Abstract:
Floods are a major problem affecting many parts of the world. Generally, the Cuvelai Etosha Basin (CEB) of north-central Namibia and specifically Oshakati and Ongwediva towns are no exceptions to this problem. Floods have ravaged the study area throughout the past and continue to do so in present times. Flood analysis in Oshakati and Ongwediva was carried out to map and determine drainage patterns, inundated zones and flood susceptibility. The research relied on collected geographic datasets of satellite images, YXZ survey points of the study area from which the DEM was created, cadastral data and participants' perceptions through a participatory GIS questionnaire. Remote sensing and GIS were used in the research. ArcGIS, Model Maker and Microsoft Excel were used in this research.
Remote sensing techniques through the use of onscreen digitising was used to map shallow depressions, streams and inundated zones. Flood susceptibility was generated in ArcGIS after classifying the DEM into five elevation categories, from which flood susceptibility classes were deduced. Participatory GIS was used to further determine flood impact and rank flood susceptibility in Oshakati and Ongwediva towns.
Parts of the study area were found to fall within shallow depressions and streams. Using
onscreen digitisation, it was found that 18.60% of the entire towns of Oshakati and Ongwediva was situated within shallow depressions and streams, leaving 81.40% of Oshakati and Ongwediva shallow depressions and stream free. Considering the two towns individually, 21.0% of Oshakati town is in shallow depressions and streams, while 15.40% of Ongwediva town is situated in shallow depressions and streams. Shallow depressions features are primarily found in the town of Oshakati, degenerating into streams towards the southern part of the town as they flow towards Etosha pan in the south. Stream features are concentrated in the Ongwediva town, mainly in the eastern part of the town running through settlements such as the Sky location.
An inundation map showed that 23% of Oshakati and Ongwediva towns was inundated during the 2009 flood season. The towns of Oshakati and Ongwediva is subjected to different flood susceptibility classes ranging from very high to very low. The very high flood susceptibility class occupied 6.54% of the two towns, while 24.48% of the Oshakati and Ongwediva towns is situated in high flood susceptible zones. Further, 32.70%, 24.52% and 11.76% of Oshakati and Ongwediva are respectively located in moderate, low, and very low flood-susceptible zones. Looking at the individual towns, Oshakati town is more susceptible to flooding than Ongwediva town, given that more of its land is situated in very high and high flood susceptible zones compared to Ongwediva town.
Several institutions, businesses, public places and critical infrastructure fell into very high and high flood-susceptible zones, especially in Oshakati. In Ongwediva town, most institutions, businesses, and public places did not fall into flood-susceptible zones; they were used to being surrounded by flood water, which restricted access to them. Of all the participants in participatory GIS, 16% were never affected by floods, while 84% reported being affected by floods. Oshoopala, Uupindi and Oneshila are the most flood affected settlements in Oshakati, whereas Efidi location, Sky location and western extensions of 12-17&20 are the most flood affected in Ongwediva town based on participatory GIS data. Ekuku location in Oshakati town and the CBD and the suburbs for both towns are the least affected by floods based on participants, perceptions.
Results of data analysis has indicated that Oshakati town is more prone to flooding than
Ongwediva town. This is evident from very high and high flood susceptibility classes that
occupies a larger area in Oshakati town than in Ongwediva town. Moreover, Oshakati town has more of its land falling within shallow depressions, streams and inundation in comparison to Ongwediva town.
