Multi-objective-rehabilitation of urban drainage systems within the flood risk framework : case study : Quito-Ecuador

Urban drainage systems are one of the most valuable public utilities in any community,which protects public health and the environment, nevertheless is one of the most overlooked infrastructures until considerable failures happens. Water companies, which can be governmental, municipality institutions or private companies, are the responsible of design, construction, operation and management these systems. If these institutions do not have an adequate management practice, rehabilitation programs of urban drainage systems, and suitable mitigations measures, this vital infrastructure does not only decreases the level of service, but also enormous expenditure has to be made for rehabilitation in order to avoid paramount impact on human societies.To come up with optimal rehabilitation measures, first of all the performance of urban drainage has to be evaluated, several procedures can be followed, in this thesis only hydraulic assessment was carried out. For this purpose, a framework was developed.This new approach is based on data observation, analysis and processing; hydrodynamic models; informatics tools; interconnected each other in a number of steps.Once the problem was defined, the indispensable data was collected, analyzed and processed to be used in the rest of the framework steps. Subsequently 1D pipe flow model was carried out for several flood events, with its outcomes critical zones in the sewer network can be identified i.e. flooding, surcharging and insufficient capacity in conduits. To simulate the overland flow from manholes when the capacity of the sewer pipes is exceeded a coupled 1D-2D model was used. The results are matrices composed of flood water depths and velocities values per each scenario of the flood event.These outputs are the main parameters to assess flood hazard. Furthermore,vulnerability assessment was undertaken based on socio-economic condition of the residents of the study case. More over with the assessment of hazard and vulnerability, both factors are combined to assess flood risk damage.Finally to have a set of optimal remedial measures, multi -objective-rehabilitation process was carried out by using genetic algorithms techniques. Where the level of service of UDS is improved by reducing flood risk costs, in the most cost effective way. Two trade-off objectives functions are evaluated, the intervention cost (upgrade conduits) and flood risk cost.Several simulations were made for different flood events, obtaining Pareto sets per each event. However in order to have more realistic solutions the approach of expected annual flood risk cost were implemented to obtain integrated solutions for a number offlood probable events. Besides of these new solutions generated, the concept of cost -benefit analysis was applied to obtain the most economical solution.The proposed framework is tested in a study area in Quito-Ecuador, where the main data was provided by the water utility company of Quito (EPMAPS)