Unlined Canal design

This ppt is about design of unlined canal sections and some basic terms related to canal design

1. UNLINED CANAL DESIGN Submitted By: Preetpal Singh B.Tech Civil Engineering (4 th Sem ) GU14-0005

2. Canal Design Dra i n a ge Ch a n n el Design Irrigation Ch a n n el Design Canal Design T ypes

3. Design P a ramete r s The de s i g n c o n s i d erati o n s nat u ral l y v a ry a c c o rding t o th e t y p e o f s o i l . V e l o c it y o f fl o w i n th e c a na l s h ou l d b e cr i tica l . Des i g n o f c a nal s wh i c h ar e know n a s ‘ Kenn e d y ’ s the o r y ’ an d ‘ La c e y ’ s the o r y ’ ar e base d o n th e c h aract e ris t i c s o f sedime n t l o a d ( i. e . s i lt ) in c a na l wate r

4. Importan t T erm s R e late d to C an a l D e sign Alluvial soil N o n -al luvial soil Silt factor C o - ef f ici en t o f rugo s i t y Mea n velocity Crit ica l velocity Criti ca l velo c i t y ratio ( C.V.R.) , m R e gime channel H y draulic mean de pth (R) Full sup p ly Level Ec on o mical se c tion

5. Alluvial Soil The s o i l which i s formed b y th e c o nt i nuo u s d e p o s i ti o n o f sil t is k n ow n a s alluv i a l s o i l . The riv e r c a r r i e s he avy c harg e o f sil t in rainy s e a s o n. Wh e n th e riv e r o v erflow s it s b a nk s durin g the fl o od , th e sil t p arti c l e s ge t dep o s i ted o n th e a d j o i n i n g area s . This dep o s i ti o n o f sil t c o nt i nue s y e a r afte r y e a r . This t y p e o f s o i l i s foun d i n de l ta i c region o f a riv e r . This s o i l i s p ermeab l e and s o ft an d v e ry ferti l e. The riv e r p a ssin g through th i s t y p e o f s o il ha s a ten d en c y t o c h ang e it s c o urse .

6. Non-alluvial Soil The s o i l whi c h i s formed b y th e d i s i nte g rati o n o f rock form a ti o n s i s k n ow n a s non - a l l uvi a l s o i l . I t i s f oun d i n the mou n ta i nou s r e g i o n o f a riv e r . The s o i l i s har d and im p ermeab l e i n nat u re. This i s n o t ferti l e . The riv e r pa s s i n g through th i s t y p e o f s o i l ha s n o ten d en c y t o c h ang e its c o urse .

7. Silt Factor Duri n g the i nv e s t i ga t i o n s works i n v ari o u s c an a l s i n a l l uv i a l soi l , Ge r a l d La c e y e s t ab l ishe d th e e f fe c t o f sil t o n t h e det e rminat io n of d i s c h arg e an d t h e c a na l s e c t i o n . S o , La c e y i n trodu c e d a fa c tor w h i ch i s k n ow n a s ‘sil t factor ’ . I t depend s o n t h e mea n p a rti c l e siz e o f sil t. I t i s denote d b y ‘ f ’ . T h e silt fa c tor i s de t erm i ne d b y the e x pre ss i o n , f = 1 . 76 d mm wh e re d m m = m e a n p a rticle s iz e o f s i l t i n mm Particle Particle size (in mm) Silt factor Very fine Silt 0.05 0.40 Fine Silt 0.12 0.60 Medium Silt 0.23 0.85 Coarse Silt 0.32 1.00

8. Coef f ici e nt of Rug o sity (n) The roug h ne s s o f the c an a l be d a f fe c ts the v e l o c i t y o f f l o w . The roughn e ss i s cause d du e t o th e ripp l e s formed o n th e be d o f t h e c a na l . S o , a c o e f fi c i e n t was i ntrodu c e d b y R . G K e nne d y for c a l c u l a ti n g th e mea n v e l o c it y o f fl o w . This c o e f fi c i e n t i s k n ow n as c o e f fi c i e n t o f r u go s it y an d i t i s denote d b y ‘ n’ . The v a l u e o f ‘ n ’ depend s o n the t y p e o f be d ma t eri a l s o f the c an al . Materials Value of n Earth 0.0225 Masonry 0.02 Concrete 0.13 to 0.018

