Application of Nature Based Interventions for Flood Control Within Greater Accra Metropolitan Area, Ghana

Abstract

Conventional engineering approaches have been used for stormwater management to control floods within the Greater Accra Metropolitan Area (GAMA) but recently, the concept of “nature based” approaches have emerged as good alternative or compliment to the conventional approach. This research seeks to address the question “why the existing conventional system of stormwater management has failed to control floods and how the problem can be addressed.” The main objective was to develop and design a stormwater management system that could complement the existing conveyance based system within GAMA. The specific objectives were: (1) to assess the existing stormwater management system to determine the causes of its failure, (2) to develop a strategy or strategies to manage stormwater to complement existing systems and (3) to design action strategies that integrate identified stormwater management interventions. Research for Design was the research strategy used to generate and integrate ideas in the process of generating form through using a combination of research methods and design methods. The first objective was addressed through the systematic review of relevant literature sources on the causes of floods. The results of the review identified two major challenges; the need to separate critical from non critical causes of floods and the absence of policy on stormwater management which is grounded on local content. The second objective was met using the Soil Conservation Service Curve Number approach to model direct runoff which showed that between 14.7% and 32.6% of stormwater runoff which accumulate in communities originate from the roofs of buildings. This was used to develop a strategy which targets stormwater management at the plot level. To meet the third objective, the developed strategy was implemented by integrating three nature based interventions (Infiltration well, infiltration trench and rainwater harvesting) at the plot level to retain up to 95% of stormwater generated from the roofs of buildings. In conclusion, the research showed the significant contribution of roofs to runoff generation and contributes to existing knowledge by providing the basis for a strategy for stormwater management at the plot level, which could form the foundation for the development of a policy on stormwater management to control floods.