Author(s)

S. R. Hosseinzadeh

Abstract

Alluvial fans create a special type of flash flood threat, especially in arid and semi-arid areas where the fans support urban development. Most of the cities in Iran have developed in such environments, and are facing flash and urban floods because of the rapid growth of the cities, and the deficiency of urban planning in the last four decades. The present study aims at analyzing the urbanization effect on natural drainage patterns and their immediate result, namely the increase of vulnerability of the metropolitan city of Mashhad. Mashhad, as the second religious metropolis of the world, and second metropolis of Iran has an annual 12 million pilgrims, and 3 million population. The results of this study indicate that the rapid growth of the city from 1966 to 2002 has had excessive destructive effects on the catchments area, and has caused the decrease of impervious surfaces, and the increase peak discharge of the urban floods. Keywords: urbanization, flash flood, urban flood, drainage pattern. 1 Introduction The effects of urbanization on the hydrology and morphology of watersheds have been studied by Leopold [16, 17], Hammer [8], Hollis [9], Dunne and Leopold [5], Klein [15], Arnold [2], Gordon et al. [7], Arnold and Gibbons [3], Christopher [4], Paul and Meyer [21] and White and Greer [23]. According to previous studies, development of cities in the watershed increases the area of impervious surfaces which decreases infiltration of precipitation and in creases runoff. Runoff increases in proportion to the cover impervious surface in a watershed and the increased storm runoff increases peak discharge and flood

Keywords

urbanization, flash flood, urban flood, drainage pattern.