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~iver Ice,susit,second draft 3/21/83
PaRe 1
----------1 and 2 are caused by the construction of these proj-
ects and regulation of flows is ~oing to change both the hydraulic regime and
the thermal regi.e and these two thinRS are the determinant of what happens
with respect to the formation of ice in the river. So we have to understand
very clearly what these changes are going to be before we can discuss these of
Items 1 and 2 are cards(?) and we are nov going to go on and
UN1VERSITY OF AL\S'<A
ARGT'IC ENVIRONME NTAL INFORMATION
ANLJ DATA vEiH ER
.ore or less, and the breakup period which occurs very fast in a short period
froa •id-to late-April to mid-May. Nov, -----the aost significant
effect of the project and with any stora1e projeet is the 1reat re-re10lation
of the flow when the chan1e in flow pattern in the river dovnstreaa. This of
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~i ver Ice .susit .second draft 3/21/83
Pat~te 1
1 and 2 are caused bv the construction of these proj-
ects and regulation of flows is ~oing to change both the hydraulic regime and
the the't1Ml regia.:! and these two thin~s are the detei'111inant of what happens
with respect to the foraation of ice in the river. So we have to understand
very clearly what these changes are going to be before we can discuss these o f
Ttems 1 and 2 are cards(?) and we are now going to go on and
UN1VERSITY OF A L \S'<A
ARGT1C ENVIRO NME NTAL I NF O ~MATION
ANiJ OAT J.. Ei..IT ER
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.ore or less. and the breakup period wh!ch occurs very fast in a short period
froa •id-to late-April to aid-May. Nov, the .est significant
effect of the project and with any storage project is the great re-regulation
of the flow when the change in flow pattern in the river dovnatreaa. This of
·,
T
This is a transcription of Tom Lavender's Susitna River
ice discussion at the Exhibit E Symposium in December.
A line ( ) indicates word or words not
intelligible from the tape of the talk. A question mark
(?) indicates word is uncertain.
t.j//}JJ
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ice cover itself, which lii8Y be of least amount of interest, but there are
generally some questions with respect to how thick the cover is going to be
after regulation~ and how it is going to respond to flow variations.
To do this I have prepared some cartoons to help explain principles. To
give first here I have a representation more or less of a median flows one can
expect in a river, the blue line indicates is the flow hydrograph for the
present condition we can see to a year in a depth to signal (?) variation
where we have suaaertime peak discharges passage of months declining to winter
lows and then the spring rise again with period of particular interest to us
in this discussion being the winter period beginning about this time mid-october
and ending about this tiae and finish at breakup in mid-to late-Hay. 1~ese
winter periods can be subdivided significantly in terms of freezeup period in
the front here which now takes place between mid-october and mid-December,
.ore or less, and the breakup period which occurs very fast in a short period
from •id-to late-April to mid-Hay. Now, the .est significant
effect of the project and with any storage project is the great re-regulation
of the flow when the change in flow pattern in the river downstream. This of
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~iver Ice,susit,second draft 3/21/83
Pa~e 1
1 and 2 are caused by the construction of these proj-
ects and regulation of flows is going to change both the hydraulic regime and
the thermal reg~.e and these two things are the determinant of what happens
with respect to the formation of ice in the river. So we have to understand
very clearly what these changes are going to be before we can discuss these of
the ice regime. Items 1 and 2 ate cards(?) and we are now going to go on and
discuss that in terms of what these do to the ice front location, where the
ice occurs, where the ice cover probably will occur and won't occur, and to
carry off the all important question of what water levels are going to be as a
consequence of these few ch anges and then there will be a discussion on the
ice cov~r itself, which may be of least amount of interest, but there ar~
generally some questions v!th respect to how thick the cover is going to be
after regulation8 and how it is going t o respond to f low variations.
To do this I have prepared some cartoons to help explain principles . To
give first here I have a representation more or less of a median flows one can
expect in a riv~r, the blue line indicates is the flow hydrograph for the
present condition we can see to a year in a depth to signal (?) variation
where we have summertime peak discharges passage of m~nths declining to winter
lows and then the spring rise again with period of particular interest to us
in this discussion being the winter period beginning about this time mid-october
and ending about this ti.e and finish at breakup in aid-to late-May. These
winter periods can be subdivided significantly in teras of freezeup period in
the front here which nov takes place between mid-october and mid-December,
.ore or less, and the breakup period which occurs very fast in a short period
from •id-to late-April to mid-Kay. Nov, the most significant
effect of the project and with any storage project is the great re-regulation
of the flow when the change in flow pattern in the river downstream. This of
-· (
River Ice,susit,second draft 3/21/83
Page 2
course is beneficial in teras of hydropower generation so the area under this
bydrograph of course represents a so we s ee the red line
would be indicated median pattern of flows throughout the year. W~ see of
course that this is more or less constant throughout the year as compared to
this very sharp peak and the volu.e of water indicated by the area be~en
'.:hese tvo lines is quite sbaplv transferred from the s~r season to the
winter season. The area here is equal to the area in here, representing a
transfer if its released in winter
.anths. From the point o f view of ice cover the most significant aspect of
this is not the difference in discharge, increased winter discharge. The
reason being the principal factor governing ice processes in the river is
discharge, the principal factor concerning water levels, thickness of ice
cover, and rate of development. the other second effect consequence
of the power regulation is its influence on temperature. We should discuss
these to soae extent. Here again I have indicated with a blue line this tiae
a thermograph with the same period of months. The blue line indicates the
natural condition where we see a summertime rise in temperature to about 9°C
declinintt to a winter temperature o• plus a fraction and so on year a f ter
year. With the pro~ect in place we will see some changes in these temperature
regimes and as T have indicated here as the temperature is thermographed for a
section a ve~y short distance downstream of the project. With regulation we
see higher vintertt.e temperatures. rising to a sum.ertime here not as high as
the natural conditions in the saall difference there and declining more slowly
in the fall as the influence of the reservoir retards the cooling down of the
river and the theraal map reaching ultimately soae
te.perature which has been discussed and would be less than 4° greatP.r than
probably about 2•. I have a scene here for illustrative purposes, soaething
(
River Ice • .u.it.second draft 3/21/83
Page 3
about 3° durin~ the winter aontbs springtime to rise. This ----------------
line corresponds to the regulated condition for. say. just a short distance
dovnstrea• fro. the project. As you .ave dovnstrea• you see a decay in these
tnperatures so there is sa.e distance dovnstreaa you would expect to see
teaperature profiles as indicated for example by the broken line here where
the au..ertiae tnperatures are a little higher because beat gain between
reservoir and that particular p~!nt and you would see some la~ or delay in the
ti.e in which the temperature decayed to o• but it does indeed get back to the
natural level and would remain there during the winter at some point downstream.
