Effects of Threshold Drainage Area and Study Region Size on HAZUS Flood Analysis

Abstract

This study investigates the trends and error bounds in HAZUS flood hazard modeling due to changes in two parameters: threshold drainage area and study region size. Using the city of Ozark, Missouri, U.S.A., as a case study area, we compared modeled floodplains, flood debris, and economic loss in 24 threshold drainage areas and 20 study region sizes. The results show that the total floodplain area and total economic loss decrease with increasing threshold drainage area while the total amount of flood debris has an increasing trend. A threshold drainage area of 2.00 square miles is regarded as the optimal parameter for future HAZUS flood modeling for Ozark, based on the comparison of modeled floodplains with the FEMA Q3 floodplains. The total floodplain area and total economic loss tend to be larger at a larger study region, while no clear trend has been observed in the amount of flood debris. A study region of one county is suggested for future flood modeling because this size produces stable flood estimates and is also a convenient choice.