I think one way would be Using the LiDAR data and developing flood grids but I am not sure.
having this would help me to develop a preliminary analysis of potentially affected area. I think that way it will help to better understand the watershed dynamics as well as a preliminary business case for further analysis.
I am looking for help for this task and if anyone can help me with the steps and ways that can be done, would help me to accomplish this task .
In summary
Can you give an example of a floodplain map you are working with? Have you thoroughly searched for an existing GIS floodplain maps? Maybe one that have some information but not all the information you want to have. Can you tell me what area of the world/country you are trying to map the floodplains? Need a little more detail to better get a picture of what your working with and hopefully getting to pointed to a solution.