TWO
M U D B A N K S OF K E R A L A - K A R N A T A K A — N E E D F O R A N I N T E G R A T E D S T U D Y
E. G. SILAS
Central Marine Fisheries Research Institute, Cochin
INTRODUCTION
We have documented reports of the mudbanks along the south-west coast between Mangalore and Quilon for well over three hundred years. However, sequential record of their occurrence in time and space is wanting. This phenomenon in Kerala, typi- cally as occurs south of Alleppey (^Fig. 1), is known as Chakara. or Santhakara ("quiet shores"). During the last two decades the presence or absence of the Chakara pheno- menon has attracted considerable attention of the fisheries sector, resulting in a number of useful studies on mudbanks covering specific aspects. Yet we are far from having precise answers to the problem of the mode of its origin, establishment, stability and dissip- ation, except propounding some hypotheses and suggestions based on physico-chemical and biological data.
The recent past has also seen large-scale erosion along long stretches of this coast and consequent serious impairment of the life of those living in the coastal zone. Since 1973, the mudbank has not developed to the extent anticipated, to sustain any major fishing activity along the coast. This, com- bined with extensive erosion, has created serious socio-economic problems in the coastal sector. Of a good mudbank season, the primary beneficiary is the artisanal fisher- man, who is able to operate his canoe from the calm waters of the mudbank and often land heavy catches of shoals which enter the area. Owing to heavy surf along other parts of the coast, fishing in the artisanal sector is generally at a standstill during the monsoon season. As such, the formation of mudbank
is eagerly awaited as it portends good fishing, and hundreds of canoes are transported by road to the sites of the mudbanks from villages even 50 to 60 km north and south.
These multifarious factors focus attention on an imperative need for developing an integrated multidisciplinary programme to study the mechanisms of mudbank formation, its life and dissipation and its impact on the coastal zone.
HISTORICAL RESUME
in the t w o volumes entitled "History of Mud Bank" Bristow (1938) refers to the early works on mudbanks, which are mainly narrative in nature. He also opines on the various possibilities of the mode of formation of the mudbanks.
Probably, the first mention of the mud- banks along the southwest coast in recorded history is a mention as early as 1678 in Pinkerton's "Collections of voyages and travels," appearing in the Administration Report of 1860 of Travancore, In his book,
" A New History of the East India," Capt.
Cope (1755) spoke of the Alleppey mudbank ("mud bay" as he calls), which, he says, is a place that few can parallel in the world.
Crawford (1860) may be credited with attempting the first possible explanation of the source of the Alleppey mudbank. Based on personal observations of mud cones on the beach and on roads of Alleppey, Crawford found cause for linking them with the back- waters and rivers. His observations of bursting of mud and water, during the widening of the Alleppey canal, and his attempt t o sound the
MUDBANKS
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CMFRI BULLETIN 33
' L i n u s ' of Chengannur River, strengthened his opinion that subterranean mud sustained t h e Alleppey mudbank. The observations o f Logam (1882) further help us t o note the importance of subterranean mud deposits. He f o u n d
" d e e p p o t - h o l e s in the lake east of A l l e p p e y and w i t h a rise of 4 ' t o 6', as occured in the f l o o d s of 1882, it can be easily b e l i e v e d that the enormous pressure thus caused w o u l d force relief w a y s for itself b e l o w the coastline through s o f t m u d s . "
King ( 1 8 8 1 ) , in a report on " C o n s i d e r - ations on the smooth water anchorage of mudbanks of Narakkal and Alleppey on the Travancore c o a s t , " discussed the m i g r a t i o n and f o r m a t i o n o f the mudbanks b e t w e e n Alleppey and Purakkad and between Cochin and Narakkal. A s i g i n i f i c a n t observation was that of Rhode (1886;//?.• B r i s t o w 1938), w h o spoke of f l u i d mud existing b e l o w Alleppey, and thereby p o s t u l a t i n g that the mudbank at Alleppey increases and diminishes as the level of the inland water rises and f a l l s , as w a s observable during the 1882 f l o o d s . Opining on the same lines Drury (1906) was of the v i e w that, in the absence of a natural o u t l e t for the vast accumulation of waters w h i c h are poured d o w n f r o m the various m o u n t a i n streams i n t o the basin of the backwater, nearer than 36 miles on either side, it is not improbable that there exists a subterranean channel c o m m u n i - cation w i t h the sea from t h e backwater, through w h i c h large quantity of mud is carried o f f and t h r o w n up again by t h e sea in the from of a bank. A c c o r d i n g t o Lake (1889), " i t is t o the observation of Mr. Rhode and of his predecessor, Mr C r a w f o r d , that w e o w e most of our k n o w l e d g e of the A l l e p p e y mudbank, and there is very little t o add t o w h a t they have already r e c o r d e d . " He also reported on the occurrence of mud cones in his report on the Alleppey mudbank.
