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Université des géosciences de Chine (2019)

Geohydrological Assessment of the Iishana Sub-Basin, Namibia

Johanna Ngula Niipele

Titre : Geohydrological Assessment of the Iishana Sub-Basin, Namibia

Auteur : Johanna Ngula Niipele

Grade : Doctoral Dissertation 2019

Université : Université des géosciences de Chine

Résumé
The study was conducted in the Iishana sub-basin located in north-central Namibia.The basin is a semi-arid environment which is characterized by low-lying interconnected ephemeral drainage networks.In the past decade,the basin has experienced frequent droughts and flooding events due to recent weather anomalies possibly enhanced by the sprawling urban development and the change in weather patterns.The enhancement of urban development necessitated a need to increase water supply to growing settlements.However,water availability is limited in the basin with most clean drinking water being supplied through the canal from the Calueque Dam across the Angola-Namibia border.The study,therefore,recognized a need to investigate for potential groundwater zones using cost-effective methods that require minimal inputs.Henceforth,different methods were employed to detect and estimate potential groundwater zones and assess groundwater quality.Firstly,was to update the existing drainage networks by automatically extracting drainage flow lines from the ALOS DEM.Secondly,was to estimate potential groundwater zones by identifying parameters that can determine groundwater availability.And thirdly,determining the quality of groundwater for drinking both for human and livestock.in the area which only indicates major known ephemeral river networks making the data limited for effective decision-making on water management strategies.,and therefore a need to ensure that the data being used are accurate and up-to-date.Automatically extracted drainage networks were validated firstly by visual observation of data overlay,whereby the networks were superimposed on the Landsat 8 imagery of the wet secondly by statistically calculating the percentage of extracted networks using the CLC metric.A 91% match between extracted and delineated drainage networks was obtained.Furthermore,the vegetation species distribution was generated from the ARVI index in conjunction with the Sentinel-2 dataset.First,a landcover map was developed with three main landcover units mainly ;bare soil,vegetation,and water.the vegetation unit was then extracted from the landcover and used together with field collected vegetation species for species distribution mapping.The landcover classification obtained a 70% accuracy using the CAC metric.The resulting vegetation species distribution map was not validated as the area was found to have a mixed vegetation species distribution as observed in the field and the resulting map.Last but not least,the potential for groundwater availability was assessed by integrating thematic maps that have the potential for determining groundwater availability.Thematic maps were individually assessed prior to the integration.A WoE method was employed in the ArcGIS software using the weighted overlay application tools for data integration.The resulting potential groundwater zones were assessed with a covariance statistical method to determine which of the parameters has a high influence in determining potential groundwater availability.Finally,groundwater quality was assessed and chemical elements thereof interpolated across the study area to determine which potential groundwater zones have suitable water quality for human and livestock consumption.

Mots clés : Drainage network; groundwater availability; ALOS DEM;

Présentation (CNKI)

Page publiée le 28 février 2020