Estimation of groundwater recharge in Makutupora basin located in a semi-arid region in central Tanzania using soil moisture balance (SMB) and chloride mass balance (CMB) techniques.
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Date
2022-02
Journal Title
Journal ISSN
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Publisher
Geological Society of India
Abstract
The objective of this study is to assess the groundwater recharge
in the Makutupora basin, Central Tanzania using the soil moisture
balance (SMB) and chloride mass balance (CMB) methods. The
SMB method considered the estimation of both evapotranspiration
in CROPWAT 8.0 software and surface runoff by the curve number
(CN) method. The CN of the basin was determined based on
hydrological soil group (HSG), antecedent moisture condition
(AMC) and land use type using Arc GIS 10.2. Distributed land-
use maps, slope and soil texture maps, daily climatological data
(e.g., precipitation, temperature, wind speed, etc.), chloride
concentration in rainfall and groundwater are the basic data used
in this study. Input data were prepared in the form of digital maps
using GIS and remote sensing tools and finally excel models were
created to compute recharge using a set of given conditions. The
results indicate that the average chloride concentration measured
in the groundwater samples of the study area is 282.88 mg/L; much
higher than the average concentration in rainwater samples which
is 3.47mg/L while the average potential evapotranspiration is
2280 mm/year with an average rainfall of 680mm/year. Runoff
computed using the CN method is ranging from 7.6-246mm/year
or 0.68-22%. The final recharge from SMB is ranging from
0.025-117.86mm/year or 0.006-10% of annual rainfall equivalent
to an average annual volume of 41.58Mm 3 while recharge from
CMB ranges from 2.57-44.6mm/year or 0.38-6.56% of annual
rainfall equivalent to an average annual volume of 23.85Mm 3 . The
results show that CMB underestimated the recharge compared to
the SMB method. The reason for this is thought to be caused by
the high chloride concentration analysed in groundwater compared
to rainfall samples which may be caused by increased chloride
concentration as water passes through the rock formations
(unsaturated zone) to the saturated zone. Further lack of
atmospheric chloride deposition data may be another contributing
factor.
Description
Journal Article
Keywords
Groundwater, small-scale irrigation, Makutupora, climate variability, Soil moisture