Wetland Classification and Mapping
of Seward, Alaska
Map Unit Descriptions
Map Component: RD4SC
Seward Area Extent: 10 wetland polygons; 56.3 acres
The dry portion of a side channel of the Snow River. Parts of this dry channel support stillwater pools, unconnected at the surface, but connected to the main river channel beneath the gravels, in the hyporheic zone. This channel becomes re-connected at higher flows.
Type: Stream side channel, often a wetland when abandoned, or a water of the US when occupied.
Average depth to water table: 32 cm
Organic layer thickness: 3 cm
Average depth to redoximorphic features: 0 cm
Common Soils: Typic Cryaquents
Common Plant communities:
Sitka Alder / bluejoint reedgrass (Alnus viridis ssp. sinuata / Calamagrostis canadesis)
Sitka Alder / field horsetail (Alnus viridis ssp. sinuata / Equisetum arvense)
Sitka spruce / field horsetail (Picea sitchensis / Equisetum arvense)
HGM: Bidirectional, non-tidal Floodplain flat
RD4SC are side channels of the large glacier-fed braided streams and rivers around Seward. Bed material is dominated by gravel, with some sand and cobbles. Side channels may be active or abandoned. Abandoned channels may reactivate during floods, or gradually convert to floodplain wetlands. Alder, and eventually spruce become established on them.
Many side channels support pools that are intermittently connected to the main channel during higher flows. These pools can be important rearing areas for juvenile salmon.
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. The area mapped as RD4SC is expected to change following floods.
The Snow River is a glacier-fed braided stream with a gravel-dominated bed. It floods every two to four years when meltwater that has accumulated in a glacier-dammed lake drains. Bedload transport, deposition, and channel shifting processes occur there too, but on a more regular basis.
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 15:25