HomeMy WebLinkAboutAPA2728by J .T. Hanscom and T .E. Osterkamp
Potential Caribou -Ice Problellls
0 5 10 15
SCALE
4
in the W ataLna ReservoiJ
..
20Miles
Figure 1. Susitna hydroel ectric site.
INTRODUCTION
Caribou from t he Ne lch ina he rd cross
the Susitna River biannually in the vicin ·
ity of the proposed Susitna Hydroelec·
tric Project. It appears that the Watana
Reservoir wi l l be sited near or on three
caribou crossi ng areas. Since past studies 1
of caribou beh avior have shown that dis·
turbance of their natural habitat by va ri ·
ous construction projects (e.g. roads,
p ip el ines etc.) can disrupt their normal
behavior, it is important to try to deter·
mine w hat effect the Susitna Hydroelec·
tric Project w il l have on the Nel c hi na
caribo u herd. The purposes of t h is a rti c le
a re to show t hat the Watana Rese rv oi r
does have t he potential to a ffect car ib ou
mi!Jrat io ns and to ra ise some question s
that shou ld be answered before th e natu re
and extent of the effec ts that the presenc e
o f the reservoir may have on t h e car ib o u
can be predicted.
T h e Watana Reservoir on t h e S u si tna
Riv er wi ll be 54 miles (90 km) in le ngt h
with the dam located about 134 mi les
(2 1 6 km) f rom the mouth of th e rive r
(Fig. 1). The reservoir wi l l be containe d
The Northern Engineer , Vol. 12, No.1
1usitna Hydroelectric Project
within a narrow canyon 1/3 to 1 mile
(0.5 to 1.6 km) wide for much of its
le ng th, except near the tributaries where
it w ill be wider, particularly at Watana
Cr ee k and to a lesser extent at Jay and
Kosin a Creeks and the Oshetna R iver _2
Th e reservoir level is expected to vary
80 to 125 ft (24.4 to 38.1 m) from Octo·
be r to April of the hydrologic year which
corresponds to the period of ice forma-
tion and growth in the reservoir . Maxi·
mum daily variations should be less than
2ft (.61 m). Table 1 shows the minimum
dra w-down schedu le for t h e pool, starting
at its maximum le ve l of 2185 ft (666.4 m).
Parts of the Nelchina caribou herd,
consisting of 15,000 animals, cross the
Sus it na River from the north to south in
late April and early May to reach their
calv in g grounds. La ter in the summer
(late July to early September), they re ·
cross the river go ing north. 3 Although
very little work has been done on current
migration routes, and these may change
periodically or may even be random, it
is t hought that the Watana Reservoir will
affect three general crossing areas at Fog
Cree k , Jay Creek, and the Oshetna River.
Caribou have been observed in these areas
at the time of breakup, possibly waiting
until the largest ice floes clear from the
ri ve r before crossing.4 It is not known
exactly how many caribou cross at these
points.
POT ENTIAL PROBLEMS
AND QUESTIONS
Po ssibly the most ser io us problem may
be the presence of the reservoir; the
ca ribou may not even attempt to cross
it. We leave this important problem to
ihe Northern Engineer, Vol. 12, No. 1
The two caribou photographs in this article are courtesy of Dr. David Klein .
TABLE 1
Maximum Water Level -Minimum Dra w-down Schedule
Mid-month Starting Level 1:-'rtding L evel Change
Oct. 2185' 2185' 0
Nov. 2185' 2 185' 0
Dec. 2185' 2175' -1 0'
Jan. 2175' 2145' -3 0'
Feb. 2145' 2130' -1 5'
March 2130' 2115' -15'
Apri l 2115' 2105' ·10'
May 2105' 2125' +20'
June 2125' 2170' +45'
July 2170' 2185' +15 '
Aug. 2185' 2185' 0
Sept. 2185' 2185' 0
5
Figure 2. Eklutna Lake showing ice shelving on a gently sloping shore. (Photograph by C. Stephens.)
students of caribou behavior and proceed
to potential problems caused by the phys-
ical nature of the reservoir.
