From damage to disaster: a study of vulnerability to flash flooding in urban Wadi Hadhramaut, Yemen.

Abstract

This research is a study of the changing vulnerability of three towns in the Wadi Hadhramaut, Yemen, to flash flooding. The predominant construction material of the towns, Seiyun, Shibam and Tarim, is the sun-dried mud-brick, a seemingly unpractical choice in an area where floods are expected annually. However, until recently, the vulnerability of the towns to flooding has been limited. The majority of the flood events in the Wadi Hadhramaut have caused little destruction within the towns, the damage being manifested in the collapse of a few houses. Reconstruction of damage caused by flooding has remained within the capability of the communities. Until recently, the protection of the towns has been through the practice of building on the raised ground beneath the mountains and on islands of colluvial material defined by channels on the flood plain. Weirs and channels in the wadi bed guide and disperse the flood waters so that their destructive effect is reduced. Mitigation has been provided by aspects of house construction, and traditions of co-operation within the communities. Unfortunately, as a result of the rapid and erratic process of urbanisation, the towns are becoming increasingly vulnerable to flash floods. The town planning principles of building on high ground and controlling flood waters have been affected by the pressing need to find more land on which to house the growing population. House construction has taken place at the edges of the flood channels. Agricultural lands that once absorbed flood waters have been developed into residential areas. Large suburbs have been developed in areas prone to inundation during major floods. These trends, coupled with the disruption caused by government intervention in community co-operation, have substantially increased the likelihood of a major flash flood causing a disaster in any one of these three towns.