JEDDAH FLOODS AND SUSTAINABILITY

Ethics about Jeddah floods and sustainability

Ethics about Jeddah floods and sustainability

Introduction

In November 2009, torrential rains and flash floods hit Jeddah when 90 mm - twice the average annual total rainfall - fell in four hours overwhelming the city's storm drainage system. A similar extreme rainfall event occurred in January 2011. The floods that swept through the Saudi city's busy highways and informally built areas in 2009 killed over 150 people and damaged over 7000 homes and vehicles. The lack of appropriate water infrastructure to handle such extreme weather events exposed the vulnerability of cities in the normally arid Gulf region to the risk of flooding. Similar extreme weather events have been experienced in Oman and Yemen and have prompted efforts to improve planning and preparedness to reduce the impact of floods, landslides and rock falls in urban areas (Gruntfest, 2011).

Discussion and Analysis

Flash floods are a deadly and costly event that can be exacerbated in arid environments. On November 25, 2009, the city of Jeddah, Saudi Arabia, received more than 80mm of rainfall in a short period of time causing massive flooding, extreme destruction of property, and an indiscriminate loss of life. In December 2010 and again in January 2011, more severe flood events wreaked havoc on Jeddah. Such extreme events have been a catalyst into furthering the understanding of flash flood events and how to properly manage their sudden and destructive nature.

Wadi Qous, one of many dry valleys that exit the mountain chains east of Jeddah, was reported to be the main cause for destruction to the city. Here, a hydrologic model driven by information on the topographic and drainage characteristics (generated from SRTM data), precipitation (constructed from TRMM data in 3-hour increments), and land cover/use plus soil properties (generated from satellite images and geological maps) was generated for this valley. Utilizing HEC-HMS, hydrographs were produced to illustrate the response of the valley to rainfalls and aid in locating high risk areas.

Analysis shows that Qous basin was affected by a high magnitude rainstorm with short duration. This resulted in a torrent of water with a short time to peak, 10 hours, and sharp peak flow of 98 m3·s-1, respectively. This resulted in the appearance of surface runoff within a narrow time slot at the valley outlet. This might be explained by the short distant and travel time of surface runoff toward the city, the funnel-shape of the basin and its narrow drainage course (less than 100 m in a few locations), and the expansion of bedrock outcrops and urban land cover as reflected by high Curve Number value. Due to the relative lack of hard structures, such as dams, there were no obstacles or impediments to slow the flood waters prior to entering the city. The area at the valley outlet was particularly hard hit as was the area around King Abdulaziz University.

A comparison of the hydrographs shows that a reduction of floodwaters on the city of Jeddah is ...