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Ground fissures and cracks in parts of Nakuru stir county administration

A  fault line that was reported in Naivasha Sub-County cutting off the busy Maai Mahiu-Narok road in the area known to have inherent geological weaknesses. Photo by KNA.

Geologists have cautioned that rapid real estate development in Nakuru with buildings exceeding four storeys is a catastrophe in making as the County sits on unstable geological zones and experiences subtle volcanic faulting.

Though the Building and Construction Standards and Codes (BCSC) developed by the defunct Municipal Council of Nakuru insisted on development of low-storey buildings- less than four floors- this is currently being disregarded.

As the experts point out that a large part of Nakuru has cracks and fissures that pose danger to tall buildings and that soil in the region and its environs is unconsolidated as a result of past eruptions from the Menengai Crater, dozens of new buildings with as many as 12 levels are now fighting for space in the County’s skyline.

The County administration has now been forced back to the drawing board following occurrences of huge ground fissures and cracks that have been reported in various parts of the devolved unit at alarming frequencies.

In the latest incident heavy rains that have pounded the region for the past three days have resulted in a gaping fault line that has cut across roads in the populous Nakuru West Sub-County sparking fears among residents of Koinange, Shabab and Kaptembwa Estates.

Governor Lee Kinyanjui has now called on investors who had developed commercial and residential properties on the path of fault lines ‘to brace themselves’ for tougher measures as his administration moves to implement directives that will be rolled out to eliminate risks associated with structural weaknesses in their buildings.

“We will ensure that people move away from all structures that are on the path of the fault lines after the studies are carried out. This is a very serious matter that will impact negatively on structural strength of most buildings.

The risks continue rising as a lot of water has entered the fissures causing underground erosion even in places that have not caved in. The County administration will make appropriate decisions once a report by the experts is ready,” said the County boss.

Kinyanjui said his administration had engaged services of geologists from Geothermal Development Company (GDC) and Kenya Electricity Generating Company (KenGen) to carry out studies in the areas affected by fault lines across the devolved unit.

In February this year, panic struck residents of Solai as the newly constructed dam locally known as Nyaru Dam, in Solai Subukia Sub County developed a huge fault. It is suspected the dam lies on the volcanic line running from the nearby Menengai crater.

The fault lines were running below the Nyaru water pan, and some of the neighboring homesteads due to deep cracks and soil slides, resulting in the loss of all the water in the dam and cracks in some houses.

Some 12 kilometres away in Nakuru East Sub-County a section of residents from Whitehouse Estate in the outskirts of Nakuru town are living in fear after ground fissures developed in the area.

The residents, whose estate is at the foot of the Menengai Crater said though the fissures have not extended for a long distance they cannot be ignored as there are signs of them widening with time.

Last year, a similar occurrence in Naivasha Sub-County cut the busy Maai Mahiu-Narok road in the area known to have inherent geological weaknesses.

The governor asked residents occupying premises along ground cracks and fissures to move to safe grounds as geologists and experts investigate their cause.

“After engineers and experts from KenGen and GDC map out the extent of the fault line, the affected areas will be beaconed to ensure that authorities make informed decisions before approvals for property developments are made in certain areas” stated the governor.

Eng. Paul Njoroge, a Geologist at GDC said whereas some parts of Rift Valley had remained tectonically inactive in the recent past, there could be movements deep within the earth’s crust that have resulted in zones of weakness extending all the way to the surface.

Eng. Njoroge said a quick assessment by his team had established that the suspected fault line at Nakuru West Sub-County could be just one of the tens, perhaps hundreds, of other weak spots on the Great Rift Valley, which runs through the continent from the Horn of Africa to Mozambique.

“During heavy rains and flush floods, the fissures, due to unconsolidated deposits accompanied by slumping and flushing of material deep down, produce holes and funnel shaped depressions, which cannot hold heavy weights,” he said. Eng. Njoroge said that the Rift Valley region is still prone to volcanicity.

Geologists hold the opinion that in the Eastern Africa region, Somalia and half of Ethiopia, Kenya and Tanzania will be cut off from the rest of Africa to create a new continent in about 50 million years- known as the Somali Plate.

Forces of the earth are the strongest at the base of the valley, yet it is also here that geological processes are most active. “The valley has a history of tectonic and volcanic activities,” said Njoroge.

Former Civic leader at the defunct Municipal Council of Nakuru, William Ating’a said the Building and Construction Standards and Codes (BCSC) which insisted on less than four floors had taken into account that the proximity of the Menengai crater to Nakuru made the region’s surface weak and therefore unable to sustain heavy weight.

“Nakuru is highly vulnerable to subsidence (sinking down of land from natural earth movement), landslides, earthquakes and related disasters. A craving to make best use of space and realize quick returns have surpassed fears that should a tremor occur, these buildings would come tumbling down like a pack of cards.

The town is located on the floor of the Great Rift Valley, in a narrow gap between Menengai Crater to the North and Lake Nakuru to the South. Therefore the town can only expand in a linear pattern from the West to East. The situation is further compounded by the presence of unstable geology and poor soils which results in frequent land subsidence,” offered the former civic leader.

A report compiled by researchers from the Department of Geology, University of Nairobi indicated that most parts of Nakuru particularly the West and Southwest, often experiences ground failure – shaking that affects the stability of the ground – during earthquakes.

Bangladesh, North of Nakuru GK Prison, Githima, Ngata, Rhonda estate, and Baruti shopping centres were identified as areas having the weakest surface points.

“These areas have very poor surface runoff because of fissures running across them from Menengai crater that erupted thousands of years ago,” stated part of the report.

A  section of businessmen occupying storeyed buildings along Kenyatta Avenue ‘complained’ of the buildings shaking whenever a heavy vehicles passes by.

Property Consultant, Gabriel Kyalo said it was the responsibility of the County and structural engineers to determine the number of floors a building should have after analysing the soil profile where the development is to be carried out.

“Legally there is a limit on the height of buildings that should be constructed in Nakuru. Construction of buildings that have more than three must have a report from a geologist,” he said.

Kyalo revealed that some spots, west of town, have very weak surface that cannot even sustain a single storey building.

By  Anne  Mwale

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