Without base flood elevation9/22/2023 ![]() ![]() The extra volume from these large rainfalls will naturally overflow into the floodplain, temporarily storing the floodwaters and reducing the impact on downstream residents. During large rainfalls, the creeks within Atlanta cannot handle the full volume of flow within the stream banks. ![]() What are the natural functions of the floodplain?įloodplains have many positive impacts on the environment. The City of Atlanta prohibits any filling in the floodplain. Filling in the floodplain nearly always alters natural drainage patterns, diverts flood waters to other properties, or affects endangered species or their critical habitat. Filling is included under the NFIP definition of “development” and therefore requires a floodplain development permit. This area is subject to inundation by the base flood but conveys little or no velocity flows.īy nature, floodplains are low-lying areas that seem to invite filling activities. The area on either side of the floodway is called the flood fringe. Regulations require that the floodway be kept open so that flood flows are not obstructed or diverted onto other properties. The floodway carries the bulk of the floodwater downstream and is usually the area where the speed and depth of flood waters are the greatest and most destructive. The floodway includes the channel of a river or stream and the overbank areas adjacent to the channel. The National Weather Service (NWS) and the National Oceanic and Atmospheric Administration (NOAA) have more information about rainfall frequency and volumes. ![]() This same home has less than a 1% chance of fire damage during the same period. Although a 100-year flood sounds remote, keep in mind that over the life of an average 30-year mortgage, a home located within the 100-year flood zone (see below for flood zone definitions) has a 26% chance of being inundated by the base flood. The base flood, sometimes referred to as the 100-year flood, has a 1% chance of occurring in any given year. These areas are indicated on the National Flood Insurance Program (NFIP) Flood Insurance Rate Maps (FIRMs) that are available on FEMA’s Map Service Center: ![]() The SFHA is often referred to as the Floodplain. The Special Flood Hazard Area (SFHA) is an area of high flood risk that is inundated by the 1% annual chance flood, sometimes referred to as the 100-year flood or base flood. In Atlanta, these areas are called “Historically Modified Floodplain” In many of Atlanta’s urban areas, past development transformed old streams and creeks by forcing those surface waters into pipes but the associated floodplains often function as though a stream or creek still existed. In fact, communities experiencing large population growth can create a floodplain where none previously existed. Floodplains have varying characteristics and may not be easily identified. You may be located five miles or more from a river or stream and find your house covered with flood waters. The non-technical and simplified definition of a floodplain is “an area adjacent to a body of water.” But using this definition to determine if your property is in a floodplain is deceiving. Please direct any questions, or requests for more information to the City’s Floodplain Administrator at 40 or Information About Floodplains and Floodplain Management Further, the Department will review and update, at least annually, the content to ensure that it is current and relevant. The Department of Watershed Management will regularly check this website to ensure that hyperlinks remain accurate. The table of contents at the top of this page provides an overview of the available information, as well as quick access to each topic. It also describes Atlanta’s floodplain management activities in detail. This webpage provides more information about floodplain management. Storm Preparation and Flood Recovery Tipsįlood Zone Classifications and Flood Zone Mapsįloodplain Management Frequently Asked Questions (FAQ) Basic Information About Floodplains and Floodplain Management ![]()
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