Document Type : پژوهشی
Authors
1 epartment of Physical Geography Faculty of Earth Sciences Shahid Beheshti University (SBU)
2 Ph.D Candidate, Shahid Beheshti University, Tehran, Iran
3 M.A. Student, Shahid Beheshti University, Tehran, Iran
Abstract
1-Introduction
One of the most elements in river geomorphology, engineering and management is the channel issue. Rivers are natural and complex systems that their classification offers a better knowledge regarding their processes and forms. Based on dynamic and channel forms, rivers are varied and find natural changes over the years. However, nowadays anthropogenic effects comprising building structures such as bridges, and roads accelerate the destructive process. River classification is a suitable way to increase our knowledge about rivers. One important aspect of river is hydrogeomorphological understanding. Therefore the objectives of this study were to assess and analyze the Taleghan river hydrogeomorphological conditions using the geomorphological quality index method (MQI) in upstream of the Taleghan dam and to validate MQI in this river.
2-Methodology
Six reaches in upstream of the Taleghan River have been selected and MQI for each reach determined using satellite images and field survey. In order to determine SQI for each reach, three aspects have considered including river processes continuity (longitudinal and crosswise), channel morphological condition, cross-section form, sediment bed
loads and vegetation. These aspects investigated in the form of three components consists of geomorphological functions, processes and river forms (F), artificial (A) and channel adjustments (CA).
3-Results
After measurement and field observation of the Taleghan River, effective variables on morphological quality index were obtained in reach. MAI and MQI values for each reach were calculated and classification was done based on the range of each class. The condition of each reach based on MQI was explained as follows:
The first reach: took place in a mountain area and upstream of the river that on both sides connected to the river and is limited.
Based on the NBS model erosion of bank steam is in a minor amount and the average bed slope in this reach is 0.028 with gravel bed.
Channel width is variable between 10 to 18 m and has a single channel pattern. The obtained MQI values in this reach is 0.714 that grouped in a good class.
Reaches comprising four reaches (two, three, five and six) have the same condition that in the point of human interfering, morphological condition and values of bed and bank erosion have a normal array and grouped in moderate class.
In reach 4 the river is fairly limited and flood plain is present discontinuously on one side and the other side is attached to the hillside. The river has a sinuouse pattern and bed load sediment formed by fine and coarse sand. Furthermore, forth reach strongly influenced by human changes consists of gravel and sand quarring, the existence of bridge structure on the river, presence of built-up area and destruction of vegetation along the river.
4-Discussion and conclusion
The results showed that reach one with score value of 0.714 due to low human interference and locating in upstream of the river categorized in a
good class. Otherwise, reaches two, three, five and six have values of 0.58, 0.54, 0.59 and 0.61, respectively and they are categorized in moderate class; in these reaches in comparison to reach one the values of human interference have been increased. The reach four with MQI score value of 0.49, is categorized in a weak class because of human interference including gravel and sand exploitation and structures such as bridges on the river. The results reveal that the MQI model is approperiate for the classification of rivers in the Taleghan River in southern of Alborz Chain Mountain.
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