Future Groundwater Resources at Risk (Proceedings of the Helsinki Conference, June 1994). IAHS Publ. no. 222, 1994. 519

Assessment of water resources and implementation of rural water supplies in western Kenya

AIMO RUQTSALAINEN Geological Survey of Finland, PO Box 1237, SF-70701 Kuopio, Finland

PERTTI TURUNEN Geological Survey of Finland, PO Box 77, SF-96101 Rovaniemi, Finland

Abstract The Kenya-Finland Water Supply Programme has been operating mainly in the Western Province of Kenya. Among other activities it has assessed the water resources and made water supply development plan for the area. It is also implementing the plan. Surface water resources are abundant, but the quality is poor. Reasons for the poor quality are effluent from some factories and fertilizers of extensive farming. Due to high annual rainfall, groundwater resources are fair. Groundwater can be tapped from springs, from shallow aquifers by hand dug wells or from deeper aquifers and from bedrock by borehole wells. The quality of groundwater is usually good. The largest contaminations are caused by cattle and poor hygiene at the water points. Proper siting and protection of the water points is important in maintaining the good water quality. The most sustainable solution to the need of potable water in rural areas is groundwater.

INTRODUCTION

The work presented in this paper was carried out as part of the Kenya-Finland Western Water Supply Programme (KFWWSP) which is a development cooperation project between the Governments of Kenya and Finland. KFWWSP was established in 1981 and is still ongoing. The company implementing the programme is a joint venture, Kefinco. The objective of the programme has been to assess the water resources of the area as well as plan and build water supplies, mainly in the rural area of western Kenya. In 1990 a Water Supply Development Plan 1990-2005 for the Western Province (WSDP 90) was prepared. The area of KFWWSP is situated at the equator mainly in the Western Province and partly in the Nyanza Province of Kenya near the Ugandan border between Lake Victoria in the south and Mt Elgon in the north (Fig. 1). This paper concentrates to the hydrogeological investigations in the Western Province. The total population of the Western Province in 1989 was estimated to be 2.7 million people and the growth rate is about 3.5% per year (KFWWSP, 1990). The average population density is 365 persons km"2. Most of the people live in rural areas and in some rural locations the population density exceeds 1000 persons km"2. 520 Aimo Ruotsalainen & Pertti Turunen

Fig. 1 Location of the study area.

GENERAL FEATURES OF THE AREA

The elevation of the area is between 1150 and 2000 m a.s.l. Characteristic of the topography are hills with rivers or rivulets between them. In the eastern boundary of the Western Province there is the steep Nandi Escarpment and in the north Mt Elgon. In the southwestern corner there is a swampy area near to the Lake Victoria (Fig. 2). In most parts of the area the bedrock consists of granitic rocks. Volcanic rocks occur in the northern (Mt Elgon) and in the southwestern part of the area. Sedimentary rocks occur in minor amounts. The uppermost part of the bedrock is usually highly weathered. In the study area the climate is tropical. Lake Victoria in the west and the Nandi Escarpment in the east have a large influence on the weather. There are more than 200

Fig. 2 Boundaries and main rivers of Western Province. Water resources and rural water supplies in western Kenya 521

Fig. 3 Mean monthly rainfall at two observation stations of Hydrological Division of Ministry of Water Development (Rural Water Supply Development Project, 1983). (a) Kakamega, mean annual rainfall 1950 mm and (b) Bunyala 1040 mm. days of thunderstorms per year which is one of the largest rates the world. The rainfall is high ranging from 1000 mm a"1 in the west to 2000 mm a"1 in the east (KFWWSP, 1990). The driest months are December and January. April and May are the rainiest months (Fig. 3). According to the observations of the Hydrological Division of the Ministry of Water Development and the Meteorological Division of the Ministry of Transport and Communication the actual evaporation from open water in the area is in the range of 1000-1500 mm a"1 (Rural Water Supply Development Project, 1983).