This is rather significant with respect to answering your questions for where
the ice front is going to be located. I would like to .. ke a very t.portant
point here which is that in looking at thermal effects we really should be
looking at totalf?) energy content. The temperature is nothing more than a
manifestation of the amount of tbermaJ energy that is present. We see in fact
that what the reservoir does with thermal energy. it is nor.ally gained in the
sua.ertiae would be quite simp)v transferred to the winterti•e just as it
transfers runoff volume to the wintertime. So that if we look at increaental
heat graph, if you like, this represents the amount of heat that is in the
water at a given tiae of the year over and above what would be there under
natural conditions. Which is to say, that ~f you take that volume flow rate
difference .ultiplied by the corresponding te11perature difference you can
convert that into BTU's per hour or as I have used here megawatts, which repre-
sents heat content. You can see that during the winter months we have an
excess ..aunt of beat being released fro. the reservoir and it is rather signifi-
cant. in terms of approxi.ately 3500 to 4000 megawatts, a tre.endous amount of
ther.al beat. Beat corresponding to that excess wintertime beat in the sumaer
80nths even though the difference here is relatively s.all the discharge is
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River Ice,susit,second draft 3/21/83
Pa1e 4
lar1e so that you see quite large negative heat content. That is, less heat
from the downstream channel durin~ the summer month\'3 or under natural conditions.
And just as in the case of the reservoir where the volume (the area here and
here must balance, and the area here and here must balance). Mean temperatures
are unchanged and quite simply affected a transfer of thermal energy from
summer months to winter months whose manifestation is temperature. You're
really talking about thermal energy when vou talk about temperature.
I have characterized here a typical hydroelectric power installation and
tried to illustrate a couple of points with respect to the influence of this
project on location of ice front. We know that the upper part of the diagram
represented the river flowing into a reservoir, with a backwater unit somewhere
up here. The reservoir and dam with power house and spillway downstream of
that point in the unchanged natural channel. Under natural conditions winter
flows are very small as we saw for the in the winter and the water
temperature is quite cool, specifically will form an ice cover throughout the
whole reach downstream. A river like the Susitna River which is a steep river
makes an ice cover by the process of juxtaposition
which I will describe later on, which is to say that it has to have enough ice
produced on the surface by heat exchange in the form of frazil and ice pans
and slush, snowfall -----------to where there is an adequate amount that the
river is covered from bank to bank, but once it's been covered and the blanket
of slush that is moving down is thick enough and develops enough friction with
the banks it will arrest a conPtriction in the river \lhich is cm.only referred
to as a lodgment point. Under natural conditions with low flows and a very
high rate of ice production you can expect lodgment points at various places
along the river, for exa.,le as I have indicated here you might expect one
with a configuratim. like this, or like this, or like this. Quite st.ply, ice
.. (
River Ice,susit,second draft 3/21/83
Page 5
is generated on the surface by cold weather and the slush rolls down to a
point like this but cannot get past it, bangs up with bridges and it will form
a float at this lod~nt point. From that point, any one of these points
under natural conditions, the ice cover can advance by juxtaposition and the
rate of advance, then is a function of the climatic condition, the rate of
which ice is being generated on the surface of the river . When we build a
hydroelectric project and regulate the flows in the manner indicated here,
there are quite significant changes made downstream at this point. First of
all the dam cuts off the supply of any ice that t s generated upstream to the
lodgment point downstream. In the case of a power project the first lodgment
point occurs under nature and appears, from our previous observations, to be
quite regular, occurs quite close to the location of the proposed location of
the dam. Which is to say the construction of the dam will not,
the diversion condit ~on when there are ver~ little thermal effect. The con-
struction of the dam will not affect the rate of ice production in the downstream
region because there is by nature a lodgment which cuts off the supply of ice.
Under the natural condition all the coverage which takes place downstream of
the Watana takes place without the benefit of ice produced from upstream. The
regulated flow increases the hydraulic forces and hydrodynamic forces that
occur in this river so that it becomes more difficult, first of all the stage
is higher so that the width of the river at the higher discharge is greater,
like the span is greater and is harder for the ice to bridge. Commonly what
happens with the high regulated winter flow at the tiae of freezeup is that
these points are eliminated as lodgment points, even if they're well downstream
of the point of theraal input from the reservoir. Quite simply because the
hydraulic forces against which the cove.r must lodge are too high for it to
lodge at that point. It will not be until they are some point well downstream
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River Ice.susit.second draft 3/21/83
Page 6
where there is indeed a very severe restriction and well removed froa any
therwal effect that we get a high rate of slush production before you will
have a lodg.ent point. The significance of this is that under natural conditions
you can see that the lodgment point occurs there with :he cover fairly early
in the year and the cover can just advance froa that position up the river
whereas at the point I have to start an appreciable distance downstream. ----
You will not see a cover there till auch later in the year for the st.ple
reason that the ice. that the river can only produce so much ice. and -----
at a certain rate and the cover has to progress all the way from here and it
takes longer to fill
it all has to become as one continuous process from the bottom end.
