¶ What Is Base Level Engineering?
Base Level Engineering (BLE) is a method of developing flood risk information, such as flood extents, depth, probability, and velocity, using ground elevation data and modeling software.
Focusing on areas that are either unmapped or lacking digital maps, BLE generates flood hazard information based on simplified hydrologic and hydraulic engineering methods that comply with FEMA’s standards for flood risk projects. In some instances, BLE data can be accessed and used prior to receiving or updating regulatory FIRMs. Information provided through BLE may be considered Best Available Information (BAI).
¶ Examples of BLE
One-Dimensional (1D) BLE Study
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Two-Dimensional (2D) BLE Study
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BLE Map Viewer (United States Geological Survey)
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¶ What Makes BLE Special?
¶ Fills Gaps in Information 🔎
BLE often covers areas of flooding not currently in the National Flood Hazard Layer (NFHL), a FEMA database that contains the current regulatory (also called “effective”) flood hazard data. The NFHL is used to inform the NFIP’s flood zone designations and insurance requirements.
¶ Current (and Best) Data 🥇
In some cases, a community’s BLE data may be more current than its FIRM. Therefore, BLE can sometimes provide more accurate information for flood risk mitigation and management. It can also serve as Best Available Information (BAI) prior to gaining regulatory status, which may be especially useful for communities without other flood data.
¶ Geographic Scalability 🏞️
BLE’s geographic scope is highly scalable, with models ranging from neighborhood-level to county-wide, broadening its usage potential and flood mitigation applicability.
¶ Base Flood Elevation 🏠
BLE analysis also provides information to support local communities’ determination of the estimated Base Flood Elevation (BFE), which can be used to understand flood event probabilities, inform building codes and land use regulations, and determine floodplain development permit requirements. FEMA defines BFE as “the elevation of surface water resulting from a flood that has a 1% chance of equaling or exceeding that level in any given year.” BFEs are provided on FIRMs for select flood zones. Communities that do not have a FIRM, and thus no BFEs, can use BLE to identify the estimated BFE.
¶ Who Is BLE Data for?
It provides a host of benefits for communities seeking to mitigate flood risk and recover from flood-related disasters, including:
- Providing a comprehensive picture of flood risk across a watershed.
- Supporting flood mitigation strategies and projects as model inputs.
- Providing data for NFIP-related documents such as Floodproofing Certificates, Elevation Certificates, and Letters of Map Change.
- Informing local and regional planning and development decisions for multiple community departments.
- Helping communities identify previously unknown flood-prone areas.
- Informing recommendations for local and regional emergency planning, response, and recovery operations.
- Enhancing local flood risk communication initiatives.
Enhanced Flood Risk Communication
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Informing Hazard Mitigation Planning
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