Man-made Islands in the Mackenzie river: Numerical modelling of ice jam development and release

G.J.A. Lor::an J.J .A. de ~O:l.g J .?. ~·~oir A. 3urgers E.J. \'err,agen 1 . :-::.'droI'.c~::iic bv

Esso ~2S0urC2S Ca~ada Ltd ~sso Resources Cc:l.aca 1td Hydrcna:Jic bv

~-:ydror.""-L~ic bv

~~-~..AD£ ISL-\.~\i)S: IN- I:1E ~~-\C:c.:::~ZIt RI\~t:R

Sliec~echt, ~~11and Calgary, C~~ada

Ca~g2ry, C~~ada

SliecY2cht, ~81~and Sliecrecnt, ~01land

Xl.:1ERICAL ~~ODELl:~G OF ICE" :.~~ JEVL=-OP~EN1 . .:.~;U K.:..L~_~_SE

AJst-:-ac:r

The des.ign of iIlan"'::.ade islands in 2. ri\:er ice ::-e.g:'::.e has to cope

~...rith

t:re

cor:plex phenor::e!'l3 associa::ed with c~e spr:":1g bre.s.k-!.rp of

the river' ice ...

Spring· break-up in northern rivers is of::en accor:?anied by ice jams, which form as a result of obstruction by ice floes .. Develop-ment o-f such ice jams can cause a sUQstantial upstream rise in 'Water level due to the hydraulic resistance of tae floating ice cover .. This leads finally to a gradual_ collapse of the ice jam,. resulting in strong surge velocit.ies within a dcwns:.ream prcpag.ac:-ing flood \.-..-ave.

In ard~ to be ~ble to design the islands su=£iciently accurately, Hyciror..amiC: bv

at

Sliedrecht, Holland, has develo?ed a numerical flow mod~l, that is capable of si~u~aring the complex ?henomena of ice. j am release .:Ln :"i..3tural rive!:"s --wi th an ir~egular c::anhel geometry_

Tb.is model has been successfully applied in the comprehensive design study regarding six man-made islands in the. Mackenzie River, conducted for Esso Resources Canada Ltd with re.spect to the Norman Wells Expansion Proj act.

This paper highlights the computational procedure and resul:::s of the nu~erical ice jam flow iliodel and so~e co~putational resulcs of the. flow patte.rn 2.round the ::;.an-sac.e. islancs. The. cpplicaticn of

' .... 7e:l~s oil field, ",-hicn is ~oc2::e.d Dn ,:~e :lOrr.n bank of ::.he ~a:'-;:2::::.zie iZive:r, 145 k.m south of :;-'e .';rctic Ci:-cle, ~or:::-.",.;'est ':'2rr::"-tories, Caecca. 7:'"1i5 SeCO:!.cary :"e:cove:r; schc::.e, :-e.rerred to as ;:ne

injection system. This ·,.;ill =--::cr22se the field ?rociuction f:-ol'J. 3,000 to about 25,000 ~2rrels ?2:r ~ay.

T~e oil will Je <::ransported :'0 at Alber:a, by a pipeline 866 Q

::1

:eng:~ (see ?igure 1).

The ~eacures of the oil ~eari::g structure call ~or six =an-~ade

platfor:::r.s 1 per:nitting \7ertical access to the. portion beneath :~e

Macke:J.zie River (see ?i3ure 2).

Hydro=amic

JV

of Sliedrecht, Solland, was retained

by

~sso ~esour­

ces Canada Ltd to develop ~ conceptual design, construction ID~·thod and sc~edule for these man-made structures.

It has been concluded, in view of the expansion project's economic viability and the expected environmental loads, that the construct-ional and operatconstruct-ional risks are illinbal -wi th :oan-I;Jade sand fill islancs.

In the concept for t~ese, Esso ::\esources and Eydrcn.amic have incorporated t:"e ::lore than 10 years I experience in designing 2!ld constructing ~an-'J:ade islands in the Arctic, as illustrated by those already Duil t in t:-~e Beaufort Sea.

'!':'1e design, ~ased on a well-cried c::ncept proven unaer various

conditions, takes into account various ~equire.rn.ents such as:

*

fulfilling the purpose of a safe drilling base

*

resisting hydraulic and ice loads

*

~inimizing environmental risks

3.

~!.e islands are loc-", ted in shallow~ ;..~ater lle2.r the ec::ge of t:-,e ::lain c~a~~el at a 2epth : f about 5 m below Low ~a:er.

