ASSESSMENT OF GROUNDWATER POTENTIAL IN ARUJO- RODI KOPANY AREA, HOMA BAY COUNTY, KENYA. NAME: AYETE DAVID OMAJILONG

ASSESSMENT OF GROUNDWATER POTENTIAL IN ARUJO- RODI KOPANY AREA, HOMA BAY COUNTY, KENYA. NAME: AYETE DAVID OMAJILONG

SUMMARY. Groundwater development for portable water supply in Kenya for rural people has increased greatly in the past few years. The study area has scarce surface water sources with the exploitation of groundwater being the only source for portable water. The study area has a poor historical borehole success rate with 70 percent of the boreholes drilled being unsuccessful. The existence of a few high yielding boreholes suggest that there are hydrogeological features suitable for groundwater development. The study area is underlain mainly by the tertiary volcanics, whose aquifers are controlled by the geological structures,i.e faults. Weathered/fractured zones too contribute significantly to the presence of aquifers. The analysis of drilled borehole data and resistivity measurements and geological structures will be used assess groundwater potential of the area.

1.0 INTRODUCTION. The water sources in the study area is limited to seasonal streams, and ponds. The largest fresh water body, Lake Victoria is located about 5 to 12 kilometers from the study area respectively. The area of study covers an area of approximately 60 square kilometers and is located at co ordinates 34 0 27 to 34 0 32 East and 0 0 34 to 0 0 39 South and altitudes between 1300 to 1450 meters above sea level. There is an increasing demand for the use of groundwater to provide portable water for domestic purposes by the area population. The geological of the area is mainly Tertiary Kaksingri Volcanics,overlain at the surface superficial deposists.

INTRODUCTION CONTINUED The study therefore is intended to carry out assessment of groundwater potential in the area by analyzing drilled borehole data, carrying out appropriate resistivity measurements, study geological and structural controls that contribute to high and low groundwater potential in the study area.

TOPOGRAPHICAL MAP OF THE STUDY AREA.

2.0 PROBLEM STATEMENT. The area has scarcity of clean portable water due to lack of reliable water sources. The current water sources are seasonal and often polluted resulting into high prevalence of water related and water borne diseases. There is therefore need to delineate high potential areas that will be suitable for drilling of high yielding boreholes and also save millions of shillings in drilling dry boreholes.

3.0 PROJECT RATIONALE. Map out high and poor groundwater potential areas that will be used as a basis for further groundwater exploitation in the area to provide portable water. It will also enrich the researcher the complexities of groundwater exploration and exploitation in different geological formations.

4.0 PROJECT GOAL To examine and understand the causes of high number of dry boreholes and provide long lasting solutions by delineating good exploitable areas/zones for borehole drilling. Improve water coverage in the study area that stands at 10 percent of the population that have access to clean water.

5.0 PROJECT OBJECTIVES Map out high, low and poor groundwater potential areas in the study area, where the demand for water for the rural population is expected to increase. Reduce the high number of dry boreholes and hence save funds for other activities. Determine the causes of the high percentage of unsuccessful boreholes. Suggest ways in improving groundwater exploration in such areas.

6.0 METHODOLOGY/SOURCE OF DATA Examine previous geological and hydrogeological investigations reports from hydro geologists, consultants and government agencies. Analyze available borehole data, that includes, drilled depths, water struck levels, water rest level, tested yields, borehole logs. Obtain some geophysical data, using electrical methods, preferably Vertical Electrical Sounding and horizontal profiling on preferred locations and sites. These will enable one to determine weathering depths of rock formations, basement, clayey formation and buried anomalies respectively that are indicators of whether a borehole can be drilled or not. Compare electrical resistivity's values of both unsuccessful and successful boreholes in similar or different geological formations. Study the geology, structures in which the unsuccessful and successful have been drilled.

7.0 EXPECTED OUTPUTS In its effort to provide clean portable water, the county government of Homa Bay has unveiled an ambitious programme to sink boreholes in various parts of the county including the study area. The study s output will therefore provide an insight into the groundwater potential of the study area and minimize the number of the dry boreholes. The study will also unravel factors that contribute to dry boreholes considering the adjacent areas with similar geological conditions have high success rates. The area being without other water resources, groundwater development will alleviate water scarcity and long distances to fetch water and reduce water related diseases.

