Flash floods prediction in South African urban areas: Jukskei river catchment as case study
- Authors: Mawasha, Tshepo Sylvester
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Geographic information systems
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/52059 , vital:43429
- Description: This study explored the change relation of multi-temporal land-use/land-cover (LULC) conditions in order to determine how they contribute to change in surface runoff volumes and peak discharge, in an effort to predict flash flooding within the Jukskei River catchment. The research is divided into three main parts: (1) LULC change modeling, (2) rainfall-runoff modeling, and (3) flash floods prediction. Three multi-temporal satellite images of Landsat-5 MMS (1987), Landsat-5 TM (2001) and Landsat-8 OLI (2015) were used for LULC modeling. The analysis of the LULC model revealed that there is a continuous increment in built-up area, from 37.7% to 56.2%, in the expense of other LULC classes for the 28-years preceding this study (i.e., 1987 to 2015). Rainfall-runoff model output results revealed that, for these 28 years, there has been an increase in surface runoff due to change in LULC by 21.5%, 32.9% and 45.5% for 1987, 2001 and 2015, respectively. Due to an increase in surface runoff volume and impervious surface over time, the analysis of HEC-RAS/GeoRAS showed that floodplain extent, flood depth, flood velocity, depth-velocity and the level of damage increases especially in low elevation areas and areas at closed proximity to the Jukskei River. Thus, the building structures and infrastructures are at risk of being affected by flash floods during the rainy season. The findings of this study are expected to be used as basic data for the identification of causative factors of flash floods, areas that generate high surface runoff volume, and the prediction of flash floods within the catchment in future. The flood damage maps developed in this study will be useful to policy-makers and the relevant authorities, as well as to local residents, in finding suitable measures for residential development along the floodplain while reducing flood risk in the study area. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2021
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- Date Issued: 2021-04
The application of GIS and remote sensing to assess the effect of periodic flooding on communities along the Juskeiriver: A case study of Alexandria Township, Johannesburg, South Africa
- Authors: Mawasha, Tshepo Sylvester
- Date: 2016
- Subjects: Remote sensing Geographic information systems -- South Africa , Remote sensing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45613 , vital:38918
- Description: Floods are water induced disasters that led to temporary induction of dry and cause serious damages in the affected location such as loss of valuable assets, lives and destruction of infrastructure. Flooding had become common in Alexandra Township during rainfall season and the recorded impact of periodic flooding on communities is increasing at an alarming rate. This study seeks to identify populations vulnerable to flooding and to map-out areas at high risk of flood disasters, using GIS and RS as a tool. For GIS application different types of maps were produced, namely, flood vulnerability, hazards, risk and risk index map highlighting areas at risk of being affected by flooding. Flood risk index maps identify three categories of risk zones; low and high risk zone. The household units within each of the risk zones was calculated and the total was estimated to be 762 for low-risk and 32 486 for high risk zone. The SRTM Digital Elevation Model (DEM) and multi-temporal Satellite Probatoire d’Observation de la Terra (SPOT) satellite images for 1997, 2006 and 2013 of the area was used for land-use and land-cover (LULC) change analyses using maximum-likelihood post-classification comparison. Results reveal that tremendous urban development had taken place in the study area along the Jukskei River area for the past sixteen years. It was observed that there was a sharp decrease in vegetation from 237ha (1997) to 134ha (2006) to 68ha (2013). This may had a negative impact on the environment around this area by decreasing surface runoff. The trend however, shows that bare surface and vegetation land-cover class has no potential to recover. Questionnaires aimed at all the residents in the study area were used to assess the effect of periodic flooding on communities. Community leader and City of Johannesburg Disaster Management Unit (CoJDMU) interviews were also conducted to get more insight about floods management in the study area. Finally, strategies for alleviating flood risk in the study area were discussed and some recommendations were made to help the government and municipal authorities to improve and development sustainable flood mitigation measures.
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- Date Issued: 2016