Tianjin Coastal Storm Surge Disaster Assessment Based on Urban Waterlogging Simulation Model

Most waterlogging models for inland city use a single boundary condition, the boundary is usually set in a small or large river, with a single flow direction towards outside the region, or set on a highway or a large dam without water exchange alternatively. However, for coastal areas, the ebb and flow lead to changes in wet and dry. Adapting to the intertidal nature, the model should involve dealing with dynamic boundary.Based on urban waterlogging simulation model, the topography and geomorphology of Tianjin coastal areas, as well as the pipe network and drainage systems, are used to expand and improve Tianjin urban waterlogging simulation model. Dynamic water level is set at the coastal border, and the water level stands for the tidal level. When the tide level is higher than the coastal embankment, the tide floods into the city and causes waterlogging. Therefore, the model simulates not only rainfall waterlogging but also the submerging scenario due to storm surge invasion. The flooding scope and standing water depth are simulated using the redeveloped model for the historically typical storm tidal cases in the coastal areas of Tianjin. Referred with the collected records of disaster and actual survey, the developed model takes on skills to some extent in simulation of the submerged scenario due to storm surge invasion. Differences between the simulation and the historical records, however, are non-intentionally increased by using the latest ground elevation data. This approach is used in operational application for simulating the storm surge caused by Typhoon Damrey on 3 August 2012. The simulated flooding scope and site are closed to the actual scene, but the simulated standing water depth is larger. Much more detailed calibration should be done in future. Furthermore, the submerging scenarios caused by storm surge in several return periods are simulated. These simulations can be directly used in projecting and assessing the submerging scenario if there is a storm surge predicted to be an N-year return-level or if it has occurred. These simulations can also be directly reported to the government and business clients for early warning.