عنوان مقاله [English]
Taleghan River is considered as one of the most important water resources for the irrigation of agricultural products in Qazvin plain. The construction of Taleghan dam and new roads and population deployment along the Taleghan River and landuse change have made it subject to alteration so that there is no awareness of Taleghan River morphological quality. It is located in west of Tehran located within 36° 00' 30" to 36° 15' 15" N latitude and 50° 30' 00" to 51° 15' 12" E longitude. It is 52 km long and originates from Asalak Ghaut in the west of Kandovan and flows into the west. After receiving numerous branches, the river finally joins the Alamut River, and then, along with Shahroud River flows into Sefidroud Lake Dam.
a) - Field Survey
We determined 6 river reach using field survey and satellite imagery. Sampling of the river reach was based on the impact of physical and human factors affecting river alteration. Data analysis was conducted using revisited morphological quality index (rMQI).The methodology was as follows. Satellite imagery in two different time intervals (2006-2016) as well as field survey indicators related to Change/Trend of Channel Adjustment Indicators (AI) and Human Pressure (PI) were identified. Next, we measured and calculated these indicators. Then, we scored them using revisited Morphological Quality Index (rMQI). Finally, the morphological quality of the Taleghan River between 2006 and 2016 was obtained using revisited Morphological Quality Index.
b) - Revisited Morphological Quality Index
rMQI method is based on 12 human pressure indicators, 10 indicators of channel adjustments, 10 indicators of functionality of a river's meandering style. It is a scoring system by which one can quantify river alterations which can be compared with the initial conditions. Using this method, it is possible to classify river alterations as very good, good, moderate, poor and extremely poor by human and physical actions. In this method, each index is assigned a point (0) a lack of alteration or pressure, and (9) the intense point for significant alteration or pressure. Finally, each indicator is calculated as the sum of points for each index obtained. Thus, if rMQI lies within the range of 0%-14%, the morphological quality of the river is in a very good physical state. For rMQI = 15%-% 29, it is in a good morphological quality. For rMQI = 30%-49%, it is moderate; for rMQI = 50%-69%, it is poor, and if rMQI is within 70%-100%, the morphological quality of the river is extremely poor.
Results and discussion
Studies for 2006 showed that reaches 2, 5 and 6 had extremely poor quality and reaches 1, 3 and 4 have moderate quality, whereas in 2016, reaches 1, 2, 4, 5 and 6 had very poor quality and reach 3 had poor morphological quality. It can be inferred that in 2016, human factors, besides the construction of bridges and rectifications activity to protect the river bank, wood removal and removal of riparian activity, have played a major role in the degradation of reach 1. Therefore, physical factors have not played a role in the degradation of reach 1 for 2016, but in 2006, the role of physical factors on river degradation is proven. In the second reach, for 2006 and 2016, both physical and human factors through meandering and human interference in upstream's basin, wood removal and removal of riparian activity have played a role in the degradation of reach 2. In the third reach, for 2006 and 2016, increased human interference in upstream's basin has played a major role in the degradation of the second reach and physical factors did not play a significant role in the third reach. In the fourth reach of 2006, the meandering indicator has played a major role in the degradation of the fourth reach, and human factors did not play a significant role in degradation of the reach, while in 2016, the impact of human interference is the greatest. In the fifth reach, for 2006 and 2016, human factors were overcome by increasing human interference in upstream's basin, wood removal and removal of riparian activity, and, as a physical factor, the meandering has played a major role in the degradation of the fifth reach. Studies carried out in the sixth reach showed that in 2006, in the human activities, increasing human interference in upstream's basin, wood removal and removal of riparian activity, among the physical factors, meandering is one of the main reasons for the degradation of the reach, and in 2016, in addition to increasing human interference in upstream's basin, meandering is one of the main reasons for the degradation of the sixth reach. In fact, we can conclude that river meandering, as human interference in the form of river morphological alteration and landuse change has the greatest role in poor and extremely poor morphological quality of the river. Not only is it an extremely poor morphological quality affecting the quality of drinking water, but also in terms of environmental point of view, it will create morphological crises such as soil erosion as well as more sedimentation in the dam reservoir, and most importantly, the river is about to be destroyed, which can degrade the environment and endangers the life of biodiverse species in Taleghan area.
The results of the present study showed that the Taleghan River's reaches do not have a good quality. Considering the extensive land use change in the river's banks, it seems that solutions such as prevention of land use degradation in upstream's basin as well as protecting and improving native vegetation and its spreading are the best options.