Évaluation de la restauration des rivières chenalisées ......WESCHE, 1985 ; YRJÀNÀ, 1995) for the rehabilitation of pool-riffle -patterns. Hydro-physical habitat characteristics,

Bull. Fr. Pêche Piscic. (1995) 337/338/339 : 407-413 — 4 0 7 —

A. H U U S K O (1) et T. Y R J À N À (2)

(1) F i n n i s h G a m e a n d F i s h e r i e s R e s e a r c h I ns t i t u t e , K a i n u u F i s h e r i e s R e s e a r c h a n d Aquacu l tu re , R IN-88300 Ra l tamo, F in land .

(2) No r th O s t r o - B o t h n i a R é g i o n a l E n v i r o n m e n t Cen te r , R O . Box 124 , F I N - 9 0 1 0 1 Ou lu , F in land.

R É S U M É ( traduit par les éd i teurs)

A u cou rs d e la de rn iè re d é c e n n i e , p lus ieu rs p ro je ts de res tau ra t ion d e r iv ières à g r a n d e éche l l e on t é té in i t iés en F i n l a n d e , a f in de réhab i l i te r la s t r u c t u r e or ig ina le d e l 'habi tat d a n s d e s r iv iè res c h e n a l i s é e s p o u r le f l o t tage d u bo is d a n s les a n n é e s 1950-1960 . L'object i f p r inc ipa l d e la res tau ra t i on est d ' a u g m e n t e r la d i ve rs i té d e s be rges et d 'amé l io re r l 'habitat d e s p o i s s o n s e n réa r rangean t le subs t ra t sur le f o n d d e la r iv ière. L e s d i g u e s d e b l o c s u t i l i sées su r la r i v i è re K u t i n j o k i o n t a u g m e n t é la d i v e r s i t é et la v a r i a b i l i t é d e s p r o f o n d e u r s , d e s v i t e s s e s et d e s c l a s s e s d e s u b s t r a t s d o m i n a n t s d i spon ib les , et on t a u g m e n t é la c o m p l e x i t é spa t ia le d e s rap ides . Su r les s i tes é tud iés , les s u c c e s s i o n s r a d i e r s - m o u i l l e s é t a i e n t c l a i r e m e n t v i s i b l e s a p r è s r e s t a u r a t i o n e t c o n t r a s t a i e n t a v e c les é c o u l e m e n t s p l u s o u m o i n s h o m o g è n e s d ' a v a n t r e s t a u r a t i o n . L ' opé ra t i on d e r e s t a u r a t i o n s e m b l e f a v o r i s e r l es t ru i tes d e u n a n ( l - i - ) e t p l us . Si l 'on souha i t e p lan i f ie r et éva lue r ce t ype d ' amé l i o ra t i on d e l 'habi tat p i sc ico le , il est fo r temen t conse i l l é d 'u t i l i ser u n e m o d é l i s a t i o n d e s c o n d i t i o n s p h y s i q u e s et h y d r o l o g i q u e s à u n e éche l le per t inen te pou r les p o i s s o n s et d 'y inc lu re une a n a l y s e des p r é f é r e n c e s d 'hab i ta t d e s po i ssons .

E V A L U A T I N G HABITAT R E S T O R A T I O N O F R I V E R S C H A N N E L I Z E D FOR L O G T R A N S P O R T : A C A S E S T U D Y O F T H E R I V E R K U T I N J O K I , N O R T H E R N F I N L A N D .

S U M M A R Y

D u r i n g t h e l as t d é c a d e , s e v e r a l e x t e n s i v e r iver r e s t o r a t i o n p r o j e c t s h a v e b e e n s ta r ted in F in land a i m e d at res to r ing the or ig ina l hab i ta t s t ruc tu re in r ivers channe l i zed for log t ranspo r t in t he 1 9 5 0 ' s - 1 9 6 0 ' s . T h e ma in goa l of t he res to ra t i on is to inc rease the d i ve rs i t y of the r i ve r ine e n v i r o n m e n t a n d t o e n h a n c e f i sh h a b i t a t s by r e a r r a n g i n g t h e subs t ra te in the r iver b o t t o m . B o u l d e r d a m s e m p l o y e d in t h e r iver Kut in jok i inc reased the d i ve rs i t y a n d p a t c h i n e s s of a v a i l a b l e d e p t h s , ve loc i t i es a n d d o m i n a n t s u b s t r a t e s i ze -c lasses m a k i n g the rap ids spat ia l ly m o r e c o m p l e x . T h e s u c c e s s i v e riffle - poo l - s t ruc ture at t he s tudy s i tes w a s c lear ly v i s ib le a f ter t he res to ra t ion , in con t ras t to the m o r e or less h o m o g e n o u s p re - res to ra t ion f l ow p a t t e r n . T h e res tora t ion p r o c é d u r e s e e m s to faveur ^ + o r o lde r t rout . For t he p l ann ing a n d é v a l u a t i o n of f i sh hab i ta t e n h a n c e m e n t of th is k ind, it is h igh iy adv i sab le to e m p l o y the mode l l i ng of t he hyd ro -phys i ca l cond i t i ons at t h e sca le re levant to the f ish a n d to i nc lude in the ana lys is t he f ish hab i ta t p ré fé rences .

