127
Journal of Hy dr odynam ics, Ser. B, 2005, 17( 2) : 127- 133
China Ocean P ress, Beijing- Pr int ed in China
*
ICE JAMS IN A SMALL RIVER AND THE HEC- RAS MODELING
SUI Jue- y i
Depa rt ment o f Enviro nment al Sciences and Eng ineer ing, U niv ersit y of No rt hern Brit ish Columbia, C ana da, e- mail: sui@ unbc. ca
KARNEY Bry an W.
Depa rt ment o f Civ il Eng ineer ing, U niversit y of T o ront o, Ca nada
FANG Da- x ian
Depa rt ment o f Civ il Eng ineer ing, H ef ei Univer sity o f T echnolo gy, H ef ei 230009, China
( Rece ived M ay 12, 2004)
ABSTRACT: T his paper describes a model of a 3. 06km long
riv er r each betw een tw o small r eser vo irs under both open flo w
and ice cover ing conditio ns for differ ent operat ional settings of
the sto plog s in the do wnstream r eser voir. T he H EC - R AS
model developed by the H ydr olo gica l Eng ineer ing Center of
U S Ar my Cor ps of Engineers w as used to com par e differ ent
appro aches in ter ms of flow velocity , w ater level and the
Fr oude number. T he impact s o f heavily vegetat ed main channel and flo odplain o n ice accumulations w ere investig ated. A nd
it is show n that this vegetat ion plays a sig nificant r ole in the
format ion of r iver ice jam during winter per io d and thus the
vegetated channel has st rong influence o n ice flo oding. In addition, the pa per ex plo res the impact both of the operation of
the sto plog s during the w inter per iod and the presence of the
do wnstream dam o n the accumulation of ice jam along this river reach.
KEYWORDS: heav ily veg etated channel, H EC- R AS mo del,
ice- co ver ing conditio n, ice jams, w ater level
INTRODUCTION
An ice jam is a n accumulat ion of f ra gment ed
ice o r f r azil that rest rict s f low . I ce ja ms pose pro blem s a cr oss Canada and are of t en accom panie d by
dr amat ic incr ease s in w at er le vel due to t heir
blo ckage ef f ects. Surf ace ice jam s and f razil ice
jams are tw o basic t ypes o f ice jam s.
An ice jam reduces the f low co nv eyance of t he
cha nnel thr oug h its blo cka ge ef f ect and the increa se in f low resist ance. T he r educed convey ance
ca uses an increa se in w at er level, a s sho wn in F ig. 1
( Sui, 2002a ) . Mo reo ver, t he backw at er ef f ect of
an ice jam on wa ter lev el increa ses w it h increasing
1.
*
jam t hickness. T he increase in jam t hickness, in
t urn, i ncreases t he channe l slope and f lo w velo ci
ty . I n shallo w sect io ns, a gr ounded ice jam can be
init iated by submerg ence a nd blo ckage ca used by
ice f lo es. T he gro unding is ser ious pr oblem since it
can lead t o a larger and f aster r ise in the r iver leve l
t ha n a no n- gr ounding jam . When t he leading edg e
of an ice cover o r jam prog resses t o the sect io n
w ith hig h f low velo city, inco m ing i ce f lo es w il l
submerg e and be co me ent rained o n the underside
of t he cov er.
In a river w it h rapids, open w at er o f te n remains co nt inually in these sect ions. T hese open
w ater r eaches can pro duce large quant it ies o f f ra zi l
ice t hat is subsequent ly suppl ied t o the underside of
t he ice cov er do wnst ream dur ing the w inter. In
t his w ay, t he entr ained ice w ill be tr anspo rt ed and
accumulat e underneat h t he ice cov er t o f o rm socalled f razil jam s. T he f or mat io n of a f r azil jam
w ill f urt her block t he f low and t hus f urt her incr ease t he w at er le vel.
