Wetland Classification and Mapping of Seward, Alaska

Mike Gracz

Doug Van Patten

Because of the success of the Kenai Lowland wetland classification and mapping project, it was extended to cover the area around Seward, Alaska.  Old maps needed updating, and easy public access to the new information was desired (the maps are available over the internet at the Kenai Peninsula Borough's interactive map viewer site, select "Wetlands" from the view dropdown menu at the top of the page).  We mapped 4,520 acres of wetlands over the 24,600 acre project area (18% of the land surface) at a scale of 1;24,000.  The project was completed in 2006.

Wetlands are mapped because activities in them are regulated under section 404 the US Clean Water Act.  Placement of fill in a wetland requires a permit from the US Army Corps of Engineers.  Permits are free, and generally easy to obtain.  Activities in wetlands are regulated because they affect others, outside their boundaries.  Habitat suffers, water quality diminishes, and flooding events become more common and severe with unregulated wetland disturbance.  Aside from regulations, building activities in wetlands are usually more difficult and expensive to undertake.  Knowing where wetlands are is useful.

Wetlands are not always easy to recognize.  A definition of a wetland is needed, because they are regulated.  A area that meets the definition is termed a jurisdictional wetland by the Army Corps of Engineers.  Criteria and methods for recognizing and delineating the boundaries of jurisdictional wetlands are described in a technical delineation manual published by the Army Corps in 1987.  A draft regional supplement to this manual, describing Alaska wetland delineation is currently under test and review (2006-07).  Generally speaking, if the water table is within a foot from the surface for two continuous weeks of the growing season, during half of all years, then the site meets jurisdictional criteria.  Much of the delineation manual focuses on how to recognize wetlands during the times of the year when the water table may be more than a foot from the surface.

Wetlands are not all the same.  This map shows greater detail than simply a demarcation between wetland and upland.  Upland is the term used to describe areas that are not regulated under section 404 of the Clean Water Act.  In Seward, wetlands are named differently depending on where they occur on the landscape and how deep the water table is.  A lake on a bedrock knob functions as a different wetland than a bog adjacent to a river floodplain.  This website describes the conditions that are commonly encountered at wetlands with different names.  It includes the methods we used to map wetlands and provides links to many wetland resources and data downloads.

Seward wetlands are classified using the same framework as used in the Kenai Lowlands.  Seward wetland soils, plant communities, and mapping units (the names assigned to each wetland) are described separately on this website because Seward area geomorphology and hydrology are radically different than conditions on the Lowlands.

In Seward, some areas were named on the wetland map that do not meet Army Corps jurisdictional criteria.  These are higher floodplain terraces.  These areas were included because of the high frequency and severity of flooding around Seward, and the dynamic nature of local rivers.    Although they were high and relatively dry when we mapped the terraces, flooding may change that at any time.  Activities on them will not require an Army Corps wetland permit, but activities on them should be considered carefully.