Wetland Classification and Mapping of Seward, Alaska



Map Unit Descriptions


Ecosystem: Riparian


Map Units: RD4F12; RD4F21


Seward Area Extent:

RD4F12: 3 wetland polygons; 37.6 acres

RD4F21: 3 wetland polygons; 30.6 acres

The margin of a beaver-dammed RD4F21 adjacent to the Snow River.


Wetland Indicators

Type: Floodplain wetland.

Average depth to water table: 17 cm

Organic layer thickness: 11 cm

Average depth to redoximorphic features: 5 cm when not an organic soil

Common Soils: Histic Cryaquepts, Fluvaquentic Cryosaprists, Aquic Cryorthents, Typic Cryaquents

Common Plant communities:


Water horsetail (Equisetum fluviatle)


Sitka sedge (Carex sitchensis)

Bluejoint reedgrass (Calamagrostis canadensis)



HGM: Bidirectional, non-tidal Floodplain flat

RD4F21 and RD4F12 are floodplain wetlands with a mix of open water and sedge-dominated components.  They lie in the river floodplain, separated by a natural levee, or other feature.  The six wetlands mapped as either RD4F12 or RD4F21 are all adjacent to the Snow River.  If sedges dominate the wetland is named RD4F21 and if open water dominates, RD4F12.  Floodwaters are slowed and stored in these wetlands which are also fed through the hyporheic zone, and by nearby groundwater discharge.

One of the wetlands adjacent to the Snow River is maintained by an extensive beaver dam, and another two by a natural river levee.  The others may be partially impounded by roads.

Braided stream systems 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.  Terraces and floodplain wetlands are affected.  These areas are expected to change character 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 15:26