ÉVALUATION DE LA RESTAURATION DES RIVIÈRES CHENALISÉES POUR LE FLOTTAGE DU BOIS : ÉTUDE DU CAS DE LA RIVIÈRE

KUTINJOKI, FINLANDE DU NORD.

Article available at http://www.kmae-journal.org or http://dx.doi.org/10.1051/kmae:1995045

Bull. Fr. Pèche Piscic. (1995) 337/338/339 : 407-413 — 4 0 8 —

1 . I N T R O D U C T I O N

Unti l 1960s, log f loat ing w a s a signi f icant part of t f ie forestry in F in land. T f ie c f ianne ls su i t ab le fo r f loa t ing i nc l uded 4 0 0 0 0 k m of thie F inn is f i wa te r cou rses ( L A M M A S S A A R I , 1990) . T h e channe l s w e r e a l te red to al low t h e f loa t ing , wh ich mean t mak ing the natura l s t r e a m b e d m o r e h o m o g e n o u s by m o d i f y i n g t h e c r o s s - s e c t i o n of t h e c h a n n e l s , s t re igh ten ing m e a n d e r s a n d us ing embankmen ts to isolate the sha l low bays f rom the ma in c h a n n e l ( L A M M A S S A A R I , 1990 ; Y R J À N À , 1995) . T h è s e measu res s impl i f ied river habi tats w i th t h e réduct ion in d ivers i ty of wa te r velocity, dep th and subst ra te part icle s izes. All th is led to c h a n g e s in f ish commun i t i es , especial ly the sa lmon ids , wh i ch decreased signif icant ly.

Dur ing the last d é c a d e severa l ex tens ive pro jects have been star ted to restore the or ig ina l hab i ta t s t ructure of channe l i zed rivers. By 1 9 9 1 , s o m e 90 restorat ion pro jects have b e e n c o m p l e t e d , cover ing an a rea of 500 hectares of rapids ( Y R J À N À & H U U S K O , 1992) . T h e m a i n g o a l of t h e r e s t o r a t i o n h a s b e e n to i n c r e a s e t h e d i v e r s i t y of t h e r i v e r i n e e n v i r o n m e n t a n d t o e n h a n c e f i sh hab i t a t s . T h e r e s t o r a t i o n is u s u a l l y c a r r i e d ou t by r e a r r a n g i n g t h e s u b s t r a t e in t h e r iver b o t t o m , m o s t c o m m o n l y by e m p l o y i n g c h a n n e l e n l a r g e m e n t s , b o u l d e r d a m s , r i f f les and d e f l e c t o r s m a d e of b o u l d e r s , p l a c e m e n t of i nd i v idua l bou lde rs , e x c a v a t i o n s , a n d spawn ing g r o u n d s m a d e of t rans fe red and s ieved mater ia l (déta i ls in Y R J À N À , 1995) .

S o far, t he éva lua t ion of the ef fects of restorat ion on lotie env i ronment have inc luded w a t e r qua l i t y mon i t o r i ng ( Y R J À N À , 1995), shor t and long t e rm effects on benth ic f a u n a ( T I K K A N E N et al., 1994) , mon i to r ing f ish densi t ies (JUTILA et al., 1994) and an éva luat ion of ar t i f ic ia l s p a w n i n g g r o u n d s for sa lmonids ( Y R J À N À , 1995) . Th is paper documen ts , by m e a n s of a c a s e study, the c h a n g e s in physical habi tat character is t ics in cer ta in rapids in o rder to s h o w the i m p r o v e m e n t of habi tat diversi ty ga ined by the restorat ion.

