Wetland Classification and Mapping of Seward, Alaska



Map Unit Descriptions


Ecosystem: Riparian


Map Component: RD4F4


Seward Area Extent: 11 wetland polygons; 284.9 acres

A Sitka spruce / alder forest covers this RD4F4 floodplain wetland, along Salmon Creek.  Some RD4F4 wetlands do not appear wet at the surface, but show wetland character in the soil.

Wetland Indicators

Type: Floodplain wetland.

Average depth to water table: 42 cm

Organic layer thickness: 8 cm

Average depth to redoximorphic features: 11 cm

Common Soils: Typic Cryaquents, Histic Cryaquept

Common Plant communities:

Sitka spruce / Sitka alder (Picea sitchensis / Alnus viridis ssp. sinuata)

Sitka spruce - black cottonwood / Sitka alder (Picea sitchensis  - Populus balsamifera / Alnus viridis ssp. sinuata)



HGM: Bidirectional, non-tidal Floodplain flat

RD4F4 wetlands support a water table near the surface in the floodplain of a glacier-fed braided stream valley.  They are forested, and are the most extensive floodplain wetland type mapped.  RD4F4 wetlands are common in the lower Resurrection River; a few are found near the Snow River.  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 15:25