Overal l, the dist ribut io n and thickness of t he
f razil jam ar e go verned by bot h t he ice supply and
t he i ce t ransport capacit y of the f low ( Shen and
Wang 1995; Shen et al. 2000; Sui et al. 2000;
2002b; Wa ng et al. 1995) . T he ice t ranspo rt capa cit y decr eases wit h a r educt io n of ei ther f low velocit y o r channel slo pe. Whenever t he ice supply
exceeds t he tra nspo rt capacit y of t he f low , f ra zi l
accumulat ion w ill o ccur ; and by co ntr ast, w henever t he ice supply is less t han the t ransport capacity
of t he channe l, t he ex isting f ra zi l jam w ill ero de.
Biography: SU I Jue- yi ( 1963- ) , M ale, Ph. D. , Assistant Pr ofessor
128
ice ret entio n behind t he ice boo m is a kind of
blockage f reezing- up pr ocess) . Based on their extensive r ese arch and pr act ical ex per ience, they
propo sed ma ximum Fr = 0. 08- 0. 12 , m axim um
surf ace w ater ve locit y v = 0. 60- 0. 76 m/ s.
In f act, t he ice jam f orm at ion w ith sur f ace
blockage pro cess and co nge st io n pro cess depends
also on t he dim ension of t he f lo es in addit ion t o t he
hydraulic f acto rs such as t he w ater surf a ce f low veFig . 1 Impact o f ice on w ater level at the H equ Gauglocit y and Fr .
ing Statio n/ Y ello w R iver
Flo w under the ice cov er/ ice jams is quit e difT he mo st co mm on lo cat io ns f or t he f or mat io ns f erent f ro m that under open f lo w condit ions due t o
of ice jam and hanging da m include places w it h re- t he nat ure o f t he shear stress caused by t his addi
duced o r non- unif or m ve locit y. Obvio us locat io ns tio nal solid sur f ace and it s w et ted per imet er. T he
where t his occurs i nclude w here t he r iver ent ers a im pact s o f t he ice co ver/ jam s should be considered
lake o r reservo ir, a t r iver bends o r w hen t he f lo w in the course o f t he hydraulic sim ula tio n o f t he
enco unte rs a deep poo l. T he f o rm at ion o f jam s ca n channel f lo w. T he v ariat io n in w at er level and t he
be par ticularly dr amat ic w hen t hese f eatures adjo in dischar ge of a gradua lly var ying f lo w in a river
an upst ream st ret ch of rapids w here large qua nt i w ith ice cov er/ jam s can be described by t he co nti
nuit
y
equat
io
n:
t ies of f razil are pr oduced.
Due t o t heir essent ial nat ure, ice pro blem s are
invaria bly co mplicat ed. T he f o llow ing are just a 5Q + 5A = 0
( 1)
5t
sample of t he f acto rs w hich must be conside red in 5x
the studies of riv er ice pr oblems:
( 1 ) River mo rpholo gy, including channel and t he m om ent um equat io n:
slope, channel g eom etr y, channel net w orks,
2
sho als, riverbed r oug hness, veg etat io n in channel Q5Q + Q 2Q 5Q - Q 2 5A +
5t
A 5x
A 5x
and f lo odplain, et c.
( 2) Hydra ulic co nditio ns, including t he f lo w
5H e
QgA
+ P i Si + P b Sb = 0
( 2)
velo cit ies, w ater dept h, w ater surf ace pro f ile, in5x
f luence o f dow nst ream.
( 3) M eteo ro log ica l f a ct o rs including air t em- w her e Q is the discharge, A t he f low a rea, H e = Z b
pera ture, w ater te mperat ure, w ind speed, sno w- + ti + h the w at er le vel, Z b t he bed elevat ion, h t he
f all, etc.
dept h o f f low , ti t he equivalent t hickness o f t he ice
( 4) M any o ther f acto rs, including things like cover/ ice jam, Qi H/ Q, P b and P i are w et ted perim eter
huma n inte rvent ions, gro und heat input , e tc.
f o rmed by t he channel bed and t he ice co ver/ ice
Fro m dat a o n t he St . L aw rence River in Cana- jam respe ct ively , Sb and Si are shear st ress at t he
da/ U S, it wa s f ound t hat a co nsist ent value of channel bed a nd t he ice co ver/ ja m r espect ively, x ,
max ima l F roude number, equal to 0. 09, is o f gr eat t are dist ance and t im e, r espect ively.
