Garissa County in north-eastern Kenya is hot, dry and flat, with rainfall that is low and unreliable. The Tana River runs along its western edge and supports irrigation and settlements, but most of the county lies far from permanent surface water. Pastoral communities, towns, schools, health facilities and large refugee-hosting areas all rely heavily on groundwater. Borehole drilling in Garissa can transform water access, but the county’s deep sedimentary aquifers, variable water quality and low recharge demand careful exploration and design.

Geological Setting

Garissa lies within the large sedimentary basin that covers much of north-eastern Kenya. Its geology includes:

• Thick sequences of sands, sandstones, clays and limestones laid down over millions of years, forming layered aquifers at depth.
• Alluvial deposits along the Tana River and its floodplain, which hold shallow groundwater linked to river flow.
• Dry riverbeds (lagas) and seasonal channels, where sand can store water after floods.
• Superficial deposits such as windblown sand and calcrete in flat plains.

Because the basin is deep and the layers are broadly continuous, aquifers can be extensive, but water levels are often deep and water quality varies with depth and location.

Regional Aquifers and Their Importance

North-eastern Kenya includes regional aquifer systems that extend across several counties. One of the best known is the Merti aquifer, which has been studied for its role in supplying water to communities in the Lagdera and wider Garissa, Wajir and Isiolo areas. Aquifers of this type can provide relatively fresh water in zones where recharge from rivers and floods occurs, but they can also contain brackish or saline water elsewhere. Their sustainable use depends on understanding recharge, flow and the effects of pumping, which makes monitoring and careful management essential.

Key Challenges in Garissa

Deep water levels. Many boreholes reach water at considerable depth, increasing drilling and pumping costs.

Salinity. Groundwater in parts of the county is brackish or saline, limiting use for drinking and irrigation.

Low and episodic recharge. Rainfall is scarce, and recharge often occurs through river flooding and dry riverbeds. Some deep groundwater may be old, with little present-day recharge.

Flooding and river dynamics. The Tana River floods periodically, which can recharge aquifers but also contaminate shallow wells and damage infrastructure.

Remote locations and logistics. Long distances, limited roads and security considerations complicate survey and drilling operations.

High demand. Pastoral herds, towns, institutions and humanitarian settlements all draw on limited groundwater.

How a Groundwater Survey Is Done

Desk study. Review of geological maps, hydrogeological reports, climate data and borehole records, which are especially valuable in sedimentary basins where aquifers are laterally continuous.

Remote sensing and GIS. Satellite imagery identifies river channels, lagas, floodplains, vegetation and land cover that indicate recharge zones and shallow groundwater.

Field reconnaissance. Inspection of existing boreholes, shallow wells, water pans and springs, with measurement of water levels, yields and electrical conductivity.

Geophysical survey. Electrical resistivity helps distinguish fresh, brackish and saline water and identify sand layers. Time-domain electromagnetic surveys can image deeper layers where aquifers are far below the surface.

Test drilling and logging. Exploratory boreholes confirm layer sequences and water quality at depth, and geophysical logging refines interpretation.

Reporting. A report presenting recommended sites, expected depths, yield and water-quality ranges, and design advice.

Targets for Drilling

• Alluvial aquifers along the Tana River and major lagas, which are shallower and recharge during floods, but must be protected from contamination and over-abstraction.
• Sand and sandstone layers at depth with favourable water quality, identified by resistivity and logging.
• Zones of fresher water within otherwise brackish aquifers, where recharge from rivers or floods has created freshwater lenses.

Hydrogeologists must weigh depth, cost and quality, since a shallow, easily accessed aquifer may be salty, while a deeper aquifer may be fresher but far costlier to reach.

Drilling and Completion

• Rotary drilling, often with mud, is typically used in unconsolidated and sedimentary formations, with casing to prevent collapse.
• Screens and gravel packs matched to water-bearing sands reduce sand pumping and improve yield.
• Development removes drilling mud and fines.
• Pumping tests with conductivity monitoring help detect salinity changes under pumping.
• Water-quality analysis should include salinity, chloride, fluoride, hardness, iron and microbiological parameters.
• Pumps and power: solar-powered submersible pumps are widely used in remote areas, with storage tanks, livestock troughs and distribution points.

Water Quality and Treatment

Brackish water can sometimes be used for livestock, depending on salinity levels, while drinking water needs lower salinity. Where water is too saline, options include drilling to a different depth, selecting another site, blending with fresher sources, or desalination using reverse osmosis powered by solar energy where feasible. Any treatment should be planned with operation and maintenance capacity in mind.

Sustainable Management

• Monitor water levels and quality regularly, particularly in heavily used aquifers.
• Set pumping rates within tested sustainable yield.
• Space boreholes to limit interference.
• Protect wellheads from flooding and contamination.
• Coordinate water points with grazing management to avoid land degradation and conflict.
• Combine sources: groundwater, river abstraction, pans and rainwater harvesting can complement each other.

Regulatory Framework

Groundwater is regulated under the Water Act 2016. Borehole projects generally require a hydrogeological report from a recognised hydrogeologist, drilling authorisation from the Water Resources Authority, a licensed driller and, where applicable, a water use permit. Community and humanitarian projects usually coordinate with the county government and relevant agencies. Confirm current requirements before starting.

Practical Advice for Project Planners

1. Start with a hydrogeological survey and consider test drilling for deep, poorly known areas.
2. Plan for deep drilling and strong pumps where necessary.
3. Include water-quality testing and treatment in the budget.
4. Design for low maintenance and train local operators.
5. Plan for security and logistics.
6. Monitor performance and share data with regulators.

Conclusion

Garissa’s groundwater is a critical but challenging resource. Deep sedimentary aquifers, variable salinity and low recharge call for systematic exploration, careful drilling and sustainable management. With sound science, appropriate technology and community involvement, boreholes can support people, livestock and livelihoods across the county.