In short, nothing. However, FEMA created the Letter of Map Amendment and Revision (LOMA/R) process to correct or change flood maps [FIRMs and FHBMs] to reflect actual ground surveys or better topographic mapping. Letters are issued by FEMA officially removing lots or portions of lots (by legal description) from the SFHA or changing the boundaries of the SFHA. These are dated and sent to the homeowner applicant and are also filed with the municipality or county within which the property is located. The building site is removed from flood zone AE, AI-30, A, etc and placed in flood zone B, C, or X, which are not part of the SFHA [Special Flood Hazard Area].
When a LOMA/R is issued removing a building site from the SFHA, the mandatory flood insurance purchase requirement is lifted. However, the lender always has the option of requiring flood insurance anyway. For example, the homesite might be just a few inches above BFE, so the lender feels that there is still a threat of flood damage to their “secured property”. Once the flood zone has been changed to B, C, or X, the building qualifies for a PREFERRED RISK POLICY, the least expensive flood insurance available.
Letter of Map Amendment (LOMA): This is used to revise the SFHA boundary based on detailed elevation surveying and/or topographic mapping of natural conditions. If the homesite and the lowest floor of the building (including basement or garage) is above the BFE, FEMA can amend the map to remove the homesite and other land areas from the SFHA. (The map will not actually be physically changed or revised, but the structure or homesite will be certified as being outside the SFHA)
Letter of Map Revision, based on fill (LOMR-F): When FILL dirt is placed on the property to raise the building site above the BFE FEMA can remove the raised area from the boundaries of the SFHA, thus revising the FIRM. This is a man-made change to the floodplain.