Base Level Engineering

Base Level Engineering (BLE) Approach

Base Level Engineering (BLE) is an efficient modeling and mapping approach that aims to provide technically credible flood hazard data at various geographic scales such as community, county, watershed, and/or state level. This data is meant to complement the current effective Flood Insurance Rate Map (FIRM) data, but not replace it. For areas where no flood hazard data exists, the BLE dataset may be the only source of flood risk data.

With a mix of currently available and future datasets from both BLE and other studies, it is expected that for some parts of the state multiple sources of flood data will be available. To decide which source takes priority, factors including, but not limited to, study level (detailed or approximate) and age of the study should be considered. BLE is considered an approximate study and users should always default to the detailed studies on the FIRM if they are available. This BLE data can be used as best available information for areas with no flood mapping information and areas identified on regulatory FIRM as Zone A. For detailed flood zones, such as Zone AE areas on the FIRM, BLE can only be used if the data is more conservative (see example below).

BLE Application

An example of BLE data taking precedence over detailed mapping would be when flood elevation is 10ft for a property according to the regulatory FIRM map, whereas the elevation as per BLE data is 11ft. Since the flood elevation for the property would have more conservative elevation requirements according to the BLE data, it is acceptable to use this information rather than the less restrictive elevation designated on the regulatory FIRM.

Please refer to FEMA's resources for additional information and tutorials for how to best to use BLE data. Additionally, FEMA's Decision Matrix is available to help users understand when it is appropriate to use the BLE data and when it is not. Additionally, if you are interested in learning more about BLE and its applications, please visit the Floodplain Management Training page to register for upcoming webinars and training events.