RUNOFF GENERATION, IMPACTS AND MANAGEMENT PRACTICES IN AMALEMBA URBAN INFORMAL SETTLEMENT, KAKAMEGA MUNICIPALITY, KENYA

Abstract

The study was carried out in Amalemba informal urban settlement within Kakamega municipality, Kenya. It concerned environmental impacts of uncontrolled runoff in the environmentally vulnerable low income settlement. Management of runoff is a significant component towards the sustainability of a sound urban environment infrastructure. Runoff management is imperative in urban informal settlements since it enhances a healthy surrounding. This study identified human and physical features that influence runoff generation, determined influence of rainfall on runoff discharge, influence of slope and ground cover on runoff discharge, effects of runoff; and investigated runoff management measures in Amalemba informal urban settlement. The study followed a quasi-experimental research design. Runoff discharge measurements, visual observations, photography, individual and focus group interviews were used to collect data. Runoff from bare ground, 50% grass cover and 100% grass cover were compared using thirty rainfall events during long rains in April/May 2020. Runoff volume was collected using the Gerlach trough setup, the precise volume of discharge was measured using a graduated one litre measuring cylinder. Data from interviews with respondents was analyzed according to themes while data from the Gerlach trough setup was analyzed using inferential statistics. The rainfall-runoff relationship for Amalemba informal urban settlement indicates a statistically positive significant correlation between daily rainfall and runoff volume with r = 0.9822 for 100% grass cover, for 50% grass cover r = 0.9672 and r= 0.9934 for bare ground respectively with p-value <0.0000001 for all the three surfaces. Bare ground coupled with steeper slope produced the highest runoff while the surface with 100% grass cover yielded the lowest runoff. The results show that vegetation cover is better at protection of the soil against erosion and reduction of runoff than bare ground. Runoff produced adverse effects such as flooding, mini landslides, soil erosion, and blockage of drains as a result of bad solid waste disposal mechanisms and destruction of shacks, farmland and roads. On-site and institutional practices complemented each other in management of runoff. This study emphasizes meaningful involvement and participation in management of runoff; adopting methodologies which withstand both social and human capabilities ranging from controlling and managing runoff to the effects of runoff in informal urban settlements. Runoff management at the catchment level, appropriate use of green infrastructure and the formulation of policies aimed at development of sustainable drainage systems in Amalemba informal urban settlement is of critical importance.