Show simple item record

dc.contributor.advisorVan Tonder, G. J.
dc.contributor.authorSteyl, Gideon
dc.date.accessioned2015-11-24T07:48:08Z
dc.date.available2015-11-24T07:48:08Z
dc.date.copyright2011-11
dc.date.issued2011-11
dc.date.submitted2011-11
dc.identifier.urihttp://hdl.handle.net/11660/1771
dc.description.abstractEnglish: The study describes the effect of calculating a generalised mean transmissivity or hydraulic conductivity value for a region or aquifer system as it pertains to South Africa. Resource determination of an area is usually driven by the determination of the bulk flow parameters, such as hydraulic conductivity and storativity values. At this stage a decision is usually made on the basis of either maintaining the area under natural conditions (no pumping), or an abstraction (pumping) scenario is envisaged. In both instances water levels, hydraulic testing and distribution of the water resources (aquifer) are required. Since it is not possible to evaluate the total area for these parameters certain assumptions have to be made such as that an average bulk flow parameter for an area can be determined. In wide-ranging situations a simple average of observation points is assumed to be sufficient. A systematic research approach was followed in which a three-step process was used to evaluate methods of calculating these mean values. In the first instance a conceptual model approach was used, and all bulk flow parameters were generated by means of matrices to represent the natural system. Three typically employed mean values (arithmetic, geometric and harmonic) were calculated for two different dimensional matrices, i.e., N x N (N = 100 and 1000) with different hydraulic conductivity zones. In addition the relative difference between these hydraulic conductivity zones were steadily increased to mimic observed parameters in the field, i.e. typical hydraulic conductivity of shale (K = 0.01 m/d) versus a fracture zone (K = 100 m/d). In all instances the harmonic mean performed the best and as the number of sample sets were increased, a reduction in mean values were observed. As part of the conceptual model approach, two typically encountered scenarios were investigated, i.e. natural flow and forced gradient conditions. Under these two scenario conditions the harmonic mean performed the best to estimate the actual observed hydraulic conductivity value. Secondly, case studies were presented which highlighted the influence of sample size on observed parameters. Additionally, the effect of the differences between the low and high hydraulic conductivity zones on the calculated mean value as a function of sample size, was also reported. In all of these case studies the harmonic mean was the closest in approximating the observed hydraulic conductivity. It is evident from this section that the number of host rock (formation) hydraulic conductivity values plays a critical part in the mean value calculation since it is general practice in South Africa not to report low yielding borehole hydraulic test values. In the third step, the results were discussed in the context of a more general approach to the problem of calculating a regional mean hydraulic conductivity of transmissivity value. The estimation of representa-tive transmissivity values were discussed as seen from a stochastic modelling perspective as well as from the deterministic point of view. A comparison between main stream groundwater and oil industry specialists were noted in which both groups share the fundamental training but differ on the methodology of determining the observed transmissivity values. The impact of horizontal heterogeneities and different fracture networks was discussed and the influence these features have on the actual transmissivity value obtained, i.e. the influence of internal boundaries on hydraulic test data. Scale effects were also addressed from a regional perspective, with a focus on apparent scaling and the actual regional transmissivity value which should be obtained. The findings of this study are that in essence using geostatistical methods are not advised if regional transmissivity values are required from a South African perspective. The reason behind this statement is that the distribution of transmissivity values in an area does not follow the basic precepts that are required for these methods to work. In general the values are discontinuous in distribution and statistically skewed. Furthermore, the presence of transmissivity areas or points that differ significantly in magnitude, i.e. transmissivity values which differ by more than two orders, can be located within one meter from each other. The explanation of this phenomenon is the presence of dolerite dykes, which create baked-fractured zones with exceptionally large transmissivity values compared to the extremely low transmissivity ranges of the surrounding country rock (shales, mudstone and siltstone). In addition, the lack of data concerning low-yielding or “dry” boreholes is a major source of concern since it influences the calculated mean value to a high degree.en_ZA
