GROUNDWATER OCCURRENCEIN

KENYA

Steven Okoth Owuor

Ministry of Water and Sanitation

1Sunday, January 20, 2019

• The Republic of Kenya is located in East Africa

• The total area of the country is 580 370 km2. For administrative

purposes the country is subdivided into 47 counties.

• The altitude varies from sea level to the peak of Mt. Kenya,

situated north of the capital Nairobi, which is 5 199 meters above

sea level (Fig. 1).

INTRODUCTIONGeography

2

Fig. 1: Kenya presented in red within the map of

Africa and a general relief map of Kenya from Digital

Elevation Model (DEM) (data downloaded from

http://datasets.wri.org/dataset/kenya-digital-

elevation-model-90m-resolution on 09/04/2018) and

modified in ArcGIS 10.5, and River/drainage network

of Kenya overlying the DEM (Permanent rivers in thick

lines and seasonal in fine dashed lines) (Oiro, 2018).3

Climate

• The climate of Kenya is highly varied from mostly cool every day

regions to always warm/hot regions

• The coastal region is characterized by higher rainfall and

temperature throughout the year.

• The average annual rainfall is 630 mm with a variation from less

than 200 mm in northern Kenya to over 1 800 mm on the slopes of

Mt. Kenya (Fig. 2).

4

• The rainfall distribution is bimodal with long rains from March to

June and short rains from October to November for most parts of

the country.

• About 80% of the country is arid and semiarid, while 17 percent

is considered to be high potential agricultural land, sustaining 75

percent of the population.

• The forest cover is about 3 percent of the total land area.

Climate Cont..

5

Fig. 2: Simplified geological map of Kenya into

three categories, namely: sedimentary formation,

volcanic (Tertiary to Quaternary), and crystalline

basement system. Rainfall Isohyet contour lines

are overlaid on the geological map, and major

towns marked in red circles (Oiro, 2018).

6

Groundwater Occurrence and Distribution in Kenya

In Kenya, groundwater occurrence and distribution is majorly

controlled by geology which is mainly (Fig. 2):

• intrusive rocks and volcanic flows characterize the Rift Valley

System and Central Kenya

• sedimentary rocks characterize Coastal and Northern Kenya

• metamorphic terrains are of very small extent and localized

largely in eastern Kenya7

Lake Victoria, covering 8.0 percent of the country;

• Rift valley and inland lakes, covering 22.5 percent of

the country;

• Athi River and coast, covering 11.5 percent of the

country;

• Tana River, covering 21.7 percent of the country;

• Ewaso Ng’iro, covering 36.3 percent of the country

(Fig. 3)

Major drainage systems in Kenya

Fig. 3: Simplified map of Kenya demarcating catchment/basin

areas in green and Rivers in blue polylines (Oiro, 2018)8

Fig. 4: Location of the

boreholes overlaid on a

drainage system of Kenya

(Kuria, 2013).

9

Why Groundwater is becoming important:

• Increase in population

• Pollution of surface water

• Climate change - drought

Why Groundwater

Groundwater Challenges in Kenya

• Insufficient scientific information

• Limited understanding of groundwater and inadequate

monitoring10

Ongoing Groundwater Projects

• Digitization of groundwater data

• Groundwater Mapping Programme

• South Turkana

• Marsabit

• Wajir

Drilling of groundwater monitoring wells under Kenya water security and

climate change resilience project

• Nairobi

• Tiwi

• Lamu 11

12

Named Aquifers General Description

Lotikipi and Lodwar

aquifersAlluvial sands and sediments, which range up to 80 m deep.

Tiwi aquifer

Small outcrop but strategically important in the Kwale area. The lithology is

alluvial and lacustrine sand and clay and is typically not more than 70 m

deep. High borehole yields can be obtained, and boreholes are typically 40 –

80 m deep. Transmissivity values range from 120 to 600 m²/d

Gongoni/Msambwe

ni Aquifer

The Gongoni/Msambweni Aquifer occurs in the Kwale area. High yields can

be obtained. Boreholes are typically 40 – 100 m deep.

