| dc.description.abstract | Population increase, change in agricultural practice and inadequacy of water resources have
prompted an evaluation of groundwater in the Njoro area. The study area has an extent
of about 100 square kilometers in Njoro Division. In the study qualitative and quantitative
analysis of groundwater resources for either domestic or irrigation purposes have been
considered. The quantitative analysis of well performance in the study area has been
evaluated mainly by considering the yield (Q), specific capacity (Qs),transmissivity (T) and
permeability (K). Qualitative studies aimed at determining the potability and irrigation
suitability of the groundwater have been done. These have been based on chemical
suitability, with parameters such as iron, calcium, magnesium, fluoride, sodium and
dissolved solids being analyzed, among others. Field work and aerial photographic studies
have enabled delineation of structural lines and their relationship to the groundwater regime
in terms of quantity and quality have been evaluated. Further, the study and correlation
of well logs has helped to identify aquifers, their extent and thickness.
As a result of this study, it is noted that the geology of the area comprises volcanic rocks
and sediments. Sedimentary units intercalated in the volcanic formation are the main
source of groundwater. Weathered trachytes and reworked coarse tuffs provide aquifers
in the volcanic formation. It is observed that for the sedimentary aquifers, the saturated
thickness may be as much as 15 m, while it is less in the volcanics.
Well yields in the study area exceed 4 l/s in some parts. In about 50% of the area yields
of more than 1.6 l/s are obtainable. Most of this water is of good quality except in the
Njoro graben, where brackish conditions occur. Thus areal variation in potability is
reflected in the dissolved solids concentration, which varies from as low as 178 ppm to
over 1356 ppm. High fluoride concentration in parts of the study area is linked to the
volcanic terrain and its associated sodium bicarbonate groundwater type.
In concluding, it is observed that groundwater occurrence and distribution in the area falls
into four zones (Zone 1, Zone 2, Zone 3 and Zone 4). Of the mentioned zones, the best
zone for future development is indicated as Zone 2, where the mean yield is 2.8 l/s.
Chemical analysis results reveal that groundwater in the area is of good to ecxellent
quality, except for waters located in theNjoro graben, where electrical conductivity values
may reach 1400 Sf em. Most of the groundwater is also suitable for irrigation, except
for the waters located in the west of the study area, where SAR-values are comparatively
higher. | en |
