Quebrada El Leon Project - Building Resilience to Manage Flash Floods

Abstract

The Quebrada El Leon project was built as part of a nation-wide program in Peru to build resilient structures to control and manage floodings caused by flash floods generated during El Niño events in the Andes Mountains and to avoid resulting damages and casualties. Two different conceptual systems were developed and compared based on a cost benefit analysis from an economic viewpoint and the use of multicriteria analysis to account for the technical, safety, resilience, environmental and social aspects. The assessment of project benefits relied on the estimated avoided flooding damage costs to justify the construction investment. Numerical simulations based on a 2D model were used to simulate floodings in natural conditions (without project) and with project to quantify avoided damages and the related cost. The preferred alternative consisted in two main intake canals to collect the inflows at the toe of the mountains and direct them into a large upstream basin enclosed with dikes to attenuate the peak flows, reduce the flow energy and trap sediments carried by the flows, a 20 km long canal and energy dissipation structure to confine the flows and discharge them to the sea, far from sensitive areas. Local materials were used for construction to reduce construction costs. The selected system is a completely passive solution involving no operations and low maintenance. The structures were designed using international engineering criteria for similar water projects and a set of specific criteria to account for climate change and resilience. Design also integrated constructability and safety aspects while focusing on approaches to meet a very aggressive construction schedule.