On the ~asis of cc=?rehe~Sive observations of the ~ac~~~zie ~iver ~3,4,5,9:" su??12=~!1:ed by cata oDc3.iL'led f:-oi:iJ. other sources :6,7 ~', Esso ::\.esource.s e.s:ablished the :::esign criteria for the ::an-ITJade islands in cooperation with Hy~rcnamic. ?i=ally, this resulted in the :ollcw'ing cesi~n (see figure 3) ':1,2 :.:

*

hydraulically fi:led islands, e2c~ consisting of a sand core. of aboL=

200,000

rn

3

~ith

layered ri?-rap slope and toe protection over a heavy fabric filter cloth.

*

at the toe of the 1 in 2 slopes, :~e rip-rap protection is extended, after exc3.vating a t=-enc~ in t:--:8 sandy top layer, up to and over t~e clay layer ly~~g benec[~; apron slope is 1 verti.cal in 6 horizontal.

*

working surface of 80

*

45 m at an elevation

or

54.00 m+GSC (=Geodetic Survey of Canada), surrounded by a 1.00 ill high dike.

*

side slopes,

1

vertical in

2

horizontal, with a

5.00

m

horizon-tal sloping berm, to be used as a ramp.

*

upstre.am slope includes an ice pi:i.e-·up storage berm,. with a length of

50.00

~ at a slope of

1

vertical in

10

horizontal.

*

the corners of the upst~eam, bluntuosed storage be~ are

protected with concrete blocks, 1.00 m thick and 2.10 m long.

3

REGL~ C~~~C:ERISTICS

OF THE

~~CKE~Z~E

RIVER

The ~ackenzie River flows in a northwesterly direction at ~orman

Wells. From early June to late. September the river is nor:nally r.avigable ove.r its 1600 km length between Great Slave Lake and the 3eaufort Sea.

In the vicinity of ~orrr.an Wells the river is exceptionally wide, with multi-chan~el reaches, enco=passing several islands (see F:'gure 2).

Dur::'ng t:'e , ... :i:1ter} t~e aver2.

_s

e thic";.-_-:.ess of ::.h2 r:;:"~'er ice

:.C1C:::-~2.S-25 from 0.8 ~ in early =ec2=~2r to 1.6 ~ in early ~ay.

flow rate on account of wel:ing rur.off in c::~.':l:::ation w·ith t:-:er:::al ice weakening, Starts in the southern ~;pst:-e2m reaches and ?rogresses aOwllstreaI:l. T:'l.2 · ... 'c:.er e2.E-;ation at :;or:::an ~~'ells, be:::ore break-up starts, usually 'v·ar:'e.s Der::_'E:2U 41.00 :n end ~ 2. 00 ~SC. During the last four years, observations of :,reak-l1p and ice jams in the ~ackenzie River neve :,een w'e11 doc'-.:::_er~i:ed. !:":'1e concl'..!sion reached is that break-up at :;'or-:::an ''';2115 ::"s consiste.!ltly accorr.panied by back-up conditions due to t},e :or:nation of ice jams dOwLlstream. These j2.I!l.S are :ilainly init::"ated by the narrow single-channel reaches upst:-eam of Ogilvie =sland and dowustream of Patricia Island (see Figure 1).

The iliaximum ~ater elevation observed at ~o~an wells during an ice jam, initiated near Ogilvie Island, is 51.39 ~sc (~~ay 20, 1982).

In order to predict the severe flooding and surgi3g associated with an acceptably low risk of occurrence during t~e l:.fet:::J.e oJ the :nan-rr.ade islands, all :he available hydrclog: :al data have been analysed. Distinction has been made bet~een pre-rele2se floods, release floods and summer floods . .extreme value ciete:-::J.in-ation has been carried out for 3 dis[ribution types) viz. ::he GU::L.":>el distribution, t.he ';o;eibull dist.ribution and the Log-?2:ars: .. n T)7e III distribution.

For the purpose of illustration, the floods and associated elev-at ions , with a return period of 500 years, are used and have been e.stimate.d to be: discharge elevation pre-release flood

34,000

53.8

slli:tI:ler flood

38,000

m /s 3,

46.3 m-+{;SC

)

.

The desi6n of the six ~G~-=2Ge is~~~ds ~ust take iura accouut c~e :~ood ~ave e::ects due to :~e sudc~~ re~e2se 0: an ice jam.

30th steady disc~arge c~~ditiDr.S) 25 -,,;ell as the ur.steady c:'scharge conditio~s duri~2

-

the build-UD

_.