impo rt ance. In part icular, f ield observa tio ns and
T o solve these t w o equat io ns f or dischar ge and
subsequent analy ses at t he Hequ Reach o f t he w ater leve l, it is necessar y t o know t he equivalent
Yello w River in China sho wed t hat the f ro nt al ice jam t hickne ss ti and the resist ance co ef f icient ni
edge of ice jam can ex tend f ur ther upstrea m o nly if of ice j am. I n g ener al, bot h t he ice ja m t hickness ti
the F ro ude number ( Fr ) o f f lo w at t he upstr eam and t he resist ance co ef f icient n i o f ice ja m are co nend of the jam is le ss t ha n 0. 09, and t hat t he ice sidered as t he f unct ion o f t im e and space. T o solv e
jam can no t pr opagat e upst ream if Fr > 0. 09 ( Sui t hese t w o equat ions, a f inite- dif f erence m etho d,
et al. 2002b) .
such as t he f our po int implicit f inite- dif f erence
Fo lty n and T ut hill ( 1996) claimed that there schem e develo ped by Pot o k and Quinn, can be
wa s a crit ical hy dra ulic co ndit ion f or re tent ion of used.
ice co ver/ jam behi nd an ice boo m ( concept ua lly,
T he f init e- dif f er ence f orm o f t he cont inuit y e-
129
qua tio n f o r a r iverrea ch co uld be wr itt en a s
1
$x
U( Q
n+ 1
d
- Q
n+ 1
u
) - ( 1 - U) ( Q - Q ) +
n
d
n
u
1
n+ 1
n
n+ 1
n
[ T d( H d - H u ) + T u( H d - H u) ] = 0
2 $t
( 3)
where t he subscr ipt s d and u represent dow nstr eam
and upst ream ends o f t he rea ch, re spect ively, t he
subscr ipt s n a nd n + 1 indicat e the tim e le vels a t t
and t + $t , T t he t op w idt h, Utem pora l weig hting
f acto r.
Sim ilarly , t he f ini te- dif f erence f o rm of t he
mo ment um equat ion:
ly.
Ho w ever, considering t he com plex it ies of a
nat ural channel, m any bo undary conditio ns m ust
be sim plif ied in o rder t o so lve t hese equat ions. F or
t his spe cif ic 3. 06km long river reach w ith he avily
veget at ed channel/ f lo o d pla in, t he H EC- RAS
mo de l w as used t o simulate the f lo w and ice a ccumulatio n dur ing t he w int er perio d.
GEOGRAPHICAL LOCATION AND ICE REGIMENS
T he 3. 06km lo ng riv er reach ( C D- T H Reach)
conside red in t his st udy runs bet ween t w o dams.
T he upstrea m sect io n is a t the Clendennan Dam
( CD- Da m ) a nd dow nstre am sectio n ends at t he
T hor nbur y Da m ( T H- Dam) . T he Be aver River itse lf runs no rt hea st , f low ing t hro ugh t he villa ge of
1
1
2Â
Q/ ( AÇ $x ) [ U( Qn+
d
- Qn+
u
) + ( 1 - U) #
Clar ksbur g bef o re dischar ging int o t he No t taw asaga Bay dow nst ream o f TH Dam in t he pro vince of
n
n
n+ 1
( Qd - Qu ) ] + gÇ
A / $x [ U( H d Ontar io, Canada. Wit hin this CD- T H Reach, t his
rive r is appr ox imat ely 20m w ide.
1
H n+
u
) - ( 1- U) ( H nd - H nu ) ] T he upper part o f t his river reach is steep w it h
lim est o ne clif f s along bot h sides of t he m ain cha nQ
Â2 / ( AÇ2 $x ) + { U[ T d # ( H dn+ 1 - Z d ) nel. T he lo we r sectio n o f t he valley is m ild and
meanders thro ug h sand, silt a nd grave l depo sit.
n+ 1
T u ( H u - Z u ) ] + ( 1 - U) #
A sit e v isit w as conducted o n F eb. 1, 2001.
