Effect of Rainfall and Urban Expansion on Runoff in the Agricultural Area

Abstract

—In Thailand, agricultural area is very important for a main occupation of Thai people. However, the agricultural areas changed to be the urban areas. Then, the objective of this study is to study the effect of variation rainfall and urban expansion on runoff. A study area is an agricultural area in the Mun river basin. To achieve purpose, there are two parts of this study. They consists of (1) the calculation of daily runoff based on land use 2008 and (2) the daily runoff determination based on the variation of rainfall and urban development. The results present that the runoff increases from the case of urban explanation 5 km to 15 km. A big change of runoff reveals from the case of land use 2008 to the case of urban explanation 5 km. Moreover, mean monthly runoff base on rainfall more than 100 mm/month is higher than mean monthly runoff base on rainfall less than 100 mm/month. The high runoff occurs during May to October. There is the lowest mean runoff in the urban area 1.00-25.00% but there is the highest mean runoff in the urban area 50.01-75.00%. The difference of runoff in the urban area 1.00-25.00% and in the urban area 50.01-75.00% is range 0.35 – 47.12 mm. or 13.97 mm. by averaging. The average runoff has a direct variation with the rainfall and urban area. It means that increased urban area can indicate a variation of runoff. In addition, rainfall is directly affect to runoff.