If a project changes where the floodplain is or how high the water gets, the flood map eventually has to change too. FEMA does that through map revisions, and the two you’ll hear about most are the CLOMR and the LOMR.
CLOMR: before you build
A Conditional Letter of Map Revision is FEMA’s comment on a proposed project. It says whether the project, if built as designed, would meet the requirements for revising the map. It doesn’t change the map itself. It gives the developer and the community certainty before construction.
LOMR: after you build
A Letter of Map Revision officially changes the flood map, based on the project as it was actually built. It usually needs an as-built survey and an as-built model.
Two cousins: LOMA and LOMR-F
- LOMA: if a lot or structure sits on natural ground above the base flood elevation, a Letter of Map Amendment can remove it from the special flood hazard area.
- LOMR-F: if it was raised above the base flood elevation by fill, the request is a Letter of Map Revision based on Fill.
When a CLOMR is required
For most projects a CLOMR is optional. It becomes required in cases like a floodway encroachment that would raise the base flood elevation: federal rules only allow that after a CLOMR is approved (44 CFR 60.3(d)(4)).
What to send your engineer
- The site location and the current flood map panel
- Survey or topo, and the proposed plan
- Any correspondence with the floodplain administrator
- Your construction schedule
See how the full process runs on the CLOMR & LOMR roadmap.
Draft written for Creel’s review before publishing. General information, not engineering advice for a specific site.