A new regime is need for flood risk insurance - in Canada, insurers are now selling overland flood insurance (separate from common sewer pipe back-up) available in areas of small local overland flow, beyond valleys. That new Canadian coverage (Intact, Aviva, RSA ...) is not available in high risk floodplains though. So highest risk are not insurable. The key problem in Canada is a fragmented insurance market with some insurers holding a couple percentages of the property and casualty market, making it uneconomical or impractical to invest in proper risk models for complex phenomena : valley riverine, urban overland, and sewer back-up risk are sometimes interrelated during extreme events as shown in a review of last 3 Toronto storms exploring risk factors holistically "from flood plain to floor drain":
https://www.slideshare.net/RobertMuir3/urban-flood-risk-from-flood-plains-to-floor-drains
New floodplain maps alone will not improve understanding of the highest risk urban flood risks.