Table 6. Winter depositional processes

Table 1. Summer erosional processes

Figure 5. Aerial photographs of ERF

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6

Table 3. Summer transport

Table 4. Winter trans-

Table 5. Summer depositional processes.

processes.

port processes.

Suspension sedimentation

Suspension sedimentation

Wind currents (pondmudflats)

Frazil ice

settling-out

Suspended load

Anchor ice

Bedload deposition

Bedload

Freeze-on

Sediment gravity flows

Gravitational slope processes

Freeze-in

Slumping

Currents (tidalgully)

Mudflats

Suspension sedimentation

Flood

settling-out

Ebb

vegetation trapping

Ground water

Marshes

Suspension sedimentation

Piping

vegetation trapping

Levees

Suspension sedimentation

settling-out

vegetation trapping

Table 6. Winter depositional processes.

Table 7. Controls on physical processes.

Internal

Morphological

River

unit

Processes

Tides

Glacial sedimentwater sources

Ponds

Ice entrapment and in-situ melting

Substrate material properties

Mudflats

Ice freeze-on and in-situ melting

Vegetation

Snow filtering and in-situ melting

Sediment influxefflux

Ice growth entrapment and in-situ melting

Weatherclimate

Ice cover confined suspension settling-out

Human activity

Ground water conditions

Levees

Ice freeze-on and in-situ melting

External

(sedimentorganics)

Earthquakes

Snow filtering and in-situ melting

Tectonic activity

Ice growth entrapment and in-situ melting

Eustatic sea level rise

Isostatic rebound

Ice cover confined suspension settling-out

Subarctic climate

Glaciers

Gullies

Ice growth entrapment and in-situ melting

Surface and ground water systems

Ice cover confined settling-out

Other important external forces include the re-

Aerial photographs show that tidal gullies have

gional surface and ground water systems, sub-

significantly extended into the mudflats by

arctic climate, eustatic rise in sea level, and gla-

headward erosion (Fig. 5). Short- or long-term

ciers as sediment and water sources (Table 1).

treatments for WP contamination may be com-

Each of these factors must be considered when

promised if such large-scale physical changes oc-

interpreting the physical dynamics of the Flats.

cur shortly after their implementation. The aerial

Tidal and river water dynamics control the

photos also show large-scale changes resulting

amount of material available for deposition in

from riverine processes, which include abandon-

ERF and affect the locations and rates of erosion.

ment of a primary river channel in the southern

The amount of sediment transported in flood wa-

part of the Flats in the last 40 years, channel mi-

ters is a primary factor determining the erosion

gration of various amounts from near the Route

and transport of sediments during ebb. This ca-

Bravo bridge north to the river mouth at Knik

pacity changes seasonally, as sediment discharge

Arm, and the apparent burial of marsh and gully

is reduced in winter, while water temperature

terrain in the Racine Island area.

decreases and salinity increases, causing a net

It is not known whether the seasonal and an-

increase in water density. Higher density water

nual variability of sediment discharge in the gla-

can erode and transport more sediment during

cial rivers is evident in the tidal waters of Knik

the winter, although the total volume transported

Arm. The Eagle River, as do other glacial rivers,

is reduced.

transports an insignificant amount of suspended

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