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Local Government Resource Desk

Planning & Land Use

Floodplain Management

Introduction

A "floodplain" is the lowland adjacent to a river, lake, or ocean. Floodplains are designated by the frequency of the flood that is large enough to cover them. For example, the 10-year floodplain will be covered by the flood having a 1 in 10 chance of occurring annually. The 100-year floodplain is more commonly referred to as the one-percent flood or a flood having a one percent chance of occurring annually.

Flood frequencies, such as the one-percent flood (100-year flood), are determined by plotting a graph of the size of all known floods for an area and determining how often floods of a particular size occur.

Narrative Frequently Asked Questions Additional Resources Applicable Laws and Regulations

Revised 12/18/2014