Evaluation of a 2D Flood Model and Mitigation Measures for Peri-Urban Areas on Lake Victoria Shores

Abstract

Lake water levels rose in Lake Victoria between 2018 and 2021 leading to inundation of periurban areas located on the shores such as Ggaba. It is predicted that Uganda will experience an increase in precipitation over the following years resulting in more flooding. This research project therefore aimed to utilize ArcGIS Pro software to represent flooding scenarios in Ggaba. Developing a comprehensive understanding of the potential impacts of flooding in the area was also required to propose relevant flood mitigation measures aimed at enhancing flood management strategies.

Geospatial data sets, including a Digital Elevation Model (DEM) and lake water levels were obtained and utilized to create a 2D model of flooding in Ggaba. Maximum water level was obtained for each year for the data available from 1992-2022. Frequency analysis was done on the lake water levels to obtain the lake water levels corresponding to different return periods. The DEM and these water levels were then used in ArcGIS Pro to create the model by using the raster calculator to visualize the flooded areas using flood maps. Field surveys were conducted to obtain field data on the flood levels and information for a comprehensive understanding of the impacts of flooding in the area to propose relevant flood mitigation measures. A flood wall was one such measure which was designed based on a 100 year return period flood event.

The highest observed water level was in 2021 at 13.49 m with the maximum water level from 2020 following closely by at 13.48 m. This is well in sync with the time period when Ggaba was flooded due to lake water level rise from 2020 to 2021. An analysis of the return period of the observed maximum water level in 2021 of 13.49 m was done to reveal a return period of 25 years. The flood map for the 2020 flood revealed that the most affected areas by the flood in Ggaba in 2020 were Katoogo residential area and Ggaba Market along the shores of Lake Victoria.

Katoogo particularly showed the largest consistence in large flood depths and flood extent in the region. This could be attributed to the low topography of the area and its surrounding wetland terrain. The greatest flood depth observed in Ggaba market was of 1.15 m and 1.65m in Katoogo area. With the information obtained from field surveys, the proposed mitigation measures included timely flood warning systems, flood resilient construction methods, maintenance and improvement of drainage systems and incorporation of a flood wall.

From this research, it was determined that ArcGIS Pro software can be used to accurately model the flooding scenario and visualize the results consisting of flooded areas and flood depths. Primary data obtained from field surveys was a reliable source of information for validation of the model and improving its accuracy. Studying the flood maps developed using ArcGIS Pro software significantly enhanced flood management strategies by enabling the prioritization of the most affected areas. The findings will contribute to building resilience in Ggaba, reducing the impacts of flooding on infrastructure, livelihoods, and the environment.