Flood Damage Assessment in HAZUS Using Various Resolution of Data and One-Dimensional and Two-Dimensional HEC-RAS Depth Grids

Abstract

The accurate assessment of flood damage in the aftermath of major flooding is crucial for studying flood vulnerability, risk mapping, and comparative risk analysis. However, the accuracy of damage prediction by a model might be affected not only by numerous model inputs and inventory data sets but also associated with flood depth grids prepared by the hydraulic model. Therefore, the overarching goal of this research is to explore how and to what extent the damage estimation is affected by the selection of one-dimensional (1D) and two-dimensional (2D) hydraulic simulation, inventory, and topographic data sets. The analysis was carried out in the Grand River, near the city of Painesville, Ohio, which has encountered frequent flooding over the last several years. The hydrologic engineering center river analysis system (HEC-RAS) models were set up for different topographic resolutions including various digital elevation models (DEMs) such as 30-, 10-, and 3-m DEMs derived from light detection and ranging (LiDAR), which were combined with the field surveyed river cross-section data to obtain the flood depths. The 1D and 2D HEC-RAS models were utilized to perform the hydraulic analysis to produce the flood depths after model calibration and validation. Flood loss was estimated by the Hazard United States Multi-Hazards (HAZUS-MH) for individual buildings within the study region for flood events of different recurrence intervals from a 10- to 500-year return period. This was accomplished by updating the default building of the inventory by the latest data available from the Lake County geographic information system (GIS) department to represent the accurate building information. The analysis indicated that the 1D model consistently overestimated the loss compared with that from the 2D model by an average of 61.48% for the default database and, 86.12% for updated inventory. Furthermore, the 2D model revealed a lesser increase (10.45% increase in 10-m DEM and 25.49% increase in 30-m DEM), whereas the 1D model exhibited a larger increment (23.17% in 10-m DEM and 76.81% in 30-m DEM) when compared with 3-m LiDAR DEM combined with surveyed data. Additionally, this analysis suggested that the estimate in an average would decrease by 76.21% after incorporating local building information into the HAZUS-MH database. The research clearly concludes that the higher-resolution topographic data and flood depth grid from the 2D simulation are essential for appropriate flood damage assessment.