Under AMC 21.67 the Municipality of Anchorage requires the submission of site-specific plans for projects which may discharge storm water onto land, surface water or ground water within the Municipality. Any person who constructs, alters, installs, modifies, or operates a storm water treatment or disposal system must comply with plan requirements and reviews as specified in guidance documents established by the Director of Project Management and Engineering. Land developers may be required to meet EPA and ADEC storm water plan requirements as well.

EPA Storm Water Pollution Prevention Plans (SWPPP)
Under the EPA’s Construction General Permit (CGP), all land developers who plan to disturb 1 or more acres of land surface within the Municipality of Anchorage must submit a Notice of Intent (NOI) to EPA and prepare a Storm Water Pollution Prevention Plan (SWPPP). Private land developers must submit the SWPPP to the WMS (in their MOA building permit packet as part of the developer’s Municipal Storm Water Site Plan). Where the land development is publicly funded, developers submit the SWPPP to the Alaska Department of Environmental Conservation (ADEC). In the latter case, the land developer must obtain and include a copy of the ADEC’s Letter of Non-Objection in their MOA building permit packet. See links in Related Resources, right, for more information.

Municipal Storm Water Treatment Plans
Chapter 21.67 of the Anchorage Municipal Code requires anyone who undertakes land development to comply with storm water treatment planning requirements as specified in the Municipality’s Stormwater Treatment Plan Review Guidance Manual, specifically through submittal of a Storm Water Treatment Plan. The storm water plan typically includes submittal forms (MOA Handout AG-21), plan sheets showing pre- and post-development site topography and drainage, and proposals for construction storm water controls (SWPPP Plan elements) and permanent storm water controls (Storm Water Quality Control Plan elements including runoff calculations and soils and ground water information). See links in Related Resources, right, for more information.

Storm Water Pollution Prevention Plans - Describes the type and location of storm water controls and a storm water maintenance and management plan that a developer intends to apply during the construction phase of a project. The MOA requires that an MOA-approved SWPPP be in place before construction begins. MOA’s requirements for an SWPPP are very similar to those required by the EPA and are detailed in the Storm Water Treatment Plan Review Guidance Manual. See links in Related Resources, right, for more information.

Storm Water Quality Control Plans - Details the type and location of permanent storm water treatment devices that developer intends to install. MOA’s requirements for a permanent storm water treatment plan are detailed in the Storm Water Treatment Plan Review Guidance Manual. See links in Related Resources, right, for more information.

Flooding within the Municipality of Anchorage
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.

Flood Insurance
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.

Flood Hazard Permits
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 all mechanical and services, is at least 1 foot above the elevation of the 100-year flood. These standards apply to 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 cost 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 riprap and other bank stabilization techniques. Municipal staff is available to undertake site visits, if requested, to review flood, drainage and sewer issues. Contact the Municipal Flood Hazard Program (907) 343-8023 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 Handout AG.19: Flood Hazard Permit Requirements.