Urban Sprawell and Landuse Change Effects on Surface Runoff Using NRCS-CN Method (Case Study: Asadabad City

1- Introduction
Land use change is a hydrological challenge for urban watershed management that effects on the management methods through surface runoff changes. Remote sensing, GIS techniques and satellite imagery can be used to improve and accelerate the management of natural resources and urban areas. This study investigates on the relationship between urban development and runoff values ​​using hydrological modeling, GIS and remote sensing. First, the land use maps of the city of Asad abad were prepared using TM and ETM + sensors of Landsat 5 and 7 in May, 1992, 2002 and 2014. For supervised classification and estimate of surface runoff were used maximum likelihood method and Resources Conservation Service National (NRCS-CN) respectively. The maps of land use, curves number and runoff amount were calculated and plotted. The results showed that surface runoff has been increased about 15.8 % due to increase of 4/59 % of urban land use.
Management of atmospheric precipitation and surface runoff from watersheds that are a factor in collecting and transporting hazardous pollutants while passing through streets, streets and other urban areas. Risk management is inevitable in relation to public health and urban environmental resources. Increasing the impenetrable levels caused by urbanization and construction of the building on permeable soils, naturally, has decreased the permeable levels of the basin, which is capable of absorbing part of the rainfall, and thus has increased the total amount of runoff in the city. One of the important issues of urban development is the change in surface runoff. So that the delay time of the hydrograph and the base time of the flood is reduced and, consequently, with an equal volume of flood, the peak flood discharge with urban development will be more than the pre-development, in addition, the runoff coefficient also increases (Amir Ahmadi, 2011:92). Regarding the management and optimization of watersheds, accurate prediction of outflow runoff can be very effective in optimizing watershed management to prevent regional flood rebound. Despite the nonlinear relations, the uncertainty and the lack of clarity and the characteristics of time and place variables in the flow systems, none of the proposed statistical and conceptual models have been able to be considered as a superior and capable model in order to accurately model rainfall and runoff. To be known. Remote sensing and GIS technology is one of the most effective and efficient technologies for environmental change and resource management that provides updated information for management purposes (Janson, 2012: 86). Therefore, this tool can be used to study urban development. Considering the previous studies and the importance of the phenomenon of physical development of the city and increasing the impenetrable levels on the relations of rainfall, urban runoff is very important with regard to the urban development process using an efficient tool such as remote sensing along with hydrological models (GIS Special Website, 2014: 1) The city of Asadabad is also no exception because of the increase in inertia levels following the expansion of the city. The location of the

 
city is such that it has spread in three watersheds, and this form of expansion, as well as the lack of such a study, requires the study of urban runoff and The impact of urban development on production runoff in the area is doubled. The present study attempts to investigate the physical development of Asadabad in 1992, 2002, 2014 and its effect on runoff rainfall relations.
2- Methodology
The city of Asad Abad, in the area of 1195 km2, forms 6.1% of the area of Hamedan province. The average elevation is 1607 meters.The  Annual rainfall is between 350 and 500 mm (Aka Iran,2014:1). In this study, the relationship between urban development with distributed hydrological modeling of the integrated approach of remote sensing and geographic information system was used. Landsat satellite data was used to detect land cover changes (Kavosi and Vatan khah, 2013:4). The SCS method estimates runoff in unobstructed watersheds according to rainfall and the characteristics of the watersheds. Basically, this method will be valid when runoff is due to rainfall, and it is not effective at a time when snowfall. The American Conservation Survey (CNS) Curve Number (CN) method is one of the most common methods for estimating and forecasting flood volume and runoff and flood altitude (Mahdavi, 2009: 86). In this research, the average monthly long-term average was calculated in inches. Then, layer the point rainfall in Arc GIS, and digital calls and using IDW interpolation was to be the second (Javadi, 2011: 59). To estimate the runoff of the study area, we calculated the weighted mean of runoff. For this purpose, the data was transmitted from the descriptive table in the Arc GIS software to the Excel environment (Zhang, 2014: 956). After calculating the total runoff heights, the values obtained were retrieved in millimeters in the tables and graphs. In this research, all of the above was done in three periods of time, 1992, 2002, and 2014, we tried to use the results of 1992 and 2014 to review the changes and to use the 2002 changes to verify. So the results are presented every three times.
 
3- Results
Land use classification maps in Arc GIS software procurement and since the purpose of assessing changes in three different periods, a guide map has been changed for better. After the land use was extracted in the time periods studied, the area of each user and the percentage of the area of each user were calculated. Generally between the years 1992 and 2014 in the area of other Land use 5.45% (equivalent to 63.9 square kilometers) declined. The urban and non-urban usage map was extracted from the land use classification map for three periods of the study, in three periods of 1992, 2002, and 2014, which were obtained in the Arc GIS environment.
After extraction of urban and non-urban when the study area and the percentage of urban and non-urban area was calculated in Excel. In order to better understand the relations between runoff rainfall in the study area, rainfall, runoff height was calculated and presented according to the curve number. The results of the study of the impact of urban development on runoff variations are presented at the time of study. By changing the type of use, including the change in area in each polyglone, the calculated CN values will vary in the polyhedron, which results in changes in the runoff height in each polyhedron. By changing the type of use, including the change in area in each polyglone, the calculated CN values will vary in the polyhedron, which results in changes in the runoff height in each polyhedron. According to the results, between 1995 and 2014, urban land increased by 4.95% (equivalent to 57.7 km2), and in the period from 2002 to 2014, urban land increased by 42.3% (equivalent to 127 / 40 sq. Km), and in this period the construction rate has been higher than the previous period. However, urban runoff runoff from 2002 to 2014 increased by 11.29% over the period from 1992 to 2002. Urban development is not the only one in metropolises. It is also important in a small city such as Assadabad. Because it will affect the relations of runoff precipitation. If the runoff height, which is a small number in the city, would be 350 m 3, this volume of runoff in a small town is significant and sometimes dangerous.
4- Discussion and conclusion
In the present study, we tried to investigate the impact of urban development on runoff using remote sensing and its integration with GIS. Finally, it was found that using remote sensing; we can consider the variation of runoff from urban development with an accurate precision. It was also determined that urban development in addition to rainfall has been effective on runoff due to the increasing urban use that is related to construction development, industrial development and road construction development. In general, the use of remote sensing because of the cost reduction of field operations, and especially because of the reduction in the time needed to analyze the issues, can be considered as possible solutions to improve the level of water resources management. In addition, using this tool, this opportunity is created for researchers and executives to evaluate different management scenarios (which cannot be executed in a short time without heavy cost), and by analyzing the results, the best Made a decision. It is suggested to use different methods of runoff estimation and compare their results with the results obtained in this study as well as a hydrological model to study the runoff rainfall relationships and compare its results with the results of this study.In order to better study land use changes (especially urban development studies), in different years, it is necessary to use a satellite data format that is also available on a given date. To study more precisely, the relationships between rainfall runoff and time intervals increase. And the last suggestion is to use long-term returns to better predict and understand the impact of urban development on runoff variations.