University of Twente Student Theses


Lake aquifer interaction north east of lake Naivasha, Kenya

Bezabih, Ahma Gessesse (2011) Lake aquifer interaction north east of lake Naivasha, Kenya.

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Abstract:The study of water resources in the Naivasha basin is important for domestic, agricultural and geothermal issues, and it depends on good understanding of the relationship between the lake and the groundwater system. The purpose of this study was to investigate the interaction between the lake and the aquifers to its northeast. To understand the interaction processes different methodological approaches have been followed. These approaches include geophysical studies, isotopic data analysis, and reassessment of geological and hydrogeological set up of the basin. And finally using the PMPATH modelling the flow paths and arrival times of the lake water to the wellfield area has been predicted. Stable isotopes of Hydrogen ( 2H) and Oxygen (18O) have been used to investigate the extent of mixing of waters and the flow direction of the groundwater system in the study area. Isotopic analysis of the water samples collected from boreholes around the lake area and the wellfield showed the following results. The shallow boreholes (17 to 37m deep) have similar isotopic composition to the lake water. Based on mixing ratio calculations percentages of the lake water in these wells was estimated up to 77 %. The main source of recharge for these wells is the lake water. The isotopic plots of the deep wells lie very close to the Global Meteoric water Line (GMWL) and they are depleted in the heavy isotopes. With the exception of one, all the deep wells are located around the well field (Panda and Delamere farms). These wells are predominantly recharged by precipitation from the eastern rift flank. Only smaller percentages of the lake water are traced here, indicating that the lake is not a major contributor of recharge to the wells. According to the current results there is no significant difference in the percentages of the lake water between 2004 and now; which are 16% and 14% respectively. The boreholes at Marula and Three Point Farms have similar isotopic compositions to that of River Malewa. Isotopic signature of the lake water is generally getting weaker further from the lake towards the well field, which is located northeast of the lake. Based on the 2D Resistivity Imaging surveys, formation resistivity ranges of the main aquifer materials is found out to be between 12 – 335 Ohm.m. No prominent geological structures are observed on the sedimentary environment of the basin but towards the eastern margin of the study area. The hydrogeological investigations have demonstrated that the main aquifer units in the Naivasha basin can be divided as sedimentary units and volcanic rocks. The lacustrine deposits are thicker northeast of the lake, where their thickness could reach up to 120m. The water levels are shallower near the lake but gets deeper towards the wellfield. Pumping test results of previous works showed that the transmissivity values of the lake bed sediments in Panda flowers ranges between 460 to 1150 m2/day. However the aquifer units are highly heterogeneous throughout the basin. And finally using the Advective Transport model, PMPATH the flow paths and travel times of the lake water to the wellfield was predicted.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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