Experts unravel puzzle of rising lakes in the Rift

Rising lakes in the Rift Valley have sparked fears of an ecological disaster even as residents are displaced and their property submerged.

Scientists have given different explanations for the phenomenon. The explanations range from siltation and increased rainfall to the shifting of tectonic plates deep in the earth’s crust.

“In around 1995, lake levels within the Rift Valley were at their lowest and people could literally walk across. What is currently happening is a reverse of the same, as water is compressed out of aquifers into the lakes,” said Sila Simiyu, a geologist.

The affected water bodies include Lakes Baringo, Bogoria, Nakuru, Elementaita, Naivasha, Turkana, Logipi and Solai.

Dr Simiyu says the Rift Valley is in the midst of a geological shift that started in 1996 and is expected to last between 25 to 40 years.

“During the 1955-1995 period, which is also known as far-field tectonic cycle, the lakes almost dried up. The current cycle started in 1996, but it has been accelerated by deforestation, which has resulted in siltation and floods that are displacing hundreds of people in the region,” he told The Standard.

The geologist adds: “Because they are cycles, the next one will result in low water levels in these lakes. And since there is massive siltation, the lakes might not go back to their original sizes but become mass areas for evaporation. With time, these lakes will dry up and become dust bowls.”

According to Simiyu, pressure from the Rift’s volcanic system has resulted in water getting into faults, lubricating tectonic plates and causing tremors that are being experienced in several parts of Baringo.

“Increasing water levels cannot be attributed to geothermal activities. The utilisation of geothermal instead reduces thermal pressures. Earlier, when lake levels were at their lowest, geothermal activities were also blamed, but this does lead to the phenomenon we are witnessing. This is the result of plate tectonic movements accelerated by deforestation.”

Former Government Chief Geologist Lojomon Biwott said water seepage into underground aquifers was being hampered by silt that clogged fault lines, leading to water retention.

“The Rift Valley has fault lines that move a few centimetres every year. These fault lines allow water to seep into underground aquifers, but because of siltation, the fault lines are either blocked or earth movements are not as active as they had been,” Mr Lojomon said.

High rainfall

Kenya Wildlife Service research scientist Joseph Edebe attributed the swollen lakes to abnormally high rainfall experienced in the region since May last year. “This, coupled with the impact of climate change, has not only led to swelling of Rift Valley lakes but all lakes within the region,” said Mr Edebe. “This is happening across East Africa, from Ethiopia, Sudan, Tanzania and Uganda.”

Jack Raini, a scientist, said siltation was to blame for the increasing water levels, coupled with surface runoff as a result of heavy rains. “Deforestation and poor farming practices that have seen people farming on riparian zones has resulted in too much silt in these lakes, thus displacing the water,” he said.

As the waters rise and cover even larger swathes of land, neighbouring lakes are merging. This has happened to Lakes Baringo and 94, Lakes Naivasha and Oloiden as well as Lakes Nakuru and Solai.

Ten years ago, Lake Baringo was 176 square kilometres while latest estimates put it at 276 square kilometres, which explains the merger with Lake 92 that formed after heavy rains in 1992.

Scientists are particularly worried by the ecological mess that results when fresh and salty water bodies merge, like could happen when lakes Baringo and Bogoria mix.

Satellite imagery of Lake Bogoria shows flooding on the north end of the lake, which is located less than 15 kilometres from the south end of Lake Baringo. Analysis of images taken in May this year and May 2013 reveal heavy loads of suspended sediment, explaining the increasing siltation challenge.

“Both lakes are increasing in volume every day. The distance apart is very close and we do not know what might happen next, but they may merge,” said Lake Bogoria senior warden James Kimaru.

Lake Baringo has a pH of 7.8 while Lake Bogoria has a pH of 10.5. While Lakes Baringo and 94 support abundant wildlife and aquatic life, the saline and alkaline Lake Bogoria is a flamingo paradise. Any change in the pH could affect the flamingo population as well as the aquatic life in the fresh waters of Baringo and 94.

Paul Gacheru, a bird expert with Nature Kenya, said the increasing water volumes had altered the conditions that favour the growth of algae and diatoms that flamingos feed on.

“Due to increasing water levels, there has been a significant decline in the flamingo population in alkaline lakes in the Rift. This does not mean they have disappeared but only that their migratory patterns have changed. These birds often make stopovers to look for other suitable habitats where algae grow in abundance,” Mr Gacheru said.

The latest water bird count in Rift Valley lakes last January revealed there were 180,000 Lesser flamingos and 8,000 Greater flamingos. A count during the same period last year showed found 419,000 Lesser flamingos and 3,000 Greater flamingos.

According to an article published in The Conversation, the world’s most ‘seemingly toxic’ lakes which are homes to flamingos are under threat.

Two of the Lesser flamingos’ preferred habitats, the article notes, are Lake Bogoria and Lake Natron in Tanzania, which are hypersaline and hostile to practically all other forms of life.

“But these places are rare. Across the six flamingo species there are only 30 or so regularly used breeding sites worldwide. And while the global population of around 3.2 million Lesser flamingos is impressive, it is largely reliant on a few huge groups. What if something happens to one of their highly-specialised breeding sites?” the article reads.

Delicate balance

It continues: “Life in the Rift Valley lakes is a delicate balance. And it is clear that we are already harming these unique and fragile ecosystems. If humans were to cause drastic changes, their spectacular pink inhabitants would vanish forever.”

The changes in salinity levels have also led to the flourishing of two new fish species in Lakes Nakuru and Solai.

“Issues of climate change are coming into play. Lakes Nakuru and Solai are becoming new fishing havens because water is becoming more diluted,” said William Kimosop, a conservationist and the North Rift Tourism Coordinator.

Officials in the Baringo County Government’s disaster management department said they are looking into long-term solutions to mitigate the problem of the swelling lakes, although no funds have been set aside for the exercise.

Deputy Governor Jacob Chepkwony said one solution that was being considered was to channel water from the lake. “A tunnel might work to drain the water to River Kerio, which drains into Lake Turkana... or put up expensive dykes that cost billions of shillings. If we do not act with speed, we will be staring at an even bigger disaster,” said Mr Chepkwony.