The consequences of thermal effects is that. as we have seen. the outflow
temperatures from the pro1ect will lie somewhere between a maximum of 4° and a
minimum of probably 1.5° between experience in Williston (?). depending on the
conditions we talked about. We see an initial temperature condition here. a
boundary condition. which has possible range lying somewhere in here. As T
described in connection with downstream temperatures as you move downstream
the channel vou have heat exchange with the atmosphere through the open water
surface and you s~e a loss of thermal energy and you see a decline in tempera-
ture in the downstream direction. The decline probably approaches 0 depends
of course on the starting teaperature. As you can see at soae point downstream
it will reach 1/10 degree c. in this case well downstreaa. in this case much
closer to the project. Froa that point the significance of the .1•c that we
have found froa observations on other rivers. aost notably the Peace River.
that froa the bulk water temperature. and this is the ~ water teaperature.
that down to about .1•c the teaperature gradients within that bulk are such
that you can begin forming ice on the surface of the river. You cannot possibly
I
River tce,susit,second draft 3/21/83
Page 7
see any ice upstream at this point, the point of where this temperature is
about .t•c. At that point the surface temperature is low enough that you
begin to see ice form on the river. Beyond that point you will be developing
ice to both the ice edge and the open water surface continue to ----------------
to the atmosphere and will climb until you have enabgh ice that you have 100%
coverage. You can understand that this position can mov~ up and down the
river under very, very cold conditions and can expect this transition point to
move up the river as the more effective to the higher rate of heat loss from
the surface. Under very mild conditions it would move downstream. There is
never in any one season a particular point where this starts. It is moving on
a daily basis depending on the current climate. The same thing applies to
------------------which you might as a function
of the current climatic conditions. Along this reach is partly dependent on
the current climatic conditions and also on the distance through the point
where the first lodgment can occur and how far the cover has been able to
advance from the beginning, from the first lodgment
We have here a system where water containing thermal energy transferred from
the summer sonths is released into tlae tail race. The thermal energy is trans-
ferred to the atmosphere when the temperHture drops to about half a degree of
bulk temperature, at which time it can start to generate ice, incr~~sing gr~h
rate, increasing the accumulation in downstream direction as it is feeding the
ice front which is advancin~ by juxtaposition from this point -------------------
You can see what happens here is the process will continue until the ice front
will continue to move up in this direction till it reaches a point where it
can advance no further for the simple reason that you cannot generate ice
because the water tewrperatures are too hot. So you would never after
you would never expect to see an ice cover
r
River Ice.susit.second draft 3/21/83
Page 8
upstream from that particular point. the location of which. remember. is depen-
dent on the current climatic year so it would be a different position depending
on how severe the winter is .
From the consequence of sort of pattern you can expect to see under both
project conditions the variation in average winter air temperature. if you
have a warm year the initial lodgment would take place a little later in the
year and you would have the ice front advancing and the refere~ce pointers
from the lodgment point ----with the passage of time and if you have
indeed a warm year all through the winter then you would find that the ice
front would not advance beyond some po!nt here. Normally what happens is. as
the ice front approaches the open water reach the rate at which ice can be
supplied to the front is ~ecreasing because that partial covered reach which
is generating the reach is becoming smaller and smaller. You indeed see a
deceleration in the rate at which the front advances. The other thing is that
this quite commonly occurs towards the end of winter when you are beginning to
see a winter warming trend. The other extreme if you had a cold year all the
way through you would see a somewhat earlier lodgment date. somewhat faster
rate of advance. and you would finish up with the cover advancing a further
distance upstream. In reality. this never happens because you never get. very
rarely get. a pure year in terms of being warm or cold. You sometimes have a
warm fall and then a very cold mid-winter in which case you depart from the
warm lines to somewhere on the -----Typically. if you plot a-------
ice front position as a function of calendar date. you are -----------
for a given year you find that they wander all over the place but you stay
within a band which you can define in terms of a cold y ear and warm ye8r
The most significant thing about this is that we are
looking at a process that is by nature very variable. You have this sort of
River Ice,susit,second draft 3/21/83
Pase 9
variation even under natural conditions as a consequence of variation in cltaatic
conditions.
Now I'd like to discuss the
That's the end of ~ discussion on the effects of the hydro project on where
the ice front is going to be located and which re.ches of the river would be
covered. We will t!IOVe on now to the issue of changes in water levels. In
order to understand so.e of the subsequent diagraas I think it is helpful to
have a bit of the notion of the complex of juxtaposition and the meaning of
leading edge stability. As I described previously, nor.ally what happens is
that open water surface or heat exchang,e develops frazil ice and slush ice in
the fora of ----------------flow down the river to so.e point and if there is
enough of these they will lodge a t soae point downstream. And froa that poin~
the cover will advance by the process called juxtaposition, upstreaa. It will
reach periodically a particular cross-section which is more difficult for the
cover to develop past than any other area and I have indicated this very clearly
by photography here . What happens is that the cover will
advance quite happily by juxtaposition to a feature such as this and then it
cannot go any further for the staple reason there is a piece of pan or cake of
ice in here butts up against this end on the water surface, it cannot stay
there because the velocitie6 are too high. Hydrodynamic forces cause it to
submerge and be carried dovnstreaa. It will be carried dovnstreaa to the
first position where the velocity in the stream is low enoush that it can stay
there and it vHl deposit in just exactly the saae .. nner as the sedt.ent
process in the alluvial fan of a river if the whole thing is upside down. It
is an inverted alluvial fan .. de up of ice. And it will keep depositing at
that point until the velocity increases to 11 critical value and
Under freezeup conditions thia has
River Ice,susit,second draft 3/21/83
Page 10
been observed to be in the neighborhood of about three feet per second. Quite
typically you have a deposit here until the velocity is increased a fev feet
per second at which tt.e the incoaing ice at this leading edge cannot stay
there and whole process moves downstreaa gradually filling in the downstream
channel . It continues to do that until such tt.e that the additional hydraulic
losses, because of the higher velocities on it, are such that you ~et a backwater
effect which in essence swings the ice cover up and drowns this constriction.
