Natural attenuation by pond drainage

Figure 34. Aerial photographs depicting the morphologic changes in the Eagle River where it enters the ERF

SEDIMENTATION AND NATURAL ATTENUATION OF WP BY BURIAL

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46

that Bread Truck pond will start to drain in 2 to 3

all of the flow in the Eagle River; the north

years or less. In about 6 to 7 years, In-Between

channel was inundated only during tidal flood-

Gully will drain parts of C and Lawson's ponds,

ing (Fig. 34b). The southern channel remained the

and in about 14 to 16 years, Parachute Gully will

principal discharge until sometime between 1967

drain parts of C-Pond (Fig. 35a). Previously, more

and 1972, when flow was reestablished in the

limited short-term data suggested that that Bread

north channel (Fig. 34d). Multiple channels then

Truck Pond would begin to drain in 35 to 50

remained active throughout the 1980s and 1990's

years, while the In-Between and Parachute gul-

(Fig. 34c); however, in September 1995, flooding

lies would begin to drain C-Pond in 17 to 20 years

of the Eagle River resulted in abandonment of the

and 25 to 30 years respectively (Fig. 35b). The

southern channel as the northern channel was

drastic change in our predictions reflects the in-

deeply scoured and eroded eastward into the up-

crease in data obtained on the highly variable

land bluffs.

short-term rates of erosion, and the longer-term

historical rates. The historical data average the

Natural attenuation

variability seen in the short-term observational

by pond drainage

data and are considered more accurate for pre-

Given the combined short-term and long-term

dicting future gully behavior.

recessional data, we revise our previous predic-

Gullies are routes for pond outflow and there-

tion of how long it will take for the ponds to be

fore potential pathways for WP transport. As the

drained naturally (see Lawson et al. 1996). These

gullies continue headward erosion into WP-con-

refined recessional data (Tables 8 and 9) indicate

Pond Beyond

2-3 Years

35-50 Years

BrePd Truck

ond

6-7 Years

17-20 Years

Eag

14-16 Years

25-30 Years

C Pond

Erosion Site

Dredicted Erosion

200

400 m

200

400 m

Rirection

elict Drainage

a. 1995.

b. 1994.

Figure 35. Predictions for pond drainage by selected gullies in Areas C, Bread Truck and C/D.

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