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UNESCO-IHE Institute for Water Education, Delft (2018)

Effects of minor hydraulic structures on the floods of the Lower Limpopo River Basin

Illangasingha, Sanjeewa Punsiri Bandara

Titre : Effects of minor hydraulic structures on the floods of the Lower Limpopo River Basin

Auteur : Illangasingha, Sanjeewa Punsiri Bandara.

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2018

Floods are dynamic in nature and cause threats to life and properties across the globe. Extreme weather conditions and rapid development activities can be identified as the main reasons for the frequent occurrence of this natural hazard. Owing to contemporary development activities taken place in river basins, number of hydraulic structures are being built to manage the flow of water across basins. However, these structures negatively affect the river flow paths and result in increased flood hazards. The main objective of this research is to address the effects of minor hydraulic structures on modeling the flood extend in the Lower Limpopo River in terms of 1D/2D modeling approach. Existing HEC-RAS hydrodynamic basic model developed by previous project was upgraded for this study by incorporating relevant hydraulic structures like culvert and bridges. Impacts of these structures were assessed in terms of flooding time, maximum water surface elevation and extent under four different return periods ; 5, 10, 25 and 50 years. Imporatance of minor hydralic structures in flood propagation is discussed for low reaturn year period ; 5, 10, 25 and 50 years. A relationship is developed between return periods and the relative importance of hydraulic structures on flooding extent to prioritize a maintenance work scheme for the Lower Limpopo River Basin. The simulations performed suggest that tides impact the hydrodynamic of the Limpopo River up to around 131 km from the river mouth. A significant effect of minor hydraulic structures is observed, particularly for floods in low return periods (5, 10 and 25 years) in terms of flooding extent and time. However, for different areas, the degree of this effect is different for different return periods. Furthermore, for the larger return periods like 50 year, 1D and 2D models do not show a significant difference in the analysis results. Thus, for larger return periods, a 1D model could have a sufficient accuracy to analyse the flooding extents and time. The prioritization of each minor hydraulic structure is therefore a function of the return period of the flood event considered. According to the analysis, most of the minor hydraulic structures located in middle part of the study area need higher priority than those in down-stream. In conclusion, this prioritization scheme will be useful for the implementation of maintenance works of hydraulic structures in the Lower Limpopo River.

Sujets  : flood hazards hydraulic structures hydrodynamic modelling Mozambique

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