Assessment of the impact of climate change and land use change on the performance of the Nsooba drainage channel.

Abstract

Urban drainage systems particularly in developing countries globally are struggling with the challenge of the deteriorating performance. The impact of poorly performing UDS coupled with increasing global change pressures (urbanization, climate change, population growth) is likely to result in extreme impacts of the urban inhabitants. The increased frequency of extreme rainfall intensities and the increased informal settlements along the channel have a direct impact on the flows in the Nsooba channel. This is the challenge we address in our thesis. Our thesis addresses this problem through the different objectives, determining the impacts of climate and land use change on flows in the channel hence the magnitudes and frequencies of flood runoffs in Nsooba channel. Prediction of the future land use and its impact on the channel flows were also carried out. The methodology includes how the different objectives were achieved. Site visits, data collection; delineation of catchment using ArcGIS to demarcate the different sub catchments, obtaining of the different land use data from Landsat images used in ArcGIS to come up with the different land use maps. Determining the different IDF curves and establishing the different intensities from the acquired rainfall data. Obtaining runoff quantity using SCN-CN method and EPA SWMM model for the hydrological analysis. The use of HEC-RAS model for the hydraulic analysis where the different flow simulations were run and the flood depths for different channel cross sections obtained. Using the SCS-CN model for the land use changes, the different peak flows were obtained and the flood volumes for the different years. The land use changes were also predicted and their impacts of the flows in the channel were obtained. The flood volumes due the changes in land use attained from the SCN-CN method over the years and the impact of the predicted land uses are discussed. The different flood depths obtained at the different channel cross- sections using HEC-RAS software and flood volumes obtained from EPA SWMM are also discussed. The conclusions give a detailed summary of our results and the recommendations provide a way forward concerning our project discoveries.