Riparian ecosystem wetlands are stream channels exhibiting a bed-and-bank morphology, and their associated valley bottoms. Valleys are various, some are carved by their modern streams, eroded either through glacial till or tertiary bedrock sediments, others were created by Pleistocene glacio-fluvial processes; and others are fed by modern glaciers.

The Kenai and Kasilof Rivers are fed by modern glaciers and flow through large lakes.  These lakes store and buffer flow, and the rivers exhibit generally straight, unbraided, moderate gradient channels (Rosgen (1996) B streams).  The rivers remain unfrozen throughout the winter for several miles from the outlets of the large lakes.  They transport large amounts of glacial silt, although the lakes allow for substantial settling.

Other Kenai Lowlands streams and rivers are fed by precipitation and groundwater, and travel over a mantle of glacial till.  Till overlies poorly lithified Tertiary bedrock  sediments, and upper reaches of many streams south of Clam Gulch have incised deep valleys into this easily erode-able bedrock.

Repeated glaciation has affected the drainage basins of all Kenai streams.  Many streams follow a circuitous course from their headwaters to Cook Inlet or Kachemak Bay.  Stream courses often change direction suddenly when they encounter barriers, such as moraines or terraces.  The Anchor River valley turns abruptly to the northwest just two miles before it reaches Cook Inlet, continuing an additional seven miles around a moraine before finally emptying into the inlet.  The Ninilchik River follows a southwesterly course nearly parallel to the coast for over 15 miles before turning to the northwest at the edge of a terrace, and running its final three miles to the inlet.

A few large sinuous streams exhibit typical meander characteristics such as abandoned meander channels, point bars and cut bank erosion.  The largest streams show similar terrace formation and successional patterns as those described by Viereck (1989) for the Chena River in Interior Alaska.  However, because even the largest Kenai Lowland stream is relatively small, and has a relatively short run from headwaters to saltwater, those features and processes act on a smaller scale.  Channels rarely exhibit any braiding.

Kenai Lowlands streams are frequently underfit, cut by large braided Pleistocene glacier-fed rivers.  Sluggish single-thread streams on Pleistocene river-deposited sediments were left far from steep valley walls after the ice retreated.  A few valleys were cut during the late Wisconsin glaciation by the catastrophic release of the ice-dammed waters of Glacial Lake Cook (Karlstrom, 1964). 

Many underfit, wide valley bottoms do flood, and serve the storage and groundwater recharge function of floodplain wetlands, but they do not function as typical active floodplains which cut banks and create point bars and terraces.  Many are sluggish, linear, pool-dominated channels cut through peat.

Other streams are not underfit; they are entrenched in steeper Tertiary bedrock or thin discontinuous till, primarily south of Clam Gulch.  These streams originate above the limits of late-Wisconsin glacial till: at headwater fen outflows; in till on high pre-Wisconsin plateaus; or as springs originating in Tertiary bedrock or thin early-Wisconsin till.  When they reach lower-elevation late-Wisconsin till they often alter course and character as they flow along terraces, across peatlands on relict glacial lakebeds, or into relict ice-marginal drainageways.

Hydrologic Budget

Stream flow and its timing exert control on channel structure (Ritter, 1986).  Streamflow is controlled by change in groundwater and surface water storage, evapotranspiration and precipitation (Freeze and Cherry, 1979). 

Precipitation

Precipitation is seasonal, and falls as snow in winter.  Rainfall is heaviest just before the winter freeze, and spring melt can occur over frozen ground.  Once precipitation reaches the ground it can follow many paths: it will run off into streams; seep into interacting groundwater flow systems; evaporate, or be taken up and give off by plants (transpired).

Ground- and surface water

Some streams are supported by significant groundwater flow from outside their watershed.  Underlying glacial till can channel groundwater recharge through coarser-textured lenses (Coble, unpublished data).  At most streams, however, the change in groundwater and surface water storage could be assumed to be zero, if averaged over decades (Freeze and Cherry, 1979), although there is some evidence for a long-term climatic drying trend. 

Evapotranspiration

Watersheds of most Kenai streams contain extensive peatlands.  Peatlands function as evapotranspiration basins during the growing season; much of the precipitation intercepted by them is exported from the watershed before it reaches a stream.  A Finnish peatland evapo-transpired up to 65% of precipitation with a water table within 7 inches of the surface (Hukari, 1959 in Ingram, 1983).  Ingram (1983) concludes that fens evapo-transpire about 1.4 times more than from open pan evaporation.  In summer, evapotranspiration probably rivals flow as the largest term in the water budget for local watersheds with significant peatlands.

Evapotranspiration probably still exerts a significant effect on stream channel structure, even if it is not the largest term in the water budget.  If less water was lost though evapotranspiration, more would be available for stream flow.  As peatlands are often dry before the onset of fall rains, they can absorb much of this heavy precipitation, and release large amounts to the atmosphere during the dry spring and early summer months.  If that precipitation was instead released as flow during the fall, channel structure on the Kenai would probably change dramatically, rapidly eroding glacial till and Tertiary sediments.