2~d re~ecse of ice jams, have been computed w'ith SyC:rvI:.2.IT.ic I 5 :1u:ue:-ical ::c,cel HYDFLOW-l.

7:~e ~E:thod of co~putatiGTI. is .~ sed on a finite -:if:erence rE:?:"esEntation of the ::lass and :-.::;:;:;entum 2quations) i-;]te~rated ac:.-css the flow sections. T,.-"2se eq1..:;:;.tio!1s a:-2, respecLively:

b 3h +

aQ

= 0 s

at

ax

3Q

3(Q2/A)

gA

(

~h

-

_{i b)} + ₉

QIQJ

= 0 + +

C"AR

or

dX oX

'..;here: h flow depth

(m)

Q

flow discharge

(m / s)

3 t time variable

(s)

x downstream direction

(m)

b storage width

(m)

s

(m

2

)

A conveying c.ross sec::ion

g gravitational acceleration

(m/s2)

'0

longi tCldinal bed slope (-)

1

C Chezy coeffi.:i.e.nt.

(m"/s)

R hydraulic radius

(m)

The ?rocedure of time and length integration employs an explicit leap-frog numerical scheme {13}. The discretization in time is achieved by using a1 te=nating time levels for the corr.putation of the. io,~ater elevation a.nd t~e channel discharge.

About 185 km of the ~ackenzie River have been scDe=.atized into various interconnected chan;nel section.s, 4-5 i:..:n in ~ ength (see Figure 1). At ~he :-l0GeS of eac:: see tie:). t'!:1e ~..;a:'2:.r ~e';el ':5 C-='~?'-.lt­ e.d; i::::. :~e ::J.i-:'dle

0:

::i.e sec:::'cns [he c.:'sc:-:ay~e is c.::-:-.?u:ed. ?or

-=:-he t=-::::e int~gratic'n step :or the :'22.p-frog sc~e::-.e is rest!"ictea

.. by ::-,e Courant-Fri;::dricts-~ew'"Y stability condition. 2ere, a +:.::"::;e

s:e? of about 200 5 T,.;rQuld :,e ?er=:1itted but for re2.sons of

::c..::~.e:--ieal acc'.J.racy, e.g. -;"Qini;nizi.ng the ?hase er:-or ane the

a.;:;:p~ific-2~ion error, a ti~e step 0: 30 5 has ~een ~sed.

Dete~ination of :~e co~?osite rough~ess, re8ulting from the

obstructed ice cover and the bottom has been based on the co~~only

lJsed Sa'ba.neev hypo=~esis c.:1d the St.rickler fOG::'..!la ".8

function of t~e ~ikuradse roughness of cover r. viz.: ~ = (r.

1I4

~ J.. ib to be eX?r2SSeC

the bed ar-d the

7his as a

ice

The stability of these fleating ice jams is gover~ed by the ice. conditions, the flow velocity and the conveyi~g width.

Tne thickness of a river ice j am is gave rued by the submergence potential and incipient motion of ice floes under the ice cover, the internal ice strength, t~e external resisting forces and the external active forces, such as flow and wind shear and the downstream weight cO'Glponent of the ice cover.

For the purpose of ar.alysi~g the ~2ckenzie River ice jams several published theories on the stabili:y of river ice jams have been reviewed tS, 10,11,12:. These theories are all based on a st:23.dy force equilibrium analysis of the le~gt~ening and thickening pnases in prismatic cfLannels. 'f:le :::'ow shear stress acting upon the obstructed ice cover, following the M2-backwater profile, is the main external active parameter. It has been concluded that, for the time being, the above theories cannot be reliably applied to ~on-prismatic natural rivers, 'Iot'"i.th single.-channel and multi-channel reaches, as stability conditions differ from those of

~~isoatic channels ~nd ~here is a complex :~eding of ice =loes at tributaries, bifurcations, conf:'ue..nces

CO:1seque.ntly, the sClbGe.rged ice thic~Qess

at t i

=

3.00

:::. s,::::.c !:. ;;

l

1.SO

c .

l

and open

leads.

2-nd t;;e ice cover

;

.

~!ow cc~d~:io~s. T~e correspondence bet~een the ~ea5ared a~d calculated ,\,a1'''';25 is e:· :.re:::ely good.

?::'.sl.1res 6 2.i.1d

i

sr.o\ol t~e c08pute.d equil':"brium oacK..-..:ater ::...:.c,..-e.s :Dr

?re-rel~ase conditio~s ~ith a re.turn ?eriod of 500 years at ti~e

t = O· ~r for i::e jc..Ir.S ini:ia-c:e.d at Patricia Island (nac.e 33) 2:ld

~o~an ~ells (~ode 11), re5?ect~vely.