9. D 0. 6 D Mean Velocity I t i s foun d b y ob s ervat i o n s tha t th e v e l o c i ty a t a dept h 0. 6 D repr e s ent s th e mea n v e l o c i t y ( V ), where ‘D’ i s t h e dept h o f water in th e c a na l o r riv e r . (a) Mean Velocity By Chezy’s Expression: V= C√RS (b) Mean Velocity By Manning’s Expression: V=(1/n)x(R^⅔)x(S^ ⅟₂) Mean Depth

10. Critical Velocity W h e n th e v e l o c i t y o f fl ow i s such tha t th ere i s n o s i l ting o r sco u r in g action i n th e c a n a l be d, th e n t hat veloci t y i s kn own a s cr iti c a l velocit y . I t is d en o t ed b y ‘ V o ’ . T h e v a lu e o f V o w a s g iv e n b y K e n ne d y a c c o r d i n g t o t h e f o l low i ng expr e ss i o n, V o = 0.54 6 D 0.64 ; wh e re, D = De p th o f wat e r D

11. Critical Velocity Ratio (C.V.R.) The ratio of mean velocity ‘V’ to the critical velocity ‘V₀’ is known as critical velocity ratio (C.V.R.). It is denoted by ‘m’ i.e. C.V.R. (m)=V/V₀ When m = 1, there will be no silting or scouring When m > 1, scouring will occur When m < 1, silting will occur So , by finding the value of m, the condition of the canal can be predicted whether it will have silting or scouring

12. Regime Channel Wh e n th e c h aract e r o f th e b e d an d ban k materi a l s o f the c ha n ne l ar e s a m e a s th a t o f t h e tran s porte d ma t eri a l s and when th e sil t c h arg e an d sil t grad e ar e c o n s tant, the n the c h ann e l i s s a i d t o b e i n it s regime an d th e c h ann e l i s c a l l ed regime c h ann e l . This i d ea l c o nd i ti o n i s no t pract i c a l l y po s s i b l e.

13. Hydraulic Mean Depth The r a tio o f t h e cross - sect i o n a l are a o f fl o w t o th e w e tt e d perim e ter o f th e c h ann e l i s k n o wn a s h y drauli c mea n dept h. I t i s gen e ral l y denote d b y R. R = A/P Wh e re, A = Cros s - s e c t i o na l area P = W ette d perim e ter

14. Full Supply Level The ma x im u m c apa c it y o f th e c ana l fo r whi c h i t i s de s i g ned , is k now n a s fu l l s up p ly d i sch a r g e . The wat e r l e v e l o f the c an a l c o r r e s pondin g t o th e fu l l s u pp l y d i s c h arg e i s k n o w n a s f u l l s u pply leve l ( F .S. L ) . FSL

15. C u t t i n g Area B al a nci n g dep th Economical Section I f a c an al sect io n i s such th at the e arth obt a in e d f rom c u tti n g ( i . e . ex c ava t io n ) can b e f u l l y u t i l iz e d i n f or m in g the ba nk s , th e n th a t s ection i s kn own a s ec on o m i ca l s e c tio n . A g ain, t he di s ch a r g e will be m axi m um wi th mi n i m um cros s - sect i on a re a . He re, n o extra e ar t h is required fr o m b o r row pit a nd n o e ar t h i s i n ex c ess t o f orm th e s p o il bank. T h i s c on d i tion c a n only ar i se i n case o f p ar t ia l cu t t in g an d p a rt i al bank i ng. S o m e ti m es, t h i s c on d i tion i s d e s i gna te d a s b a la ncing of cut t i ng an d ba n kin g . Here, t h e de p t h o f cu t t i ng i s cal l ed ba l a ncing d ept h . Filling Area

