OPENING LINES HOW TO BUILD AWARENESS OF FLOOD RISK AND GAIN BUY-IN FOR FLOOD CONTROL MEASURES Source: americancityandcounty.com, Katherine Osborne, First Published Sept 13th, 2024 Floods are one of the most devastating events to strike a community—costly in terms of lives lost, damaged or destroyed homes, economic disruption, and damage to critical infrastructure. However, improvements in technology are helping local governments provide accurate assessments of flood risk, so steps can be taken to provide early and accurate warning of flood events, minimize potential losses, and improve outcomes and overall resilience after a flood occurs. WHAT’S MISSING FROM CURRENT METHODS OF MANAGING FLOOD RISK? To understand how local governments can better manage flood risk, it is important to understand how this work is done at present. Many municipal and county governments rely primarily on Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) and Flood Insurance Studies (FIS) for flood information. Per current standards, these flood hazard products use a deterministic assessment of six flood events: the 10% annual chance (10-year), 4% annual chance (25-year), 2% annual chance (50-year), 1% annual chance (100year), 1% annual chance “plus” (100-year plus), and 0.2% annual chance (500-year) flood events based on historic data. The 1% and 0.2% annual chance events, or the Special Flood Hazard Areas (SFHAs), are the mapped flood events shown on the FIRMs. However, extreme rainfall events, which are becoming much more prevalent, are not well depicted in the existing FEMA Risk Mapping, Assessment, and Planning (Risk MAP) datasets. Pluvial (rainfall-related, or “flash”) flood information is not generally available or accessible to communities. It is also rare that local governments have real-time flood risk information for decision support, especially in low population areas, disadvantaged communities or near un-gaged streams. THREE MAIN CHALLENGES LOCAL COMMUNITIES FACE ARE OBTAINING INFORMATION BASED ON: • Current conditions: Most available flood risk information is based on historical hydrologic data and does not account for extreme rainfall events. Current extreme rainfall events are often beyond the 1% or 0.2% annual chance events. Also, due to the large investment of funding and labor required for traditional modeling and mapping methods, analysis may not account for current infrastructure and impervious development. 15 CIVIL AND MUNICIPAL VOLUME 05, ISSUE 09
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