Hydrogeological System Analysis of the Abaya Chamo Lakes Basin, With Special Emphasis on Using Chemical and Isotopic Signatures In the Characterization of the System
| dc.contributor.advisor | Ayenew, Tenalem (Professor) | |
| dc.contributor.author | Asha, Abrham | |
| dc.date.accessioned | 2020-10-30T07:47:08Z | |
| dc.date.accessioned | 2023-11-09T14:11:12Z | |
| dc.date.available | 2020-10-30T07:47:08Z | |
| dc.date.available | 2023-11-09T14:11:12Z | |
| dc.date.issued | 2018-06-05 | |
| dc.description.abstract | Hydrochemistry and stable isotopes have been used as powerful tool in the analysis of the hydrogeological system analysis of the Abaya Chamo Lakes basin. This large basin (18,100km2) is situated in the complex volcano-tectonic terrain of the southern main Ethiopian rift with three distinct physiographic sectors where major surface drainage converges towards the Lakes. The source and mechanisms of the recharge, the configuration and relations of tectonic structures controlling the occurrence, composition, and flow of the groundwater systems have been investigated and conceptualized in the study area. The stronger summer rainfall contributing half of annual amount is depleted (ŏ18O‰=-4.2 to -0.39) having altitude effect Ő18O =-0.2‰ per 100m (depletion) and pseudo altitude effects of δ18O = 0.12‰ per 100m (enrichment). Whereas, slightly enriched (ŏ18O‰=-2.6 to -0.01) Spring rainfall contributes about 35% of the annual showed an altitude effect about 0.1‰ per 100m (enrichment) and pseudo-altitude enrichment rate of 0.15‰ per 100m. Direct recharge form infiltration of rainfall is the dominant source for groundwaters in all River basins. Combined with the sets of tectonic systems, the hydrostratigraphic units determined the mechanism of the recharge, groundwater occurrence, distribution, flow dynamics, mixing of the groundwaters, the composition and hydrogeochemical processes. The groundwater head is deeper in the highlands and escarpments, shallower in the rift floor, and complex where inter-basin transfer and faults control the flow. The hydraulic properties of volcanic rocks increase from the highlands towards the rift floor (T=50 to more than 800m2/d and K=1 to 15m/day) in the well depth range of 60 to 400mbgl. The discharge of the spring flow increases from the highlands towards the rift floor (0.036 to 260lit/Sec). Water type maps, piper plot and dendrogram clustering diagram revealed the occurrence of four main groups and eleven subgroups of groundwaters. The highlands Group I (G1) Ca2+and HCO3- rich and the escarpment Group II (G2) Mg2+and HCO3- rich waters are dilute with average EC= 324 μS/cm and 237 μS/cm respectively. These hydrogeological systems are unconfined to semi-v confined/ and confined having depleted (ὁ18O‰= -4.2 to -1.4, and d-excess ‰ = 10.6 to 25.1), groundwaters , but in places, where there is evaporation, there occur relative enrichment. The rift floor Group III (G3) Na+ and HCO3- rich hot springs and wells are located along active rift faults and are relatively more mineralized (average EC=467 μS/cm) compared to Group I and II. The fourth highly evolved outlier Group IV (G4) water Na-Cl/HCO3- type volcanic water is represented by one thermal spring with EC (5450μS/cm) and at a temperature of 960c. The groundwaters evolution showed that G1→G2→G3→ G4 along the groundwater flow direction as indicated in PC1 and the reverse in PC2. But, in places, the existence of deep escarpment faults blocked the consistent groundwater evolution. This has clearly revealed the NNE-SSW inland alignment of NaHCO3 rich and less d-excess groundwater across the Gidabo basin towards Dilla. Rift floor hot springs in recent volcanics, Pleistocene basalt, and rift sediments are interconnected and meteoric in origin. But, deeper depleted (ὁ18O‰= -6.82 to -5.07) rift hydrogeological systems in sand and gravel aquifers (below150mbgl) of old waters sources and highly enriched (ὁ18O ‰ = 5.04 to 6.54) waters from evaporated sources (Lakes) showed no hydraulic connection with other aquifers. These groups of waters are formed mainly due to silicate weathering, ion exchange and evaporation hydrogeochemical processes occurred in the hydrogeological systems. Based on the findings, the hydrogeological systems are conceptualized including into: highlands (dilute, Ca–HCO3 type, EC=324 μS/cm, ŏ18O‰ ≥ -4.2), escarpment (dilute, Mg–HCO3 type, EC=237 μS/cm, mixed waters), upper rift floor (Na-HCO3 and Na-Cl type, EC= up to 5450μS/cm, meteoric origin), and deeper rift floor (Na-HCO3 type, EC= 341 to 1179μS/cm,ŏ18O‰= -6.82 to -5.07 , non-recent meteoric origin). The study addressed major objectives and ends with recommendation of some instrumental issues to upgrade the research in future. | en_US |
| dc.identifier.uri | http://10.90.10.223:4000/handle/123456789/22974 | |
| dc.language.iso | en | en_US |
| dc.publisher | Addis Ababa University | en_US |
| dc.subject | Abaya Chamo Lakes Basin | en_US |
| dc.subject | Aquifers | en_US |
| dc.subject | Groundwater Recharge | en_US |
| dc.subject | Hydrogeological Systems | en_US |
| dc.subject | Hydrochemistry | en_US |
| dc.subject | Hydrogeochemical Processes | en_US |
| dc.subject | Stable Isotopes | en_US |
| dc.subject | Volcanic Rocks | en_US |
| dc.title | Hydrogeological System Analysis of the Abaya Chamo Lakes Basin, With Special Emphasis on Using Chemical and Isotopic Signatures In the Characterization of the System | en_US |
| dc.type | Thesis | en_US |