Muhammad Shareef Shazil

Using the 99th percentile streamflow value to generate a flood inundation map in HEC-RAS can be appropriate for representing extreme flood conditions, but it requires careful consideration. Since daily streamflow data might not capture short-duration peak flows, you need to construct a realistic flood hydrograph with rising and falling limbs rather than relying on a single value. Validation against historical flood extents or high-water marks is crucial to ensure accuracy. While suitable for assessing extreme flood risks, check local guidelines to ensure compliance with any specific return periods required for regulatory or design purposes.