Let’s tap underground water with caution

The governor of Nairobi County has embarked on making city residents’ lives more bearable and one of his action plans is to drill boreholes to supplement water supply from the now-unpredictable Ndakaini Dam.

However, Mr Mike Sonko is not the only one thinking of boreholes. With the devolved government many people have moved to the counties, putting pressure on groundwater for development, industrial use, irrigation agriculture, domestic use and many other uses.

Investing in groundwater is, therefore, the right thing, given that it is often safer than surface water. But experts have noted a problem: We are exploiting the groundwater resource and yet we do not really know how much we have or fully understand the nature and geometry of the aquifers.

SUSTAINABILTY

We also don’t fully understand how these underground reservoirs replenish during the rainy season and behave during different climatic conditions and, so, we risk depleting or destroying them soon.

Prof Daniel Olago, a senior geologist at the University of Nairobi, reckons that “we do not know what we have, because we have not done adequate studies on groundwater”.

In their County Integrated Development Plans (CIDP), counties have groundwater exploration as a major component. But they only talk about drilling and developing groundwater systems without underlining the need to study and understand those systems to know their limits of sustainability.

As Governor Sonko plans to commission the project as announced during the first Nairobi Cleanliness Day, he should look at the city’s groundwater potential.

HYDROLOGISTS

In the late 1950s, say World Bank reports, groundwater in Nairobi was accessed at just 80 metres. By the mid ’90s, the depth had almost doubled to 140 metres. In the next century, it should be even deeper — perhaps more than 200 metres.

With the increasing population and, hence, demand for water, the situation is bound to worsen in the near future. That means Nairobi is literally chasing water downwards, and that is not sustainable. Hydrologists also say the water table has retreated in the flower-growing areas of Naivasha and Nanyuki.

But there is hope. Counties should exploit the ongoing scientific research under a programme that seeks to unlock the potential of groundwater for the poor.

For the past two years, scientists from the University of Nairobi, Oxford University, Jomo Kenyatta University of Agriculture and Technology and also University of Barcelona have been studying the groundwater system in Kwale County.

ABSTRACTION

Using a computer programme, the scientists will flag risks associated with groundwater quantity and quality based on hydro-meteorological, hydro-geological, water abstraction demand and socio-economic data.

The scientists have mapped out aquifers that provide water to Kwale and traced the source to two paleochannels — buried river channels. They have ascertained the water quantity and quality in the aquifers and given it a clean bill of health.

But they have flagged a major risk associated with the paleochannels that constitute the Msambweni aquifer: If water is over-abstracted from the reservoir, there is a high possibility of intrusion of salt water from the sea, which can ruin the aquifer even after it replenishes.

The regulator should issue borehole sinking permits depending on user needs and monitor the amount of water that can be abstracted from particular sources in a given season.

Mr Esipisu is a freelance journalist and the coordinator for Pan African Media Alliance for Climate Change (PAMACC). [email protected]