2 . A C A S E S T U D Y

2 . 1 . S t u d y area

T h e River Kutinjoki (26 km in length, drainage area 120 km^, E 28° 20 ' , N 65° 40 ' ), a th i rd order r iver in Nor thern Fin land, is a tr ibutary of the River Kostonjoki , one of the main t r i bu ta r ies of t he River l i joki , a r iver running to the Bal t ic Sea . T h e gradient of the River Kut in jok i is 0.3 % , the annua l mean f low being 1.4 m^/s, the mean low summer f low 0.55 m^/s a n d the m e a n high f low (in spr ing) 17.4 m^/s. T h e river runs through peat lands and coni ferous fores ts wi th s o m e dec iduous t rees and bushes along the shores. In gênerai , the canopy is o p e n . In the 1950's, all the sa lmonid reproduct ion and nursery a reas (covering the total length of 6.6 km) w a s d redged for f loat ing .

2.2 . Mater ia l a n d m e t h o d s

T h r e e s tudy s i tes w a s se lec ted f rom the d redged river sec t ion . In it's pre- restorat ion State, e a c h s i te w a s approx ima te l y 100 m long and 9 m w ide (Table I). T h e main m e t h o d e m p l o y e d in the restorat ion of the s tudy sites was the cons t ruc t ion of boulder d a m s (see W E S C H E , 1 9 8 5 ; Y R J À N À , 1995) fo r the rehab i l i t a t i on of poo l - r i f f le - pa t t e rns . H y d r o -phys ica l hab i ta t character is t ics , inc lud ing water depth (in cent imeters ) , mean wa te r -co lumn ve loc i t y (in c e n t i m e t e r s per s e c o n d at 0.4 t imes dep th f r om the bed) and subs t ra te (for c lass i f i ca t ion s e e M A L A V O I & S O U C H O N , 1989) , w e r e m e a s u r e d at 10-30 po in ts a long e a c h of 10-12 t ransec ts at th ree s tudy s i tes both before and after the restorat ion dur ing the low f l ows (abou t 0.8-0.9 m^s ' ) in Augus t and Sep tember 1993. T h e t ransects es tab l i shed w i th in e a c h s i te we re se lec ted to represent longi tudinal s e g m e n t s hav ing simi lar hydraul ic a n d m o r p h o l o g i c a l c o n d i t i o n s f o l l o w i n g gu ide l i nes of B O V E E ( 1 9 8 2 ) a n d M A L A V O I & S O U C H O N ( 1 9 8 9 ) . F r o u d e n u m b e r a n d R e y n o l d s n u m b e r w e r e c a l c u l a t e d f r o m t h e m e a s u r e d var iab les by us ing the me thods in DAVIS & B A R M U T A (1989) .

In o rde r to have a f ish p ré fé rence perspect ive for the restorat ion we c o m p a r e d the m e a s u r e d d a t a to t h e h a b i t a t p r é f é r e n c e d a t a of b r o w n t r o u t (Salmo trutta L.). T h e p ré fé rence da ta of th ree s ize g roups (young-of -year (5-10 c m long) , l-i- (10-15 cm long) and o lde r (over 15 c m long)) w e r e b a s e d on the mater ia l f rom the nea rby River Kuus ink i jok i ( M À K I - R E T À Y S et al., 1 9 9 4 ) a n d w e r e c a l c u l a t e d a n d s t a n d a r d i z e d by t h e m e t h o d

Bull. Fr. Pêche Piscic. (1995) 337/338/339 : 407-413 — 4 0 9 —

Tab leau I : M o y e n n e et va leurs e x t r ê m e s des pr inc ipa les carac té r is t iques de l 'habitat sur les sites d 'é tude à fa ib le débi t est ival (0.8 - 0.9 m^s"') avant et après la restaurat ion .

Table I : M e a n and range of m a i n habi ta t characrer is t ics at t h e s tudy si tes before and after restorat ion at low s u m m e r f low (0.8 - 0.9 m^s-^).

Befo re

Site 1 Site 2 Site 3

Af ter

Si te 1 Si te 2 S i t e s

M e a n width m 8.5 8.8 9.5 10.5 11.2 14.5

R a n g e 7.6 - 9.9 7.3 - 9.9 8 . 3 - 10.2 9.2 - 11.9 9 . 6 - 12.4 9 . 2 - 1 9 .

