Dam break modelling and flood inundation mapping for Kabuyanda multi- purpose Dam, Isingiro district.

Abstract

In many locations around the world, dams are essential for flood control, water supply, irrigation, hydropower, navigation, and recreation. This is synonymous with Uganda, where the one single investment that would lay the foundation of industrial development was the construction of Owen Falls dam (Nalubale dam) in 1954. Since then, other large and high hazard dams such as Bujagali, Karuma and Isimba have been constructed majorly for hydroelectric power generation. Kabuyanda dam, which shall be an embankment dam (earth dam), shall be the first large and high hazard dam in Uganda solely constructed for irrigation development, with a Storage Capacity of 8.8Mm3 . For large and high hazard dams, it is a requirement that consideration is given to the number of people, property, infrastructure and ecosystem at risk downstream of the dam. This paper provides results of a dam breach analysis and mapping of the downstream area to be inundated by the resulting catastrophic dam break flood of Kabuyanda Multipurpose Dam. Flow simulation of the dam break was performed using HEC-RAS and the results were mapped using ArcMap. The resultant flood hazard map which was based on water depth and flow velocity showed that the potential failure of Kabuyanda dam will cause part inundation of 31 of the 38 villages with in the irrigable command area of Kabuyanda Irrigation Scheme, thereby placing a large number of people and property in danger. The total area to be inundated shall be up to 1,197.6 Hectares, these area accounting for 33% of the total irrigable command area. All the 31 villages to be part inundated were ranked from highest hazard potential to lowest hazard potential and the village found to be with the highest hazard potential is Kagoto II. At Kagoto II, it is expected that the impact of large volumes of instantaneous flow may destroy houses and flood farmlands, resulting in significant casualties and property losses. Therefore, in the eventuality of a dam-break, rescue attempts for the highest hazard potential villages should be prioritized. The results of this study can be used by stakeholders such as emergency responders and the community at risk in formulating evacuation procedure.