GROUNDWATER DISTRIBUTION AND AQUIFER CHARACTERISTICS

Sedimentary Aquifers

13

Baricho Aquifer

The Baricho aquifer is small but strategic in the coastal zone and comprises

approximately 20 m of alluvial sand and gravel overlying around 40 m of

Jurassic Mazeras Sandstone and Kambe Limestone. Boreholes are typically

drilled to 25 – 60 m depth. transmissivities of 3,750 to 25,000 m2/d for a

saturated thickness of 50 m

Merti Aquifer

The Merti Aquifer occurs in Wajir County and comprises semi-consolidated

clays, sands, sandstones and limestones . Groundwater is usually confined

and water levels lie at 90 to 120 m below ground level.

found at fairly uniform depths of between 110 and 180 m below ground

level. The aquifer is thought to be between 80 and 280 m thick. Successful

boreholes are commonly between 105 m to 150 m bgl (GIBB Africa Ltd 2004).

Transmissivity ranges from 0.2 to 840 m²/d depending on the facies, with

higher transmissivities in coarse grained materials.

Distribution and Aquifer Characteristics of Intrusive andVolcanics

14

Nairobi Aquifer It comprises Plio-Pleistocene volcanics

interbedded with old land surface and

intervolcanic sediments, and underlies much of

the Nairobi metropolitan area. It is a complex

multilayered aquifer system, recharged along the

eastern edge of the Rift Valley with groundwater

moving toward the east. The main aquifer layer,

the Upper Athi Series, is confined and typically

found at depths of 120 to 300 m bgl.

Transmissivity values range from 0.1 to 160 m²/d,Kabatini

aquifer

The Kabatini aquifer occurs within the volcanic rocks of

the Nakuru area. Boreholes are typically drilled to about

150 m depth.

15

Turkana

Aquifer

Turkana Aquifer in the Rift System, as marked by

major boundary faults, is characterized by well-

defined aquifer systems whose location

corresponds to the location of the Rift Lakes, that

is, the Turkana aquifer. The aquifer roughly has a

rectangular shape and occupies both the western

and eastern part of the Rift Lakes.

Baringo-

Bogoria Aquifer

The Baringo–Bogoria aquifer stretches from the area

south of Lake Logipi and terminates weakly at the area

south of Lake Bogoria. Characteristically, the Baringo–

Bogoria aquifer has very high groundwater potential

zones.

The aquifers in the metamorphic rocks are characterized generally

by a very low primary and (depending on the degree of fracturing)

variable secondary porosity of the metamorphic rocks. The

thickness and mineral characteristics of the weathered layer play

an important role in the determination of the amount of

groundwater it can hold. Topography, drainage pattern, rainfall and

evaporation are some of the major factors that determine the

amount and occurrence of groundwater.

GROUNDWATER DISTRIBUTION AND AQUIFERCHARACTERISTICS OF METAMORPHIC ROCKS

16

Fig. 5: Transmissivity map of Kenya

showing distribution of groundwater

potential zones (Kuria, 2013).17

18

Aquifer Sharing Countries Area (Km2)Merti Aquifer Kenya, Somalia 13,623Coastal / Karoo

sedimentary

aquifer

Kenya Tanzania 17,067

Sudd Basin Kenya, Ethopia and

South Sudan

370,648

Dawa Kenya, Ethiopia and

Somalia

34,007

Kilimanajro

Aquifer

Kenya, Tanzania 14,576

Mount Elgon

Aquifer

Kenya, Uganda 5,398

Rift Aquifer Kenya, Tanzania 21,145Precambrian

basement aquifer

Kenya, Ethiopia

(Nijsten et al., 2018; Abiye 2010)

Fig. The Transboundary Aquifers of Kenya

GROUNDWATER GOVERNANCE IN KENYA

• Water resources in Kenya is governed by Water Act 2016

• Every water resources are vested in and held by the National

Government in trust for the people of Kenya as per section 5 of Water

Act, 2016.

• The Ministry’s current policy (1999) focuses on decentralization,

privatization, commercialization and stakeholder participation

• The Water Resources Authority established in section 11 of Water Act,

2016 serves as the agent of the National Government and regulate the

management and use of water resources (both surface and groundwater)19

• To construct a borehole or well one must first apply to the

Water Resources Authority for a permit and comply with the

requirements imposed by the Authority.

• The Water Resources Authority shall first give an authority in

the form of authorization to construct the borehole or well.

• The Borehole developer then contracts a licensed Borehole

contractor to drill and equip the borehole ready for use by the

developer.20

21

22