M e a n depth cm 2 4 32 32 27 2 9 3 0

Range 1 - 4 7 7 - 9 4 2 - 7 5 3 - 6 5 0 - 1 0 0 0 - 150

M e a n veloc i ty c m s ^ 29 41 36 27 25 2 7

Range 0 - 121 0 - 1 2 6 0 - 1 3 0 0 - 123 0 - 1 2 9 0 - 110

M e a n subst ra te s ize-c lass 5.9 6.4 6.7 6.2 6.9 5 .7

R a n g e 2 - 8 3 - 8 2 - 8 0 - 9 0 - 9 0 - 9

M e a n Froude number 0.19 0.24 0.20 0.41 0.17 0.21

Range 0 - 0 . 8 1 0 - 1.03 0 - 0 . 8 9 0 - 1.42 0 - 0 . 9 7 0 - 2.05

Mean Reynolds number x 10* 7,2 13.6 12.7 7.1 8.4 7 .5

Range 0 - 30 .4 0 - 6 1 . 9 0 - 55 .0 0 - 34 .0 0 - 53 .0 0 - 37.8

3. R E S U L T S

T h e restorat ion i nc reased the river w id th f rom 2 2 % (si te 1) to 5 3 % (si te 3) (Table I). A s a resuit, the new river w id th a p p r o a c h e d the natural state of the river, wh ich could be de tec ted f rom the p résence of old river banks in the r ipar ian zone . N a r r o w ' U ' or 'V ' -shaped cross-sec t ions typ ica l of the river in its pre- restorat ion s tate w e r e c h a n g e d into wider and more var iab le c ross-sec t ions .

T h e s h a p e a n d l oca t i on of the f r e q u e n c y d i s t r i bu t ion of t h e m e a s u r e d va r i ab les changed markediy in the restorat ion in ail the other study sites (Fig. 1 , for ail var iables KSm-test p < 0.005, G-test p < 0.0001) except at site 1 for veloci ty (KSm-test , for depth p < 0.0005, but for velocity p < 0.1120). T h e f requency distr ibution of subst ra te c h a n g e d markediy in ail the study sites (G-test, p < 0.0001) . T h e restorat ion increased the diversi ty a n d patchiness of avai lable depths, veloci t ies and dominant substrate s ize-c lasses mak ing the rapids spatially m o r e c o m p l e x . F r o u d e a n d R e y n o l d s n u m b e r s i n d i c a t e d sub -c r i t i ca l o r tu rbu len t f l o w condi t ions (Table I). The success ive riffle - pool -structure at the s tudy sites w a s clearly seen after the restoration in contrast to the more or less homogenous pre-restorat ion flow pattern.

Before the restorat ion, there was a s igni f icant d i f férence be tween the s tudy sites in the veloc i ty and the depth d is t r ibut ions (K-W anova , for both va r iab les p < 0.01) a n d aIso in

présentée) in BALTZ et al.. (1991) . T h e p ré fé rence indexes for dep th , ve loc i ty a n d subst ra te we re g iven for each m e a s u r e m e n t point . Méd ian , m e a n , s tandard dév ia t ion a n d coff icient of var ia t ion of thèse point p ré fé rence indexes w e r e c o m p a r e d before and after res torat ion.

W e u s e d t h e K r u s k a l - W a l l i s o n e - w a y ana l ys i s of v a r i a n c e a n d t h e K o l m i g o r o v -Smi rnov test for con t inuous var iab les and the l ike lyhood ratio ch i - square test (G-test) for d iscrè te ones to dé te rm ine if d i f fé rences occu r red in the f requency d is t r ibut ions be tween va r iab les m e a s u r e d be fo re a n d af ter res to ra t i on . T h e re la t ive c h a n g e in the f requency d is t r ' bu t ions w a s d e s c r i b e d by J a k o b ' s i ndex : D = (i- - p) * ((r - p) * 2rp)" ' w h e r e r = propor t ion of resource before restorat ion and p = propor t ion of resou rce after restorat ion.

Bull. Fr. Pêche Piscic. (1995) 337133SIZ39 : 407-413 — 4 1 0 —

the subs t ra te s ize-c lass d is t r ibut ion (G-test, p < 0.0001) . Af ter the restorat ion, only a smal l d i f f é rence in t h e d e p t h a n d the ve loc i ty d is t r ibut ion b e t w e e n t h e m w a s not iceab le (K -W a n o v a , fo r dep th p < 0 .6220 a n d for velocity p < 0 .2125) . Ins tead of that, there ex is ted a s i g n i f i c a n t d i f f é r e n c e in t h e s u b s t r a t e size c l a s s d i s t r i bu t i on (G- tes t , p < 0 .0001 ) . T h e p r e c e n t a g e s of subs t ra te s ize c lasses from 3 to 6 (grave l , cobb les , pebbles) of the s tudy s i tes 1 , 2 a n d 3 w e r e 6 7 , 58 a n d 2 3 before the restorat ion a n d 42 , 33 and 48 after the res to ra t ion . The re fo re , the restorat ion s e e m e d to m a k e the hydro-phys ica l condi t ions in ail s t u d y s i tes qu i te similar.