NWI and HGM

The US Fish and Wildlife Service's National Wetlands Inventory (NWI) classifies the streams themselves as as Riverine.  Riverine 3, (upper perennial) with fast velocity, gravel to boulder beds and little floodplain development, is the most common NWI type on the lowlands.  They correspond to "B" streams.  R2 (lower perennial) rivers and streams are also common.  These are low gradient, slow velocity "E" and "RDA" streams, although, unlike typical NWI R2 streams, floodplains may be poorly developed and oxygen deficits probably never occur.  Stream-adjacent wetlands are mostly intermittently flooded PSS/EMJ Palustrine shrub/scrub and emergent wetlands.

The Hydro-Geomorphic Model key written by Tiner (2003), would classify lowland stream-adjacent wetlands as Lotic Stream fringes.  Type B and C streams are middle gradient streams; while E and RDA streams are low gradient streams.  Rib's are Bidirectional-nontidal River Island wetlands.

Classification

We classify streams and their associated valley wetlands together as a polygon feature; we don't delineate streams separately as waterbodies.  We use Rosgen’s river classification (Rosgen and Silvey, 1996) a basis to classify stream reaches and their associated valley bottom wetlands because it is well known, and provides more information then simple stream order.  We use a modification of Level I, which has seven classes, three of which are common on the lowlands: Types B, C and E (Figure 1.):

• B reaches are moderately entrenched, riffle dominated upper reaches with narrow fringe wetlands;

• C reaches possess riffle/pool morphology with point bars and broad fringe wetlands on floodplains; and

• E reaches are slightly entrenched, stable, pool- dominated channels within relict channels (underfit) supporting wide stream fringe wetlands

Type B stream draining the Epperson Knob area on the southern Lowlands.

Type C stream, Deep Creek, E of the Sterling Highway.

Type E stream. The middle Ninilchik River.

Figure 1.  The common stream types on the Kenai Lowlands.

A fourth type, DA, is used to describe a small, multiple channel stream reach and associated wetlands as the reach fans out onto a glacial terrace, usually in a peatland.

Steep, entrenched 'A' stream reaches, with rapids, waterfalls, and narrow associated wetland margins, occur along a few streams flowing into Kachemak Bay, such as McNeil and Falls Creek.

On the Kenai Lowlands many streams begin as B types, especially south of Clam Gulch.  They are moderately entrenched, post-glacial features. At level II in  Rosgen's classification, The dominant types are B4, with moderately steep valley walls and beds dominated by gravels, and B3 over cobbles.

On many upper B stream reaches, a steeper, more entrenched upper valley abruptly becomes narrower and less entrenched.  This marked change in valley cross-section occurs where a glacial advance pushed material part way up the valley, sometimes changing the stream's course.   

This processes can be easily observed east of Homer, along the south slope of Bald Mountain where a late-Wisconsin (Killey) glacial advance stopped well below the summit (see glaciation section).  The upper valleys are steep, and their streams well entrenched.  Downstream, the valleys abruptly flatten, and still further downstream, they change course abruptly to the west when they encounter the moraine that Hutler Road follows.  

Type B reaches frequently flow into Type E reaches.  E reaches (E for “evolutionary”) on the Kenai are slightly entrenched, stable, low gradient pool-dominated reaches with low width/depth ratios, densely vegetated banks, and low sinuosity (though the typical Rosgen E reach has high sinuosity) and narrow active floodplains.   Although many E reaches have narrow active floodplains and stable banks, occasional abandoned channels and oxbows are evident, and steep valley walls are distant from the channel.

Type E reaches occur on  relict deposits, within wide valley bottoms cut by large amounts of Pleistocene glacial meltwater or on relict glacial lakebeds. A good example of a type E reach is the upper portion of the Ninilchik River, which flows along a terrace.  The most common reach types are E3 and E4 at level II in Rosgen’s classification, with cobble or gravel beds, respectively.

E Reach subtypes

We divide E reaches into four sub-types based on channel sinuosity and form:

• Sub-type 'l' are linear E reaches, with a sinuosity (channel length/valley length) of less than 1.3 (and often less than 1.2). 

• Sub-type 's' indicates sinuous Type E reaches with a sinuosity greater then 1.3. 

• sub-type 'a' indicates E reaches whose channels are not visible on the 1996 1:25,000 black and white aerial photography we use to map the project area, but are obvious during a field visit. 

• Sub-type 'b' describes bank-full linear or sinuous reaches.  These reaches are backed up by an obstruction, such as a beaver dam or road.

Sub-type El stream reach; middle Ninilchick River.  Sinuosity = 1.23

Sub-type Es stream reach; middle Stariski Creek.  Sinuosity = 2.52

Sub-type Eb stream reach; Soldotna Creek.

