Decant calculations and groundwater: surface water interaction in an opencast coal mining environment
| dc.contributor.advisor | Dennis, I. | |
| dc.contributor.author | Du Plessis, Johannes Lodewiekus | |
| dc.date.accessioned | 2015-09-08T08:47:44Z | |
| dc.date.available | 2015-09-08T08:47:44Z | |
| dc.date.issued | 2010-11 | |
| dc.description.abstract | English: Acid mine drainage is by far the most significant long term groundwater quality impact associated with both opencast and underground coal mining, in both a local and international context. The modern day geohydrologist has access to numerous tools, which can be used to determine important decant issues – issues ranging from when decanting will begin to occur, and the volumes of water that are expected to decant. The continuous development and improvement of numerical groundwater flow models is steadily leading to an increasing dependence on them. The main aim of the thesis was to determine whether there exists any correlation between modern day numerical groundwater flow models and analytical calculations, and the presentation of a toolbox of tools that may be used for decant related issues. The following conclusions were drawn after numerous numerical and analytical scenarios and statistical correlations were performed: • Given the amount of uncertainty regarding aquifer heterogeneity, there do exist a good correlation between the numerical and analytical groundwater decant volume estimations, • An increase in the effective porosity of the backfilled opencast pits cause an increase in the time-to-decant, as more water is required to fill the pits to their decant elevations, • An increase in the effective aquifer recharge cause an increase in the decant volumes and a decrease in the time-to-decant, because more water is available to fill the pits to their decant elevations, • The effective aquifer recharge is a very sensitive parameter (more so than specific yield, storage coefficient, and transmissivity), as significant decreases in the time-to-decant were simulated with an increase in the aquifer recharge, as were significant increases in decant volumes simulated with an increase in recharge, • The volumes of groundwater decant are more sensitive to variations in the transmissivity of the surrounding aquifer/s compared to the transmissivity of the backfilled opencast pits, • During the numerous flow model scenarios it was found that the groundwater contribution to pit water is far less compared to the recharge component. The above conclusions prove that there are still applications for analytical calculations in modern day geohydrology, despite the continuous development of numerical groundwater flow models. Based on experience in similar coal mining operations within the Mpumalanga coal fields, the results of both the analytical decant volume and time-to-decant estimations correspond well with actual figures. One must however understand and master the various equations and keep in mind that an aquifer is a highly heterogeneous system. The results of both numerical groundwater flow model simulations and analytical calculations are only as good as the understanding of the geohydrological environment and the data they are based on. | en_ZA |
| dc.description.abstract | Afrikaans: Die dreinering van suur myn water is by verre die belangrikste lang termyn grondwater kwaliteit impak wat geassosieer word met beide oopgroef en ondergrond steenkool myne – beide op nasionale en internasionale vlakke. Die moderne geohidroloog het toegang tot verskeie metodes om menige grondwater oorloop probleme op te los. Die belangrikste probleme sluit in die verwagte volumes van grondwater oorloop, asook die tyd wat dit gaan neem vir die myn om oor te loop. Die aanhoudende ontwikkeling en verbetering van numeriese grondwater modelle is geleidelik besig om te lei tot `n totale afhanklikheid van numeriese modelle. Die hoof doel van die tesis is om te bepaal of daar enige korrelasie is tussen numeriese en analitiese metodes, asook die akwifeer toestande waarin die metodes gebruik kan word. Die resultate van `n aantal numeriese en analitiese modelle het gelei tot die volgende gevolgtrekkings: • Tenspyte van die hoogs heterogene natuur van `n akwifeer sisteem, bestaan daar wel `n goeie korrelasie tussen numeriese en analitiese oorloop-volume berekeninge, • `n Toename in die porositeit van die gerehabiliteerde oopgroewe lei tot `n toename in die tyd wat dit neem vir die groewe om oor te loop, aangesien meer water nou benodig word om die groewe te vul, • `n Toename in akwifeer aanvulling lei tot `n toename in oorloop volumes asook `n afname in die tyd wat dit neem vir die groewe om oor te loop, aangesien meer water beskikbaar is om die groewe te vul, • Akwifeer aanvulling is die sensitiefste parameter, aangesien `n beduidende afname in oorloop tyd gesimuleer was tydens `n toename in aanvulling, terwyl `n beduidende toename in oorloop volumes ook gesimuleer was tydens `n toename in aanvulling, • Oorloop volumes word eerder deur die transmissiviteit van die omliggende akwifeer beinvloed as deur die transmissiviteit van die groewe self, • Die numeriese model simulasies het getoon dat die grondwater bydrae tot groef water veel minder is as die akwifeer aanvulling komponent. Die bogenoemde gevolgtrekkings bewys dat analitiese metodes steeds gebruik kan word om akkurate resultate te lewer, tenspyte van die aanhoudende verbetering en ontwikkeling van numeriese modelle. Gebasseer op ondervinding in soortgelyke steenkool myne in die Mpumalanga steenkool velde, die resultate van die analitiese oorloop volumes en tyd van oorloop berekeninge korreleer met bevestigde waardes. `n Persoon moet egter die vergelykings en berekeninge verstaan en baas raak, en in ag neem dat die akwifeer sisteem hoogs heterogeen is. Die resultate van die analitiese berekeninge is dus net so goed as wat `n persoon se begrip van die akwifeer sisteem is en die data waarop dit gebaseer is. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/1187 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Groundwater -- South Africa -- Delmas | en_ZA |
| dc.subject | Groundwater -- South Africa -- Delmas -- Mathematical models | en_ZA |
| dc.subject | Acid mine drainage -- South Africa -- Delmas | en_ZA |
| dc.subject | Hydrogeology | en_ZA |
| dc.subject | Coal mines and mining -- South Africa -- Delmas | en_ZA |
| dc.subject | Correlation | en_ZA |
| dc.subject | Dissertation (M.Sc. (Institute for Groundwater Studies))--University of the Free State, 2010 | en_ZA |
| dc.subject | Analytical calculations | en_ZA |
| dc.subject | Decant volumes | en_ZA |
| dc.subject | Numerical groundwater flow model | en_ZA |
| dc.subject | Time-to-decant | en_ZA |
| dc.title | Decant calculations and groundwater: surface water interaction in an opencast coal mining environment | en_ZA |
| dc.type | Dissertation | en_ZA |