T his inspect ion sho wed many f eat ures of signif i
[ T d ( H nd - Zd ) - T u ( H nu - Z u ) ] } +
ca nce t o ice f orm at ion. F or exam ple, it wa s f o und
t ha t alo ng t he CD- T H Reach ther e are sever al pro2
4/ 3
7/ 3
1
no unced bends, wit h o ne occur ring w it hin t he
4. 417ne QÂ | Q
Â| P
 / AÇ +
#
2 $t
ba ckw at er re gion o f t he T H da m and hav ing a particularly sharp cur ve. As F ig. 2 indicates, the co m1
1
[ ( Q n+
d
- Q nd ) + ( Qn+
u
- Qnu ) ] = 0
( 4)
plex f luv ial geo mo rpholo gy is char acter ized by
heavily v eget ated channel/ f lo od plains sectio ns
where
w ith so me sho al reaches, resulting in a co mplicat ed
set of f lo w condit ions.
1
n+ 1
n+ 1
n
n
Q
Â=
[ U( Q d + Q u ) + ( 1- U) ( Q d + Q u ) ] ( 5)
By lat e in No v. o r ear ly in Dec. t emperat ur e
2
w ill cause f razil ice t o be pro duced in t his r iver.
T he r iver ty pical ly breaks up by lat e M arch or ear1
n+ 1
AÇ = 1 [ U( H n+
u T u + H d T d ) + ( 1- U) #
ly Apr il.
2
Ice co ndit io ns a long t he CD- T H Reach wer e
observed
dur ing site v isit. Bot h reserv oirs w ere icen
n
Qi
( H uT u + H d T d ) - ( Z u + t i ) T u cover ed. T he CD r eser vo ir pro vides a depo sito ry
Q
f o r the f razil ice com ing f ro m t he upper river
reach. I t helps t o r educe the sever ity of ice jam
( Z d + Qi t i ) T d ]
( 6)
Q
f o rma tio n in t his river reach by reducing t he ice
supply t o do w nst ream . Velo city and ice thickness
u
d
in w hich, Z and Z are t he ref erence elevat io n of measurement s w ere m ade in t he vicinit ies of Sect.
the upstrea m a nd dow nstr eam e nds, re spect ively, Q 757 ( dist ance in m et er f ro m t he do w nst ream T H
and Qi are m ass density o f w at er a nd ice respect ive- Dam ) and the upper end of t he T H reserv oir
2.
130
ice co ver by reducing the f lo w v elocit y ( see F ig.
2) . Bo th the ice co vers and t he t rees/ bushes w ould
collect t he ice f r om the upst ream . T hus, t his area
appea rs t o be the m ost likely lo catio n of init iat io n
and deposit ion o f ice jam . Not surprising ly, t he n,
ice f o rm at ion a nd jamm ing f requent ly occur in t his
rive r re ach and o f t en lead t o ice f loo ding, such as
t ho se o ccurred in Jan. 1996 and Jan. 1997. T he
w inter o f 1996 w as o ne o f t he co ldest in recent
Fig . 2 M ain channel/ flood plain with t ree/ falling tree/ bush
year s and 1997 w as a w ar mer w int er w ith a sever e
( Beaver Riv er, in Ontario, Canada)
cold spell lat e in t he season. Bot h of t hese co ndi
( Sect . 857) . No f razil accumulat ion w as f o und un- tio ns w ere f a vourable f o r i ce jam f loo ding. I t is
der ice cov er in the T H reserv oir.
likely t ha t during the w int er o f 1996, the ice co ver
Using the survey of t he channel prof ile, it i s pe rsisted f or lo ng er, and t he cause o f t he f loo di ng
f ound that t her e is a ver y shallo w sect ion a t Sect . w as lar gely due t o the co ntr ibut ion o f a f razil jam.