% Depth Velocity Substrate

5 15 25 35 45 55 65 75 85 95 5 15 25 35 45 55 65 75 85 95 0 1 2 3 4 5 6 7 8 9

5 15 25 35 45 55 65 75 85 95 ' 5 15 25 35 45 55 65 75 85 95 0 1 2 3 4 5 6 7 8 9

F i g u r e 1 : D is t r ibut ion d e f r é q u e n c e s des c lasses de p r o f o n d e u r (cm) , de v i tesse d e c o u r a n t (cms" i ) et d e ta i l le de subst ra t (0 = v a s e , 9 = roche mère) avant (bar res g r i s e s , N = 2 0 0 pour chaque var iable) et a p r è s (barres noi res , N = 2 2 6 pour c h a q u e var iable) restaurat ion (en haut ) avec les va leurs d ' index d e J a k o b (-1...1) d e l 'évolut ion relat ive d e la d is t r ibut ion d e f réquence (en b a s ) sur le s i te d 'é tude 2 .

F i g u r e 1 : F r e q u e n c y d is t r ibut ions of depth (cm) , ve loc i ty (cms^) and substrate s ize c lasses ( 0 = silt, 9 = bedrock ) before (grey bars , N = 200 for each var iable) a n d after (b lack bars , N = 226 for each var iable) restorat ion (above) wi th J a k o b ' s i n d e x v a l u e s (-1 ... 1) o f the r e l a t i v e c h a n g e in t h e f r e q u e n c y d is t r ibut ions (be low) at s tudy site 2 .

T h e a s s e s s m e n t of t h e po ten t ia l habi ta t su i tab i l i ty fo r b r o w n t rou t i nd ica ted tha t s u b s t r a t e ava i lab i l i t y w a s l im i t ing for O-i- and ^ + t rou t a n d d e p t h ava i lab i l i ty w a s l imi t ing f o r o l d e r t r ou t both b e f o r e a n d a f ter res tora t ion (at l ow s u m m e r f low, Tab le II). Af ter the r e s t o r a t i o n , a sma l l i n c r e a s e w a s d iscern ib le for ^+ t rout a n d a sma l l d e c r e a s e for O-i-a n d 2+ o r o l d e r t rou t in s u b s t r a t e p ré fé rence i ndexes . T h e s a m e w a s t rue for d e p t h for a g e - 0 f i s h .

Bull. Fr. Pêche Piscic. (1995) 337/338/339 : 407-413 — 411 —

D e p t h

Befo re Af ter

Veloci ty

Befo re Af te r

Subst ra te

Before After

Size-c lass 1 ( 5 - 1 0 c m )

M e a n 0.67 0 .44 0.61 0 .62 0.28 0.21

Méd ian 0 .77 0 .58 0 .60 0 .60 0.22 0.19

S. D. 0 .26 0.38 0.31 0 .26 0.06 0.21

C. V. 39 8 7 5 0 41 2 3 95

Size-c lass 2 (10 - 1 5 c m )

M e a n 0.33 0.41 0.52 0 .53 0.29 0.33

Méd ian 0.37 0.37 0 .50 0 .50 0 .17 0.38

S. D. 0 .20 0.28 0 .22 0.21 0.14 0.26

C . V . 6 0 6 7 4 2 3 9 4 9 78

Size-c lass 3 (over 15 c m )

M e a n 0.02 0.05 0 .50 0 .54 0.40 0.32

M é d i a n 0.01 0.00 0.52 0 .50 0.41 0.34

S. D. 0 .03 0.16 0.27 0.21 0.17 0.29

C. V. 157 301 5 3 38 4 2 91

4. D I S C U S S I O N

The tempora l sca le of our s tudy is fair ly narrow, bo th w h e n it cornes to t h e annual hydro iogica l rég ime of t he r iver a n d to the t ime lapsed af ter t h e res tora t ion . It is obvious that annua l even ts , s u c h as f loods (h igh f lows) , ice p rocesses , séd imen ta t i on a n d others, wi l l , t h rough t ime , mod i f y the habi tat s t ruc tures c rea ted du r i ng the restorat ion. T h e m a i n habi tat s t ructures c rea ted in the restorat ion, however , will p robab ly resist t he normal fo rce of natural d is tu rbances , wh i ch m e a n s tha t most of the habi tat d ivers i ty wil l b e permanent .

