Abstract
River Malaba sub-catchment tends to experience dramatic flooding events, with several socio-economic impacts to the nearby communities, such as loss of lives and destructions of physical infrastructure. Analysis of spatiotemporal extents to which settlements, crops and physical infrastructures tend to be inundated are vital for predictive planning of risk-based adaptation measures. This paper presents a case study on flood risk assessment for Ugandan River Malaba sub-catchment. We applied the two-dimensional Hydraulic Engineering Center’s River Analysis System (2D HEC-RAS) for modelling of flooding extents. We considered extreme flow quantiles, lower and upper quantiles corresponding to the 95% confidence interval limits aimed at determining uncertainties in the flooding extents. Spatial extents of inundation on human settlement, land cover and infrastructure were analysed with respect to return periods of extreme flow quantiles. Finally, we estimated economic loss on infrastructure due to flooding. Results from the 2D HEC-RAS model were satisfactorily comparable with the results of observations. Amongst the land use types, cropland exhibited the highest vulnerability with at least 10,234.8 hectare (ha) susceptible to flooding event of 100-year return period (YRP). Inundated built-up land-use exhibited the highest vulnerability percentage increase (90%) between 2- and 100-YRP. In US Dollar, about US$ 33 million and US$ 39 million losses are estimated at 2- and 100-YRP, respectively, due to inundated rice gardens and these indicate a looming high risk of household food insecurity and poverty. Several infrastructure including 15 academic institutions, 12 health facilities, 32 worshiping places remain annually vulnerable to flooding. At least 6 km and 7 km of road network are also susceptible to flooding under extreme flows of return periods 2 and 100 years, respectively. Churches exhibited the highest economic losses of US$ 855,065 and US$ 1,623,832 at 2-YRP and 100-YRP, respectively. This study findings are relevant for planning the development of sustainable flood risk adaptation pathways given the established destructions within the sub-catchment due to flooding.
Highlights
Floods are natural disasters with the highest global occurrence and broader physical distribution producing severe damages in many countries (Najibi and Devineni 2018)
River Malaba originates from Mount Elgon at about 4315 m above sea level criss-crossing through districts of Bududa, Manafwa, Tororo, Butaleja reaching the shores of Lake Kyoga on the western side at about 1055 m above sea level, where it discharges into Mpologoma River
The river flow variation and or damage from floods within River Malaba sub-catchment could be attributed to other factors beyond Land use land cover (LULC) changes, such as climate variability
Summary
Floods are natural disasters with the highest global occurrence and broader physical distribution producing severe damages in many countries (Najibi and Devineni 2018). Conversation of land use types from one state to another for various purposes, such as settlement, agriculture, urbanisation, and other recreational activities especially near the river banks (Alawamy et al 2020). This can result in extensive unexpected implications, such as alteration of the hydrological processes, exacerbating the occurrence of weather disasters (Apollonio et al 2016; Kilama Luwa et al 2020; Szwagrzyk et al 2018; Zope et al 2016). The most updated climate projections indicate that floods in several parts of the world will likely increase in intensity and frequency in the future (Hirabayashi et al 2021)
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