Hydrologic Analysis of Flash Floods in Sana'a, Yemen

Floods, especially flash floods, have killed many people in Sana'a in the past years. The urban development of Sana'a, the capital of Yemen, has led to an increase in flood hazards due to rapid changes in existing landuse to impervious surfaces and the presence of increased population and buildings in flood prone areas. A comprehensive hydrologic analysis of the Sana'a Basin was conducted using GIS for pre- and post-processing of large datasets, HEC-SSP for rainfall frequency analysis and HEC-HMS for hydrologic modeling. This analysis identified the basin characteristics, estimated rainfall distributions, depth, and frequencies, and developed flows for different storm frequency events to be used in hydraulic modeling and floodplain mapping of Sana'a floods. Significant challenges were addressed during the modeling process including: limited historical flood data, short historical rainfall records, non-standard hydrologic input data, poorly understood local hydrology, and major changes in the landuse from rapid urbanization. Based on the results of the hydrologic analysis and further hydraulic modeling, the floodplains were effectively mapped along Sana'a major stormwater channel and the Sana'a flood hazard areas were identified for extreme storm events. This information is being used to support a natural disaster risk evaluation for Sana'a.