Integrated Hydrological and Hydrogeological System Analysis of the Lake Tana Basin, Northwestern Ethiopia
| dc.contributor.advisor | Ayenew, Tenalem (Professor) | |
| dc.contributor.author | Mamo, Sileshi | |
| dc.date.accessioned | 2018-07-10T13:21:16Z | |
| dc.date.accessioned | 2023-11-09T14:09:28Z | |
| dc.date.available | 2018-07-10T13:21:16Z | |
| dc.date.available | 2023-11-09T14:09:28Z | |
| dc.date.issued | 2015-06 | |
| dc.description.abstract | Integrated hydrological, hydrogeological, hydrogeochemical and isotopes hydrological studies have been done in Lake Tana basin to understand the nature of aquifers and aquifer systems and their interactions and groundwater flow regime, to reveal and estimate the basin groundwater outflow and decipher the out flowing area, estimate groundwater inflow to and leakage rate from the Tana Lake and trace leakage area, determine groundwater and surface waters interaction, evaluate the basin groundwater recharge rate, and determine the origin of local high groundwater salinity. The basin is characterized by different volcanic rocks overlain by sediments. The lithologic units include Quaternary lacustrine sediments, basalt and rhyolite, Tertiary flood basalts: Lower, Middle and Upper basalts, and Mio-Pliocene Shield volcanic rocks: Sekela Basalt, Degoma Basalt, Guna Tuff, Guna Basalt and trachyte flows and plugs. These lithostratigraphic units have been grouped into hydrostratigraphic aquifers and confining units. The aquifers are ranked from low to moderate to high productivity. Productivity increases when the whole multi layers volcanic aquifers are intersected in fractured area. The results of the study revealed three aquifer systems, which are termed as the upper, intermediate and lower aquifer systems. The Upper Aquifer System has set of independent unconfined and (semi)confined aquifers in the northern, eastern, southwestern and western areas, and has isolated shallow and deep groundwater flow systems in the area that all flow toward the Tana Lake. The shallow unconfined aquifer interacts with and often feeds the rivers and the lake, while the deep groundwater in this system underflows out of the basin to Tis Abay area. The intermediate and lower aquifer systems have been ascertained to be found in the eastern area below the Upper Aquifer System and are under confined condition, and have regional outflow to Tis Abay area. Recharge rates of 195.6, 284.0 and 285.4 mm/year have been estimated based on baseflow analysis, chloride mass balance (CMB) and soil water balance (SWB) methods, respectively. Baseflow separation method shows shallow groundwater recharge that returns to streams. The recharge estimates from CMB and SWB are nearly similar and the average of the two (284.7 mm/year) can be taken as the mean basin recharge rate. The difference between the basin recharge and the baseflow to streams (89.1 mm year-1 or 31.3% of the recharge) contributes to deep groundwater recharge and groundwater discharge to the Lake Tana. Basin water balance evaluation has given inter basin groundwater outflow of 3333.5 hm3/year. Hydrogeochemistry and isotopic data suggest that the basin groundwater outflow is mainly to the adjacent low lying Tis Abay area. Tana Lake balance study has also given leakage outflow of 954.8 hm3/year, which mixes with groundwater mainly in the Beles basin and to certain extent in the Tis Abay area. Groundwater inflow directly to the lake is found to be not significant. Origin of groundwater salinity in the volcanic area is mainly silicate hydrolysis. However, in lacustrine sediments aquifer, pockets of ground waters attain relatively high salinity (brackish) due to dissolution of evaporites and cation exchange. Key words: hydrogeological system analysis, groundwater recharge, inter basin groundwater outflow, leakage, Lake Tana, Ethiopia | en_US |
| dc.identifier.uri | http://10.90.10.223:4000/handle/123456789/7725 | |
| dc.language.iso | en | en_US |
| dc.publisher | Addis Ababa Universty | en_US |
| dc.subject | Hydrogeological system analysis | en_US |
| dc.subject | Groundwater recharge | en_US |
| dc.subject | Inter basin groundwater outflow | en_US |
| dc.subject | Leakage | en_US |
| dc.subject | Lake Tana | en_US |
| dc.subject | Ethiopia | en_US |
| dc.title | Integrated Hydrological and Hydrogeological System Analysis of the Lake Tana Basin, Northwestern Ethiopia | en_US |
| dc.type | Thesis | en_US |