Browsing by Author "Ayenewa, Tenalem"

Now showing 1 - 2 of 2

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.
(Geological Society of India, 2022-02) Kisikia, Clarance Paul; Ayenewa, Tenalem; Mjemah, Ibrahim Chikira
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.
Geospatial application on mapping groundwater recharge zones in Makutupora basin, Tanzania.
(Elsevier Ltd, 2022-09) Kisikia, Clarance Paul; Bekelea, Tilaye Worku; Ayenewa, Tenalem; Mjemah, Ibrahimu Chikira
Management of groundwater systems is indispensable to countries that depend on groundwater as the primary source of community water supply (e.g. Dodoma, Tanzania). Urbanization and industrialization lead to groundwater over-pumping and reduced recharge zones in the basin. This study used Remote Sensing and geo- spatial datasets to determine the groundwater recharge zones (GWRZ) followed by sensitivity analysis to identify the influence of geologic and hydrologic factors on the variation of the GWRZ in the case of the Makutupora basin, Tanzania. The implementation of weighted overlay analysis aimed to determine the GWRZ using different the- matic maps created from land use land cover (LULC), drainage density, lithology, lineament density, rainfall, slope and soil datasets. The analytical hierarchy process (AHP) and multi-influencing factor (MIF) are the multi- criteria decision analysis (MCDA) implemented to assign weights to the selected influencing factors. Either, the map removal method was implemented for the sensitivity analysis. Pumping wells were overlaid to validate the GWRZ map determined. The overlay of seven thematic maps resulted in the GWRZ map being categorized as good (35.79% for AHP and 21.68% for MIF), moderate (40.98% for AHP and 58.39% for MIF) and poor (23.22% for AHP and 19.95% for MIF). Good recharge potential areas lie in an area characterized by thick forest, high lineament and water bodies around the northwestern and central-eastern side of the basin. Validation of GWRZ indicated that 33.33% for AHP and 30% for MIF are in good GWRZ, 41.6% for AHP and 28% for MIF are in moderate GWRZ and 25% for AHP and 42% for MIF are in poor GWRZ. The sensitivity analysis revealed the high effect of GWRZ on the removal of the LULC, lithology and lineament thematic layer in both AHP and MIF- generated GWRZ maps. This implies that the expansion of settlements is not considering recharge zone protection. Lineaments are also a very important factor governing groundwater recharge which needs to be protected. The result displays that urbanization dramatically reduced the potential area for groundwater recharge. Protecting the potential recharge zone from any activity that reduces the recharge is vital for the sustainability of groundwater.