Origin of High Groundwater Salinity in the Omo Delta and its Surroundings (Southwestern Ethiopia) Hydrochemistry and Isotope Approaches
| dc.contributor.advisor | Kebede, Seifu (PhD) | |
| dc.contributor.advisor | Asrat, Asfawossen (Professor) | |
| dc.contributor.author | Tadesse, Abebayehu | |
| dc.date.accessioned | 2021-08-05T08:01:50Z | |
| dc.date.accessioned | 2023-11-09T14:12:52Z | |
| dc.date.available | 2021-08-05T08:01:50Z | |
| dc.date.available | 2023-11-09T14:12:52Z | |
| dc.date.issued | 2020-09-23 | |
| dc.description.abstract | The groundwater of the Omo Delta is characterized by the presence of fresh and saline groundwater side by side and the success of having fresh water is well below 50%. Therefore, most wells are abandoned due to elevated salt content. However, research on the origin of groundwater salinity and salinization processes, detail hydrochemical and isotopic composition of the Delta groundwater are lacking. The main objective of this work is to characterize the source of salinity and mechanism(s) of salinization in the Omo Delta (Southern Ethiopia) groundwater giving special emphasis on characterizing various morphological units and depositional environments recognized in the area and their implication on groundwater salinity. To achieve the objectives converging pieces of evidences from the conventional hydrogeological investigation, litho-hydrostratigraphic relationships, water chemistry, and isotope hydrology were used to elucidate the cause of groundwater salinity. The geochemical dataset and isotope were analyzed using different but complementary, approaches that allowed for insights into the process of salinization of groundwater in the study area. The correlation matrices of major anions, cations, and physical parameters of water indicate that elements chloride, sodium, fluoride, sulphate, and bicarbonates contributed from mineralization processes. The dominant effects of rainfall, rock weathering, and evaporation play a major role in the geochemical evolution of groundwater. Rock weathering was the main mechanism controlling the chemical compositions of the Hammer basement groundwater whereas; evaporation–crystallization is in the Delta aquifer groundwater system. The saturation index of anhydrite, aragonite, calcite, dolomite, gypsum, and halite shows that the groundwater in the study area was below the saturation with anhydrite, gypsum, and halite, indicating that these minerals are anticipated to dissolve. Moreover, groundwater samples were saturated to over-saturated with aragonite, calcite, and dolomite, implying that the three major carbonate minerals may have affected the chemical composition of groundwater in the study area. The variation of the hydraulic parameters at different locations and layers have been resulted from aquifer materials formed under different depositional environment. These deposits represent different aggradations and degradation phases that were usually accompanied by lake level changes. Groundwater movement and recharge are highly dependent on geomorphic features and depositional environments. Groundwater that is close to surface water sources ii (River and Wadies) is fresh relative to other farther away from it, in the alluvial fan geomorphic feature, the fan apex is characterized by fresh groundwater compared to fan toe, which is more saline. The thickness of clay layers significantly affects the salinity of groundwater as it acts as the adsorption media and filtering membrane for groundwater in the Delta. The isotopic composition of most groundwater samples from sediment plot slightly far from the Global meteoric water line (GMWL) compared to the waters from the Hammer basement indicating that evaporative fractionation before recharge the sediments. The increase in groundwater salinity due to evaporation has resulted in a simultaneous isotopic enrichment. Both hydrochemical and isotope techniques indicate the dominance of local recharge and flow systems. The radon-222 concentration in groundwater samples showed a very wide range from 58.7 to 982.5Bq/m3 compared to the River and Lake Water samples that are range from 18.65 to 105.2Bq/m3 and 10.49 to 10.85Bq/m3 respectively. The highest concentration was found in the samples that were collected from wells close to the Omo River. From converging evidence of geology, hydrogeology, hydrochemistry, and stable isotopes of water, three processes are responsible for the salinization of groundwaters in Omo Delta: salinity originated from water-rock interaction, evaporation at or near the surface, and clay membrane filtration. The results of this study will also be useful to the development of a sound management plan for water resources and the direction of further research in the study area. | en_US |
| dc.identifier.uri | http://10.90.10.223:4000/handle/123456789/27605 | |
| dc.language.iso | en | en_US |
| dc.publisher | Addis Ababa University | en_US |
| dc.subject | Geomorphology | en_US |
| dc.subject | Hydrochemistry | en_US |
| dc.subject | Isotope | en_US |
| dc.subject | Omo Delta | en_US |
| dc.subject | Radon-222 | en_US |
| dc.subject | and Salinity | en_US |
| dc.title | Origin of High Groundwater Salinity in the Omo Delta and its Surroundings (Southwestern Ethiopia) Hydrochemistry and Isotope Approaches | en_US |
| dc.type | Thesis | en_US |