Hashweh, Layla: Modeling of Ewaso Narok floodplain : a study of the hydrochemistry and hydrogeology in a data scarce environment. - Bonn, 2023. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-69986
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-69986,
author = {{Layla Hashweh}},
title = {Modeling of Ewaso Narok floodplain : a study of the hydrochemistry and hydrogeology in a data scarce environment},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2023,
month = mar,

note = {The Ewaso Narok wetland, a floodplain intensively used for grazing, drinking, and agriculture, is part of Kenya’s largest drainage basin. This study lies within the water and food security scope, in affiliation with the ‘GlobE project’ of reconciling future food production with environmental protection. The primary objective is to quantitatively evaluate the surface water-groundwater interactions in the Ewaso Narok wetland in terms of water recharge/discharge and water flux. This is done by developing a comprehensive interdisciplinary approach to understanding the aquifer’s structure, water dynamics, and water composition and modeling this scarce data wetland.
The field data were collected using surveys, water, soil, and rock measurements. It was processed and analyzed while combined with secondary data. The survey results show that people rely on the wetland for most of their daily livelihoods, including drinking. However, there is a lack of responsibility and awareness of the wetland’s pollution and well-being, seen in the direct conscious disposal of fertilizers, manure, and plastic containers in the Ewaso Narok wetland. The survey further provided potential input points of water and pollution into the wetland for sampling and then modeling the Ewaso Narok wetland.
The field and laboratory results show that the dominant process controlling groundwater chemistry is silicate weathering expressed in low electric conductivity and high content of HCO3- and SiO2, with the topsoil layers experiencing more weathering. Two aquifer systems exist. The regional confined aquifer is recharged from high altitudes reaching the Ewaso Narok wetland by the lateral flow of groundwater and the local semi-confined aquifer that occurs in the weathered basement rock system. Recharge is small in the Ewaso Narok area and occurs by direct infiltration of rainwater along with fractures within the rocks and in the weathered zones of the metamorphic rocks and by indirect infiltration of the run-off along the river courses. The surface water is a mixture of rainwater and groundwater. There are perched aquifers underneath both the wetland and the river. Additionally, the weathering profile acts as storage for groundwater. The groundwater is discharged to the ephemeral streams, the main river, and the wetland. In addition, flash floods contribute to the water balance of this wetland. These results provide the hydrogeological and hydrochemical database for characterizing the Ewaso Narok wetland. They further set a conceptual framework building a base for the mathematical model to run. As data and information regarding the physical hydrogeology of the basin and the wetland are rare, the Mixing Cell Model (MCM) is used to identify and quantify the active sources of recharge and their contribution to the total water balance at the wetland and catchment scale.
The results of the statistical cluster analysis and the subsequent single and multi-cell modeling, indicate clear hydraulic connectivity between the wetland’s surface water and groundwater, with 17 to 84 % of the inflow originating from groundwater. The groundwater feeding the wetland is evident upstream of the wetland and even more vivid downstream. The downstream part of the Ewaso Narok wetland is the main contributor to the total amount of water in the whole system. However, the middle part of the wetland does not show any contribution from groundwater. In this middle part, the impermeable clay layer separates the wetland from groundwater, and faults and fractures act as hydraulic barriers. The river courses show advanced weathering profiles, allowing groundwater discharge and thus suggesting permeability. The model results show a high negative error indicating one or several additional missing sources contributing to the calculated mass balance. Regardless, the MCM provides meaningful results with the limited information available. These results are used to develop a conceptualized model summarizing the Ewaso Narok aquifer system. The study also compares the water quality to human drinking standards and irrigation guidelines.
Ewaso Narok wetland is the backbone of people’s local livelihoods; however, it is a diminishing resource. More attention is needed for it to maintain this role. A holistic approach is recommended to manage the basin and the Ewaso Narok wetland in particular. The study’s unique results of quantitatively assessing the groundwater and surface-water interactions, despite scarce hydrological information, can be used to develop such an approach. They clearly demonstrate the need for management approaches that consider both surface water and groundwater alike to ensure the wetland’s long-term sustainability of the wetland.},

url = {https://hdl.handle.net/20.500.11811/10672}

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