dc.description.abstractAfrikaans: Die gebruik van grondwater as ʼn alternatiewe bron van varswater in Suid Afrika is geïdentifiseer as ʼn heel bruikbare opsie. Die bestuur van die hulpbron is stadig maar seker besig om weier impak en erkenning te kry by regeringsinstansies. ʼn Werklike probleem in die ontwikkeling van hierdie hulpbron is die konsepsiuele interaksie tussen oppervlakswater en grondwater. Die beskikbaarheid van ʼn volledige stel data van reënval, vloeivolumes en watervlakke in boorgate het tot gevolg gehad dat opvulling van verlore data benodig word deur die gebruik van neurale netwerke. In hierdie ondersoek is gefokus op die voorspelling van die invloed wat reënval en vloeivolumes in riviere op die omliggende boorgat watervlakke het, dus word neurale netwerke ingespan om beide onvolledige data stelle te voltooi en om voorwaartse skattings te maak van watervlakke in boorgate.In hierdie studie word die berekening van 'n algemene gemiddelde transmissiviteit of hidroliese geleidingswaarde bespreek soos dit onder Suid-Afrikaanse toestande beleef word. Dit word gedoen omdat hulpbronbeplanning grotendeels gedryf word deur massavloeiparameters soos hidroliese geleidings en stoorwaardes. Gewoonlik word daar beplanning gedoen deur na die gemiddelde waardes te kyk en deur 'n besluit uit te voer of daar onttrekking in 'n gebied moet plaasvind, al dan nie. In beide gevalle word watervlakke, pomptoetse en verspreiding van waterbronne benodig. Aangesien net selektiewe datapunte beskikbaar is, moet 'n gemiddelde massavloeiwaarde bereken word en oor die algemeen word net 'n gemiddelde waarde van die datapunte bereken. 'n Sistematiese navorsingsbenadering is gebruik deur 'n driestapproses the volg wat verskillende gemiddelde waardeberekeningsmetodes gebruik om die gemiddelde waarde te bereken. In die eerste geval is 'n konsepsuele model gebruik om massavloeiparameters te skep sodat dit natuurlike toestande naboots. Drie algemene gemiddelde waardes is gebruik, naamlik rekenkundige, geometriese en harmoniese gemiddelde om twee verskillende matriksstelsels te bereken (N × N, N = 100 en 1000) met verskillende hidroliese geleidingsones. Verder is die relatiewe verskil tussen die hidroliese geleidingsones ook ondersoek aangesien dit natuurlike stelsels naboots, naamlik skalie (K = 0.01 m/d) versus fraktuursones (K = 100 m/d). Oor die algemeen het die harmoniese gemiddelde die beste gevaar soos die aantal waarnemingspunte verhoog is. 'n Verder deel van die konsepsuele metode is om die twee algemene stelsels wat in die natuur voorkom, te ondersoek, naamlik natuurlike vloei en onttrekkingstoestande. In beide gevalle het die harmoniese gemiddelde die beste gevaar om die hidroliese geleidingswaarde te bepaal. In die tweede geval is toetsstudies gebruik om die invloed van monsternemingspunte op veranderlikes te bepaal. Verder is die invloed van die verskille tussen die hoë en lae hidroliese geleidingsones as 'n funksie van monsternemingspunte bepaal. Weereens het die harmoniese gemiddelde die beste gevaar, alhoewel dit duidelik was dat die aantal lae hidroliese geleidingswaardes 'n kritiese impak op die gemiddelde waarde het. Verder word dit ook beskou dat lae opbrengs boorgatdata gerapporteer moet word om hierdie verskynsel teen te werk. Estimation of Representative Transmissivities of Heterogeneous Aquifers In die derde stap word die resultate oor die algemeen bespreek en hoe gebiedsgebonde gemiddelde hidroliese geleidingswaardes bereken kan word. Die skatting van verteenwoordigende transmissiwiteits-waardes word bespreek van 'n stochastiese sowel as 'n deterministiese benadering. 'n Vergelyking tussen grondwater en olie-industriegebruike word ook uitgelig, aangesien dieselfde onderliggende metodes gebruik word maar verskillende resultate verkry word. Die invloed van horisontale heterogeniteite en fraktuurnetwerke is ook bespreek aangesien dit die hidroliese geleidingsvermoë van die sisteem beïnvloed. Die bevindings van die studie is in kort dat geostatistiese metodes nie vir gemiddelde waardes van hidroliese geleiding in Suid-Afrika gebruik word nie. Die rede agter hierdie stelling is dat die verspreiding van waardes nie die algemene onderliggende geostatistiese raamwerk volg nie. Oor die algemeen is die waardes se verspreiding diskontinue en statisties assimetries. Verder is daar substansiële verskille in die relatiewe verskil in waardes binne 'n meter of twee van mekaar. Agter hierdie verskynsel is die voorkoms van dolerietgange en plate wat gebakte sones vorm met aansienlike hoë hidroliese geleidings-waardes in vergelyking met die omringende geologiese materiaal. Verder is die tekort aan data vir droë boorgate ook 'n bron van kommer aangesien dit gemiddelde waardeberekeninge beïnvloed.af
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectModellingen_ZA
dc.subjectGeostatisticsen_ZA
dc.subjectRegional mean valuesen_ZA
dc.subjectTransmissivityen_ZA
dc.subjectHydraulic testen_ZA
dc.subjectGroundwateren_ZA
dc.subjectAquifersen_ZA
dc.subjectGeology -- Statistical methodsen_ZA
dc.subjectThesis (Ph.D. (Institute for Groundwater Studies)--University of the Free State, 2011en_ZA
dc.titleEstimation of representative transmissivities of heterogeneous aquifersen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record