A n inc reased hydro -phys ica l habi tat comp lex i t y m e a n s tha t t h e potent ia l avai labi l i ty of su i table mic rohab i ta ts fo r f ish a n d a Iso for their f o o d resou rces wi l l be greater , improv ing t h e c h a n c e s for s u c c e s s f u i e n c h a n c e m e n t of f i sh s t o c k s . T h e l o n g - t e r m e f fec ts of t h e res to ra t ion béné f i c ia i fo r f i she r ies a re l inked no t on ly w i t h t h e s t o c k i n g of the fisfi a n d m a n a g e m e n t of the f i sher ies but aIso w i th the deve lopmen t of t h e b io log ica l complex i ty a n d i ts d y n a m i c s ( m o s s e s , h i g h e r v é g é t a t i o n , b e n t h i c a n i m a i s ) i n t h e r e s t o r e d a reas . T h e reco lon izat ion rate of macro inve r teb ra tes to res tored a reas s e e m s to be fast , s ince in mos t c a s e s p a t c h e s of t h e r iver b e d w e r e left in tac t , w h i c h s e r v e s t h e co l on i za t i on sources ( T I K K A N E N et al., 1994) . T h e réduct ion of m o s s cover in res to red a reas a n d its recovery ra te , wh i ch is obv i ous i y s low, m a y e m p h a s i z e t h e i m p o r t a n c e of subs t ra te as a f iabi tat componen t dur ing the f irst two or th ree years immedia te iy af ter t he res tora t ion .

Tab leau II : I n d e x d e p r é f é r e n c e d e s d i f f é r e n t e s t a i l l e s d e c l a s s e d e t r u i t e s c o m m u n e s (voi r t e x t e ) p o u r la p r o f o n d e u r , la v i t e s s e d u c o u r a n t et le subst ra t d o m i n a n t , basé sur d e s m e s u r e s d 'habi ta t ponctue l les (N = 2 0 0 avant et N = 226 a p r è s restaurat ion) sur le s i te d 'é tude 2, d o n n é à t itre d ' exemple . Pour c h a q u e m e s u r e p o n c t u e l l e , u n index d e pré férence est at t r ibué à c h a q u e var iab le , basé sur les p ré fé rences d 'habi ta t de la truite c o m m u n e .

Table II : B r o w n t rou t p r é f é r e n c e i n d e x e s of d i f fé rent s i z e - c l a s s e s (see text) f o r d e p t h , ve loc i ty a n d d o m i n a n t subs t ra te b a s e d o n habi ta t m e a s u r e m e n t po in ts ( N = 2 0 0 be fo re a n d N = 226 after restora t ion) at t h e s tudy si te 2 a s a n e x a m p l e . For e a c h m e a s u r e m e n t po in t , e a c h v a r i a b l e w a s g iven a pré fé rence index b a s e d o n the habitat p ré fé rence d a t a of the b r o w n trout.

Bull. Fr. Pêche Piscic. (1995) 337/338/339 : 407-413 — 4 1 2 —

6. R E F E R E N C E S

B A L T Z D.M. , V O N D R A C E K B., B R O W N L R . , M O Y L E R B . , 1 9 9 1 . Seasona l changes in mic rohab i ta t sé lec t ion of ra inbow trout in a smal l s t ream. Trans. Am. Fisti. Soc, 120, 166-176 .

B O V E E K., 1982 . A gu ide to s t r eam habitat ana lys is us ing the ins t ream f low incrémenta l m e t h o d o l o g y Ins t ream f low informat ion paper 12, U.S.D.I . Rish and Wildi i fe Serv ice , Of f ice of B io log ica l Serv i ces . FWS/OBS-82 /26 .

D A V I S J.A., B A R M U T A L.A., 1989. A n ecological ly usefui c lass i f icat ion of m e a n and near-b e d f l ows in s t r e a m s a n d r ivers. Freshwat. Biol., 21, 2 7 1 - 2 8 2 .

