عنوان مقاله [English]
Rivers are one of the best geomorphic landscapes in which the connection between the system of forces and the forms of unevenness can be clearly understood (Chorley et al., 2000: 163). Various sites, especially sedimentology, are important. Zab River is one of the most water-rich rivers in the country, which due to the high discharge, causes a lot of damage annually due to floods on agricultural lands located in the river. This river, by changing its course in the bed and creating erosion along the bed, exposes the lands around the bed to destruction, and considering that the farmers of the region use the river water for agriculture, it is of great economic importance for them.Therefore, it is necessary to classify and determine the boundaries of the riverbed and thus understand the existing processes and morphological knowledge of it. Therefore, it is necessary to classify and determine the boundaries of the riverbed and, as a result, to understand the existing processes and its morphological knowledge.
Data and Method
River classification according to Rosegan method: Rosegan classification is divided into four levels: In this research, for the morphological classification of Zab river, first by scrolling along the study area, an almost uniform set of geomorphic units is identified. Then, using GPS in three paths upstream, middle and downstream of the study area were segmented. After intercepting the river route and then entering the required data into the WMS9.1 and HEC-RAS software environment and executing the hydrological model, the geometric properties of 24 transverse sections of the total sections in all intervals The studied route was extracted and all the parameters required for classification and geometry of the duct in those intervals were calculated. To determine the overflow discharge of the intervals, the discharge with different return periods obtained from the relationship between Fuller and smada software with The prepared sections were given to HEC-RAS software and then based on one of the methods to determine the full cross section (level at which the ratio of width to depth to depth in an orthogonal device is minimized) the overflow flow is determined Took. Accordingly, in each cross section of the curve, the ratio of width to depth of flow versus depth for each section was plotted and the minimum point on the curve was selected as the discharge of the full section. After determining this discharge in each transverse section, using frequency analysis, the full section discharge has been determined for the whole river. Finally, by introducing flow characteristics, geometric characteristics and manning coefficient of each section in HEC-RAS software, flow simulation was performed and data related to cross-sections and water surface profiles including width to depth ratio, indentation index Bed, cross-sectional area in overflow, overflow width, maximum depth, flood plain width and water level slope, etc. were calculated. The implementation steps of the HEC-RAS model are shown in Figure 2.
Results and Discussion
According to field and laboratory studies, Zab River is in the alluvial group in terms of classification based on the type of bed sediments (rocky and alluvial). In summer, due to dehydration, fine-grained sediments are placed on coarse-grained sediments, as a result of which sand particles get stuck between the sand particles and cause the bed to solidify. These sediments are sandy but in winter Due to the flood, fine particles are displaced along with the flood and large particles remain at the bottom of the bed, so the type of sediments on the bottom of the Zab River are sandy. To obtain the average size of duct material, 15 samples were taken along the river at different distances and granulated in the laboratory. Due to the fact that the intervals 4 in the upstream and 11 in the middle part of the studied route have a mixed bed of irregular rapids or erosion basins and the bed (profile) and sides are relatively stable and have a limited sediment transport system with type B Roses are compatible. Also, moderate roughness and narrow valleys with a gradual slope are other reasons for confirming this claim. Intervals 1, 2, 3, 4, 5 upstream, 10, 12, 13, 14 in the middle and 17, 20, 21, 22, 23, and 24 downstream of the studied route with respect to stability They and their sediment load and limited transport are Type C compliant. The predominant morphological feature of these areas is wide valleys with alluvial terraces associated with the flood plain, which are again the characteristics of this type. Section 18 is located in the downstream part of the studied route in type D, which is witnessed by the following reasons. The river is arterial in this area and rock fragments are rarely seen in the bed. The ducts also have erodible edges and high suction load. The morphological appearance of most areas has this type of wide valleys with alluvial and clovial cones. Interval 12 is located in the middle part of the studied route in type E. Here the ducts show significant sinusitis and the ratio of width to depth is low. The river is stable in this area and one of the reasons is the development in the floodplain with dense grass cover on the vertical shore of the duct. The predominant morphological feature of this section is the type of wide valleys with grasslands.
The characteristics of these intervals indicate their conformity with the Rosgen model. High instability of the riverbed in the range of intervals of types C and D is a threat to agricultural lands and surrounding structures. The results of evaluating the stability conditions of the intervals of the study area in the third level of Rozgan showed that in the upstream path of the study area, the intervals of 2, 5, and 8 intervals have more stable conditions at a good level than other intervals. Flow conditions in the intervals 1, 3, 6, 7 are at the intermediate level and in the interval 4 are at the weak level, which have more unstable conditions. In the intermediate path, the range 11 is better and more stable, and the 10, 12, 13, and 15 ranges are at the intermediate level, which is less stable. In the downstream direction, the studied areas are intervals 19, 21 and 22 at a good level and with more stable conditions, intervals 18, 20, 23 and 24 at a medium level and range 17 at a weak level and instability conditions. The results of Zab River evaluation based on Rozgan classification system at levels two and three showed that the canal patterns in Zab River and consequently the effective parameters in classifying and separating the canals are consistent with Rozgan system. However, there are differences in the values and parameters that are due to specific conditions of local influencing factors. However, the Rozgan system is responsible for the morphological knowledge of the Zab River and similar fluvial systems. کرد. Therefore, this model has the ability to quantitatively predict the geomorphism of the Zab River and rivers with similar conditions.