757 having poo l sect ions bot h upstrea m and do wn- T he 1997 jam wa s caused by t he ja m init iat ed in t he
st ream of t his sect ion. T he po ol upst ream o f thi s vicinit y of the w o oded reach, and t he w ater leve l
se ct io n w ill help to init iate t he surf ace jam f or ma- w as backed- up due to t he heav y accumulat ion bo t h
t io n. T he po o l dow nstr eam pr ov ides a sect ion f or here a nd upst rea m f ro m this.
ice a ccum ula tio n. T hese co ndit io ns, to get her w ith
the hea vily wo ody co ndit io n at t he sit e, indicate 3. HEC-RAS MODELLING
that an ice ja m w ill of ten be init iat ed near Sect .
Cur rently , it is im possible t o precisely simu757. As a direct result , ice f r om upstr eam wi ll be late a river system under ice- co vered conditio ns due
co llecte d in t his sect ion and w ill no t e asily be tra ns- t o the co mplex ity o f a nat ura l riv er sy stem and t he
po rt ed do w nst ream because of the low f low v eloci associat ed met eoro lo gical condit ions. H ow ever,
t ies and the inf luence o f t he t rees/ bushes.
appr ox imat io ns are possible and helpf ul, and t his is
T he f lo w velo cit ies in o pen area and under ice t he approa ch ado pted here. In part icular, t he
co ver in t he vicinit y of Sect. 1400 w ere measured HEC- RAS sof t w are can be used no t only t o simuduring site visit :
late t he f low velo cit y and w at er level under open
( 1) Open w at er conditio n: the f lo w velo cit y f lo w co ndit io ns, but also to det erm ine the t hickof open w at er at the f ro nt al edge o f ice cover wa s ness of ice jam if an initia l cov er is give n. T he en1. 4m / s at t he dept h of 0. 1m be low the w at er sur- tered value of the ini tia l ice t hickness represent s
f ace, 0. 95m/ s at t he dept h o f 0. 2m , 0. 66m / s at t he m inimum al low able thickness o f ice co ver. T his
the dept h of 1m and 0. 51m/ s at t he dept h o f 2m t hickness wa s select ed o n the basis o f f ield observa( near the river bot t om ) .
tio ns, w hich show ed that no cro ss sect ion ha d a
Ice cov ered condit ion: the f low v elocit y under m inim um t hickness less t han 0. 1m here.
ice cov er ( 10m do wnst ream f ro m the f ro nt al edge
Fo r t his specif ic sit e, t he ice jam s could be
of ice cov er ) is 0. 46m / s imm ediate ly under ice caused by one o r mo re o f the f ol low ing pro cesses:
co ver ( t he t hickness o f ice cov er is abo ut 0. 3m ) ,
( 1) Ice accum ulat io n m ay occur in t he back1. 22m/ s at 0. 5m f ro m the bo tt o m of ice co ver and wat er regio n o f t he T H reservo ir. T his co uld initi
0. 8m / s at 1. 5m f r om the bot t om of ice co ver ( 0. ate t he ice jam due t o lo w f low velo cit y in t he
2m abov e riv er bo tt o m) .
ba ckw at er reg ion. I f the v elocit y o f incom ing ice is
In t ot al, 7 ho les wer e used t o m easure t he f lo w less t han the div ing velo city of ice blo cks, t he ice
velo cit ies under ice cov er in t he T H reservo ir re- cover ( ice jam) w ill pro gress upstr eam w it h co rreg ion ( at Sect. 549) . T he f low velo cit y under ice spo nding increases in w at er level.
co ver in t he T H r eser vo ir is less than 0. 50m/ s
( 2) T he meandering channel w ith shoa ls and
( m ain channel ) . In addit io n, no f r azil ice wa s heavily veget at ed channel/ f lo odplain a long t his
f ound under ice co ver in t he reser vo ir.
rive r r each is likely t he m ain reaso n f o r t he f or maHy dra ulically, at lea st , t he tr ees in t he chan- tio n o f an ice jam . T he ice jam s generally init iat e
nel/ f loo d plain w o uld prom o te t he f o rm at ion o f a n at t he locat ion w her e an ice bridge f orm s. T his
131
specif ic river reach, hav ing as it does trees a nd bushes in channel/ f lo odplain, creat es f avo urable condit ions f o r the f or mat io n o f an ice br idg e and thus
of an ice jam t hat w ill t hen pro pagat e upst ream .