H E G G E N E S J . , S A L T V E I T S.J . , V A S K I N N K.A., L I N G A A S O., 1994 . Predic t ing f ish habi tat use responses to c h a n g e s in water f low rég ime : model l ing cr i t ical m i n i m u m f lows for a t lan t i c s a l m o n , Salmo salar, a n d b rown t rou t , Salmo trutta, in a h e t e r o g e n e o u s s t r e a m . P r o c e e d i n g s of t h e f i rs t i n te rna t iona l s y m p o s i u m on hab i t a t h y d r a u l i c s (Augus t 18-20 ,1994) . T h e No rweg ian Institute of technology. T rondhe im, Non/vay.

J A G E R H.I. , De A N G E L I S D . L , S A L E M.J., v a n W I N K L E W., S C H M O Y E R D.D., S A B O M.J. , O R T H D.J. , L U K A S J.A., 1993 . An ind iv idua l -based m o d e l for sma l lmou th bass reproduc t ion a n d young-o f -yea r dynamics in s t reams. Rivers, 4 (2), 91-113.

J U T I L A E., K A R T T U N E N V., N I E M I T A L O V , 1994 . Better one s tone in the rapid than ten o n the bank - In f luence of va r ious restoring methods on the parr densi t ies of b rown t rou t in t he rap ids of t h e t r ibu ta r ies f lowing into the l i joki River . Ka la tu t k imuks ia -F i s k e r i u n d e r s ô k n i n g a r 8 7 , 2 9 p. F inn ish G a m e a n d F i she r i es R e s e a r c h Inst i tu te , He ls ink i , F in land. (in F inn ish wi th English summary ) .

In the river Kut in jok i , post- restorat ion subst ra te avai labi l i ty seems to be l imit ing for t he y o u n g e s t âge g r o u p s of t rout . T h e restorat ion p rocédure e m p l o y e d seems to favour l- i -or o lde r t rout , wh ich is in a g r e e m e n t wi th the s tock ing and e lect ro f ish ing results of JUT ILA et al. ( 1994 ) . Large bou lde r d a m s h a v e a lso tu rned out to be t h e mos t e f fect ive s ing le res to ra t i on m e a s u r e to i nc rease smo l t product ion of t rout in d r e d g e d r ivers ( N À S L U N D , 1 9 8 7 ) . In t h e r iver Ku t in jok i t he restorat ion mater ia l w a s t aken f r om the e m b a n k m e n t s s u r r o u n d i n g the or ig inal f loat ing c h a n n e l . In mos t cases , bou lder d a m s were fi l led up wi th c o b b l e s a n d p e b b l e s , i m p o r t a n t c o m p o n e n t s o f p r e f e r r e d s u b s t r a t e in o p t i m u m mic rohab i ta t s of young-o f -yea r t rout ( H E G G E N E S et al., 1994) . However , part of this smal l s i z e d ma te r ia l shou ld p robab ly have been u s e d for cons t ruc t ing sha l low riffle habitat for sma l l t rout .

Eva lua t ion of t rout habi ta t on the basis of point sui tabi l i t ies, wh ich w a s carr ied out in th is s tudy, is at least part iy unre l iab le , since t h e point indexes do not take into account t he a r e a t hey represent . Ins tead of compa r i ng point sui tabi l i t ies a bet ter so lu t ion might b e t h e P H A B S I M - p r o c e d u r e ( B O V E E , 1982) and its di f férent app l icat ions (e.g. S O U C H O N et al., 1990 ; J A G E R etal., 1993 ; H E G G E N E S et al., 1994 ; PAYNE, 1994) . Model l ing hydro-phys i ca l cond i t ions at a sca le re levant to the f ish (or its l i fe-stage) comb ined with the f ish (or its l i fe -s tage) hab i ta t p r é f é r e n c e s can be a pract ica l too l in r iver res tora t ion . A m o n g o t h e r th ings , t h e p rocédure of fers o n e the possibil i ty to eva luate the effects of the water f low v a r i a t i o n b e t w e e n t h e s e a s o n s to ident i fy t e m p o r a l bo t t l enecks in the ava i lab le spat ia l hab i ta t in o rder to f o c u s the mi t igat ing measures at the most l imi t ing habitat componen ts . P H A B S I M a lso e n a b l e s o n e to eva lua te the restorat ion p r o c é d u r e wh i le it is stil l in t he p l a n n i n g p h a s e ( W E G N E R , 1980) .

5. A C K N O W L E D G E M E N T S

T h a n k s are d u e to OUI v a n der M E E R , Pasi H A U T A J À R V I , Harr i A H O and Esko K O l V U R A N T A for t he he lp in the f ie ld work. Pàiv i T I M O N E N is great ly acknow ledged for v a l u a b l e a s s i s t a n c e in d a t a a n a l y s i s and E e v a - K a i s u K E M P P A I N E N for c h e c k i n g t h e Eng l i sh l anguage .

