Assessing the impact of urban growth on surface runoff using SCS-CN model.

Abstract

Due to an increase in impervious surfaces from human construction and a decrease in porous regions, rapid urban growth causes noticeable changes in land cover. Urban ecological security is currently facing a significant challenge from increasing direct runoff brought on by changing land cover. For large unmeasured urban areas, it is intrinsically difficult and time-consuming to make accurate predictions of the amount and rate of surface runoff. The overall aim of this study was to examine the impact of urban growth on runoff response in Kampala City, UGANDA during the study period of 1995 to 2016. The study was carried out using remote sensing techniques and hydrological modelling for examining the spatial patterns changes in urban areas and their impacts on surface runoff. The estimation of surface runoff based on the Soil Conservation Service Curve Number (SCS-CN) method was performed by integrating both remote sensing and Geographic Information System (GIS) techniques. The study analyzed and employed the supervised classification method on four Landsat images of 1995, 2003, 2010, and 2016 to detect Land-cover changes through remote sensing applications. Results indicated that Kampala experienced rapid urbanization from 1995 to 2016. Vegetation cover has been clearly reduced from 105.60 km² to 38.83 km². After Land-cover change detection, a GIS-based SCS-CN model was developed to examine urban growth and surface runoff estimation. As a direct result of the urbanization from 1995 to 2016, the annual surface runoff volume increased from 102.58 million m³ to 186.2 million m³. The correlation between runoff coefficient and rainfall indicated the significant impact of urban growth on surface runoff over the studied 21 years. Hence the proposed integrated approach could classify land-cover information to understand urban growth and its potential impact on the area. The results of this study can be used by different stakeholders and government units that have been tasked with managing the environment in order to come up with management strategies for proper control of surface runoff and management of water resources in urban areas.