WATER RESOURCES

In the programme area several rivers flow into the Lake Victoria (Fig. 2). The rivers and rivulets are rather evenly distributed and offer an abundant amount of water for domestic use. Due to the peneplain topography which slopes towards Lake Victoria there are no other lakes in the programme area. The quality of the surface water is poor. The chemical quality of many rivers is poor due to discharge of poorly treated effluent from sugar, paper and coffee factories (KFWWSP, 1990). Also fertilizers from sugar, coffee and wheat farms contribute to the pollution. The poor quality of the river water has had an effect on the water quality of Lake Victoria at the coast of the Western Province. In addition bacteriological quality of the surface water is poor and full treatment is required before it can be used for domestic purposes. KFWWSP has carried out inventory of spring potential. It is based on discharge measurements of more than 5000 springs during both rainy and dry seasons (Fig. 4). Most of the springs are perennial but the yields vary very much during the year. Springs are traditional water sources of the people. The quality of spring water is usually rather good. Problems are mainly caused by runoff of surface water, cattle or poor hygiene at unprotected springs. Proper protection (concrete wall, outlet pipes and cattle trough) and fencing maintains these problems at a minimum. From 1981 the KFWWSP has protected about 900 springs. Many piped gravity schemes have been built to utilize spring water e.g. on the slopes of Mt. Elgon in the north. The thickness of overburden varies from few metres to some 50 m. Typically the overburden consists of three different layers. Loamy or clayey lateritic topsoil (murram) 522 Aimo Ruotsalainen & Pertti Turunen

Fig. 4 Generalized map of spring water potential in Western Province (KFWWSP, 1990). is usually from 2 to 5 m thick. Next layer is decomposed clayey or silty rock material. The thickness of this layer varies usually from 20 to 30 m. Deepest is a disintegrated bedrock layer which is on the average 20 m thick and alters gradually to fresh bedrock at the bottom. The decomposed and especially the disintegrated layers are the main overburden aquifers in the study area. Occasionally confining clay or fresh bedrock layers occur inside the aquifers. In many parts of the area the depth to the water table is so small that it is possible to construct hand dug wells (Fig. 5). The aquifer is usually the decomposed rock layer and in many cases it is a perched aquifer. Due to fluctuation of the groundwater level (more than 2 m) from rainy to dry season the yield of a well may reduce or it may even dry up and requires deepening. All hand dug wells (about 900) have been equipped with concrete slabs and hand pumps. The most important aquifer is the disintegrated part of the rock. The permeability of this layer is generally good (Fig. 6). The drawback is that it usually lies so deep that a drilling machine must be used. The top of this aquifer is typically at a depth of 20-30 m and the thickness is about 20 m. The average static groundwater level is 10 m. In some parts of the area the aquifer is at the depth of more than 50 m and in regions of

Fig. 5 Generalized map of groundwater potential in the shallow aquifers. The classes show the possibilities to find a site for a successful hand dug well (KFWWSP, 1990). Water resources and rural water supplies in western Kenya 523

Fig. 6 Generalized map of groundwater potential in the deep aquifers in overburden and in fractured bedrock (KFWWSP, 1990). Typical yield of a borehole well is: less than 1 m3 h"1 in poor, 1-2 m3 h"1 in fair, 2-5 m3 h'1 in good and more than 5 m3 Ir1 in the very good areas. porous volcanic rocks it does not exist at all. The average depth of the boreholes in the programme area is about 50 m. Fractured and faulted zones of the bedrock are good sources of groundwater. If higher yielding production wells for bigger communities or institutions are needed, a site with a thick overburden aquifer and a fracture zone in bedrock should be found. Most of the borehole wells are equipped with hand pumps (about 1000 in all). The water quality of the groundwater in the study area is normally good. Most quality problems in hand dug wells arise from worn constructions and from the usage of the wells (KFWWSP, 1990). Because the depth to the groundwater level is small, contamination from cattle and people using the well infiltrates with rain water through permeable soil to the aquifer or enters as surface runoff through cracked concrete slabs into the well. The construction of cattle troughs and large enough fence around the well decreases this problem. Borehole wells abstract their water from deeper, and in many cases confined, aquifers. That is why the quality of the water is good throughout the year. The largest problems have been high salinity and high iron content in some limited areas. One reason for high iron content, aside from a natural origin, is corrosion of either iron casings or galvanized iron rising pipes especially in areas where saline water occur. For this reason at present boreholes are furnished with PVC-casings.

