Evaluation of groundwater resource potential of Pallisa district in eastern Uganda
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Date
2003-09
Authors
Nyende, Jacob
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
This study aimed at assessing the ground water resources potential in Pallisa district, which
is found in the eastern part of Uganda.
The aims of the investigation can be Iisted as follows:
~ To determine the reliability and applicability ofVES in Pallisa district;
~ To evaluate the potential for sustainable harvesting of groundwater resource;
~ To determine the hydrogeological properties of the aquifer and make
recommendations;
~ To suggest improved management strategies of water resource in Pallisa district in
order to provide basic water services to the rural population and;
~ To propose a monitoring programme in the area that will include boreholes to
determine the variation of water quality and quantity with time.
The majority of the population of Pallisa district mainly uses groundwater as a source of
supply for potable water. Groundwater is increasingly on demand in Pallisa district due to:
(i) Population growth, (ii) Modem agricultural practices (iii) Livestock demands. Though
springs and shallow wells are a source of groundwater in Pallisa, many of them have not
been developed. There is need to have many of them developed to provide clean water and
increase in the number of deep wells also in case of consistent droughts.
The geological environment covered by this study consists of a Gneissic Complex
Formation or Gneiss and granitic formations of the Pre-Cambrian origins. The study shows
that Gneiss complex forms the principal source of ground water supplies while fresh
metamorphic rocks are impermeable.
From the hydrogeological investigations, it is clear that among the three water bearing
zones (the upper, the middle and the lower), the metamorphic formations are widely
weathered as you go deeper the earth, meaning that the lower zone of fresh geological
granitic material are of a fractured bedrock. The study further revealed that the fracture
zones have higher hydraulic conductivity with low storage coefficients and are generally
confined. The hydrogeological investigation shows that groundwater in Pallisa district lies right
below 30 - 70 m from the surface topography. This was shown by the hydrogeological
profiles constructed through the underlying aquifer of the wells around Pallisa town.
Higher transmissivity values were observed in the crystalline rock aquifer which related to
the western and north - western of Pallisa district, with an average of 13.5 m2/d, due to the
presence of open waters of Lake Kyoga, Mpologoma and Dodoi rivers. Such transmissivity
values typically corresponded to drawdowns in order of a few meters at pumping yields of
about 1 m3/hr.
The recharge rate of 110 mm/a, taken as uniform throughout Pallisa district, had the total
amount of groundwater recharged being l.956*109*0.11 m3/a = 215.2 million m3/a. The
amount of water demanded by both the rural and urban is 35.7-million m3/a, which
represents 17% of the groundwater currently used. The rest 83% of groundwater is
unutilised.
The hydro-chemical characterisation of waters in the study area show that the groundwater
from the bedrock aquifers of Pallisa district represent regimes where there are
predominantly calcium enrichment, which is typical of lime dosing to neutralize acid
waters and both the regolith and bedrock groundwaters are dominated by the carbonate
ions. This diversity of bedrock types is as a result of weathering of the underlying material.
However, groundwater from many of the boreholes in Pallisa district is generally
acceptable for human and livestock consumption.
Stable isotopes of oxygen and hydrogen has been extensively used to investigate the
rainfall and seasonal patterns of deuterium and 180 content of rainfall in the study area i.e.
Pallisa district. This was inferred from historical observations at Entebbe, approximately
180 km to the south. The average monthly rainfall and 018 clearly demonstrates a
relationship between the amount of rainfall and depletion in 180. As. part of the present study, monitoring of the groundwater resource in terms of yield
aquifers with respect to drawdowns and water quality, consumption at water using
production boreholes and management of these boreholes play important roles that can
never be underestimated as per the recommendations made.
Description
Keywords
Groundwater -- Uganda -- Pallisa, Water resources development, Water-supply, Rural -- Uganda, Dissertation (M.Sc. (Geohydrology))--University of the Free State, 2003