Urban flooding is a key driver behind mainstreaming Nature Based Solutions (NBS) into planning in Kigali. As a continuation of our pre-feasibility study for NBS in Kigali, we developed technical guidelines for the implementation of NBS. To demonstrate the application of these guidelines for site specific designs, we selected Rebero-Karugira as the case study area. The case study was selected in consultation with local stakeholders from the Government of Rwanda and the City of Kigali.

The technical guide was designed to act as a complementary design manual for the integration of NBS in Kigali. It can be used by NBS proponents and implementers in the process of selecting measures that fit their specific situation whether it is protecting and enhancing existing natural ecosystems, integrating NBS into development plans (e.g. neighbourhood plan) or retrofitting measures in existing urban areas. As such, it is a useful tool that can be used by engineers, planners, developers, students or local communities to explore a range of possible measures and their technical requirements or preconditions to select the most suitable for the site specific context.

Per NBS element, the technical guide includes a description, considerations for implementation, maintenance, monitoring and design. It also includes technical drawings and bills of quantity (BoQs), as well as indications of regulations that are relevant for the implementation of the measures and stakeholders involved.

An important aspect for the (site specific) design of NBS is the adoption of a systems thinking approach to address the cause of a problem, which requires a system analysis on a bigger scale and an understanding of the position of the specific project area within it. The Rebero-Karugira case study area reaches from a forested area on the northern part of the slope below Rebero Hills along a drain towards Rwampara wetland. Due to this location the area is susceptible to different water related challenges, such as erosion on the upper sections of the slopes and sedimentation and flooding downstream close to the wetland. The diversity of urban typologies, including unplanned settlements and low to mid-density residential areas, forest and urban farming makes it an ideal location to demonstrate the integration of different types of NBS in Kigali.

The proposed NBS layout is based on the main principles ‘big difference’ and ‘1.000 x 1’, the NBS hierarchy, the effectiveness of types of NBS in relation to the location on the slope and the location specific characteristics. Existing wetlands and forests are the backbone of the city’s stormwater management system, thus need to be protected and rehabilitated to harness their full potential. Whereas integrating smaller scale NBS in urban developments increases resilience to flooding over time by capturing and delaing storm water and reducing the velocity. Four NBS are designed in more detail to illustrate the application of the technical guidelines and the combination of different NBS elements into site specific integral designs:

• Stabilized natural channel with gabions
• Integrated constructed drain
• Multifunctional detention basin
• Drain outlet

The multifunctional detention basin has great potential to become a pilot location to implement, test and monitor NBS. The area has a prominent location within the case study area. This could be further enhanced by integrating a sports field or play facilities into this zone, whilst being careful to ensure that safety aspects related to flood risks are appropriately mitigated. Eventually, the concept could also potentially be adopted and replicated by other schools across Kigali, and with a pilot like this, Kigali could become an international leader in NBS that leads by example.

Client: World Bank

In cooperation with: Deltares, SHER Ingénieurs-Conseils