16. U n l i ned C a nal D e sig n on Alluvial soi l by K e nne d y’s The o ry A f t er lo n g i nvest i gat i o n s, R . G K en n e d y arr i ved a t a th e o ry wh i ch states tha t , the s i l t carr i e d b y f lowi ng w ater i n a c h an n el i s k e pt i n sus pe nsion b y t h e ver t ica l c o m pon ent o f eddy c urr e n t wh i ch i s f or m e d o v e r t he e n t i r e be d wi d t h o f t h e ch anne l an d t h e susp ende d sil t rises u p gen t l y t o war d s t h e surf a c e. T h e f o l low i ng as s u m p t i o n s are m a d e i n su p p o rt of h i s t h e o r y : T h e edd y curr e nt i s d e ve l o p ed du e t o t h e ro u g h n e ss o f t h e bed . T h e q u a l i t y o f t h e susp e n d ed s i l t i s pr o p o rti o n a l t o be d wi d t h . I t i s ap p l ic a ble t o t h o se c han n e l s wh i ch are fl ow i n g t hrough th e bed co n s isti n g o f sa n dy s i l t o r sa m e gr a de o f s i l t. I t i s ap p l ic a ble t o t h o se c han n e l s wh i ch are fl ow i n g t hrough th e bed co n s isti n g o f sa n dy s i l t o r sa m e gr a de o f s i l t.

17. He es ta b l is he d t he id ea o f crit i cal ve l ocity ‘ V o ’ which will m ake a c han nel free fr o m s i l t i n g o r sco u r ing . Fr o m , lon g o bservati o ns, h e es ta b l is h ed a relati o n b etwe e n t h e crit i cal ve l ocity an d t h e f u l l su p p l y d e p t h a s f o l l ows, V o = CD n T h e va l u e s o f C an d n where f o u n d ou t a s 0.54 6 an d 0.6 4 resp e ct i ve l y , t h us V o = . 5 4 6 D 0. 6 4 A g ain, h e r e a l ize d th at th e crit i cal velocity was a f fe ct e d b y th e gra d e o f s i l t . So, h e intr od uc e d ano th er f act o r (m) which i s k n o w n a s crit i cal v elocity r a t i o (C . V . R ) . V o = . 5 4 6m D 0. 6 4

18. Drawbacks of Kennedy’s Theory T h e t h e o ry i s l im i t ed t o aver a ge re g i m e ch a n n el o n l y . T h e d e s i g n o f ch a n n el i s b a sed o n t h e tri a l an d err o r m e t h od . T h e va l ue o f m was f i xed ar b i t rar i l y . Si l t ch a rge an d s i l t gr a de are no t co n s i d er e d. T h e r e i s n o e quation f o r de t e rmining th e be d s l ope and i t dep ends on K u tt e r ’ s e q u a t i on o n l y . T h e ra t i o o f ‘B’ t o ‘D’ ha s n o s i g n i f i ca n ce i n h i s t h e o r y .

19. Critical Velocity, V o = . 5 4 6 D 0. 6 4 Mean Velocity B/D ratio i s assum e d accordingly D i sch a rg e , Q = A V W he re, A = Cr o s s- secti o n a rea i n m 2 , V = me a n ve l ocit y i n m / sec T h e full su p pl y de p th i s fixed b y tr i a l t o satis f y the va l u e o f ‘m ’ . G ene ra l l y , the tr i a l dep th is assum e d be tween 1 m to 2 m. If the c onditi on i s no t satisfi e d w i thin this l i mit , th e n i t ma y be assum e d accor d i n gl y . De s ig n P r ocedure

20. U n l i ned C a nal D e sig n on Alluvial soi l by Lacey’s The o ry L a c ey ’ s theory i s b a s ed o n t he c on ce p t o f r e g i m e c o nditi o n o f the channe l . T h e re g i m e co n d i t i on will b e sa t isfi e d i f , The cha n n e l flows u n iforml y i n u n limi t ed i n c o he r e nt a lluvi u m o f t he s a me ch a racter which i s tr a nsp o rt e d b y t h e ch a n n e l . T h e s i l t gr a de an d s i l t ch a rge re m a i ns co n st a n t . T h e d i sch a rge re m a i ns co n st a n t . But in practice, all these conditions can never be satisfied. And, therefore artificial channels can never be in ‘True regime’.

