Document Type : Research Paper
PhD Candidate, Geomorphology, Department of Natural Geography, Science and Research Branch, Islamic Azad University, Tehran, Iran
Professor of Geomorphology, University of Tehran, Iran
Assistant Professor, Climatology, Department of Natural Geography, Science and Research Branch, Islamic Azad University, Tehran, Iran
Professor of Natural Geography, Department of Natural Geography, Science and Research Branch, Islamic Azad University, Tehran, Iran
The Khoshk River is originated from Golestan and Ghalat highlands and flow in a northwest and southeast direction. After traversing a short distance it covers Golestan and Dukohak from the right and the Ghasr Ghomshe tributary from the left. Then, in a direct cross from the middle of Shiraz metro police, it will divide it into half in south and east and at the end it will pour into Maharlo Lake. Numerous researches with different methods and purposes have been done. The aim of this paper is to investigate the changes of manipulation of the zones in time-place range in the sanctum of the river.
The main research method, in this paper is the traversal and analytical method. Thus, to determine the ranges in the limitation of the case, we have used existing maps, scope revision and Google earth software. Then, the oldest satellite images of the zone (Lansat8 OLI imagery) have been provided for 2015 with the power of 30 meter state dividing coherent to Shiraz metropolis. By the use of geological maps and topography, air shots and satellite images of Shiraz were studied and geomorphologic annotation of them were done to expand the city in sanctum of the river as to recognize the changes of dry riverbed due to urban expansion in two time sections 2015 and 1967.
Results and Discussion
In this paper the riverbed divides into 3 ranges as follow:
First range: the direction of Chanarsookhte is from Tange Sorkh to Maliabad Bridge with 8 km long and average slope of 1.42%. Riverbed is formed by generally marine stages and Razak marine condition. The feature of this part of river is rash slope, severe erosion of near lands, and brinding of strand. The width of alluvial sediments has been reported about 70 meters. The average of river width on the aerial image of 1967compared to 2015 revealed 19 m reduction. The river has been changed to 56 ha in 2015. This means 27.5 percent of river space has been reduced because of human operations in the sanctum of river, removing sand from the riverbed and the buildings.
Second range: the river has a distance of 15 km from Maliabad Bridge to Fazilat Bridge and the slope is 0.90%. In this direction, Nahre Azam sideway, Ghoran Gate, Sadi, Bajgah and etc. are flowing into Koshk River. Because of appropriate soil and enough mineral water, the gardens and agricultural lands has been expanded near the river. The property of this range is that the river channel has been shored by the stile barrier. The main characteristics of the river are narrow pass way of river channel, unsuitable bridges, floor fraction, lateral erosion of river, building sideways in both left and right shores of the river with the length of 7 km and urban buildings in the foot print of river. Thus, most of the violation to the sanctum of river has been occurred in this range which has caused some problems for Shiraz metropolis.
The average width of river in 2015 compared to 1967 has been reduced 140 meters. On the other side, the space has been changed from 312 ha in 1967 to 92 ha in 2015. This means 70.5% of river space has been reduced because of the change of controlling the lands due to human operation in the sanctum of the river.
Third range: the river is 10 km long from Fazilat Bridge to the terminal point of the city. The kind of bed sediment is formed by torrential alluvial sediments and Kovaterner sediments. The thickness of the alluvial sediments has been reported 200 meter. The property of this part of low slope channel is sedimentation of the alluviums and reduction of river tension, and low capacity at the time of big floodwaters.
Most of the river direction has been ended to shore by the stile barrier and the mean width of river compared to second range is lower (42m) and its mean depth compared to around deserts is 1.5m-2m. Nowadays, the average river width compared to 1967 has been reduced about 49 meters. The river space in this range in 1967 is about 95ha but nowadays it has been reached lower than 50ha. It means that 57% of river space has been decreased. The urban expansion and agricultural operations in this range has caused the constriction of the river pass way. As in every raining, it causes the uprising of river down the Sardkhane Bridge.
Investigation about the changes of urban expansion effects and changes in the lane controlling in the sanctum of Khoshk River are the most important aims of this paper. According to the results of urban expansion investigation in the first range, there is alluvial fan in the foot of mountains foothill stone which is firmed by sediments, shale and weak seeds. In the second and third local sections, the city is placed in a desert zone where the sediments of alluvial sediments are in Kovaterner. Urban expansion in the sanctum of river in the above time-local ranges causes the reduction of riverbed space compared to last year. The space of river bed has been changed from 77ha to 56 ha (27.5%) in the first range,, from 312 to 92 ha (70.5%) in the second range and from 95 ha to 41 ha (57%) in third range. The width displacement of the river was 176 meter in the first range, 145 meter in the second range and 68 meter in the third range. In the past, the city was nuclear and compressed and occupied lower space of river sanctum. It can also be argued that the type of physical expansion of this city has proceeded in thorough linear type.