Wetland Classification and Mapping
of Seward, Alaska
Map Unit Descriptions
Map Units: RD4F1-3; RD4F1-4; RD4F2-4
Seward Area Extent:
RD4F1-3: 5 wetland polygons; 47.3 acres
RD4F1-4: 1 wetland polygon; 6.9 acres
RD4F2-4: 1 wetland polygon; 4.8 acres
An RD4F1-3 along Nash Road. It is fed by groundwater, hyporheic water from Salmon Creek, and by occasional flooding.
The RD4F2-4 portion of a wetland along Nash Road.
Type: Floodplain wetland.
Average depth to water table: 0 cm
Organic layer thickness: 7 cm
Average depth to redoximorphic features: 0 cm
Common Plant communities:
Water horsetail (Equisetum fluviatle)
Sitka sedge (Carex sitchensis)
Bluejoint reedgrass (Calamagrostis canadensis)
Sitka alder / field horsetail (Alnus viridis ssp. sinuata / Equisetum arvense)
Sitka alder / bluejoint reedgrass (Alnus viridis ssp. sinuata / Calamagrostis canadensis)
Sitka spruce / Sitka alder (Picea sitchensis / Alnus viridis ssp. sinuata)
Sitka spruce - black cottonwood / Sitka alder (Picea sitchensis - Populus balsamifera / Alnus viridis ssp. sinuata)
NWI: PEM2C (F1 and F2); PSS1C (F3); PFO4(1)B (F4)
HGM: Bidirectional, non-tidal Floodplain flat
These floodplain wetland complexes are a combination of several floodplain wetland components from open water to forest. All have the sedge-dominated (RD4F2) and shrubby or bluejoint reedgrass dominated components (RD4F3). Five floodplain wetlands also support the open water (RD4F1) component, and they are named RD4F1-3. One other floodplain wetland supports only and additional forested component (RD4F4) and is named RD4F2-4, while a seventh wetland supports all of the floodplain wetland components and is named RD4F1-4. These wetlands are fed by a combination of river floodwaters, hyporheic water, and groundwater discharge from adjacent bedrock knobs.
They all lie in a river floodplain, separated by a natural levee, or other feature. Four of the five wetlands mapped as RD4F1-3 all lie on the lower Salmon River floodplain along Nash Road. The fifth is along the Resurrection River, dammed by the Seward Highway.
The RD4F1-4 wetland lies along the Snow River, separated by a natural levee. The RD4F2-4 wetland lies near the Seward airport, in the Resurrection River delta, and is slowly being captured by a changing river channel.
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.
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."
|Contact: Mike Gracz Kenai Watershed Forum Homer Field Office Old Town Professional Center 3430 Main Street Suite B1 Homer, AK 99603 907-235-2218||
12 February 2007 15:27