Assessing the Impact of Land Use and Solid Waste Management on Flooding in Kinawataka Catchment

Abstract

Over the last years, there has been massive land use change in the Kinawataka catchment area. The effect of this has been increased runoff beyond the capacity of the existing drainage channels and this, coupled with climate change effects has consequently resulted into flooding. However, the problem of flooding cannot be solely attributed to land use change only. It is quite evident that this area is also characterized by poor solid waste management practices for instance, huge volumes of solid waste in form of garbage, empty plastic bottles are seen blocking existing drainage channels thereby reducing the hydraulic capacity of these channels and consequently resulting into flooding. (Ochwo, 2019). Land use change parameters analyzed with ArcGIS over the last 30 years shows a 66% decrease in the percentage of vegetation cover with increasing built-up area (industries, residentials, roads). A model for the study area was developed in the Environmental Protection Agency Storm Water Management Model (EPASWMM) interface and simulations run. The results from the simulation indicated nodal flooding on 7 junctions for the present scenario (baseline scenario), the highest flood volume being at junction 6 (15.193 x10^6 liters) and junction 5 (9.495 x 10^6 liters). These two junctions are found at the Kyambogo junction which is often reported in newspapers to be experiencing flash floods whenever it rains. The flood volume increased to 28.193 x 10^6 liters and 11.807 x 10^6 liters respectively for the present scenario with solid waste in the drainage channels. The percentage of built-up area in this catchment is only expected to increase since the area was earmarked for industrialization by the Government of Uganda. This is represented as a future scenario in the SWMM interface with 95% imperviousness. The climate change effects have also been catered for in the future scenario by factoring the peak intensity with 1.2. This future scenario indicates a higher nodal flood volume of 71.095 x 10^6 liters at junction 6 and 98.817 x 10^6 liters at junction 5. Due to the limited space requirements and high economic costs in the urban areas, expanding the existing drainage channel with intentions of increasing its capacity may not be an applicable solution, hence the need to apply Low Impact Development practices – LIDs such as pervious pavements, green roofs, and rainwater harvesting. These LIDs facilitate attenuation, reuse, retention and infiltration of surface runoff which controls floods. A simulation of the future scenario with LIDs shows an overall reduction in the volume of floods.