Streams, rivers, lakes, and coastal areas in Anchorage are susceptible to flooding that can threaten lives and damage property. The Municipality has close to 10,000 acres of floodplain and more than 3,500 individual parcels that are partially or entirely located within the floodplain.
This webpage provides information about the Municipality's floodplain and about local rivers, streams, creeks, and other drainageways in general. Municipal personnel are available to provide specific flood and flood-related information and make site visits to review flooding, drainage, flood-related sewer problems and advise and assist on retrofitting techniques. To speak with someone directly about these issues, please call the Municipality of Anchorage's Flood Hazard Program at (907) 343-8078 or (907) 343-8135.
To minimize damage to structures during flood events the Municipality of Anchorage requires a Flood Hazard Permit for all new construction in the floodplain. Construction must be anchored against movement by floodwaters, resistant to flood forces, constructed with flood-resistant materials , and flood-proofed or elevated so that the first floor of living space, as well as mechanical and services, is at least 1 foot above the elevation of the 100-year flood. These standards apply to all new structures and to substantial improvements of existing structures. The Municipality defines a Substantial Improvement as any reconstruction, rehabilitation, or addition to an existing structure, the value of which exceeds 50 percent of the structure's appraised or market value (whichever the builder chooses to use).
Additionally, most other types of development within the floodplain also require a Flood Hazard Permit, such as grading, cut and fill, installation of rip-rap, and other bank stabilization techniques. Contact the Municipal Flood Hazard Program (907) 343-8078 or (907) 343-8135 for further information and prior to undertaking any activity within the floodplain. A link is provided on this page to the Flood Hazard Permit Application and the basic submittal requirements outlined in AG:19 Flood Hazard Permit Requirements.
Floodplain maps help identify flooding risk and who qualifies for flood insurance. FEMA publishes flood hazard maps showing Municipal areas prone to flooding that are regulated by FEMA. You can review floodplain maps in our map viewer, in the data library, or from FEMA’s online map service center.
The Municipality of Anchorage participates in the National Flood Insurance Program (NFIP) that makes available federally backed flood insurance for all structures, whether or not they are located within the floodplain. Membership within NFIP - and the availability to municipal residents of flood insurance - requires the Municipality of Anchorage to manage its floodplain in ways that meet or exceed standards set by FEMA. Federal financial assistance requires the purchase of flood insurance for buildings located within the SFHA - a requirement that affects nearly all mortgages financed through commercial lending institutions. While the mandatory flood insurance purchase requirement has been in effect for many years, not all lending institutions required flood insurance in the past. Today, however, most institutions are now requiring the flood insurance purchase, and some are reviewing all mortgage loans to determine whether flood insurance is required and should have been required in the past.
The Municipality of Anchorage features many small streams and several larger rivers that are susceptible to annual flooding events that pose threats to life and safety and can cause significant property damage. Large rivers include the Glacier Creek, Twentymile River, Portage Creek, Placer River, Ship Creek, and Eagle River. Smaller streams include California Creek, Virgin Creek, Alyeska Creek, Fire Creek, Chester Creek, Campbell Creek, Little Campbell Creek, Fish Creek, Furrow Creek, Rabbit Creek, Meadow Creek, Fire Creek, and Peters Creek. Additionally, the shorelines of many of the small lakes in Anchorage are subject to periodic flooding. Lastly, coastal areas may experience flooding associated with extreme high tides.
The Municipality of Anchorage has close to 10,000 acres of floodplain and over 3,500 individual parcels that are partially or entirely located within the floodplain. Rainfall runoff and snowmelt from the Chugach Mountains contribute substantially to flooding, and ongoing development within the Municipality continues to displace natural areas that have historically functioned as flood storage.
While some sort of seasonal flood-related damage occurs nearly every year, and can occur at any time of year, notable flooding from prolonged precipitation and warmer than average fall temperatures, caused by a warm-weather trend known as a “Pineapple Express” occurred in Anchorage and Southcentral Alaska during the falls of 1995, 1997, 2002 and 2005. Flooding from these events caused millions of dollars of damage to property and infrastructure and disrupted local and regional transportation.
During the winters of 2003 and 2006, colder than normal temperatures, combined with later than normal snowfall, caused the formation of aufeis in local streams, leading to overbank flooding, particularly on Peters Creek. Aufeis, or icing, forms when water in streams and river falls below freezing and ice crystals begin to form within the flowing water. The ice crystals adhere to the stream bottom and continue to grow into large masses that obstruct flow. Rivers and streams in this situation are essentially freezing from the “bottom-up.” Within localized areas, flooding from aufeis can extended well beyond the mapped extent of the 100-year flood.
During the summer of 2008, an intense localized “cloudburst” caused flooding on the east side of the Anchorage Bowl. Stormwater runoff exceeded the capacity of the constructed and natural drainage system. Floodwaters flowed into the crawlspaces and lower floors of some local residences. Similar occurrences have occurred in other areas of towns during past summers.