Stream raises(?) it until the water level reaches a critical level which can
be defined in terms of what is referred to as lead:ing edge Froude stability
nu8ber. Froude number is defined in these ter.s as velocity divided by the
square root of db, where h is the depth at that particular point. It can be
expressed in terms of ------discharge quite si~ly in this •Aay and if
we rearrange this thing and solve for the critical depth we find that we can
express it in teras of constants, which includes some critical value in Froude
numbers and the specific discharge or discharge per unit with the channels to
2/3 power. This is an extremely useful expression. When enough staging has
taken place here, when the backwater effect with these depositions is sufficient
~hat vou exceed the critical level; I have indicated the critical H and depth
of depth by the red line through here. I have indicated here a situation
where it is ___ stage quite enough to get out to the maximua level. The
deposition will continue in this case until the water level is just at that
point, then the incoming pieces of ice would stay at the leading edge and the
process of juxtaposition would continue thereby ~ncreasing ice coaes up and
butts against the distal cover and stays in place and it graduallv progresses
in the upstreaa direction. The key thing here i ~ this critical value as indi-
cated by the red line here. You can calculate this for any section if you
knov the cross-section data. Conversely, if you have an a.ount of field
aiver Ice,suait,second dt"aft 3/21/83
Page 11
observations you can define this relationshi p ~irically and you'll find that
this value a critical value of R as expt'eseed in te~ of Froude nu8ber, or
cr1tical Proude nu.ber, will be such that the Froude nUih~er is always be~en
the value of .154 and .08.
On that basis we can define what appear like rating curves and they at'e
in fact a t.-porary or tt"ansient rating curve. I have indic.ated on here this
dischar~e factor vhicb is quite siaply the discharge divided by the channel
width to the 2/3 power which conveniently linearizes the equation that vas in
a previous viewgrapb. I have indicated here an upper liait with a Proude
nu8bet' of .08 and a lower limit of .154. This nu8ber has been established on
a theoretical basis. This number bas been been established on an eapirical
basis, both in laboratory tests and in field observations and is extt'e.ely
well docu•ented. As also indicated on here, the open water rating curve which
is to say the relationship between discharge and water surface level. We have
a particular discharge that is described by this factor. You would expect to
see a particular stage correspondinR to that. This represents the water level
that would pt'evail for a given discharge given that there is no ice present in
the river. These two red lines represent the range in possibilities that
would direct the water level the range in water level will be required in
order for the cover to be able to advance by juxtaposition . It will not advance
for a given discharge until the water level, in a case like this you have at
the time of freezeup a discharge in this range before the ice front gets to
your section of interest you will see it over both the water level like this.
As the ice cover approaches there will be a backwater effect froa it, water
level will increase. The increase will continue until you would be on this
line, but not higher than that line. So under freezeup conditions, depending
entirely on the ~ature of the inflovtng ice, can generally be descr:!.bed in
River lce,eusit,second draft 3/21/83
Page 12
terms of velocity and depends on the shape, size, density, strength of the
pier.es that are coaing in. You will always have on the Susitna type of river
an increase in stage where the open water condition to a mini.ua value indicated
by this and a •xbua value indicated by this upper line before the ice cover
can advance. You can see that under natural conditions when winter discharges
are down in the range of 1,000, say aaybe 900 to 1600 cr 1700 CFS, on the
Susitna River when freezeup occurs you would be laid back in this region here.
Under that flow condition you would expect the water level in the mainstea,
corresponding to the blue line, --------advance increase to soae posi-
tion here. So if the regulated flow, the increase in discharge, is soaething
in the range 8,000 to 12,000 CFS you would of course be causing freezeup to
occur at sa.e position over here. Your open water stage at the ti .. of freezeup
would be higher and the amount of additional staging is not as far as the
leading edge stabilitv there, and will increase to sa.ething between -----
here and here. To illustrate th:t s 1 have an overlay here assuming that in
this particular year the freezeup is a condition of the ice, so feeding the
front requires that they be on the upper liait. We see for a natural freezeup
discharge they start at a level like this and you would end up with a level
like this. The regulated discharge would start at a level like this, appreciably
above that level. You would advance to a level up here. When there is a
change in water surface level in the presence of an ice cover it would be
sa.ething like this. Now in the case of the Susitna River, this difference at
Talkeetna is going to be about 4 feet and out in the Sheraan area is going to
be about~~et. If however you have a condition that you are upstream of the O .. j..
point o~C water, i.e., in a reach where an ice cover can never form because
of the therul effects, then you would in fact anticipate an open water condition
throughout the entire winter. Whereas under the natural regulated flow you
•
River Ice,susit,second draft 3/21/83
Page 13
would have seen a stage froa this level to that level, under the reJUlated
flow where the ice cover cannot occur because of the theraal effects you would
see quite st.ply an open water stage and there vould in fact be a slight decrease
in water level in that particular reach of the ice-free reach. On the Susitna
River it appears that this is 'oing to be about a foot, or less than a foot.
And of course there is a range of possibilities; I have one over there to
indicate that. If in fact in a particular year the ice conditions were such
that ve didn't ~ve to stay to the upper line in order to get an ice cover to
advance you would see that there is a little difference in here. In this case
under the natural flow you would see a very ... 11 stage increase
Under the reJUlated flow an ice cover at t)\is
section you would have an increase here smaller than the previous one indicateo
and if you in fact were in the open water reach you would see higher open
water levels than would have occurred under the natural discharge with staging
Where there is a vide range of possibilities depending on the
particular ice condition at the time of foraation in a particular year where
there would be an ice cover you can expect increases in stage, when there will
not be an ice c~~r there .. Y be a ... 11 aecrease in ------------------------------
stage.
So that defines the water levels that you can expect at the freezeup
condition. Nov this condition applies only te~~porarily. It will only maybe
satisfied at the period of ti.. that the ice front is advancing through that
particular reach. Once the ice front has advanced through, different things
can happen. You referred to a unifora flow situation and to what the level
control soes back to the question of channel gea.etry and channel friction.
This condition no longer applies. Rovever, this condition after freezeup
deteraines what your prevailing winter water levels are going to be for a
•
liver tce,susit,secood draft 3/21/83
Page 14
given discharge during the rest of the winter. To shov this I have prepared
another diagraa here on the aa.e basis. I'll ~ust put it on here long enough
to shov vou that I aa ta1tin~ off this particular line ----------------------
Por th~ moaent I'a ignoring this possibility vbich reaaina
unsolved. You can see as I ~-.ve indicated; let's suppose that a natural freezeup
discharge is 2 1 in which case you would be at this point on the scale of 10
and the freezeup level req~ired, given in this ice condition at the tt.e of
freezeup, would require a stage of that ..aunt. Once the cover is established
it has a certain thickness vbich is deterained by the hydraulic forces prevailing
at that discharge. And that thickness prevails for the rest of the winter.