Al:~O'Jgh it ~s ~arc.ly ccnceivable :ha~ an ice ja3 could ~e

init~at-cross-section by only 5%, Esso Resources 2~Fhasiz2s the ~ntegri:y of che =an-~ade island design by taking t~is unli~21y-event i~to account. From observation, it ~as been concluded t~at in :he worst ?cssib2.e event the obstructed ice cover 'Jill ex~end to the u?-stream single-c~an~el re3ch at Gaudet Island (~ode 47).

The co=;)Ute.d \.;ater ele.vation at }l"or.r.an wells for the. Patricia !sland j am is 53. 6 ~SC, al:::nost rese!Ilbli:lg the ext-:eme value predicLion. The computed

~axiillum

surface gradient is 700*10-6 for the Patricia Island jam and 552*10-6 for the

~o~an

Wells jam.

L~e

former ~s of the same order as observed.

Both ice jams have been released iustantaneously, which is an unrealistic but cor..servative approach, since actc;ally t~e disi:-.tegration of the ice cover proceeds over a ?eriod of time. Figures 6 and 7 show t~e computed propagation and defor:uation of the flood wave. The t~e development of some water elevations and channel-averaged velocities is illustrated in Figl.lres 8, 9, 10 and. 11. :'he COUipute.d peak surge ' ... ~elocity for the estimatec. SGO year return ?e~ioc event in the ~or:::lan Wells section., branch 17, is about 2.9 m! s for the Patric::ia Island j am and about 3.4 m/ s for the No~an Wells jam.

5

COMPUTATION OF FLOW

PATTE&~

AROUND

~~-~_~E ISL~'TIS

In oreier to c.2te.r::J.ine the local peak surge. velocities cc::ross and :c.1ong ::le f1'O;,.- section at XO:-='2n 'V,-ells, 2::. overall c::,C'cel ane a

.

.

cor:di::'ons for c:"e c\lerall :::.:~el, w:-.ic.h in ".::.t.:::.-n ?r::..-;i.des :~e

~o~~ca~y ccndit~o~s for tje ce:ai~ed ~:~el.

7~e c~~?utation of the local ?eak surge ve.:ocities has ~e2n

ca.rried out with t:J.e aid of =:/drcTIa::;.':'c' 5 nu=e.ric.al =_CV :J.ocel, H":lYFLQl,..'-2, ror uI'.st.e.ady, 2-di:::e:-.sional :'e.?th-avcraged f~'Jw.

The I1c.:c::erical :node'l :'5 based on a £:"n::2 diffe.re.nce :-e.p:'2.se"!1tation of the shallow r ... -ate.r equatioI"_s. The cc,-:::put2!:3.0n :l:2tj,od is an

i:;)proved version of the se.mi-i=plicit ~:::2ncer!.se sc:,e~e, e.e:ploying a space-staggered grid.

The overall :::nodel and the detai2.ed ::lacel :"'13Ve a square =esh-size of 125 ill and 10 m, respectively.

Figures 12 and 13 il1ustra'[e the coc~uted flow patte.rn for the overall and detailed ~odel, respec t i vely, clur:ing the ?eak-surge condition of an ice jam init::"ated and rele2.sed at Nor::.an Wells. The ulti::J.ate local vel·oeity has been cou:.puted for the 500 year return period event at 6.8 mls at tbe upstream cor..,.ers of the blt.:.nt~osed ice pile-up berm.

6 CONCLUS IONS

The i:' • .:draulic consequences of the rise and release of ice jams have Jeen computed with the aid of an explicit numerical model, pe~itting open chan~el flow as well as flow with an ice jam. For 185 km of the ~ckenzie River the steady d:::"scharge conditio:1s were adequately ~eproduced.

The computed channel-averaged surge ·.~elocities of the ice jam release have been transfar.ned to local surge velocities by means of a semi-implicit numerical model for computation of the 2.-dime.nsional, depth-averaged flow.

These results could be used for the detailed design of the slope protection of the man-made islands, as ... e11 as for the prediction of morphological changes.

9.

