Flooding in Riyadh? "Storms rage across the Arabian Peninsula"

[pampango]

At least 18 people have been killed as torrential rain pours across the region.


The storms caused widespread power cuts in Riyadh, and closed schools and universities across the capital.

A weather system has caused widespread flooding across the Arabian Peninsula over the past few days.

In Saudi Arabia, the storms killed at least seven people, with five more still missing.

The capital, Riyadh, and the northeastern city of Arar were amongst the worst hit.

The region regularly floods when it rains. This is partly due to the lack of drains and also thanks to the sandy soil of the region, which cannot readily absorb water. In May last year, around 20 people were killed after torrential rain swamped parts of Saudi Arabia.

http://www.aljazeera.com/weather/2013/11/storms-rage-across-arabian-peninsula-2013112192521403489.html

Not surprised that it happens there, just never saw a story on it before.

[tularetom]

1. Sandy soil can't absorb water? WTF?

That may be true if the sand is underlain with hardpan or a layer of impenetrable clay, but in general sandy soils are quite efficient at soaking up excess surface water.

[kestrel91316]

3. Actually the sand doesn't absorb water the way clay soils do.

The much coarser sand particles allow the water to filter right through to soils below, or aquifers, or if it hits bedrock then it just flows down and out to a lower surface.

Clay holds onto water much more effectively because of the fineness of its particles.

When I had my garden, in this heavy clay soil, the ground stayed a mucky, wet mess for days after a rain. Sand dries out almost immediately.

[tularetom]

6. Actually that's true, it doesn't "absorb" it it just passes it

But the end result is the same - the water doesn't pond on the surface while it slowly filters into the soil. It just disappears.

Where my son lives the soils are expansive clays. In the winter the ground holds the rain water and swells up to the point where it can cause the sidewalks, driveways and patios to crack and in some cases actually displace upwards.

[On the Road]

4. That Doesn't Make Sense to Me Either

I am wondering if the author just made an unwarranted assumption about the soil, because, you know, it's Saudi Arabia -- it has to be sand. Looks like it's more complicated. Maybe floods were localized in areas with clay or rocky surfaces:

Soil
Valley sedimentation soil which is mostly composed of silt sands that are linked by Carbon substance of different levels. Test Results showed that soaking of soil reates further downfalls. Since data of Al-Kharj formation soil and gravel is very scarce, it May cause similar down falls though with minor effect because of the age of Al-Kharj formation and its stronger adherence. Soil at the east is clay soil that keeps high level of water due to low porosity in addition to bad slope. Density of granule soil at the northern part of Riyadh valleys varies between moderate to high density. In the case of water level fluctuation, this dense granulose soil causes slight earth down fall in clay soil and thus causes surface soaking when ground water rises. While decrease of water results in slight down fall that may affect buildings and roads at City-center.

Sedimentary soil and high weathering rocks are characterized by varying density and high water level that may cause down falls and sedimentation of harmful salts due to evaporation action. Exposed rocks composed of Jubailah formation west of the city. Arab formation is found to the east of these rocks. Also there exist hidden cavities concentrated in Arab formation soil, followed by cracks to the east that are widely spreaded in Arab and Al-Sulay formations. Jubailah formation has low porosity while porosity in Arab and sulay formation is highly various due to the existence of substances that fill cavities and cracks. When water level rises up, these substances moves due to solvency and drifting and hence increases the porosity of soil. Dumping area: varies according to dumping materials from granulose materials to fine materials. Mostly found in valleys. Mostly coming from quarries existing at Wadi Hanifa and its subsidiaries.

http://events.alriyadh.gov.sa/sites/English/AboutRiyadh/Pages/AboutRiyadh2.aspx

[MineralMan]

7. Sandy soils, when dry, often don't absorb water very well.

Surface tension and the small gaps between fine sand particles can keep water from penetrating. Once the water finally does, it drains well, but the initial result is runoff.

I used to live in a town built on ancient sand dunes. It took quite some time for rain to begin draining during a storm.

I know it seems odd, but it is a factor with very sandy soils.

[DrDan]

2. lived there for 4 years - there were cases of campers

who drowned while camping in dry riverbeds (wadis) and were caught in torrential rain.

The sandstorms were the worst - I had a friend who was caught in a sandstorm driving from Dhahran to Riyadh in his Maserati and the storm took the chrome off the bumper. They could be brutal.

[oneshooter]

5. My son is based in Kuwait and reported to me that

they have had several very heavy rainstorms. Compared them to rain from a stationary storm front here in southeast Texas. One of them washed away their arms shack, no weapons lost, but nothing left to clean/maintain their rifles with.