Nov it can in fact change. If it happens to be very thin relative to the
thickness required for theraal equilibrium through the ice cover, that is,
equilibrium in the heat exchanged from the river to the ice cover and the ice
cover to the at.osphere, then it will grow theraal1y. If it is thicker than
is required in terms of equilibrium then it can nov become thinner. Ri~ht
after foraation, essentially you have a fixed ice cover and you have it fixed
on a point on a rating curves where you revert to the unifora flov and you in
fact then, the discharge varies around that, you would follow a rating curve
which is .ore or less parallel to the open water rating curve that has been
fixed for the winter or at least for the next short period of time by this
freezeup condition. Then your rating curve comes th~ugh along the line like
this. So if you had an increase to 4 say, or to S, having closed in at this
discharge the aaxt.ua level you would see would be indicated by a point up
here.
-Hiatus between tapes -
•
R.iver Ice,eullit ,second draft 3/21/83
Pqe 15
••• ve revert to unifora flow control the rating curve we -------
are following will begin .ore or less parallel to the open water curve and is
at auch higher level. Then we would experience a value of up to (?) 5 we can
see a water level appreciably higher than those that had been at lower discharge.
For the winter water level regi.e is fixed by the discharge that occurs at the
time of the ice front advance through a particular region. Now this is all
very idealistic principally for the reason that I have indicated because quite
often the -------------adjustaent in the ice cover, that you would
have quite uniform growth in the thickness of the cover with the passage of
winter , then you would gradually move from the rating
curve upwards. If on the other hand you hav e thinning, or for example in this
present year when you get considerabl e thinning, you're used to the water
underneath warm.ing up, then the rating curve would be .aving down on this
scale. Generally speaking, the adjustment that takes place on an ice cover on
the Susitna River would be such that you'll always be moving down on this
scale. The actual curve that y ou'1e on any time subsequent to fr~ezeup depends
on what readjustments ------would come -------------cover and in general
would be moving down .
Under the breakup condition, when the cover has fragmented an advance is
transported downstream by the flow of the increasing discharge; ~he whole
process of staging to satisfy Froude criteria is again applicable.
Under natural conditions this occurs usually at a auch
higher discharge. So if you like, spring breakup follows sustained laws of
8echanics to satisfy equilibrium of forces of equilibrium at the leading edge
in the saae diagraa applied. But, generally speaking, I did not show this
eubject under natural condit!ons that occurs at a higher discharge and you're
operating at some condition up here. The sa.e process governs spring breakup
•
..
River lee,ausit,second draft 3/21/83
Paae 16
water levels. There is, however, in the spring a limit to the worst thina
that can happen to you. Por exa.ple. you can envision a very high discharae
that could put you out in a doaain here ------------------------------------
give you very. very high discharges. In fact this doesn't occur because you
have a limitins factor, there appears to be a !baiting factor, and that is the
volume of ice that is available to form jams. Under the freezeup condition
you have, for all practical purposes, an infinite supply of ice available to
you as long as the winter lasts long enough. It just keeps churning away
generating ice and feeding the front so that it has enough volu-. to be able
to raise the water level for it to advance. Under the spring condition there
is in fact a limit to the volume of ice available to you and that is limited
to extre.e physical limits than would have by these water surface area upstream
of the point and in fact is generally limited by a combination of ---------
and the amount melting that has taken place subsequently in the beginning of
spring breakup. So you can, in fact, as a function of spring breakup ice
voh111e, you find an upper limit on what can happen to you that's as good as
your family of curves (?) for an increase in volume. What happens is that
even if you get this d~scharge there is not enough ice available to effecti~ely
get the c~ver thick enough through hydraulic losses large enough to increase
the stage to satisfy the leading edge Froude criteria; we just cannot get to
this line or not even to this line. You can in fact define a limit here and
it in fact defines the point of intersection -------------------physical
upper lt.its are highly improbable at the 1:100 year volume because we find a
critical discharge which is the worst thing that could happen to you, the
worst level you would ever see would be something defined by this point of
intersection. That deals with water levels at freezeup mid-winter and during
breakup.
Uver Jce,sudt,second draft 3/21/83
Pa1e 17
We will eave on nov to talk about ice thickness. We .entioned the ice
cover thickness is also deterained in lar~e aeasure by the discbar~e at freeze-
up. I don't have calculations for the Susitna River. I brought sa.e for some
that I have done on a reach of the Peace River to quite simply illustrate the
influence the discharge has on the ice cover profile that can form. We can
see in the upper diagram the ice cover thickness has been calculated usi.ng an
I l'l >u"il rf~)
ice program for discharge of 500 cubic meters per second. The cover bas formed
her2 by the process that we described meeting a stability requirement and it
has required a certain thickness to get suffici.ent hydraulic mean depth at a
critical point right here. This happens to be the controlling section. Once
we have reached that the cover can advance very easy through here until your
~~ velocity gets j6 high again and then go through the whole process. It 1s
significant then as you can see for this 500 cubic meters per second that
requires a certain thickness of ice. Under 1000 cubic meters per second you
can ~~e that the ice cover required to achieve that same thi.ng is soaevhat
thicker and it has, because of the nonuniformity of c),.annel geometry, you have
considerable variation in shape of this ------And at the higher di.scharge
you can see that it has one hell of a time getting through this section. It
required an appreciable thickness here to keep the water level up. Plus it
does because of the velocity in this pond (?) created by the reduction in
conveyance of -----------mass of tee, the velocities are so low that
the ice cover can advance quite a distance upstream, quite slowly. The point
is that the thickness of the ice cover that is going to prevail for the winter
is deterained in large measure also by the discharge that occurs at the time
of freezeup.
The last itea then vas with respect to what happens to an ice cover once
its established; if you change the discharge. If you freeze in at a very low
River Ice,eusit,second draft 3/21/83
Paae 1~
level and very small discbarae you can see you have a very thin cover. If you
increase the di~cbarge very markedly right after that is formed and very weak,
you can on the Peace River that
cover is unable to withstand the high to dry forces at a high discharge. It
collapses and you have in effect spring breakup in the freezeup period. The
cover will reform at the higher levei in accordsnce with the diaRram, the
leading edge stability require.ent as I've indicated. However, it need not be
that you precipitate a breakup of a cover like that every time you change the
discharge because the ice cover generally when given a chance will develop an
ability to tolerate rather large level changes as a consequence of variations
in flow. There are two types of things that happen. The second one I will be
discussing is actually a limited case for this. In the case where you form a
very strong, thin cover, gives it h chance to develop considerable strength.
