Investigating the effects of urban development on the pollution and flooding of rivers in Rasht city

Academic Thesis for Master's Degree Field: Natural Geography, Geomorphology in Environmental Planning

Abstract:

Studies of the effects of urban development on Zarjob and Goharrood rivers in Rasht city have been conducted with the aim of improving the environmental quality of changing the conditions of rivers from pollution and tuberculosis to favorable and sustainable conditions. In the current conditions, the mentioned rivers are practically open to the sewage of the city, and the state of pollution and infection has made it impossible to be close to a long distance. Urban development developments have caused the disconnection of the relationship between man and the environment with the primary link of ecology, and unfortunately, the unbridled growth of urbanism is moving towards the destruction of the environment, and the lack of a sustainable attitude towards the position of the environment in order to erase and destroy any presence of this phenomenon from the urban living environment, and we are witnessing the transformation of the highest environmental resources in the city of Rasht into sewage canals. Natural and ecological organs are one of the most important elements of the spatial organization of the city, whose stability is considered a condition for the sustainable development of the city, health and environmental health. The stability of these organs, as the natural lungs of the city, provide the conditions for the improvement and expansion of the city's junction with the natural environment. It is obvious that the improvement of the quality of the river will have positive effects on the performance system and activity of its surrounding area. Population growth, urban development and the industrialization of societies have adverse effects on the hydrology of the catchment basin. It reduces the amount of permeable surfaces of the basin that are able to absorb part of the rainfall, it reduces the impervious surface of the city such as streets, the reduction of parks and gardens, and the lack of use of clay roofs will increase the intensity of flooding in urban basins. And it reduces the water infiltration time in the soil.   

Key words: urban development, river, river flooding, river pollution, Rasht

Introduction:

At the beginning of the 21st century, human society has been involved in new experiences, for the first time the majority of the world's population has settled in urban areas, and man has become an urban-oriented being, instead of villages and small towns, in big cities Cities become homes. Today, cities have become centers that will determine not only the fate of humanity, but also the future of life on earth, and without doubt, we will not have a stable world without long-standing cities. City managers and planners are generally involved with complex and extensive issues including environmental, social and economic problems. The result of these land problems will be the decline of people's living standards. In addition, the economic and social development policies of developing countries have changed agricultural and rural communities so that migration to cities continues and cities are always developing and expanding. United Nations reports in the late 1990s indicate that after the year 2000, half of the world's population will live in cities. The concentration of social activities in cities greatly increases the competition for various resources. The most basic source of human life is water, which is available to people directly (drinking water) and indirectly (agricultural and industrial products) at a very high cost in cities. Water, as the main source of life, threatens human activities in many cases due to improper management. Floods, flooding of rivers, water erosion of fertile lands, sedimentation and pollution of domestic and industrial effluents are among these threats, which are multiplied in urban areas with changes in land use, soil compaction, impenetrability of lands, and destruction of vegetation. In this case, we can refer to the devastating floods of 1969 and 1977 in Rasht city due to many constructions, encroachment on Goharroud and Siahroud river boundaries, and the destruction of vegetation in the region, or the frequent and yearly flooding in the city of Rasht, which occurs due to the inability of the 700 km mixed sewage network in Rasht city to collect and transfer rainwater, the all-round development and expansion of Rasht city, and the increase of urban impervious surfaces.Also, Hamshahri newspaper in No. 4793 dated May 15, 2016 about the flooding of most of the country's cities under the title "Surface water in the city" in the language of engineer Mahmoud Reza Rahmani writes: "According to statistics, despite the existence of a network for collecting and transferring surface water and sewage in northern cities, 90% of flooding is due to the presence of garbage that is poured into the surface water collection pipes." Therefore, the need for a correct understanding of hydrological processes in order to manage and make correct decisions seems certain and necessary. It is necessary to address the issue of urbanization a little. Urbanization is a process during which natural agricultural lands are transformed into man-made areas. The concentration of money and capital, the high price of land and the ease of access to facilities and resources have caused overcrowding in the big city of Rasht, so that the uncontrolled development and without proper management in the past years and the expansion of urban places and facilities due to the increasing population are currently causing the hydrological balance of the watersheds overlooking the city, which is in addition to erosion. Urbanization is the most important cause of disruption of the soil hydrology cycle, causing an increase in the occurrence of large floods and extensive flooding and an increase in pollution caused by sewage in cities, and Rasht city is no exception to this rule. Urban development, urbanization and land use changes in Rasht city have increased the volume of urban runoff, increased peak discharge and its occurrence in a shorter time, and increased the probability of flooding in the downstream areas of the city. Surfaces that increase floods in the rivers of Rasht city are generally hills, public roads, roads, streets with smooth surface and low permeability. The ability to retain moisture and the permeability of the mentioned area and areas is far lower than the natural and untouched lands.

Statement of the problem and the need to conduct research

The development of the urbanization industry and population increase in the quantity and quality of water pollution and the rapid destruction of natural resources have always played a role in the water pollution and flooding of the Zarjub and Gohar Rud rivers. This issue is not an exception. In any case, this general approach to the environmental issues of Gilan province shows that the water pollution of the Zarjob and Gohar Rood rivers is caused by the discharge of all kinds of sewage, urban waste water and waste materials in the environment, which is the way of urban household sewage, public places such as hospitals, hotels, and surface sewage due to being washed by water. The resulting rain enters the rivers. Rainfall is one of the climate elements that has a direct effect on the rivers. When the amount of water in the river is low, the river becomes a place of pollution, and if the amount of water is more.  The diluted environment is worth mentioning that the same climatic element in Rasht city due to the change of land use causes many problems, including the increase of the flooding potential of the rivers. Continuing the issue of river pollution due to the lack of an advanced and efficient urban sewage treatment system and considering the current growth rate of the urban and limited population. Due to the presence of rivers, in terms of urban and domestic sewage, measures should be taken so that the rivers can recover their self-purification capacity, for this purpose, sewage spillage should be prevented. Also, on the other hand, the increasing development of urban areas has made the rivers of Rasht prone to flooding. By studying watersheds, periods of flooding and ways to prevent them can be determined. The increase in population, along with poor planning for land use, destruction of forests and pastures, as well as the development of impervious surfaces, have caused less water to penetrate into the ground and faster in watersheds. As a result, floods become more frequent, more intense and more sudden and cause more damage. The development of cities has affected the natural channels of watercourses and their path in the flood plains, and the overall flow of water, the characteristics of the maximum flow, the water quality of watercourses and finally the behavior. Their hydrology has been effective. One of the most important changes affecting the urban development on the roads is covering them and reducing the privacy of the roads.