8.0 LITERATURE REVIEW The study has been extensively covered by McCALL G.J.H 1958...Geology of the Gwassi area, Degree sheet number 41,S.W Quarter and part of N.W.Quarter.The report discusses the geology of Gwassi area which is divided into four major divisions namely the Kuja basin,the Lambwe Valley, the Gwassi hills and the Islands comprising of Mfangano and Rusinga islands respectively. The study area falls under parts of the Lambwe and kuja basin areas respectively. The report describes the geology of these areas as consisting of sediments, lavas, volcanic rocks, igneous intrusions, and corbonatites. The main structures near the study area are the kanyamwa escarpment and lambwe fault. Development of groundwater in the tertiary volcanic, sediments, Nyanzian volcanic is considered successful because of its easy weathering and decomposition

LITERATURE REVIEW CONTINUED------ The Lake Basin Domestic Water Supply and Sanitation Programme, through the DHV Consulting Engineers...1985,Water Resources survey report on Rangwe division, describes the geology of the study area as comprising of Nyanzian systems,kavirodian systems, granitic rocks, tertiary volcanic etc. The stratigraphy of the area is based on the following geological events that occurred in the area; Pleistocene Recent...black cotton soil Tertiary...kaksingri lavas and lateritic layers Paleozoic...no deposition Precambrian...granitic intrusions,kavirondian system(conglomerates, grits and mudstones)

LITERATURE REVIEW CONTINUED---- The report describes the area has having good groundwater prospects through drilling, though construction of wells will encounter hard rocks. A number of hydro geologists have carried out investigations and wrote reports of the area, among them are Anthony Ndungu, Isaiah Mawinda, and Joseph Mirobe. The reports describe the area as consisting of mainly Tertiary Kaksigri Volcanics, recent deposits, conglomerates e.t.c. The groundwater potential is concluded as being generally fair.

9.0EXPECTED INPUTS The following area the expected inputs, Desk studies including study of topographical and geological maps, collect borehole data and take a reconaisence to the study area and hold discussions with the leaders of the area. A tetrameter ABEM 300 will be used to conduct geophysical measurements. Other instruments include a GPS for measuring co ordinates of sites of interest. Personnel to assist in taking measurements and finances has to be availed for the study.

10.0 SCOPE/ LIMITATIONS. SCOPE The scope of the study area includes but not limited to the following. Collection and analyzing of borehole data including, total depths, Water Struck levels, Water rest levels and the yields. Data of electrical resistivities of successful and unsuccessful drilled boreholes will be collected and analyzed with an appropriate model. A number of electrical measurements including, Vertical Electrical Sounding, and horizontal profiling will be undertaken to probe depth of aquifers and delineate

LIMITATIONS With the onset of the El Niño rains, the accessibility to sites will be difficult and the water logging of the study area will not be conducive for collection of electrical resistivity data. Most of the area is also under cultivation and there is chances of hostilities by the concerned farmers to access their farms. The instrument to be used an ABEM 300 that cannot be used for 3D measurement for the sub surface conditions.

ITEM NO. DESCRIPTION OF ACTIVITY REQUIREMENTS 1 2 MONTHS 3 4 5 6 1 Desk study Reports 2 Reccoinacence of the study area. Visits drilled sites GPS 3 Carry out resisistivity sounding/horizontal profiling on selected areas Resistivity equipment Personnel Transport Finance 4 Analyse resistivity data Software, laptop.stationery 5 Prepare draft report stationery 6 Final report stationery 7 Report presentation Final report

REFERENCES. 1). McCALL G.J.H (1958)...Geology of the Gwasi area,degree sheet 41,South- West quarterand part of North-West Quarter. 2). DHV Consulting Engineers (1985)...Water Resources survey report for Rangwe division. 3). Ndungu A.( 1999)...Hydrogeological /Geophysical investigations reports for various sites in West and East Kanyanda location,homa bay District.