پديد آورندگان :
روستايي، شهرام نويسنده دانشيار گروه جغرافياي طبيعي، دانشگاه تبريز , , خورشيد دوست، علي محمد نويسنده دانشيار گروه جغرافياي طبيعي، دانشگاه تبريز , , خالقي ، سميه نويسنده دانشجوي دكتراي ژيوموفولوژي، دانشگاه تبريز ,
چكيده لاتين :
Introduction
River channel morphology (geometry) determine by channel forming discharge (bankfull discharge) that has most effect on erosion, aggradations, morphology and form of cross-section. Interaction bankfull discharge and channel provides a variety of cross-sectional area forms. Specifications of cross-section in bankfull discharge shows the morphological characteristics of the river. Therefore with collection of cross-sections data can be evaluated channel type base on classification systems. One of the famous classifications of stream systems is Rosgenʹs classification that was divided to four levels. In level II, morphological descriptions based on field-determined reference reach informa tion that streams are classified into types (A–G) based on the following seven channel attributes: (1) mean bankfull depth; (2) maximum bankfull depth; (3) bankfull width; (4) flood-prone area width; (5) channel sinuosity; (6) mean channel slope or water surface slope; and (7) median channel material size. In this paper, Lighvan river (located on Lighvan catchment in northern slope of Sahand Mountain mass at 37o 43ʹ 30"–37o 55ʹ northern latitude and 46o 22ʹ 25" – 46o 29ʹ 15" eastern longitude) channel morphology in some reaches have been computed by different methods and evaluated by Rosgenʹs classification. In this level, the more detailed description of the river morphology presents that obtain from field visits. River trenches, dimensions, patterns, longitudinal and cross-sections profile and bed material present in this level as quantity and in terms of stream type.
Methodology
In this paper, in order to analyze the past condition of the Lighvan river channel morphology (Between Lighvan and Hervi stations), river cross-section data that obtain from field visiting in 1379 with 1:1000 scale. First, these maps was scanned, digitized and georefreced in Auto Cad and then 28 cross-sections selected and was introduced to the HEC-RAS software. This software compute water surface profiles by geometric and hydrometric data. Here, we applied HEC-RAS and input geometric, flow data and boundary conditions in order to estimate morphological parameters such as width/depth ratio (W/D), entrenchment ratio (ER), bankfull cross sectional area (Areabkf), bankfull width (Wbkf), maximum depth (dmax), and flood prone width (Wfp), water surface slope. Finally, these information and other parameters such as sinuosity and median channel material size was utilized for classification of each reach according to Rosgen’s Level II classification system.
Results and Discussion
After extracting parameters, all reaches categorized by Rosgenʹs classification. According to it, all reaches defined by one of type B, C, and E. Entrenchment ratio (ER) is higher than 2.2 in C. Width/depth ratios (W/D) is lower than 12 in E and higher than 12 in C. According to sinuosity index that is lower than 1.05 for straight, between 1.05-1.5 for sinusoidal and higher than 1.5 for meandering rivers. Result showed that river is sinusoidal type and according to Rosgen classification reaches 2,6,21 and 26 are type B, reaches 1,4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 17, 18, 19, 23, 24, 25, 27 and 28 are type C, reaches 3,15 and 16 are type E. In type B, bank and bed are relatively stable and have limited sediment supply. In type C, width/depth ratio is more than 12 and entrenchment ratio is medium and in large events, the flood fills floodplain. In type E, width/depth ratio is low and sinuosity is high. These rivers are stable and one of its reasons is development floodplains with dense often grassy vegetation in vertical banks.
Conclusion
Channel morphology in upper catchment is defined by type B and C, in middle and lower catchment is defined by one of types B, C, E. According to Ward (2008), almost any channel can fit into it and be classified, even if some landscapes are not described as well as they are typi fied by outliers. Application of Rosgen classification system for Lighvan River showed that some of channel well adjusted with this classification and few of them not. Therefore, this method has ability of geomorphic quan titative predict of Lighvan river. So this type of morphological classification of river channel can be applied in development of engineer design and issues management and river restoration.
