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dc.contributor.advisorDe Lange, Fanie
dc.contributor.advisorHay, Rowena
dc.contributor.authorTowers, Luke
dc.date.accessioned2018-08-27T12:04:02Z
dc.date.available2018-08-27T12:04:02Z
dc.date.issued2017-07
dc.identifier.urihttp://hdl.handle.net/11660/9172
dc.description.abstractEnglish: This dissertation investigates three alluvial fans in the Northern Danakil Depression, Ethiopia for potential groundwater supply to a solution mining operation. The presence of groundwater seeps at the toe of the alluvial fans further indicated the potential of the alluvial fans for groundwater exploration and possible abstraction to meet the mine water demand of 30 cubic hectometres (30 hm3) or 30-million cubic meters per annum. Cumulative life of mine demand was determined to be 450.73 hm3. Lithological, structural and hydrostratigraphic investigations revealed that the Precambrian basement rocks of the Dogua Mountains outcrop in the west adjacent to the Bussaba and North Dogua fans, while further south, Cenozoic-Jurassic rocks of the Antalo Limestones and Adigrat sandstones are juxtaposed against the Asabuya fan. Structural mapping showed the presence of north-south trending rift related faults, including the Main Danakil Rift-boundary Fault, which transect and underlie the alluvial fans. These faults were determined to be likely pathways for deep hydrothermal fluids to vertically recharge the fans with hot, hypersaline groundwater and brines. Additionally, east-west trending fault and fracture zones identified in the Cenozoic-Jurassic rocks implied that fresh-brackish water is likely transmitted from the west into the Asabuya fan, but no such through flow is expected into the Bussaba and North Dogua fans due to the Precambrian basement rock acting as an aquitard. This was determined to cause a considerable difference in recharge sources and hydrochemical signatures between Asabuya fan in the south and Bussaba and North Dogua fans in the north. Two automatic weather stations, were established in recharge zones of the Dogua Mountains. The annual average rainfall was determined to be 90 mm/a with an average evaporation rate of 66 mm/a. Moving Loop Electromagnetic geophysical surveys showed low conductivity zones extending through each fan from south to north, confirming the presence of mapped faults transecting the alluvial fans. A maximum fan thickness of 160 m was determined to occur toward the centre of each fan. The low conductivity fault zones and active depositional channels informed the final positions for production and monitoring boreholes. Drilling results of three production boreholes and five monitoring boreholes confirmed the unconfined nature of the aquifer. Drilling depths proved a minimum thickness of 170 m. Analysis of time-drawdown data yielded high Transmissivity values in the order of 11 000-20 000 m2/d. Due to a lack of observable drawdown in the monitoring holes, storage estimations were inconclusive. Water level response during pumping increased confidence in the assumption of recharge by hydrothermal water upwelling via rift related faults. An Aquifer Stress Test (AST) showed minimal drawdown and rapid recovery proving that pump rates of up to 60 l/s were sustainable for up to two years. A total of 603 370.7 m3 was abstracted during the AST. No cross-fan interaction was observed. Hydrochemical analyses indicated boreholes nearer the wadis at the head of the fans had improved water quality compared to boreholes targeting the MDRF. Water quality in the Asabuya fan deteriorated as pumping continued, while the quality of the Bussaba and North Dogua fans both improved, implying different recharge sources to specific fans. Insights gained from works carried out were used to inform a regional conceptual and numerical model. The numerical model assessed the influence of regional boundary conditions on the groundwater flow system as well as the feasibility of three different recharge scenarios to the alluvial fan aquifers. Calibration results indicated that only scenario 3 was feasible to use for predictive simulations. 20 wells spread across the fans were simulated to pump 22 hours/day at 60 l/s for 20 years and further for 40 years. Results showed an average drawdown of 5.5 m in the alluvial fans and that the mine water demand could be met in terms of quantity. Quality considerations however, were not incorporated into the model results and outcomes. Resource estimation determined that with a Sy value of 0.2, the life of mine demand could be met for only 18 years at which time 96% of water in storage, without recharge contributions, would be depleted from the aquifer.en_ZA