Warm water released from the reser-
voir wi ll prevent a stable ice cover from
forming on the river. T his open water
may extend downstream to Ta lkeetna
or farther, depending on weather condi-
tions, so that th e Fog Creek crossing wil l
be open water at all times of the year. Th is
should not create a problem for the cari·
bou since they normally swim the river,
un less they somehow depen d on the ice
cover for crossing at certain times.
Winter d raw-down o f the reservoir will
produce ice-covered shores or so-ca ll ed
ice shelves . T hese ice shelves are formed
when the floating reservoir ice cover be-
6
comes grounded on the shores as the res-
ervoir level decreases during the wi nter.
An example of ice shelving on a gently
sloping shore at Eklutna Lake, near
Anchorage, is shown in F igure 2. The
grounded ice cover may assume the same
shape as the shore or it may fractu re,
creat ing deep cracks, or it may even re-
main suspended in some places. We sug-
gest that an ice-covered shore that is steep ,
contains cracks, or has the potential for
caving under the weight of caribou, may
present a serious obstacle to their c rossing
the reservoir.
T he s lope of the ice-covered shores
in the draw·down zone can be used t o
give an indication of t he location o f very
steep areas that the caribou may have d if-
ficulty negot1atmg. We have measu red
the slope of the north and south shores
of the rese rv oir using a 1 :63,360 scale
map. The slope was measured betwe en
the 2075 ft (632.9 m ) contour line a nd
the 2185 ft (666.4 m) contour line w hich
corresponds to t he la rgest draw-d own
when starting from maximum p ool.
Figures 3 and 4 are graphs of the slope
values along th e north and south sh ores
of the rese rvoir.
The north shore of Watana Rese rvoi r
will b e 67.1 m iles (108 km) in length and
the south shore 51.5 miles (83 km ) in
le n gth. Jay Creek area l ies between 3 8.8
· 45.1 miles (62.5 · 72.5 km) on the n o rt h
shore and 18.6-28 miles (30-45 km ) on
the south shore. The Oshetna River is at
The Northern Engineer , Vol. 12, No.1
-1 ::r
CD
z
0 ... ::r
CD
3
m 11 0
::l 10 0 "' :;· 90 CD
~
< 80
~ 70 .... w
1\) 0.. 60 0 z ....J 50 ? (f)
4 0
30
20
10
00
Figure 3 .
NOR TH SHOR E
.JAY CREEK
OSHETNA RIVER
75 8 0 85 9 0 95 10 0 105
DISTANC E (km)
%slope vs. d istance along the north shore. The t wo cr o ss in g areas o f J ay Creek a nd Oshetna River are ma rked on t h e graphs both where they flow in to th e
proposed re se rvo ir and on the opposite shore . It should b e noted that th e scal e m a p from which these slopes we re ta ke n wo uld not sh ow features such as a
small gully whic h c ou ld en a ble c a ribou to n egotiat e eas il y an a rea that t h e graph s indicate wou ld b e difficu lt.
Figu re 4. % sl o pe vs. distance a long south shore of Wa tana Rese rvoi r .
SOUTH SHORE
110
100
90 .JA Y CREEK
80
7 0
uJ 60 0..
0 50 ....J
(f) 40
30
20
10
0 0 35 40 45 50 55 60 65 70 75 8 0
DI ST ANC E ( km )
65 -67.1 miles (104.5-108 km) on the
north shore and 47.8-51.6 miles (77-83
km) on the south shore. It appears that
the two areas have little in common and
must be considered separate ly as caribou
crossings.
Realistic assessment of the effects of
ice shelving requires consideration of both
caribou behavior and ice conditions. With
regard to the ice conditions, the greatest
need is for a realistic model of the forma-
tion, growth and decay of the reservoir
ice cover. Some questions that should
be addressed are: What are the shore
conditions or slope va lues that may cause
the settling ice cover to break, leaving
cracks in wh ich caribou could be injured
or possibly trapped? What is the timing of
this settling, cracking and snow cover de-
velopment that might mask the cracks?
