1 dimensional modeling for FEMA floodplains vs 2 dimensional modeling for FEMA floodplains.
My stance is until the floodplain administrators have the technical knowledge and or resources to review 2D models its not doing anyone any favors. Some agree and some do not. I have seen more and more 2D models using quais steady state modeling over large areas and in places where the model domain covers a lot of insurable structures and includes floodways. I have even seen large wood represented in RAS mapper which is interesting since wood floats and rots and moves. Are they going to tell the wood to stay put to match the model?
When I was at CDOT, we advocated for maintaining effective models in 1D and using 2D to inform the 1D models You adjust the 1D modeling based on your 2D but still have the simplicity of regulating to a 1D standard. This simplifies the job for the administrator and helps developers understand the cost and time to meet the floodplain development permit requirements.
My example work from Trinidad Colorado is here. I am not looking for technical comments on my work. This was completed a while ago and the work was done with public funds and has been shared through the local nonprofits. I am providing it as an example for comparing 1D HEC-RAS with 2D HEC-RAS. It is in an older version so the tools and components within HEC-RAS have changed a lot over the last 5 years or so.
If you have questions or want a presentation on 1D and or 2d modeling please reach out. It may help with those who are trying to learn modeling with a short course (which makes me a little nervous). There are additional results/maps in appendices comparing different flows but the file is large. I can share that as well if you are interested please email me.
