Remote sensing for assessing wetland-groundwater interaction in the Kogelberg Biosphere Reserve

Engelbrecht, Jeanine (2005-12)

Thesis (MA)--Stellenbosch University, 2005.

Thesis

ENGLISH ABSTRACT: The Table Mountain Group (TMG) Aquifer System is a regional fractured aquifer system with a large potential as a source of future water supplies in the Western and Eastern Cape. This system is currently under consideration for large-scale water abstraction. Many terrestrial ecosystems, however, are dependent on these groundwater resources for survival. Exploitation of ground water resources at a rate exceeding the rate of natural recharge would result in a lowering of the water table and the drying up of seeps. The main objective of this study was to determine if satellite remote sensing data can be used for the detection of groundwater-dependent wetlands, and secondly, to use multi-temporal imagery for estimating seasonal changes experienced in wetland communities in relation to surrounding vegetation. The Kogelberg Biosphere Reserve, situated approximately 30km to the east of Cape Point in the Western Cape, South Africa, was selected for investigation. To accomplish the objectives, three Landsat 7 ETM+ images (path/row: 175/84) captured on 22 September 2001, 18 May 2002 and 23 September 2002 were acquired. Image fusion of the multispectral bands (30m resolution) with the panchromatic band (15m resolution) provided 15m multispectral images for analysis purposes. Geometric correction, radiometric normalisation and atmospheric corrections was performed in order to ensure pixel-level comparability between images. Once comparability between images was guaranteed, vegetation indices and tasselled cap components were derived to provide threshold values of moisture stress indicators and productivity estimations of wetland communities in relation to surrounding non-wetland communities. Additionally, change vector analysis on these transformations provided the ability to detect and assess the seasonal changes experienced by these communities during an annual cycle. The results of these transformations were combined in a rule-based image classifier in order to assist in estimating the seasonal dependency of observed wetland communities. The ability to use Landsat 7 images and the abovementioned image processing procedures to identify wetland communities with a high probability of groundwater interaction was demonstrated with a high degree of accuracy (78%). It is recommended that future studies concentrate on increasing classification accuracies, while focusing on incorporating these techniques into a remote monitoring system for assessing the impacts of groundwater extraction on the groundwater-dependent wetland communities.

AFRIKAANSE OPSOMMING: Die Tafelberg Groep (TBG) Akwifer is 'n regionale verskuiwingsakwifer sisteem met groot potensiaal as toekomstige waterbron vir die Wes- en Oos-Kaap. Grootskaalse grondwateronttrekking uit hierdie sisteem word tans ondersoek. Baie terrestriële ekosisteme is egter vir oorlewing van grondwaterbronne afhanklik. Grondwaterontginning teen 'n tempo hoër as die natuurlike aanvultempo sal die watertafel laat daal en syfersones laat opdroog. Die hoofdoel van die studie was om te bepaal of satellietbeelde gebruik kan word om grondwater-afhanklike vleilande waar te neem, en om 'n tydsreeks van beelde te gebruik om die seisoenale verandering in vleilandgemeenskappe relatief tot omliggende plantegroei te raam. Die Kogelberg Biosfeer Reservaat, ongeveer 30km oos van Kaappunt, is as studiegebied geïdentifiseer. Drie Landsat 7 beelde (baan/ry: 175/84) van 22 September 2001, 18 Mei 2002 en 23 September 2002 is ontleed. Die Landsat 7 multispektrale bande (30m resolusie) is met behulp van beeld-fusietegnieke met die panchromatiese band (15m resolusie) gekombineer om multispektrale beelde te lewer met 15m grondresolusie. Geometriese korreksie, radiometriese normalisering en atmosferiese korreksie is op elk van die beelde toegepas om beeld-selvlak vergelykings tussen beelde 'n moontlikheid te maak. Met beeldvergelykbaarheid verseker, is plantegroei-indekse en 'tassled cap' transformasies gebruik om afsnywaardes vir vleiland-identifikasie te bereken. Verder is veranderingsvektoranalises op die transformasies bereken om die seisoenale veranderinge oor die jaarsiklus in vleilande te bepaal. Die resultate hiervan is vervat in 'n reël-gebaseerde beeldklassifiseerder waarmee vleilande se seisoenale grondwater afhanklikheid geraam is. Die vermoë om vleilande met 'n hol! waarskynlikheid van grondwater interaksie uit Landsat 7 beelde te identifiseer is met 'n hol! vlak van totale akkuraatheid (78%) gedemonstreer. Die aanbeveling is dat toekomstige studies moet fokus op die verhoging van hierdie klassifikasie akkuraathede. Die tegnieke moet toegespits word op die ontwikkeling van 'n afstandswaarnemingstelsel om die

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