Bull. Fr. Pêche Piscic. (1995) 337/338/339 : 407-413 — 413 —

L A M M A S S A A R I V., 1990 . F loa t i ng and its e f fec ts on w a t e r c o u r s e s . Pub l i ca t ions o f t h e Wa te r a n d E n v i r o n m e n t A d m i n i s t r a t i o n . Sé r i es A 5 4 , 235 p. He l s i nk i , F in land ( in F innish wi th Eng l i sh s u m m a r y )

M À K I - P E T À Y S A., M U O T K A T., T I K K A N E N P. H U U S K O A. , K R E I V I R, K U U S E L A K., 1 9 9 4 . S i z e - c l a s s d i f f é r e n c e s in m i c r o h a b i t a t u s e by j u v é n i l e b r o w n t r o u t . K a l a t u t k i m u k s i a - F i s k e r i u n d e r s ô k n i n g a r 8 0 , 3 8 p. F i n n i s h G a m e a n d F i s h e r i e s Research Inst i tute, He ls ink i , F in land. (in F innish w i th Eng l ish s u m m a r y ) .

M A L A V O I J . R., S O U C H O N Y., 1989 . Mé thodo log ie de desc r ip t i on et quant i f i ca t ion des var iab les m o r p h o d y n a m i q u e s d 'un cou rs d ' eau à f o n d ca i l l ou teux : e x e m p l e d'une stat ion sur la Fi l l ière (Hau te -Savo ie ) . Revue de Géographie de Lyon, 64, 252-259.

N À S L U N D I., 1987 . Ef fects of hab i ta t i m p r o v e m e n t on t h e b r o w n t rou t {SaImo trutta L.) p o p u l a t i o n of a N o r t h S w e d i s h r iver . I n f o r m a t i o n f r â n S ô t v a t t e n s l a b o r a t o r i e t , Dro t tn ingho lm. 1987 /3 , 28 p. (in Swed i sh w i th Eng l ish s u m m a r y )

PAYNE T. R., 1994. R H A B S I M : user- f r iendiy compu te r m o d e l to ca lcu la te river hydraul ics a n d aquat i c hab i ta t . P r o c e e d i n g s of the f i rst i n te rna t iona l s y m p o s i u m on habitat hydrau l ics (Augus t 18, 20 ,1994) . T h e Nonwegian Inst i tute of techno logy . T rondhe im, Nonway.

S O U C H O N Y., T R O C H E R I E R , F R A G N O U D E., L A C O M B E C , 1 9 9 0 . Les m o d è l e s n u m é r i q u e s d e s m i c r o h a b i t a t s d e s p o i s s o n s : a p p l i c a t i o n e t n o u v e a u x déve loppemen ts . Revue des Sciences de l'Eau, 2 (4), 8 0 7 - 8 3 0 .

T I K K A N E N R, L A A S O N E N R, M U O T K A T , H U H T A A., K U U S E L A K., 1994 . Shor t - term r e c o v e r y of b e n t h o s f o l l o w i n g d i s t u r b a n c e f r o m s t r e a m h a b i t a t r e h a b i l i t a t i o n . Hydrobiologia, 273, 121 -130 .

W E G N E R D.L., 1980. Eva luat ion and s imulat ion of aquat ic habi tat improvemen ts . Thesis for Master of Sc ience . Co lo rado State University, Fort Co l l ins , Co lo rado , U.S.A. 155 p.

W E S C H E T.A. , 1 9 8 5 . S t r e a m c h a n n e l m o d i f i c a t i o n s a n d r é c l a m a t i o n s t r u c t u r e s t o enchance f ish habi ta t . In G O R E J.A., T h e res tora t ion of s t reams and r ivers, 103-164. Buttenworth, S t o n e h a m .

Y R J À N À T., 1995. Restora t ion of Runn ing Wate rs wi th in t h e l i joki R iver A rea . In D e W A A L L , L A R G E A . R . G . & W A D E M. (eds) , Rehab i l i ta t ion of R ive rs , W i ley Pub l ica t ion , (accep ted manusc r ip t ) .

Y R J À N À T., H U U S K O A., 1992 . E n h a n c e m e n t of f ish hab i ta ts in F inn ish rivers. Suomen kalastusiehti, 99(6), 2 6 - 2 7 . (in F innish) .