GROUNDWATER OCCURRENCE IN KENYA

GROUNDWATER OCCURRENCE IN KENYA Steven Okoth Owuor Ministry of Water and Sanitation Sunday, January 20, 2019 1

Geography INTRODUCTION The Republic of Kenya is located in East Africa The total area of the country is 580 370 km 2. 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). 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-digitalelevation-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

Climate Cont.. 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. 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 Kenya 7

Major drainage systems in Kenya 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) 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 Why Groundwater is becoming important: Increase in population Pollution of surface water Climate change - drought Groundwater Challenges in Kenya Insufficient scientific information Limited understanding of groundwater and inadequate monitoring 10

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

Named Aquifers Lotikipi and Lodwar aquifers Tiwi aquifer Gongoni/Msambwe ni Aquifer GROUNDWATER DISTRIBUTION AND AQUIFER CHARACTERISTICS Sedimentary Aquifers General Description Alluvial sands and sediments, which range up to 80 m deep. 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 The Gongoni/Msambweni Aquifer occurs in the Kwale area. High yields can be obtained. Boreholes are typically 40 100 m deep. 12

Baricho Aquifer Merti 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 m 2 /d for a saturated thickness of 50 m 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. 13

Distribution and Aquifer Characteristics of Intrusive and Volcanics 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. 14

Turkana Aquifer Baringo- Bogoria Aquifer Turkana Aquifer in the Rift System, as marked by major boundary faults, is characterized by welldefined 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. 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. 15

GROUNDWATER DISTRIBUTION AND AQUIFER CHARACTERISTICS OF METAMORPHIC ROCKS 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. 16

Fig. 5: Transmissivity map of Kenya showing distribution of groundwater potential zones (Kuria, 2013). 17

Aquifer Sharing Countries Area (Km 2 ) Merti Aquifer Kenya, Somalia 13,623 Coastal / Karoo Kenya Tanzania 17,067 sedimentary aquifer Sudd Basin Kenya, Ethopia and South Sudan 370,648 Dawa Kenya, Ethiopia and 34,007 Somalia Kilimanajro Kenya, Tanzania 14,576 Aquifer Mount Elgon Kenya, Uganda 5,398 Aquifer Rift Aquifer Kenya, Tanzania 21,145 Precambrian basement aquifer Kenya, Ethiopia Fig. The Transboundary Aquifers of Kenya (Nijsten et al., 2018; Abiye 2010) 18

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

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

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