Type E reaches typically flow into C reaches, which are characterized by a broad floodplain with well-developed sinuosity, riffle-and-pool morphology, and point bars.  C reaches can also flow in broad Pleistocene drainageways, but have point bars, floodplains and, on the Kenai Lowlands, greater sinuosity than typical E reaches.  At Rosgen's level II, the dominant types are C3 (on cobbles) and C4 (on gravels). Stream type is independent of stream size; smaller C streams can flow into larger C steams. 

The lower reaches of the Anchor and Ninilchik Rivers, and Deep Creek are good examples of  C reaches on the Kenai Lowlands, where terrace building and steep bank erosion on a broad floodplain is common.  On smaller type C reaches, such as lower Stariski Creek, the floodplain is narrower, not as active, and the underfit nature of the stream is more evident.

Frequently, B reaches will flow directly into C reaches with no intermediate E reach.  Short run B reaches are also common along the coastal bluffs.  Streams are frequently heterogeneous.  An E reach on a terrace tread will flow into a C or B reach across a riser then back to an E reach on a lower tread without a change in stream order.

Two Riparian ecosystem mapping components are not part of Rosgen's classification.  These are tidally influenced river reaches (Tr), and abandoned meander terraces and channels (AMT).  Tidally influenced reaches have a salinity of greater than about 0.5 parts per thousand on the highest spring tides.  The exact spot on each western peninsula stream where this occurs has not been reported; we rely on local knowledge, especially Robert Begich and Larry Marsh of the Alaska Department of Fish and Game to map Tr units.  Most streams are relatively small, steep and short run, and have a tidally influenced component too small to map at 1:25,000.  On the large glacier-fed streams, the Kenai and Kasilof Rivers, the tidal influence extends for miles upstream.

The second mapping component that is not part of Rosgen's classification, but we include in our Riparian Ecosystem are Abandoned Meander Terraces and Channels (AMT).  These are relict features, created when the glacier-fed rivers were larger, or outburst floods more intense.  These features, which are limited to a few lower reaches of the two glacier-fed streams, are now occupied by peatlands.

Soils

Soils are typically the stratified alluvial entisols of the Killey (stratified loamy over stratified sands and gravels) or Moose River (stratified loamy alluvium) Series.

Fifty foot habitat protection area

Fourteen streams in the project area are covered under Kenai Peninsula Borough's Anadromous Streams Habitat Protection Ordinance.  Many activities require a permit, or are prohibited within 50 feet of these streams.  For a list of the streams, rationale for the ordinance, and details on obtaining a permit, visit the link highlighted above.

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."

Plant Relationships

Type B reaches have narrow riparian zones and are usually dominated by spruce forest with a bluejoint grass (Calamagrostis canadensis) and field horsetail (Equisetum arvense) understory, sometimes with a narrow bluejoint streamside community immediately adjacent to the stream.

Type E reaches are typically bordered by broad wetland margins beginning with bluejoint streamside meadows immediately adjacent to the channel, then spruce forests with field horsetail and either bluejoint grass or willow in the understory (often on the foot- and toeslope).  Occasionally, willow / bluejoint communities are present between the bluejoint meadows and forest.  Bluejoint streamside communities will also occupy the low berms which indicate the bank-full stream margin.

Type C reaches support the largest variety of plant communities.  Tall, thick Barclay willow can dominate, especially along Starisky Creek.  Along other reaches, a patchy mosaic of bluejoint grass and Barclay willow (the Natural Resources Conservation Service's willow-grass ecosite) is often found, and tall cottonwoods. 

Frequently, a ponded water zone forms at the position of toe-slope discharge, adjacent to steep valley walls.  A variable willow - marsh fivefinger (Comarum palustre) community often occupies this zone.  Side channel flooding will also create ponded water there.  Beaked and/or water sedge (Carex utriculata and C. aquatilis) often occupy the shallow pools.

Barclay willow and bluejoint inhabits a transition zone between the ponded water zone and more or less pure bluejoint grass closer to the channel.  A diverse bluejoint streamside community occurs immediately adjacent to the channel, with a diverse mixture of Jacob's ladder (Polemonium acutiflorum) paintbrush (Castilleja unalaschcensis), yarrow (Achillea millefolium ssp. borealis) and others. 

Patchy, diverse cottonwood (Populus balsamifera ssp trichocarpa) stands are found along the lower reaches of the larger Type C streams.

An E5 stream reach with bluejoint streamside community and a gravel bed in the large fen complex east of Anchor Point.

A moderately entrenched B stream reach with thickly vegetated banks and riffle dominant morphology over a gravel-dominated bed at the east margin of the large fen complex east of Anchor Point.

Bluejoint, and tealeaf and undergreen willow at the margins of an underfit C reach (along Soldotna Creek).  A ponded water zone forms here with standing water at the toe-slope edge of the larger relict valley.

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 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary

03 May 2007 18:04