نوع مقاله : مقاله پژوهشی
1 دانش آموخته کارشناسی ارشد هیدروژئومورفولوژی، دانشگاه تهران.
2 دانشیار گروه جغرافیای طبیعی، دانشگاه تهران.
3 دانشجوی دکتری ژئومورفولوژی دانشکده جغرافیا، دانشگاه تهران.
عنوان مقاله [English]
Numerous Classification Schemes According to Geomorphic River from the late Nineteenth Century has been done that reflects the diversity of Environmental Situations. The aim of this study is investigate in Vulnerable Areas this Kashkan River for a reach length of 5000 m using Channel Stream Classification in level one and two as Rosgen. In Level I, Classification using Satellite images and field visits and investigation Maps and at level II, for morphological parameters of the digital map with scale of 1:150, Rider HEC-geo-RAS and HEC-RAS Model Measured and calculated parameters required. The results show that interval between the primary arterial patterns of DA6, the center of a single branch pattern of A4 And the final section of the D3 range and is also the arterial pattern that the flow rate increases sediment and changes in flow designing has very high sensitivity and Most of the sediment fed with high sensitivity and caused severe morphological changes that are unsustainable pattern of River Reorganization measures in this sector must be carried out according to morphological variables.
Rivers influenced by different variables in terms of size, shape, direction and pattern change. Rivers based on historical factors, tectonics, lithology, climatic and human divided into types is dumped. Several factors including time, discharge, sediment load and on the level its influence and for digging river, sedimentation, changing patterns of deformation and conduit, responds to it. Rivers flow conditions or with respect to their geometrical characteristics that are natural or synthetic (human intervention) is applied sensitivity and react. By knowing the rules governing the river, we can recognize and change its behavior, it is qualitatively and quantitatively predicted. Kashkan watershed with area of 9300 km2 is located in southwest of Iran in longitude of 47° 48' E and latitude of 33° 43' N. Annual mean discharge of this watershed at outlet point is 33 m3/s with specific discharge of 9 lit/s.km2. Annual mean precipitation of this watershed is 550 mm. The maximum precipitation in the watershed is occur in February, whereas the maximum discharge of this river has occur by two months lags in April. This denotes to dominance of snowmelt runoff in river discharge. From viewpoints of geomorphologic indices, the streams of this watershed has low potential of erosivity and low tectonic activity.
Matarials and methods
In this study Classification as Rosgen in level II, First, scrolling along the study area, part the Section thre upstream, intermediate and downstream the interval was set up. The maximum instantaneous flow rate statistics related to 24-year period Kashkan Bridge station is used to determine the flood return periods. The cross sectional geometry data and topographic maps of 1: 150 on the river Satellite images to determine the grain size distributions and calculating the Manning roughness coefficient As well as field visits were made to increase the accuracy of information. The following software needed to evaluate the river was used: Google Earth software to identify the exact area, HEC-RAS hydraulic calculation software for morphological parameters and the extension HEC-geo-RAS to transfer data from GIS to RAS and vice versa. Easy fit software to perform frequency analysis on data up to discharge and Finally Rosgen model for morphological classification channel is used.
Result and discussion
Determine of river plans in level I, Rosgen classification that based on the appearance of the river, the study Section was divided into three parts. With the help of satellite images and field visits to the site, and Google Earth images were obtained necessary information about the type of Plan Rivers. In the first part of the arterial channel model, in the second place and the third part of the rivers of arterial was found. In addition, field visits it was found that the wide and shallow channel in the first and third sectors, and in the second part narrow and relatively deep. Channel slope is calculated using longitudinal profile. To determine the required parameters for the level II, by extracting the geometric characteristics of the cross sections in different parts and Run of the hydraulic models HEC-RAS All parameters required Including Width to depth ratio, The ratio of hole, The curvature coefficient, Channel slope and Bedding materials for classification and identification of conduit geometry, respectively. After calculating the required parameters of this section, the results they were averaged and based on the results of River pattern was determined in accordance with the Rosgen classification.
According to the results, it was found that interval between the primary arterial patterns of DA6, the center of a single branch pattern of A4 And the final section of the D3 range. The last two sections of river sediments is high in nutrition and the potential erosion is also very high and the potential for recovery is poor in these sectors River that these sectors are vulnerable areas range. The final section of stream rate increases sediment and changes in flow designing has very high sensitivity and Most of the sediment fed with high sensitivity and caused severe morphological changes that are unsustainable pattern of River Reorganization measures in this sector must be carried out according to morphological variables.