If you exercise the cover it will form an articulated bin~e along the shoreline.
It requires a minimum of 3 fractures which would parallel the shoreline, and
here where you have contact with the bank with its first piece, one a little
offshore and one further offshore. As the discharge increases, the water
level rises, the central part of the cover just quite simply follows the water
level, and as long as you maintain contact at these binge points the cover
will follow quite happily without breaking up. You get the hydrostatic level
over here and over flooding, and in fact you get both ----------------------
channel. These can tolerate quite appreciabl~ increases and one exaaple in
the Gatineau River, which is between two power plants that are operated by
Hydro Quebec, and that little sucker can tolerate 2~ feet of change and never
lose that contact. The other type of liaited case is contact between ----
is quite typified by rivers in western Canada and Alberta and the Rocky Mountains.
Their class of rive~ is very comparable in so.e respects to certain regions in
•
River Ice,susit,second draft 3/21/83
Page 19
the Susitna River. The process of foraation is as I described by juxtaposition
you for. the be~een covers. That this is a vide channel -------------------
in terms of the ability of the ice to expand the ri7 er reach. Subsequent to
the foraation of the advancing cover upstre .. would be a collapse and telescoping
of the separate part of the cover and it will develop a shear line establishing
grounoed regions on the banks which would beca.e the new river banka. Subse-
quent to telescoping and a certain amount of squeezing, the disparity would
nov be -------------------The cover will settle down in between these grounded
ice banks and in effect the channel is now defined by these. You don't see
this happr 1ing on, I have not seen this anywhere on the Susitna River. There
is some telescoping in certain reaches both particularly in the reach 5 or 6
miles downstream from the canyon. There is not a tremendous a~nt of this
type of process taking place in the Susitna River for any length. Subsequently,
if you decrease the flows to very low values the central part of the cover
will quite simply float down. As it floats down it will develop fractures in
the same manner as we ha,~ articulated. Then the pieces will quite simply lie
in the river bed. When the water level comes back up if it hasn't been down
too long, and sa.etimes if it hasn't refractured, the pieces will all float
back up into place quite happily to retain the bank contact be~en the central
pieces of ice and the shoreline and will all then stay in place very happily,
and it will stay there and follow the water level. In springtime
----------------------------------flow, discharge is higher than the f reezeup
discharge and it will in fact float the ice c over up to the bank without flooding
of the overbank areas as long as that cover retains contact with the grounded
ice on the side here will stay in place and not fracture. As soon as the
discharge is such that stage comes up and ruptures ---------------------------------
the whole cover will collapse which is the breakup. I don't have
River Ice,susit,aecond draft 3/21/83
Pqe 20
----------------------------
slides of these processes. I do ba"e four photographs which I'll pass "rtv.md
indicating this sort of thing. The top one is Hollingsworth Reservoir which
belongs to Great Lakes Power in northern Ontario. It is a little reservoir
but in this instance we've drawn down 30 feet in order to effect repairs in
the intake structure. It was subsequently brought back up 20 feet and you
u ill see vheu y ou get a close look at it the pattern of fractures that occur
along the ice cover as the water level is brought down. You will see an area
that has been flood.ed, corresponding to an articulated-type hinge, quite typi ca:
of this sort of thing which you can expect a aajor drawdown on an ice cover in
place. The second photograph is froa Jakineau (?) River which I .entioned
which is a very fine exaaple of the articulated hinge. This is the one that
Quebec Hydro has exercised in experiment, to the extent of 2~ .eters of vertic1.l
variation. The third photograph illustrates the type of hinging that takes
place on the Peace River. and here's a section of the Peace River near
And yvt can see along the shoreline the overcrowding has
taken place as the cover has be~n exercised all operations near ---------------
upstrea.. The cover stays quite ha~oily in place following the water levels.
The lover diagram is also a Peace River further downstreaa and it shows the
last condition I had on the slide here of overflooding of the bank has occurred
in this condition here. OVerflooding of the banks has occurred but the~e is
still bank contact and the cover still stays quite happily in place.
Pire away, gentlemen.
Q: Toa, would you elaborate a l ittle on the breakup process downstreaa of
Talkeetna if we have during the wintertt.e twice the flow that we presently
have, let's say at Susitna Station. therefore there is going to be a substantial
River T ~-,susit,second draft 3/21/83
Pase 7.1
..aunt of ice inctease. and during existing conditions, could you explain how
what could possibly happen vith ice ja..tns during the springti•.
A: There are tvo things that happen here. First of all. its important to
note with respect to the change in flow that under the breakup conditions the
regulated flow is appreciably less than particularly at the later beginning of
the breakup period. The regulated flow is appreciably less than the natural
flow. This is sisnificant in teras of the staging required to satisfy the
Froude leading edges stability criteria. In teras of this diagraa. under the
natural conditions you can expect breakup for that reach to occur somewhere in
here which means that you would expec t to see a high discharge as high breakup
levels. Under the regulated c ondition you will unlikely ever see discharges
that high again and will in f a ct be very close to the regulated flow which
will brin~ you back down here somewhere. Now there is a very clear benefit to
flood c~trol in the lower reaches as a consequence o f production of spring
flows at the time of breakup. The other factor is a question ------------------
We will indeed be more ice in the river as a consequence of the developaent of
cover at higher levels. Now that becm~es relatively minor stsnificance for
the st.ple reason that it only takes a certain volume of ice at the discharge
to establish the critical Froude level. It takes a certain volU11le of ice in
this area to produce the hydrauli c constriction to stage to the critical Froude
level at this point. So the question is not necessarily ••• ; the fact that
you have more ice is not necessarily of significance because if under natural
conditions you have enough ice to stage to that level under the reduced spring
discharge due to regulati~, if natural conditions would provide that voluae
of ice it is irrelevant that you have more because all it means is that the
stage will go to that saae level here and you will have a longer extension of
River lce,susit,second draft 3/21/83
Page 22
the ice cover upstreaa because there is more ice under that condition. The
general consequence is that the benefit of reduced discharges far outweighs
the difference in voluae of ice.
