Cost-Effective Optimization of Nature-Based Solutions for Reducing Urban Floods Considering Limited Space Availability

The conventional urban stormwater management practices focus on carrying away runoff quickly by lined conveyors, which increase the surface runoff and reduce the time of concentration, subsequently causing floods in downstream areas. Ecological Management Practices (EMPs) provide nature-based solutions for reducing flood risks in a sustainable and economically viable manner. However, in the rapidly urbanizing setups in developing nations, the application of EMPs is limited due to space availability, data scarcity and limited funding. This study uses a Non-Linear Programming Optimization Technique to provide modelling solutions in optimizing the land-use and costs under EMPs to reduce flood risks in the Quebrada Aries watershed in the Municipality of Heredia in Costa Rica. Depending on the availability and ease of execution, a combination of three EMPs (bio-retention areas, infiltration trenches and green roofs) were tested. The effect of the application of derived optimal combinations has been analysed. The optimal combination of EMPs analysed for different channel capacity was able to reduce the peak discharge for the worst flood causing event of 50 years return period from 16.86 m(3)/s (under current land-use) to 9 m(3)/s, 9.51 m(3)/s, 8.38 m(3)/s and 9.13 m(3)/s in four hypothetical scenarios considered. In urbanized catchments, EMPs cannot be applied indefinitely to avoid floods. However, an optimal combination of EMPs can drastically reduce the requirement of large capacity drainage channels. This information can help policy-makers to analyse trade-offs between urban development and flood control measures. The study is suitable for other data-scarce regions as well.