dc.description.abstractAfrikaans: Hierdie verhandeling ondersoek drie alluviale waaiers in die Noordelike Danakil Depressie, Ethiopië vir moontlike grondwatertoevoer na 'n oplossing-mynbouoperasie. Die teenwoordigheid van grondwater syfering aan die toon van die alluviale waaiers dui verder op die potensiaal van die alluviale waaiers vir grondwater eksplorasie en moontlike abstraksie om die mynwater aanvraag van 30 hm3/jaar te verskaf. Lithologiese, strukturele en hidrostratigrafiese ondersoeke het getoon dat die Prekambriese keldergesteentes van die Dogua-berge teenaan die westelike grens van die Bussaba- en Noord-Dogua waaiers staan, terwyl die suidelike Cenozoic-Jurassicgesteentes van die Antalo-kalkstene en Adigrat-sandstene teenaan die Asabuya-waaier staan. Strukturele kartering het die teenwoordigheid van noord-suid-neiging verskywings, insluitend die Hoof Danakil-kloofgrensverskywing, getoon, wat die alluviale waaiers onderliggend maak. Hierdie verskywings was bepaalend om waarskynlik vloei paaie vir diep hidrotermiese vloeistowwe te wees om die waaiers vertikaal te laai met warm, hipersaliene grondwater en pekelwater. Daarbenewens het oos-westelike verskywings- en breukgebiede wat in die Cenozoic-Jurassic-gesteentes geïdentifiseer is, geïmpliseer dat vars brakwater waarskynlik van die weste na die Asabuya waaier oorgedra word, maar daar word nie verwag dat hierdie vars brakwater in die Bussaba en Noord Dogua waaiers in sal vloei nie omdat die keldersteen nie as ‘n akwifer dien nie. Dit was bepaalend om 'n aansienlike verskil in herlaaibronne en hidrochemiese handtekeninge tussen Asabuya waaier in die suide en Bussaba en Noord Doguawaaiers in die noorde te veroorsaak. Twee outomatiese weerstasies, is in herlaaissones van die Dogua-berge gevestig. Die jaarlikse gemiddelde reënval is vasgestel op 90 mm/jaar met 'n gemiddelde verdampingstempo van 66 mm/jaar. Beweginde Lus Elektromagnetiese geofisiese opnames het lae geleidingsvermoë sones wat deur elke waaier van suid na noord voorkom geidentifiseer en die teenwoordigheid van onderliggende gekarteerde verskywings bevestig. Maksimum waaierdikte van 160 m is bepaal. Die lae geleidingsvermoë sones en aktiewe deposisionelekanale het die finale posisies vir produksie en moniterings boorgate ingelig. Boorresultate van drie produksie boorgate en vyf moniterings boorgate het die onbeperkte aard van die akwifer bevestig. Boordieptes het 'n minimum dikte van 170 m bepaal. 'n Akwifer Spanning Toets (AST) het getoon dat daar ‘n minimale mate van vermindering en ‘n vinnige herstel van watervlakke was. Dit toon aan dat pompkoers van 60 l/s in die produksie boorgate volhoubaar is. 'n Totaal van 603 370,7 m3 is gedurende die AST uit gepomp. Ontleding van mate van vermindering en tyd data het hoë Transmissiwiteitswaardes in die orde van 11000- 20000 m2/d opgelewer. Weens 'n gebrek aan waarneembare mate van vermindering in die moniteringsgate was opbergingsberamings onbevredigend. Watervlak reaksie tydens pomp afskakeling gee verhoogde vertroue in die aanname van groundwater herlaaing deur hidrotermiese water wat deur middel van verskywings vloei. Hidrochemiese ontledings dui op dat boorgate nader aan die wadis aan die hoof van die waaiers beter waterkwaliteit het in vergelyking met boorgate nader aan die Hoof Danakilkloofgrensverskywing. Waterkwaliteit in die Asabuya-waaier het agteruitgegaan, terwyl die pompe gehardloop het terwyl daai van die Bussaba en Noord Dogua-waaiers albei verbeter het, wat verskillende herlaaibronne aan spesifieke waaiers impliseer. Insigte verkry uit werke uitgevoer is gebruik om 'n konseptuele en numeriese model in te lig. Die numeriese model het die invloed van streeksgrenstoestande op die grondwatervloeistelsel beoordeel, sowel as die uitvoerbaarheid van drie verskillende herlaai-scenarios aan die alluviale waaier akwifers. Kalibrasie resultate het aangedui dat slegs scenario 3 moontlik was vir voorspellende simulasies. 20 boorgate versprei oor die waaiers is gesimuleer om 22 uur per dag by 60 l/s vir 20 jaar en verder vir 40 jaar te pomp. Resultate het 'n gemiddelde mate van vermindering van 5.5 m in die alluviale waaiers getoon en dat daar in terme van hoeveelheid genoeg water aan die myn verskaf kan word. Kwaliteit oorwegings is egter nie opgeneem in die modelresultate en uitkomste nie. Waterbron bepalings toon aan dat met 'n konserwatiewe effektiewe porositeit van 0.2 kan 96% van die myn se water benodiging verskaf word. Binne 18 jaar sal daar niks meer water beskikbaar wees nie in die akwifer. Saam oppervlak waters is dit voldoende om die hoeveelheid water aan die myn te bevredig, maar moontlike gehaltebeperkings bly nog ‘n probleem.en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectGroundwater resourcesen_ZA
dc.subjectPotash miningen_ZA
dc.subjectAquiferen_ZA
dc.subjectAlluvial aquifersen_ZA
dc.subjectHydrogeological systemen_ZA
dc.subjectDissertation (M.Sc. (Institute for Groundwater Studies))--University of the Free State, 2017en_ZA
dc.titleWater resources evaluation in the danakil basil, Ethiopia: groundwater supply for potash solution miningen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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