Technical and Financial Analysis of Flood Control with Detention Reservoirs: Case Study in a Coastal Municipality, Southern Brazil

Intense and disorderly urbanization in Brazilian cities has been increasing water-related disasters, amplyfing river flooding frequency and magnitude and giving rise to localized flood points due to urban drainage systems overflow.

The use of compensatory techniques in urban drainage planning is suggested as a tool to control floods, seeking to ensure greater protection to the population and the environment. The adoption of these techniques in fully urbanized areas can be difficult to implement, due to local conditions, such as hydraulic drainage network capacity, availability areas for detention basins and construction costs. Therefore, planning the urban space before its consolidation is one of the best practices, to be able to reserve areas for flood control devices.

In this context, the present work evaluated the amount of area of detention basins required for runoff control, in order to get minimum total cost of the system (conduits and reservoirs). A technical and economic analysis was performed, considering five different scenarios of percentage area reserved for detention basins (0%, 0.5%, 1.0%, 2.0% and 4.0% of the total area and with reservoir depths up to 1.5 m). The analysis was performed for an area to be developed in the coastal municipality of Tubarão, in Southern Brazil.

The SWMM (Storm Water Management Model – EPA) hydrological simulation model was used for the scenario’s analysis. A project rain of 24 hours duration and 25-year return period was adopted, discretized every 5 minutes.

The results indicate that, up to a baseline, when increasing the area of reservoirs, the total costs of the system reduce; however, above this value, the total cost increases with the growth of the area of reservoirs. The best of the proposed scenarios was the reservoir area of 2.0% of the total area. This scenario presented a reduction in peak flow of more than 32%, in addition to a reduction of costs of more than 8% when compared to the scenario without reservoirs.