Fo r t his sim ulat ion, the M anning roughness
co ef f icient ( n ) is o ne of the key input par amet ers. Co nsider ing t he f eat ures of this river reach,
the M anning ro ughness coef f icient f o r ma in channel and f loo d pla in was a ssumed t o be 0. 035 and 0.
06, respect ive ly.
T he simulat ions w ere conducte d f o r dif f erent
discharg es including 10m 3 / s, 20m 3 / s, 60m 3 / s and
3
100m / s. Acco rding to t he f ield o bser vat io n of t he
Canadian Weat her Service, t he m axim um insta nt aneo us discharge in t his river reach ( at C larsburg
gaug ing st at ion) f ro m 1957 t o 1988 w as 96. 3m 3 / s
on 13 Ma rch 1977. T his va lue is less t han 97. 8m 3 / s
( quant ity le of t he 100 yea r ret urn perio d)
T he f ol low ing f o ur dif f erent simulat ion alt ernat ives have been chosen in o rde r t o co ver all aspect s considering ice co ndit io n and operat io ns of
sto plogs of t he dow nstrea m T H dam ( rem ov al or in
place) under ice- cover ing co ndit io ns:
Case 1: open f low co nditio n ( remo ve all
sto plogs) ,
Case 2: open f lo w co ndit io n ( a ll sto plogs in
place) ,
Case 3: ice cover ing condit ion ( remo ve o f all
sto plogs) ,
Case 4: ice cover ing co ndit io n ( all st oplog s in
place) .
Figures 3, 4 and 5 sum mar ized the result s of
HEC- RAS sim ula tio n w it h respect t o the sim ulat ed
wa ter surf ace elevat io n, t he f low v elocit y and Fr .
Case 2 ( o pe n cha nnel co ndit io ns, all sto plog s
in) is t he m ost crit ical f o r f lo w under open channel
co nditio ns, simi larly, Case 4 ( ice- co ver ing co ndi
t io n, all st oplo gs in) is the cr itical co ndit io n f or
the f lo w under ice- cov ering co ndit io ns. Ho w ever,
Case 4 is no t an a llow able operat io n alt ernat ive
w ith the T H Da m since a ll st oplo gs m ust be rem ov ed out in w int er.
T he simulatio ns sho w t hat t he Fr o f str eam
f low s under open channel condit ion dow nstr eam
f ro m Sect. 857, nam ely t he reser vo ir reg ion, i s
generally less tha n 1. 0, as sho w n in F ig. 5. T hi s
means that the o pen f low a long t his riv er rea ch i s
generally subcr it ica l f low , since Fr < 1. 0 . H ow ever , hy dr aulic jum p ma y be f or med near Sect .
1000, since t he sim ula ted Fr is abo ut 1.
Fig . 3
Simulated w ater lev el along river reach ( Q =
20m 3 / s)
F ig. 4 F lo w v elocity along r iver reach ( Q = 20m 3 / s)
By com paring t he sim ulat io n result s bet w een
Case 3 and Case 4 ( as sho wn in F igs. 3 and 4) , it is
f o und t hat t he o perat ions of st oplog s ( m ov ed o ut
or in place) do not play a signif icant r ole o n t he
accumulat ion of ice upstr eam of t he T H reservo ir,
since t he w ater lev el, f lo w velo cit y and t he Fr under bo t h co ndit io ns ar e appro xim at ely identical.
Upst ream f ro m t he Sect . 1097, t he f low velo city
and Fr increase signif ica nt ly. As sho w n in F igs. 6
( a) and 6( b) , re lat ively mo re ice accum ulat es in
t he reservo ir if all o f st oplog s are rem ov ed o ut during w int er perio d. Co nce pt ua lly at lea st , t his is
reaso na ble, since t he rem ova l of t he st oplog s incr eases the f low velo city a nd Fr in the reserv oir due
t o the decrease in w at er depth.