Q: Okay, you're going real fast here. I'a going to have to slow you down
because I'm a little slow. I want to ask several questions. First of all,
let's take at Su Station, way down river. During winter flows of regulated
flow, if ay ae.ory serves me, we're going to have approxiaately double the
noraal discharge on a normal year as we do with no hydro dam and no regulated
flow. True or false?
A: True.
Q: Okay, so we have twice as much water during a regulated time and this
exercise you just put us through, which I found very informative, was that
that tells me that we will probably have a lot more ice formation in that
lover part ot the rivei.·. Right? Because of the physics it takes to do that.
We're certainly going to be below natural temperature, you know, a type of
thermal effect from the hydroplant down that far, but we're going to twice as
much water in the system so it seems to me that we're going to have a lot more
ice down there than we normally would.
A: Because of the thicker cover you will you have more ice.
Q: Right, okay. Now, during breakup, you're saying the regulated flow is
going to be very important but if you go back to the initial stuf f we're looking
at during those months when you start to get your breakup the effect of the
liver lce,ausit,second draft 3/21/83
Pase 23
discharge froa the Susitna portion that is coains froa the reservoir is a
pYetty saall percentase of the actual discharge of that syat... Because you've
g~t the Yentna and the rest of your aysteas du.ping in. What effect is that
goins to have with all that noraally very high discharse on a lot .are ice
we're soing to have down in that systell. I'a really concerned about that.
A: One of the consequences through the coapensating effect for the greater
thickness and the greater voluae of ice under the regulated condition, and
that is the heat content of the reservoir. The water teaperatures in the
Susitna will rise because they have never gone down to 0, they will be waraer
earlier in the season. The consequence of this is that, with the regulated
flows, you tend to get a very rapid rate of melting erosion of the ice cover.
So it disappears very qu.ckly.
Q: So you're saying that even down below the confluence of the 7alkeetna and
the Yentna and these areas we're goin~ to have, with a regulated flow in the
wintertime or in the fall and starting in the winter, a lot more water than
norwal, that when the source breakup in the spring that there's going to be
enough temperature naturally that its not going to make any difference?
A: I'a not saying that its not going to make any difference. I'a saying
there is a complicating effect.
Q: Well, would you expect that for downstreaa, Toa, that there would be a~y
residual 1-,act from the reservoir temperature?
•
River Ice,euait, .. cond draft 3/21/83
Paae 24
A: Yeah, I just realized that I have (aoofed up), just aaking a point aa I
vent through here (let ae find ~ diagraa). Under the freezeup conditions
here, I'• &oing back to freezeup conditions to give you &a.e feel for the
extent of this open water bit . I don't have any calculations to be able to
talk specifically about the breakup. Under freezeup conditions, if this ia
vith \latana only, operating and the outflow te~~perature here is 4•c, then this
location is about Shel'lllln. If this is \latana and the outflow te.perature here
is 2• then this is about downs t ream of Devil Canyon, Quartz Creek. If this is
Devils Canyon and the outflow t-.perature is 4•, this is dovostreaa of Talkeetna.
If this is Devils Canyon aud this is 2•, then this is about Sheraan. Nov this
is under the freezeup condition where you have net heat loss through this
reach. Under the s ~-:ag condition we were coming out at aoae temperature in
this range and will be adding heat here starting from base level not at 0 buc
from a base level significantly above. This open water reach, the te.perature
defined here, and is quite sensitive to freezing temperatures, and both particu-
larly where you have a net heat gain instead of a net heat loss. You would
see teaperatures rising around this point. Under breakup condition the tempera-
tures here would be, instead of this declining this way, they would be growing
this way. And in light of the tremendous amount of heat, even though it is
low grade beat, a tremendous aaount of heat is available --------these covers.
Specifically, on the Peace River downstream of Williston Lake, whereas under
natural conditions they used to have spring breakup ice j am problems in the
town of Peace River. As a consequence of ice breakup on the mainste. of the
Peace River and a aajor tributary just upstreaa of the town of S.oky River,
what happens now typically is that the aainstea river ice is long gone because
of this spring thermal effect before the Saoky breaks and you nov have a much
•
•
River lce,suait,aecond draft 3/21/83
Paae 2S
saaller total volu.e of ice available to cause flooding in the town of Peace
River under the regulated condition.
Q: I 'a having no problea with vbat you're discussing right there and I do
understand that . I vas wondering basically vhere you're talking about open
water and ice coverage. That wasn't exactly ay point but that's okay, I want
to ask you a couple other things. And that is, vhen you were discussin1 vhat
it took for the ice buildup by the juxtaposition and you do need basically, it
increases the level of the river to do so, we're talking in the teras of even
12,000 CPS and, just for arguments sake, let's say one of the sloughs that
Woody vas working on in that area vhere 12,000 aight potentially be that point
vhere the upstream bera would keep water from going through, or 11,000 or
whatever. What happens then vhen we get this buildup, depending on the tempera-
ture, and as the ice moves forward you need the increased water level, it
floods over into these slough areas you wouldn't normally flood during that
tiae o f ye.ar.
A: I don't know. That depends on the elevation of the bera end of the slough.
Q: I'm just trying to say, just theoretically, I'm trying t~ be as theoretical
here as you are.
A: That's right. That's fine. You ·raise that possibility. That has to be
deterained on a slough by slough basis. The next step beyond this is to run a
backvtter calculation with the ice cover in the position where you are not
going to go and at the thickness that you're going to form at. The calculations
require starting froa this point to exactly the saae type, we're saying that,
• J •
liver Ice,auait,second draft 3/21/83
Paae 26
-------on Suaitna I used the Peace liver ex.aple. So, if you lmcv what
you're freezeup flow is yo•• can calculate, as we've done here in an ice profile
that you would expect the consequence of that flow. Then, having that established
you can do full calculations with REC 2 in order to get water surface profiles
which gives you the water levels for each specific point. Nov, in this particular
case we were doing this because there is a flooding problem in vest Peace
liver and we have flood dikes in p la~e the elevation of the crest which is
indicated here. I'm quite cortcerned about whether winter levels under power
regulation will exceed these levels or not. Exactly the saae problem in hydraulic
teras as the slough problea. You would have to do this sort of analysis on
the Susitna River and then find a particular berm location for a particular
slough you have to know what that elevation is and relate it to the berm eleva-
tion. If its higher than flood, or lover than flood.
