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Nation Investigates
The Anatomy of deadly Mai Mahiu flash floods
by Mike Yambo,Illustrated by Geoffrey Onyambu
Published 20 May 2024
The magnitude of the floods
The aftermath of catastrophic flash floods in Mai Mahiu has amplified the extreme damage brought by flooding over the last month in Kenya. As of 14th May, the severe weather conditions had killed 289 and displaced over 57,120 people, according to the statement posted on X by the government spokesperson - Dr. Isaac Maigua Mwaura.
Satellite imagery
The massive flooding was captured by satellite imagery after flash floods raged through the heart of Mai Mahiu. The vivid images show houses and major roads submerged in vast floods.
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Area affected by the floods
Mai Mahiu, located in Nakuru County, sits at the base of the escarpment of the Great Rift Valley. A 2010 report by Relief Web International classifies the area as susceptible to flash floods often caused by heavy rains that leads to landslides and blockage of river channels.
As Kijabe town became overwhelmed by heavy rains, the area worked as a funnel, forcing the rushing water into the heart of the villages, farms and the town. Riverbanks swelled, bridges were washed out, and a blocked railway line tunnel burst, adding their waters to the deluge. The preceding days became catastrophic.
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The blocked tunnel
The Nation reported that this tragedy was not a result of a dam failure as earlier circulated on social media, but rather a gulley burst caused by a blockage in a culvert beneath a railway embankment. This was also highlighted by Water Cabinet Secretary (CS) Zechariah Njeru who said, In a statement to newsrooms, that a blocked railway line tunnel preventing proper flow of water through River Tongi was the genesis of the flash floods.
"The channel got blocked due to debris, stones, trees, and soil brought about by the heavy downpour in the area thereby preventing water flowing through the River Tongi course and its small tributaries from moving downstream," explained Njeru.
Genesis of the flooding
This blockage led to a gradual accumulation of water forming a temporary water catchment over time. As the heavy rains continued, the gulley eventually broke off, leading to water collected pouring downstream at a very high speed and velocity to lower-lying areas in the form of violent floods through the river channels.
Alternative routes
Subsequently, the river channels were overwhelmed by the intense volumes. Unable to contain the deluge, they burst their banks, thus forming alternative routes.
The resultant flash floods, carrying with it mud, rocks, and uprooted trees, swept through houses and cut off a major road. The floodwaters flowed to the lower-lying areas, leaving behind a trail of death and destruction.
We used a live-streamed video showing the vastness of the destruction to identify one of the worst-hit sections by matching its features on Google Earth.
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An analysis of the topography, using the elevation tool on Google Earth, shows the town’s approximate elevation is 1,868 meters, with a minimum elevation of 1,794 meters and a maximum elevation of 2,226 meters. The tool further highlights the sharp gradient between the high and low grounds. This varied elevation, combined with the town’s location in a valley, makes it particularly vulnerable to flash floods.
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The Nation established the death toll had risen to 60 a week after the tragedy struck, but the vast areas covered by debris raise concerns about the 20 missing people.