As show n in F igs. 6( a) and 6( b) , near Sect.
857 there is a deep po ol t hat is o ne of t he mo st po ssible sit es f or f or mat io n o f ice jam. In addit io n,
heavily veget ated shallo w channe l and f lo odpla in
bet w een Sect . 549 and Sect . 857 sho uld help to stabil ize the f o rm ed ice jam upst ream . T his w ide shal
low sect io n should be caused by t he deposit ion of
sedim ent in t he backwa ter reg ion of t he reservo ir.
T he im pact s of ex isting t rees and bushes in t he
channel and f loo d plain alo ng t his river r each o n
t he accum ulat io n of ice jam mig ht be sim ilar to t he
/ st eel in co ncr ete0.
Dow nst ream o f t he Sect . 857, beca use of lo w
f lo w velo cit y in the reservo ir, the ice accum ulat io n
132
Fig. 5
Fr oude number alo ng riv er reach ( Q = 20m 3 /
s)
belo ngs t o r eser vo ir ice jam t hat sho uld be dif f erent f rom t he upst ream ice jam .
Since t he crest elev atio n of spi llwa y o f t he
do w nst ream T H da m is the bot t om eleva tio n of t he
reservo ir in f r ont o f t he dam , it ma y be concluded
that t he dam ha s only a lit tle ef f ect o n the accum ul atio n of ice upstre am f ro m t he reservo ir. H ow ever , t he dam is an indir ect f act or causing t hat ice
pr oblem along t his 3. 06km lo ng river reach, because the dam should be r espo nsible f or the deposi
t io n of sediment in t he backw at er regio n and thus
the f or mat io n o f t he deep poo l t here.
Wit hout deco mm issioning of t he T H dam, t he
cha nnel im pr ovem ent m ay be t he po ssible m easure
f or reducing t he f lo od po tent ials f r om ice jam s al ong this rive r reach, such as re mo val o f t he tr ee s
and bushes in t he m ain channe l and f loo d plain.
T he clear ing o f t he heavi ly ve geta ted sect ion m ay
ena ble the channel to t ransport t he ice f rom upst ream t o t he T H re ser vo ir. Of course, t his m ight
have t o be count ered wit h ot her ero sion co ntr ol
measures t hat the v egeta tio n is curr ent ly per f or mi ng.
Fig . 6( a)
Fig. 6( b)
Simulated accumulatio n o f ice alo ng the r iver
reach ( Case 3, Q = 20m 3 / s)
Simulated accumulat ion o f ice along the r iv er r each
( Case 4, Q = 20m 3 / s)
vourable t o t he init iat ion of ice jams, such as t he
w oo ded channel a nd f loo d plain as w ell as deep
poo l upst ream o f t his sect io n. T he w int er operatio n can be adjust ed by adding or r emo ving st oplogs
at t he T H da m has been sho wn not to a f f ect t he
f o rma tio n of ice jam in the CH- T H reach. T he sectio n in the v icinit y o f Sect . 757 is t he lo cat io n
w her e an ice jam w ill f o rm and collect m ost of t he
ice f r om upst ream because of t he heavily veget at ed
channel/ f loo dpla in and deep poo l, and t hus ca uses
upstr eam wa ter levels t o r ise. Ho w ever, the dam is
likely an indirect f acto r t hat causes t hat ice pro blem alo ng t his 3. 06km lo ng river reach, be cause
t he dam is likely responsible f o r t he depo sitio n of
sedim ent in t he backw ater reg ion and t hus t he f ormat io n o f t he deep po ol in the backwa ter regio n of
t he T H reserv oir.
CONCLUSIONS
Key f eatures o f channel/ f lo od plain hav e been
sho w n t o play an impo rta nt r ole o n t he f or mat io n
and accumulat ion of ice cov er/ jam a long a 3. 06km
long heav ily veget at ed riv er reach bet ween 2 sm all
reservo irs. U sing t he HEC- RAS mo del, t he accum ula tio n o f ice jam and the associat ed hydraulic
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