Wetland Classification and Mapping of Seward, Alaska



Map Unit Descriptions


Ecosystem: Riparian


Map Component: RD4F3


Seward Area Extent: 25 wetland polygons; 251.1 acres

Alders cover this RD4F3 floodplain wetland along Nash Road.

Wetland Indicators

Type: Floodplain wetland.

Average depth to water table: 20 cn

Organic layer thickness: typically very shallow (0-10 cm) but occasionally a Histosol (>40 cm)

Average depth to redoximorphic features: Typically 6 cm, unless a Histosol

Common Soils: Typic Cryaquents, occasional Typic Cryohemist

Common Plant communities:

Sitka alder / field horsetail (Alnus viridis ssp. sinuata / Equisetum arvense)

Sitka alder / bluejoint reedgrass (Alnus viridis ssp. sinuata / Calamagrostis canadensis)

Barclay willow / bluejoint reedgrass (Salix barclayi / Calamagrostis canadensis)



HGM: Bidirectional, non-tidal Floodplain flat

RD4F3 wetlands support a water table near the surface in the floodplain of a glacier-fed braided stream valley.  They are usually alder dominated.  RD4F3 wetlands are common in the lower Resurrection River; a few are found near the Snow River, where they tend to be dominated by Barclay willow, rather than alders.  These wetlands are fed during floods, and may be a significant area for retention of floodwaters.  They are also fed and supported by hyporheic water.

These wetlands occupy the floodplain of braided stream systems.  Braided streams carry large amounts of material during frequent floods.  As floodwaters subside the material is deposited, resulting in streambed aggradation; as much as several feet during a larger event.  When the bed aggrades, it becomes higher than the surrounding valley, so the stream channel often shifts to a lower position.  Because of this process, which dominates most of the valley floors and alluvial fans in the Seward area, prediction of where a stream channel might be following a flood event is probably impossible.  The area mapped as RD4F3 is expected to change following floods.

Floodplain regulation

From The Kenai Borough website:

"The Kenai Peninsula Borough manages a Floodplain Ordinance that addresses proper development to reduce flood risks and lessen the economic losses caused by flood events. The ordinance provides building standards for construction projects within the floodplain to ensure the availability of flood insurance through the National Flood Insurance Program. These building requirements also are intended to minimize or prevent damage when flood events occur. The ordinance requires floodplain development permits for all projects in floodplains."


Do I Need a Permit?

 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary



Contact: Mike Gracz
Kenai Watershed Forum 
Homer Field Office
Old Town Professional Center
3430 Main Street Suite B1
Homer, AK  99603

12 February 2007 15:24