- Murunga said boreholes that were drilled in the city in the past were as low as 100 meters.
- Today, he said, boreholes are going up to between 300 and 400 meters as water levels have gone down.
Image: Alice Waithera
The continued drilling of boreholes within Nairobi could soon make the city to ‘gently sink’, an expert in ground water has warned.
Patrick Murunga, an Assistant Director for Research and Mapping with Regional Centre on Ground Water Resources, said the city has sunk so many boreholes that have left several ‘voids’.
“There has been the lowering of water table due to a lot of abstractions,” he said.
Murunga was one of the panelists at the ongoing seventh edition of regional international conference on earth observation technologies, at the Kasarani-based Regional Centre for Mapping of Resources for Development.
The theme of this year's conference will be "NEXT LEVEL: Space to Community".
Land management, policy and development, innovations and data, agriculture and food security, biodiversity conservation and blue economy will be discussed during the conference.
Murunga said boreholes that were drilled in the city in the past were as low as 100 meters.
Today, he said, boreholes are going up to between 300 and 400 metres as water levels have gone down.
“There are two reasons responsible for that. One of the reasons is that we are abstracting too much. We are pumping out much of the water,” he said.
Murunga said many buildings that have been erected have made it impossible for water to go down and recharge aquifers.
“The traditional places where ground water would be recharged are no longer the same. We have to come in with mitigation. The only way is through artificial ground water recharge,” he said.
Murunga said it is important the artificial ground water is done as soon as possible since Kenya is very close to volcanic and tectonic centres.
We have to accelerate the artificial recharge and not leave it to nature. We have to come up with structures to ensure that more of the water recharges our aquifers. This will ensure the voids that are left over by abstractions are filled again with new water,” he said.
Murunga said if the voids are left, then it means that the weight of the city will take up those voids that are free spaces.
“Therefore there will be the gentle sinking of the city because of the over-burden which we are calling subsidence.”
Murunga said well managed aquifer recharges will ensure there is sustainability of the water resources and ensure that there is safety for the buildings.
There are over 300 boreholes sunk in the city.
During the Covid-19 pandemic, a number of boreholes were drilled in the city to complement water to the city residents.
The 2019 census showed that the city had a population of 4.3 million people.
The population in the county of Nairobi and satellite towns is projected to rise to 13.4 million by 2035.
Nairobi City Water and Sewage Company is currently producing 525,000 cubic metres per day against a demand of 850 million litres, leaving a shortfall of 325 million litres.
Out of the water supplied, 300,000 cubic metres are lost daily through leaks also known as non-revenue water (unaccounted water).
Nairobi, according to the water master plan, will require 1.2 billion litres of water daily by 2035.
Nairobi county gets its daily supply from four main sources — Kikuyu Springs, Ruiru 1 Dam, Sasumua Dam, Ndakaini Dam and Ng'ethu.
The Northern Collector Tunnel in Murang’a county has rescued Nairobi residents as it has started collecting floodwater.
The tunnel that was once condemned by some politicians as "the tunnel of death", is meant to boost the water supply to the city by channelling more than 140 million litres of water into Ndakaini Dam daily.
The project entailed construction of a fully lined 11.8km tunnel with a diameter of 3.2 metres and is set to collect 40 per cent of the floodwaters that flow into the Maragua, Gikigie and Irati rivers.
In 2019, former Water CS Simon Chelugui ordered Nairobi to stop drilling all boreholes, as they are competing for the water from the same aquifers.
Chelugui said they will focus on sustaining existing boreholes and investing in water resources outside the county.
“To address and to sustain the few existing boreholes, you have to limit the number of boreholes per area,” he said.
Chelugui said one licensing condition was limiting the distance from one borehole to another by a minimum of 800 metres.
He said Nairobi’s Eastlands area has fewer boreholes and geological surveys indicated water capacity is less than two or three cubic metres, unlike those in the Western side of the city, Kileleshwa, Karen and Upper Hill.
Chelugui said the only works to be done will be repairing, maintaining and possibly replacing the existing boreholes.
“We have not exhausted (the water table) but we have to make sure we manage and sustain the existing boreholes,” the CS said.