Urban Dam Break Flood Inundation and Damage Modeling

To prevent loss of life and property during a dam failure, properly developed flood risk management plans are necessary. Such efforts rely on hydrodynamic models to simulate flooding and predict flood damage losses so strategies to reduce flood damages can be developed. In urban areas where high population regions exist, and where structures such as residential, commercial and public facilities exist, precise and accurate methods to predict both flood extents and damage losses are necessary. In this study, the Baldwin Hills dam-break flood of 1963 and its impact on structural damage is investigated. Modeling is performed using BreZo, a finite volume model that solves the shallow-water equations. The model is validated with flood extent and stream flow measurements, and a sensitivity analysis is completed to identify the necessary level of data and model complexity for accuracy purposes. Results show street depressions in the land surface should be resolved by the computational mesh for flood extent and stream flow accuracy and a ca. 5 m resolution mesh that spans streets by approximately 3 cells achieves a good balance between accuracy and computational effort. Results also show that heterogeneous resistance is important for stream flow accuracy, and the interception of overland flow by storm sewers is important for flood extent accuracy. The sensitivity of predictions to several additional factors is also investigated. In addition, several existing damage functions are evaluated to study flood-induced structural collapse on residential structures. The damage functions, coupled with the urban flood model, predicts structure failure upon exceedance of a hydraulic intensity parameter, which in turn triggers a localized reduction in flow resistance that affects flood intensity predictions. Several established damage models are tested to evaluate the predictive skill for two damage states defined by destruction (Level 2) and washout (Level 3). Results show that high-velocity structural damage can be predicted with a remarkable level of skill using established damage functions, but only with two-way coupling of the hydraulic and damage models. Existing force-based damage functions performed well while a calibration of the force threshold suggests optimal thresholds for Level 2 and 3 damage levels.