Methodology for determining the optimum return period of design for flood mitigation, case Bogota river

Juan Quijano, Mario Díaz-Granados

Tuesday 30 june 2015

11:45 - 12:00h at South America (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flood risk assessment

Parallel session: 5J. Floodrisk - Assessment

Damage and flooding events derive in the need of cost-effective investments for prevention and control. Computer programs have been turned in useful tools to support decision making. This study proposes a methodology applied in Bogota River upper watershed to find an optimal return period for design of levees in river banks, using several of these tools. A register of soil uses was made determining urban, agricultural, animal breeding, flower crops, educational and other zones. At the same time, unit costs, quantities and assets inventory were established for each type of soil in the study area. Flood footprints, water height, velocities and levee height for different return periods flows (2, 3, 5, 10, 20, 50, 100, 200, 500 and 1000 years) were determined. Flooded areas were crossed with land use and damage costs were calculated. Since the construction of any levee does not eliminate completely all the risk of damage, expected cost of damage were estimated. Based on the levee heights and lengths, construction costs were generated as the sum of manpower, materials and machinery costs. Finally, total costs were established (expected cost plus levee construction costs for each return period) whose minimum was the optimal return period for design. This methodology was probed for two scenarios in Bogota River upper watershed and it resulted in optimal return periods of 150 years for the actual scenario and 125 for the expected scenario.