INVESTIGATIONS

The KFWWSP has concentrated on rural water supplies. The initiative for a water point must come from the community itself. Before the investigations the villagers form a well committee. The community proposes a site for the well and also to some extent participates the building of the water point. The choice of the investigation methods for a proposed well site depends on existing information from the area and required yield of the well to be constructed. When a hand dug well is possible the investigation is usually carried out using hand auger drill. This method gives reliable results about the depth to the aquifer and the properties of the soil. 524 Aimo Ruotsalainen & Pertti Turunen

Almost all borehole sites are surveyed using geophysical methods. The main method applied in KFWWSP is seismics. It works well almost all over the programme area. Exceptions are some limited areas with volcanic rock types with seismic velocities lower than 2000 m s"1 and thick lateritic clay formations. Using profile interpretation thicknesses of different overburden layers are obtained for the whole length of the survey line and also fractured zones of the bedrock are interpreted. The seismic velocity of fractured crystallized bedrock is usually in the range 2700-4500 m s"1. In weathered rock the velocity is of the same order. Vertical electrical soundings (VES) have been carried out mainly in areas with volcanic rocks. It is not easy to detect fractured zones of the bedrock with VES because this method gives information mainly from the central point of sounding. The VLF- or horizontal-loop electromagnetic profiling can be used in selecting the VES-points. During the rainy season the electric resistivity of the topmost part of overburden decreases causing problems to electrical and EM methods. The walking distance to the water point should be as small as possible. This means that the well should be near to the school, market, church etc. in the centre of the village. These are usually far from the best sites in the sense of availability of groundwater. Sometimes a borehole must be drilled to get water for the community even after rather poor results in the survey, taking the risk of making a dry hole. If a high yielding well for production is required, the degree of freedom in choosing a drilling site is bigger. Then, for example, aerial photographs or VLF-method is used to locate fractured zones. Seismics and/or VES-measurements are then used before selecting the drilling point. EM-, VLF- and DC-profile measurements are quick and cheap, but give only qualitative results and the vertical structure cannot be interpreted. Problem in the use of VLF-method is weak signal due to long distances to the transmitting stations. Seismic profiling gives more widespread and more accurate information than VES. When seismics is done routinely two sites per day (600-800 m of profile) can be surveyed by a team of six men. With new sensitive digital equipments the consumption of explosives is very low. In many cases the stacking of the signal makes it possible to use even a hammer as the source of signal. There is no absolute truth about the best method. The choice should be done according to the nature of the site and the feasibility of the method in regard of its resolving power. If success rates of different methods are compared, the region and circumstances should remain the same for all of them. Otherwise the results are not relevant.

AQUIFER TESTS

Most of the wells are equipped with hand pumps. The maximum intake of a hand pump is about 1 m3 h1 which practically means about 12 m3 day"1. Most of the boreholes yield much more than that. First approximation for the yield of a borehole well is obtained during development of the hole. The discharge is measured during flushing by use of a V-notch weir. Because of low discharge requirement of hand pump, only six hours con­ stant rate pumping test is usually carried out. For high-yielding holes, especially when equipped with an electrical pump, a test duration of 24 h is used. In addition step-draw­ down tests are carried out. The yield of hand dug wells are estimated using slug tests. Water resources and rural water supplies in western Kenya 525

PLAN FOR THE FUTURE

KFWWSP has implemented and rehabilitated many piped supplies and constructed about 2800 water points in the programme area. These water points serve about 700 000 people mainly in rural areas. All information collected during the hydrogeological investigations and the water point construction has been analysed during preparation of the WSDP 90. In the plan a programme is presented how to best utilize the assessed water resources in implementing the most feasible water supply network to serve the whole population of the Province by the year 2005. Surface water requires full chemical treatment and in the case of shortages of chemicals or problems in operation of the water supply, risks for health of the people arise. Surface water supplies are feasible only for bigger towns or in areas where groundwater does not exist. Generally, where groundwater is adequate, it is the best and most sustainable alternative in the long run. The cheapest type of water point is protected spring followed by hand dug well, whereas borehole well is the most expensive. In the future the availability of funds will be the biggest problem in achieving the target of getting clean water to everyone. Since most of the contamination of groundwater happens between the tap and mouth, it is very important to educate people to understand the importance of clean water for health.

Acknowledgements We want to thank Geological Survey of Finland for the opportunity to participate to the KFWWSP and to publish this report. We also want to express our gratitude to Mrs Anu Rosendahl and Mr Reijo Hâkkinen from the KFWWSP for kind assistance and permission to publish this article. Many persons from the Programme were involved in preparation of the WSDP 90. Among others, Mr James Muriuki was in charge of the water quality aspects.

REFERENCES

Kenya-Finland Western Water Supply Programme (1990) Water supply development plan 1990-2005 for Western Province (Bungoma, Busia and Kakamega Districts). Ministry of Water Development, Kenya and Ministry for Foreign Affairs, Finland (unpublishedreport). Rural Water Supply Development Project in Western Province of Kenya (1983) Development plan. Ministry of Water Development, Kenya and Ministry for Foreign Affairs, Finland (unpublished report).