Download GEOELECTRIC STRUCTURE BENEATH A 14 KM TRANSECT

GEOELECTRIC STRUCTURE BENEATH A 14 KM TRANSECT ACROSS
THE BOUNDARY BETWEEN NAKURU AND KERICHO COUNTIES
AND ITS RELATION TO THE GROUNDWATER OCCURRENCE IN THE
AREA
Geo-electric resistivity survey was conducted along a 14km transect at the
boundary between Kericho and Nakuru counties to observe the structure beneath
and its relation to ground water occurrence. The study area is located between
Latitude 35.5820700 to 35.792290o and Longitude 0.1556140 to 0.2557630. The
area consists of volcanic rocks which include Pliocene trachytes, phonolites and
basalts, Holocene basalts flows, pyroclastic and volcanic soils, Holocene
colluvium deposits, pebbles sheets and basalts and Neogene (undifferentiated
sediments intercalated in volcanics. In order to understand the aquifer distribution
in the area and subsurface lithology, 58 Vertical Electrical Sounding (VES) were
probed within the study area and data obtained were then interpreted using
EarthImager 1D software, RES2DINV software and Surfer 11.
The top most layers have high resistivity values ranging from 130 ohm meter to
430 ohm meter which is then underlain by pockets of low resistivity values of less
than 100 ohm meter. Bottom layers have got very high resistivity values of up to
1390 ohm meter and probably infer fresh bedrock of basalts. Generally, the
resistance variation in the area is related to the geology of the subsurface, revealing
the stratigraphic layering and the rock characteristics in terms of
weathering/fracturing.
Major fault lines found, conform to the major incised valleys and streams
transecting while minor structural lineaments are observed to assume the general
trend of the weathering profile. Additionally where fractures are present in a
geologic medium, the bedrock is expected to be more strongly weathered to a
greater depth and can greatly influence its hydrogeological characteristics. The
present study has proved the use of resistivity method as an excellent tool to
delineate groundwater potential zones and subsurface lithology.