21. Initial Regime and Final Regime When only the bed slope of a channel varies due to dropping of silt , and its cross-section or wetted perimeter remains unaffected, even them the channel can exhibit ‘no silting no scouring’ properties, called INITIAL REGIME. IF there is no resistance from the sides, and all the variables such as perimeter, depth, slope etc. are equally free to vary and get adjusted according to discharge and silt grade, then the channel is said to have achieved permanent stability, called FINAL REGIME.

22. De s ig n P r ocedure Calculate the velocity from equation Where, Q is discharge in cumecs , V is velocity in m/s f is silt factor Workout the hydraulic mean depth (R) from the equation Compute area(A) of channel section by using

23. Compute the wetted perimeter, P Knowing these values, the channel section is known; and finally the bed slope (S) is determined by the equation B/D ratio of channel is assumed accordingly.

24. Drawbacks of Lacey’s Theory T h e c o nc ep t o f tr u e re g i m e i s t he o re t ica l and c o n n ot b e achiev e d p r a ctica l l y . T h e var i o us eq ua t i o ns a r e d er i ved b y c o nsidering t he s i l t f ac t o r f wh i ch i s no t a t a l l co n st a n t . T h e co n ce n tr a t i on o f s i l t i s no t t a ken i n to ac c o u n t . S i l t g r ad e an d sil t ch a r g e i s no t t a ke n i n to a c c oun t . T h e eq uat i o n s a r e e m p ir i cal an d ba sed o n the ava i la ble d ata f rom a p a r t icu lar t y pe o f c ha nn e l . S o, i t ma y not b e t rue f o r a d i f f e r e nt ty p e of ch a n n e l . T h e ch a racter i st i cs o f re g i m e ch a n n el ma y no t b e sa m e f o r a l l cases.

25. Kennedy’s Theory Lacey’s Theory I t states that the s il t carr i ed by the f l o w i n g w a ter i s ke p t i n s usp e n s i o n by t h e vert i cal com po nent of eddi e s w h ic h are gener a t e d f r om the bed of the ch a n n e l . I t states that t h e s il t carr i ed by t he f l o w i n g w a ter i s k e pt i n su s pens i o n by the vert i cal co m pon e nt of e d d i es w h i c h are genera t ed f ro m the e n t i re w e t t ed p e r i m eter of the ch a n n e l . I t gi v es relation b e twe e n ‘V’ and ‘D ’ . I t gi v es relation b e twe e n ‘V’ and ‘R ’ . I n this th e or y , a factor k n own as cri t ic al veloc i t y rat i o ‘m’ i s int r oduc e d t o m a k e t h e equat i on ap plic a ble t o di f ferent ch a n n e l s with di f ferent s il t gra d e s I n this t h eor y , a f a c t o r k n own as sil t factor ‘ f ’ i s int r o d u c ed t o m ake the eq u a t i o n applic a ble t o di f f e rent ch a nn els with di f ferent s il t gra d e s . I n this t h e or y , K u t te r ’ s e q u ati o n i s u s e d for f i n d in g the m ean veloc i t y . T h i s t h e ory gi v es an eq u ati o n for f in d i ng the m ean veloc i t y . T h i s the o ry gi v es no e q u a t i on for bed s lo p e . T h i s t h e o ry g iv e s an eq u ati o n for bed s lo p e . I n this theor y , the de si g n i s ba s e d o n t r ial and error m etho d . Th i s t h eory d o es n ot in v olve t r ia l a nderror m etho d . Comparison of Kutter’s & Lacey’s Theory