عنوان مقاله [English]
Water is among the basic needs of human beings, without which life would be impossible on the earth. Today, water shortage is an important problem in many regions of the world. Accelerated growth of world population, especially in developing countries, absence of control over exploitation of water resources and excessive water consumptions can jeopardize human communities worldwide. Each country endeavors to tackle the water shortage problem based on its particular climatic conditions. Located in a semi-arid zone, Iran has always been exposed to a permanent hazard of water shortage. Accordingly, since long ago a wide range of methods have been applied to optimize use of water resources as well as tackle the water shortage plight. The Need to water is the main necessity of human and the shortage of water is considered as a serious crisis in the world. Because of the increasing growth of the world population particularly in developing countries and not controlling the amount of removal and irregular consumptions, this crisis seriously threaten human societies, especially in developing countries. According to lodgment of 56% of world population in cities and increasing process of urbanization in south countries, researchers believe in water shortage era, citizens from Beijing to Founics in USA will compete with farmers on the right of using water, so the pressure on limited water sources will be increased. In other words, the war of the next century will be over water not oil. On the other hand, one of the most important problems in urban planning scope is about spatial growth and development of city and the patterns. The pattern resulting from spatial distribution of human activities in cities as City Form or Shape is always changing, according to the dynamic and changing nature of urban areas. But the most unsustainable and unfavorable shape that cities have ever seen is the wide-spreading or horizontal expansion. Mashhad as the second megalopolis in Iran is selected as the case study of this survey. Thus, the main goal in this research is analysis of horizontal extension of Mashhad city over late decades and its effects on water resources. The main question is: what is the impact of horizontal expansion of Mashhad on quality and quantity of water resources.
The research method in this study is a combination of qualitative and quantitative techniques by the processing of satellite data and aerial photographs for land use within the city of Mashhad. The spatial data used in the research are aerial photographs for the years of 1956, the various bands of MSS and TM of Landsat satellite for the years of 1976, 1986 and 1996 and IRS-1D LISS III bands for 2006. Thus, the maps of the city of Mashhad in mentioned years were extracted using the ENVI application - to process satellite images- and ArcGIS as the geographic information system application. We also used SPSS application in order to analyze collected data.
Results and Discussion
Analysis of the pattern of population density of Mashhad has indicated that this city used to grow slowly, both in spatial and demographic aspects, as in the first official census (1956) Mashhad had a population of 242000 people and an area of 16 square kilometers. In that era, this city was fairly compact and had rather high density (151 persons per hector). In the next periods of expansion, the growth rate of the city size exceeded the growth rate of the population as the population density of Mashhad decreased to 124 people per hector in 1966 and 85.5 persons in hector in 1976. The extent of the city was 220 square kilometers in 1986 and the population density was 66.5 persons per hector as the least. This pattern and the spatial pattern show dispersed growth, peripheral, exterior and disjointed expansion over different periods. The results show that the rapid and chaotic vertical growth of Mashhad and the disjointed expansion of urban and industry districts in suburb over the recent decade (1996-2006) cause environmental crisis, particularly scarcity of water recourses directly or indirectly. Since Mashhad is located in a semi-arid region, there are a large number of qanat (aqueduct) fields antecedently existed there and exploited for cultivation and drinking water uses. However, due to urban sprawl and the expansion of city construction, almost all these qanat ranges have essentially been destroyed. This paper initially allows a brief reference to qanats and their importance in Iranian cities. Then, urban sprawl and its expansion in Mashhad have been surveyed at different times. Maps of urban growth and qanats have been acquired and explained. Finally, alternative methods for providing water after the destruction of qanats and disadvantages of these systems have been presented briefly. As the resistance of the city decrease against disasters such as flood and the vulnerability of the city may increase because of impermeable surfaces and shifting of the watercourse, this may also disrupt supply of underground aquifers. There were about 162 aqueducts in Mashhad and suburbs; but as it gradually changed to arid up to 88 aqueducts, with a discharge of 10736 liter per second, because of the rapid growth of city. As now just two aqueducts (Emamiye and Ghasem Abad) with a discharge of 320 liter per second are survived that are used for urban uses. There are a lot of ruined spas, as now just one spa (with permanent the capacity to provide for a mere months) and two aqueducts have survived.
The destruction of water resources sustainability and water crisis in the city caused application of new techniques such as deep wells and dams which are unstable. Indiscriminate exploitation of water resources and restoration of underground water lead to deepening of the wells to 28 meters to extract the underground waters over two recent decades. As a result, the city cannot survive by using existing resources. However, despite the already high costs for drinking water supply, the city still faces serious water shortages.