Wetland Classification and Mapping of Seward, Alaska

 

 

Map Unit Descriptions

 

Ecosystem: Riparian

 

Map Component: RD4F2; RD4F2c

 

Seward Area Extent: 4 wetland polygons; 28.8 acres

A sedge-dominated area in the large wetland complex adjacent to Nash Road is fed by springs, and probably by both flooding and hyporheic water from the Resurrection River.

Wetland Indicators

Type: Floodplain wetland

Average depth to water table: 30 cm

Organic layer thickness: 39 cm

Average depth to redoximorphic features: 8 cm when not an organic soil

Common Soils: Aquic Cryorthents, Fluvaquentic Cryosaprists, Histic Cryaquepts

Common Plant communities:

Bluejoint reedgrass - field horsetail (Calamagrostis canadensis - Equisetum arvense)

Sitka sedge (Carex sitchensis)

 

NWI: PEM2C

HGM: Bidirectional, non-tidal Floodplain flat

RD4F2 wetlands support a water table at or very near the surface in the floodplain of a glacier-fed braided stream valley.  Four of these wetlands are mapped in the Seward area, two adjacent to the Resurrection River, one near Salmon Creek, and one adjacent to the Snow River. 

One in the Resurrection system is fed primarily by groundwater originating on the large rock drumlin to the north.  They are largely cut-off from the river by both Nash Road, and recent flooding.  A Resurrection River channel is shown flowing through the wetland complex the two RD4F1 wetlands are located in, on 1:25,000 USGS topographic maps.  Field visits indicate that recent deposition between the current river channel and the wetlands has resulted in some isolation.  The next flood could either increase that deposit, further isolating the wetlands, or cause the channel to re-occupy its former position.  The other lies between the airport runways and is mostly cut off from the river, except through the hyporheic zone.

The RD4F2 wetland adjacent to the Snow River is primarily fed by surface and groundwater from upslope.  The one adjacent to Salmon Creek is probably well maintained by both hyporheic water, and periodic flooding.

RD4F2c refers to the vegetated portion of the created wetland near the coal loading facility, north of "Roundhouse Pond."  That wetland was created by a combination of the railroad tracks and the Seward highway.

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 RD4F2 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."

 


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Contact: Mike Gracz
Kenai Watershed Forum 
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Old Town Professional Center
3430 Main Street Suite B1
Homer, AK  99603
907-235-2218

12 February 2007 15:24