The -thickness of the settling ice cover
will increase through the winter but what
wi ll the thickness distr ibution be? Will
the w ind keep the ice clear of snow? What
are the maximum slopes of clear ice and
snow-covered ice that caribou can n egoti-
ate? How long will the ice shelves remain
after breakup, and will caribou be forced
to n egotiate melting (wet) ice shelves?
During the spring caribou migration,
the reservoir may still be frozen in the
Jay Creek area, where the caribou wi ll be
coming from the north down a slope that
varies from 109% to 21.5% with much of
the shore between 40 -60% slope. Prob-
ably the only problems the caribou would
have getting down this shore would be
falling into cracks formed as the ice sheet
settles or breaking through t he areas w here
the ice has bridged gaps. The south bank
has a slope that varies from 109% to 9 .0%,
with much of the shore between 30-60%
slope, so it is possible the caribou wou ld
have trouble climbing out on the south
side.
8
' . a • If
Th e breakup dates of Jay and Kosina
Creeks would also be impo rtant. If these
two creeks break up before the caribou
try to cross, there could be water flowing
on top of the reservoir ice , and melted
areas formed at the mouths of the creeks.
An overflow, by itse lf , would probably
cause no problems unless it cut a channel
through the ice. Then t he caribou might
have trouble climbing out on the floating
ice cover after swimm ing or walking
through the overflow.
In the Oshetna River area these same
questions need to be answered, but the
situation is a little different. The slope on
the north shore varies from 53.8% to 6.8%
and on the south shore fro m 35.9% to
6.8%, so both shores have a more gra d ua l
slope than do those at Jay Creek. This
area may be affected by the breakup of
the Tyone River as we ll as t he Oshetna
River. For 3.7 miles (6 km) upstream of
the Oshetna River, the draw-down of the
reservoir may leave an ice sheet on the
river bed and flood plain. Wh en the Tyone
River breaks up, water will be flowing in-
to this ice-covered area . The actua l effect
is unknown but there could be ice jams
and/or ice chunks floating in the area
which would make it di ffic u lt or impos-
sib le for caribou to cross.
In conclus ion, it seems likel y that the
reservoir wil l cause the caribou some prob-
lems, but the seriousness of the prob lems
cannot be realistically assesse d unti l more
information has been gathe re d on caribou
behavior and on the ice conditions in the
reservoir.
ACKNOWLEDGMENTS
Th e Geophysical Institute acknow-
ledges wi th thanks the ass istance o f the
Department of Commun ity & Re giona l
Affairs, State of A laska , and the United
States Go ve rnment , Department of Labor ,
fo r provid ing fund in g for the labo r o n
this report under the Comp re h ensiv e
Employment and T raining Act.
We a lso wis h to than k Dr. D. Klei n,
Univers ity of Alaska; Mr. Ji m Dav is ,
Department of Fish a nd Game, Fa ir·
banks; and Mr . Sterling Eide, Depa rt-
ment of F is h and Game, Glena lle n , fo r
info rmat ion on caribou beh avio r.
REFERENCES
1 Kl ein , D. 1971. Reaction o f re inde er
to obstructions and disturbances.
Science July 30, Vo l. 173, p p. 393 ·
398.
2 U.S. Army Corps of Engineers. 197 5.
Draft Environmental Im pact Stat e·
me nt, Southcentral Rail belt Are a;
Hydroelectric Power Develo pment, Up·
per Susitna River Basin, U.S. Ar my
Corps of Enginee rs, Alaska D ist ric t ,
Anchorage, Alaska.
3 Eide, Sterli ng . 1979. Personal comm uni ·
cation.
* * * *
Janice Hanscom received her B.S . in
Biology from the University of Main e at
Orono. She has been a technician for Dr.
T. Osterkamp fo r the last year.
T .E. Osterkamp is Associate Profess or
of Physics, Geophysical Institute, Unive r·
sity of Alaska, Fairbanks. His inte rests
lie in the scientific aspects of environme n·
tal and engineering problems involving
snow and ice, including permafrost a nd
frozen ground.
The Northern Engineer, Vol. 12, No .1