphological-hydrological phenomena and ultimately result in the increase of sediment load in rivers. The intensity of lateral erosion and middle erosion in flood plains is so high that lateral and medial trees are not obstacle against erosion.This article intends to study the meander's characteristics and the time of movement, by using Dt, S, R/W… indices. The results of this study suggest that the rate of sinuosity in river courses and also the rate of movements during this time is high and because of the high rate of these lateral movement, the risk of erosion along the middle of the bank is high.

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.

Introdution: Alluvial floodplains, and in particular those associated with the world's largest rivers, have a complex relief that is produced by recurring erosional, and depositional events. The magnitude, heterogeneity, spatial distribution, and connectivity of this relief controls river floodwater routing and storage, sediment dispersal, and biogeochemical cyclingChannel Lateral movement and course changes are main causes for floodplain extend, bank erosion and soil loss due to cut bank. Aras river that located in NW of Iran(from 45° E to 48° E), have many curvatures on course and due to this reason Aras is made high rate movement yearly. Aras is a boarder river and for this reason is very important that direction is determined. Methodology: In this article for determining the rate of lateral movement is used landsats 5, 2 (Mss) landsat5™landsat 7(ETM) and landsats(OLI) with 30 and 15 resoulation in 1985 to 2015 epoch. In this study is used Rm, R and MI for rate and degree movement and rate of river course curvature. In order to determining of power flow against instability of mater in this article is used MI idex: MI=S√ Q/D50 And for determining of rate of displacement of channel, is used of Rm index: Rm=(A/L)/Y Discusses: Investigation on the curvature radial Aras channel show that average rate of radial is 509. 62 m. In other site this rate is 515. 71 m. The study also show that changes in Aras river course is vary. When wide is high, channel migration is excess. In recent time this changes is high, but rate of migration in Iran site and other site is decrease to compare of past time. The average of channel migration to Iran site is 27, 21m in 2010 and other site rate is 28, 32 m. Results: Sum all area that located at other site due to displacement are 1410255 m3 (1985-2015). Area in site of Iran is 2230869 m3 (1985-2015). That is to say, difference is 820614 m3. This has meaning that our land and soil is placed other site due to channel movement. Yearly average displacement of channel Aras river is 475 m at Iran site and 353 m at other site. So, displacement at two site is vary. Over the past three decades, the fluvial dynamics of meander bends, including processes related to outer bank erosion, have been the focus of numerous scientific investigations. Despite this effort, a comprehensive understanding of the hydraulic processes of outer bank erosion—especially the role of flow turbulence—remains elusive. Because natural river flows are fully turbulent, the erosive stresses acting on the banks of meandering rivers should be related to turbulent stresses. Current models of outer bank erosion, however, rely on simple parameterization of the flow via excess velocity, excess shear stress at the bank toe, or excess flow depth. Aras River is very dynamic. This river make curvature in its curse and cut bank. When river make meander in flow curse, cut power of flow is increase. This high power is energy for bank cut and movement. Soil lost is other result for cut bank. This story is happened in northern border of Iran.

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.

Flood is a complex natural disaster and a destructive phenomenon that causes considerable annual damage. Floodplain and lands alongside river beds are always at the exposure of flood, while most of economic activities are also concentrated in these areas. Therefore, in these regions, flood zoning is indispensable. Flood zoning maps, could be a suitable and well as lawful tool for use in determination of development strategies. In this research, a map of flood zoning with different return periods was prepared. Hydrological data and information were collected and analyzed. Natural unit hydrograph (N.U.H) was derived. In addition, 262 cross sections were surveyed for Broudjerd Seilakhor River and its branches. Some floodplain characteristics, such as situation of bed and river banks as well as vegetation cover were noted. Flood routing was carried out in different branches and reaches employing Muskingum-Cunge method. Finally, by using HEC-RAS model, flood-zoning maps with a scale of 1:50.000, water surface profiles and flow characteristics in different reaches and for different return periods, were derived. Then, the accuracy and precision of maps, by use of historical films and pictures and through regional investigations, were evaluated. The results indicated that by even considering the HEC-RAS limitations, the final flood maps were still accurate enough for the aim followed in this kind of study.

Background and Objectives: The floodplains are relatively flat lands in the vicinity of the rivers with the residential, industrial or agricultural usage. The sudden breakdown of large dams leads to the formation and propagation of devastating flood waves over the downstream. The flood propagation occurs over the floodplains due to the topographic variations and in-stream obstacles such as bridges. These waves are developed one and two dimensional over a small reach of the river and floodplains, respectively. In the hydrodynamic simulations, two-dimensional characteristics of the dam-break flow over the floodplains have been studied scarcely. Therefore, the combined effects of the floodplains obstacles, constriction and the bottom barriers are calculated over the dam-break flow characteristics. Materials and Methods: In the present study, the moving particle semi-implicit (MPS) method was used to the numerical study of the dam-break flow characteristics over the floodplain. From advantages of this method are including the incompressibility, the particle-based and using of powerful models of gradients and Laplacian in velocity-pressure corrections without any complex smoothing functions. Hence, the effects of the reservoir initial water level, the shapes of the obstacles-lateral transitions as well as the bottom barriers on the hydraulic parameters were studied in 15 various cases. The floodplain obstacles are cylindrical, cubic, rhomboidal and asymmetric, and the bottom barriers are cubic. At first, the sensitivity analysis was carried out on three particles diameters including the 0. 01, 0. 015 and 0. 20 m. Finally, the diameter of the particles equal to 0. 015m was adopted as the water particles size in the model. The simulations carried out through more than 280000 spherical particles, with the second order spatial and temporal accuracy. Results: The precision of the numerical results was calculated using the NRMSE normal error through the comparison with the previous experimental one. The results demonstrated that evacuation of the reservoir occurs in numerical solutions faster than the experimental. Therefore, the MPS model under and overestimates the values of the free-surface profile height and the flow propagation velocity, respectively. The impact of flow to the floodplain obstacles leads to the rising up and the formation of a three-dimensional flow at the obstacles place, the lateral constrictions and the bottom obstacles. Further, the shape of the obstacles represents a crucial factor in the free surface profile deformations, the horizontal component of the surface velocity and the drag resistance forces applied to the flow. Conclusion: Normal error values showed that the accuracy of the MPS method in the calculation of the free surface longitudinal profile deformations are variable between 88 and 91 percent.

Their fertile rivers and plains have been the point of convergence of formation and growth of human civilizations since a long time ago. Khuzestan plain in Iran is a low height plain with mild gradient that river Karon Stream in it. These rivers along the geological times, especially in forth times- quaternary-era-had have a special flow and motional stream so that constantly have changed their primary-courses to other directions and in additional they caused to change both social-civilization and water ways' patterns. In this research by means of a combination of library-field techniques and historical studding, and based on systematic method plus, satellite pictures, numerical data, topography maps, and using GIS techniques and statistical software, and also global positioning system (GPS) we made and effort to recognize the primary and primitive courses of major rivers of Karon plain and we reached the following results. Taking this point to consideration that in changing of directions of rivers in quaternary, there are four major factors playing role as follow. Changes in base level, tectonic, climate changes (catastrophe) and human parameters. Has track the trace of Karon river. That caused to recognize 4 major primitive courses plus a lot of derivative courses.