Q: Just one more point. From what I'm gathering then and what you tried to
relate to me here a couple of minutes ago, am I to assume that the increase
regulated flow d~wnstream, even from Talkeetna, even down into say to the
Yentna, will not have any appreciable effect on the ice cover or the consequences
of breakup due to regulated flow, just by the basic physics that its going to
take to change ice cover and the flow its going to take to discharge it. Is
that true or not?
A: 1 carefully avoided saying e~actly what those changes are. What I've
tried to do here is to give you SOlie understanding ••••••
Q: Okay I know, but I'a asking a pertinent question. Can you give ae an
answer or no.
• ;J •
• River Ice,susit,second draft 3/21/83
Page 27
A: There will be changes of the type I've indicated . The aagnitude I don't
knov. It will be less because the gradient of the river will be the deter.inant
of all these things; the slope of the river. As the slope is decreasing in
the downstream direction, i.e., the flatter the river slope less severe in
this effect.
Q: Okay, that's fine, that's good.
Q: You don't know at this point even if ice is going to form downstream of
Devils Canyon all the way to Talkeetna, anywhere within that entire reach, or
it may not?
A: It's going to depend on the type of climatic conditions of a given year as
they influence the resentoir temperature and as they influence the heat exchange
in the river, downstream from the reservoir.
Q: What about, can you put some numbers on these elevations, on the stage
elevations?
A: Yeah, in the Talkeetna area you can expect a stage increase of about 4
feet and at the Sherman area an increase of about 3 feet.
Q: That translates, the equivalent open water flow would be substantial under
those increased stages. You can just look at any of the cross sections that I
showed for exaaple this morning and look at what 3 feet will do and so.e prelimi-
nary, ve haven't run the BEC backwater prograa with ice cover for the conditions
what we've just been discussing, but we looked at it by inspection and if the
. ,, .
• River Ice,euait,aecond draft 3/21/83
Pa1• 28
ice cover proceeds upstream of ao.e of these alou1hs there is absolutely 1oin1
to be overtoppin1. Unquestionably. Plow is goin1 to ~o up throu1h the slou1b.
Q: Does that have any influence on sedt.ent transport or araoring or any
.ov..ent of materials within the sloughs especially within the aainstem?
A: It can do. Under the ice cover condition. I'm not sure what this river
ie, and I'• not familiar with the morphology of the ------------------------------
to take velocities of this sort of calculation describing this. One of the
thin1s you get out of this Bort of calculation is the velocities in the area
when you make an assessment then what is going to happen to the bed of the
river. There are two limiting velocities, two limiting conditions under ice
cover which determine whether. you ~et bed scour or not. I mentioned the limiting
velocity under the equilibrium deposition velocity or erosion velocity here of
about 3 feet per second. Under formation condition we have never seen velocities
in excess of 3 feet per second. So under this formation condition if the bed
of the river is paved with cobbles that will resist that sort of velocity then
the bed will not be disturbed by the fact that you have graded ice thickness
et a higher freezeup discharge condition. If the bed material is s uch that it
will be eroded by the velocities it means that that is occurring right nov in
the river as a nor.al annual consequence and is going to continue in the future.
For example, in channel in the dovnr~ver in Toronto, Ontario the
variance because the bed of the channel is where most of the ice ------
jaa t a kes place is very fine material. The ice jam, ice responds to flows
under it and the ice just keeps following scour holes. The same ------
thin1 applies downstream of Muskrat Falls in the Churchill River in Labrador,
a 150-foot-deep scour hole downstream of Muskrat Falls because the bed resistance
• •• •
•
•
River lce,sueit,second draft 3/21/83
Paae 29
is lover than the ice resistance. The daa just keeps puaping ice froa the
falls downstream in this aanner and it just keeps, the velocity increases the
load, more ice deposits than this ---------------------------------------
The critical question here is, under formation conditions, what is the present
state of the bed. Will it resist velocit ies or not. If it -----------------
will, it shouldn't change ---------------then you can see erosion but you
should be seeing erosion anyway under natural conditions. Under breakup where
you can get, the process with respect to this is the same as the process whereby
you get the staging, its quite clear in the summer these are quite different.
You will get an abrupt breakup of an ice cover with a mass of ice moving down
the river to a point where it comes against ~ solid piece of ice at rest.
They will all jaa in and, instead of having this gradual deposition process
taking place all the way down the river, you just quite simply form a hanging
dam and get tremendous resistance. There have never been direct measurements
of those velocities for the simple reason that I haven't been able to find a
aucker to go out on an ice jam that I'm familiar with. (laugh track) We have
inferred velocities from calibration of our ice mechan i cs model which suggests
that under that condition we may have short term velocities under an ice jam
in the area of 9 or 10 feet per second, or about 3 meters per second, so those
are not direct measurements, they are inferred and we don't know how good they
are. But again, if you are getting that sort of jamming condition which you
will on the Susitna in two or three places under spring breakup discharges you
can expect to see those sort of velocities under natural conditions. I under-
stand from the conversations with the people here that there have been quite a
readjustment to some of the river cross-sections since the last survey as a
consequence of the rather large spring breakup discharge this year. And that
is probably ---------------------------area you get those high velocities and
••••
•
liver lce • .ueit.aecoad draft 3/21/83
Pqe 30
it takes quite an appreciable cobble or boulder to reeist 10 feet per second.
so even under the natural process you are getting that sort of breakup velocity
froa that sort of readjust.ent of the bed. We would not expect the net velocitiee
to change by the fact that you are regulating the flow. In the Susitna Kiver
itself. you would be less likely to fora that sort of jaa because of the heat
content and greater info~tion ------------the cover in place because you
are liaiting the aaxt.ua discharge under nor.al power flows ------------------
the sort of event that occurs by nature ---------------You would expect to
see those 10 foot per second velocities under ice jaas less frequently after
the project.
Q: Can we talk about fish for awhile. I'm getting a headache? (laugh track)