JEDDAH FLOODS AND SUSTAINABILITY

Jeddah floods and sustainability

Jeddah floods and sustainability

How floods like this can happen in a modern metropolis of five million people is a good question. It needs not only answers, but answers that lead to direct action to ensure that similar deluges don't happen again. The simple answer is that the city's infrastructure was not able to handle the rain run-off. More important is why that is the case.

Other than a few puddles an inch or two deep, the water was gone withing hours of the rain's passing. The city has a population of about 52,000 people and nowhere near the financial assets of Jeddah. So what's the difference? Part of the difference is in geology: Florida is largely sand, with a limestone deep beneath the surface (Jan , 2010).

Jeddah is also sandy, but the sand is mixed with clays, making them impermeable (that is, the water doesn't 'sink in'), and relatively shallow. That means that when water builds up, there's no place for it to go other than to flow. In comments to earlier posts on the flood, I argue that the principal problem is a deep shortage of competent city planning. City planning isn't only about meeting immediate needs-though of course, those must be met. It is also about planning for the unusual, though not unexpected. It doesn't rain much in the Kingdom, but when it rains, wadis flood.

They've been doing that for millions of years. Even prehistoric Arabs of the Peninsula knew to avoid the wadis when it rained. That knowledge appears not to have been carried over to the modern cities, however. Cities, no matter where they are, are strapped for funds. When they draw up their budgets, they allocate money toward things that need doing immediately. Things that happen rarely just don't get funded.

Hindsight shows how the funding decisions ended up being poor ones, but that tends to be the case everywhere, e.g. New Orleans and Hurricane Katrina. Direct rainfall occurs from the rain falling over the lake surface area. The surface area is 2.88 km2.

The active precipitation stations in the surrounding area are located at Jeddah, Bahara and Usfan area. The precipitation data are available for the most recent 30 years period from 1973/1974 to 2002/2003 water years. Analyses of rainfall data in Jeddah and Usfan indicate an average annual fall range between 46.1 and 63.3 mm as shown in Table 5. As a consequence, direct rainfall over the lake area is between 132,538 and 181,988 m3/year. Temporal variability of runoff is very high, typically as arid environment. Annual runoff is not common. The worst case occurs with floods of higher return periods. Therefore, floods of 50 and 100 year return periods have been estimated as shown in the previous section. It has been found that the amount of runoff that would have been summed to the lake storage ranged from 2.6 million m3 to 2.8 million m3 ...