1. ~Y~RO:;;',,-'1IC )V, Jesig:1 2nd Construction ?:an for =',,=velop:-:.2T'!.t IslCi:1cS at :~or::-_c.n "wells. ~rch 1979

2. ~YJ?"O:-~). .. _~'_1IC bv, ~1.an-::J.ace Islands in t;,e ~·~Ck2::Z:~ ?.i \ .. oer;

~valuation of 3ydraulic Jesign. ~2rch, :981, ;2~ort ~o. ?5C8 3. !-:..-\:fPH1.jIS, J. W., Ice Break-up and Ice Ja=:::::i:lg a=-,.:ng t~e

~2S0urces Canada Limi:ed, ~ay

:981

along :~e ~~ac:,2!lzie River. ?roc. CSeE, :'~y 1982

j . tc:JofP, ~.S., :fac:":'euzie ?.iver :~or::an r ... ~ells, 1982 3reaKup. ~sso

~2S0urces Canada Li3iteci, Inter~al RepoTt, ~an~ary 1983 6. Y~~C~~Y, D.K.

&

Y_;CKAY, J.R., Breakup and Ice Ja~~ing of ~~e

~ckenzie ~iver, N.W.T. Repor~ 73-3, Task Force on ~or~hern Oil Developoent, Depart::lent. of ::nviroru:::e.nt, C a::.. ad a , 1973 7. ~~CKAY, D.K.

&

~~C~~Y, J.R., Locations of Spri~g Ice Ja~ing

on the ~ckenzie River, ~.W.T. Report 73-3, Task Force on Northern Oil Development, De?art~ent of Enviro~ent, Canada, 1973

8. ~ICHEL, B., Ice ~echanics. Quebec, Le.s ?resses de l'Universite Laval, 1978

9. MOIR, J.R., Breakup Observations, 1979. ~sso Resources Canada Limited, Inte~al Xernoranda, July 1979

10. MOIR, J.R., A Review of t~e Design and I~pact on the River of Artificial Islands in t~e ~ackenzie River at No~an Wells.

Esso

Resources Canada Limited, In~ernal ;eport, December 1979

11. TATINCLAUX, J.C., River Ice Jam Models. Proc. L~ Synposium on Ice Problems, August 1978, Lulea, Sweden

12.

UZUNER, M.S.

&

KENNEDY,·J.F., Theoretical Model of River Ice Jams. Froc. ASCE, Journal of the Hydraulic Division, 1976, Vol.

102,

No. EY9

13. VREUGD~~nIL, C.B., Waterloopkundige Berekeni: ~~n (in· Dutch). Delft -:"·niversi:y of Tec~'''101ogy, Jept.. of Civil -:'ng., Lecture :;otes, 1979

• NE TWOR,c. NODE - River System 1 Mackenzie FiS·

"

Curve Rating . ____ _ _ .- 4 S;eady, ______ _ J-IS_

---Fig. 3 Fig !..ONGITUDI'<<l.L SEC-:"ION m ade island Man

- f-'f-~

"

I o Z1 I

,

~I

Fig.6 ?alricia island Ice J:lm L::mgitudinol ?rof:\es

-'-

---.,

c

,

I. _TIME ("'ours) :'m~ of 'f'.!!,QSf'

F'ig.8 Patricia ISland Ie!? Jam ::levations Q~ter Reteuse

+

•

---_16

/ 0

,

r 0 c

"

,

•

I. ;ilo4E

'''''''

-.

" .. ",~f'

Fig. lC ~:. tr ic'a ~siGnd C2- ::;cm

+- "

I !C

"

-:-:''12! '00

•

'<0' '"'QJ' w.-!Lt.

"

,.

I "20

'"

·co JISTA.'<cr :~m)

r!g 7 Nor-:'J.n V/e~:s iCe Jam

~o:--;;~,..Jdir,QI Profiles ... "-""""'-... ..

-._-...

----

-._-... , - -_{... ---~---47} - - . --·_D

-_ ----_r:

_---1

,

. F----~_-.J

'-Fig. 9 Nor:":lon Wells Ice Jam Elevations citer Rete-ese

w % % ~ V r->

I-f<'\--- ---';;"'

1/, . :q--

!f '-.

'~-

!3

1=-'-=1.

.'-... '-

~---

---

,-j,\ ... - - · - - _ . _ _ _ _ _ _ _ _ _ _ 11 'I-

'L

,

---._.

__

.-

--'-'-'-'---'

,

c o

.,

,t;;.11 ~c:--:-,c.n \Ve(~s :ce JOO'i"'l

\.'ei~.:-~'~s 0::2, ~2

----~---~'.

~ V8...ll:ITl' - 2. ~ .,/.

Fig,12 Surge Flow Patiern in River Reach

after Re!ecse of ~~orman We!! 5 Ice Jam

Fiq.13 Surge ~:''Jw ?o.t:e--n a;-cl.::>C ~StcnC