Map Unit Descriptions
Geomorphic Component: Riverine
Map Unit: RA
Extent: 145 wetland polygons; 836.1 ha; 0.59% of wetland area; 0.87% of wetland polygons.
 A steep, entrenched stream mapped as RA flowing into the Fox River near the head of Kachemak Bay (polygon 32145). |
Wetland Indicators No data for RA streams Type: Stream Average depth to water table: n/a. Organic layer thickness: n/a Average depth to redoximorphic features: n/a Common Soils: Common Plant communities: NWI: R3US1 HGM: High Gradient Natural Stream-single thread. |
Accuracy assessment: 12 polygons interpreted as RA on aerial photographs were field checked. 6 remained RA; 4 were revised to RB; 1 each was revised to SA and upland. |
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Stream reaches mapped as RA are Rosgen's (1996) 'A' reaches. These are entrenched, steep gradient (4-10%), cascading, step-and-pool reaches, with cataracts and waterfalls. Only a few RA stream reaches were mapped on the Kenai Lowlands. Examples are found along McNeil and Falls Creek, which drain southward across a steep, high bluff into Kachemak Bay near the southern end of the Kenai Peninsula. Reaches mapped as RA support wetlands along only a very narrow margin adjacent to the channel. Occasionally, reaches mapped as RA include short reaches with wide, relatively flat valley bottoms where shallow groundwater discharging from adjacent slopes supports more extensive wetlands along the margins of the stream, such as where Jones Road crosses Eastland Creek in Kachemak Bay State Park. These wide, flat valley bottoms are where streams traverse narrow terrace treads formed during the Last Glacial Maximum (LGM). The narrow treads often support small peatlands.
During the LGM, glaciers expanding southeastward from the Kenai Mountains carved steep bluffs in the Tertiary sediments above Kachemak Bay at some locales and deposited a series of narrowly terraced moraines over the sediments at others. The ice crossed the structural tough between the Cretaceous and Jurassic rocks of the Kenai Mountains on southeast side of bay and often weakly lithified Tertiary sediments of the Caribou Hills on the northwest side.