For more on these and f o r other references t o the mudbfcnks, I w o u l d direct the reader t o the comprehensive treatise of Bristow (1938) on the " H i s t o r y of the M u d b a n k s " , wherein he has also added his exhaustive observations on the f o r m a t i o n , maintenance and movements of the mudbanks at Alleppey and Narakkal.
The mudbank at Narakkal plays an important role in the silting o f the Cochin Harbour c h a - nnel and was the cause for a Special report by
Du Cane et a i . (1938). This report also does not favour the v i e w that an increase in the water level in the lake w o u l d result in mud being pushed up in the adjacent coastal area*
due t o the insufficient pressure (2 Ibs/sq. inch) t h a t even a 5 ' rise in water w o u l d create. Nor
is t h e consistency of the mud of the mudbank t h e same as t h a t f o u n d in t h e lake, t h e latter
having a high percentage of carbon and a l o t of vegetable debris. However, I feel that a critical study of t h i s is necessary, w h i c h w i l l also necessitate borings and s o i l studies at d i f f e r e n t depths in the lake, intervening land area and the Purakkad inshore waters.
The post-war period saw a renewed inter- est in t h e studies on the coastal ecosystem.
This has l e d t o more specialised i n v e s t i g a t i o n s on t h e mudbank ecosystem as summarised b e l o w : Seshappa (1953) and Seshappa and Jayaraman (1956) have s t u d i e d the phosphate content of the mudbank at Calicut and noticed higher phosphate concentrations. Ramasastry and M y r l a n d (1959) stated that the forma- t i o n of the mudbank is associated w i t h u p w e l l i n g and divergence near the b o t t o m between 20 and 30 m along the coastal line, w h i c h produce vertical acceleration, w i t h resultant l i f t i n g of the b o t t o m waters; the l i f t e d b o t t o m water carries along w i t h it the fine mud of the b o t t o m . Nair et al (1966) have studied the mud deposited on the sandy beaches of the Vypeen island near Cochin after a storm, for its physical and chemical properties, in order t o understand the source and mechanism of mud d e p o s i t i o n . A comparative study of these sediments w i t h that obtained f r o m o f f s h o r e samples has also been made. They came t o the c o n c l u s i o n that the m u d d e p o s i t e d on the beach was f r o m the nearshore areas, as it was composed of dredged material transported n o r t h w a r d from
Ernakulam channel. Varadachari (1966) has discussed the part played by the estuaries and mudbanks o f Kerala coast on s h o r e - l i n e c p r i f i g u r a t i o n . Varadachari and Murty (1966) have made some observations on a temporary mud flat that appeared b e t w e e n C o c h i n harbour entrance channel and Elamkunnapuzha, d u r i n g a storm in December 1965. Damodaran and Hridayanathan (1966) suggest that l o w e r i n g of surface salinity and a f l o c c u l a t i o n effect caused by t h e same keeps t h e mud in suspension. Rao (1967) has given an account
MUDBANKS
F U R Y O F T H E S E A
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PLATE II. Heavy monsoon seas and coastal erosion at Chellanam and adjacent areas on the
Alleppey-Cochin coast.
M U D B A N K A T P U R A K K A D
PLATE I I I . A: Calm waters of the mudbank; B: Boat-seine, Thanguvala, operation; C: Awaiting
the catch; D: Ice packing of fish before loading on cycles; E: Catch of Lesser
sardines; and F: Heavy catch of Parapenaeopsis stylifera at the Purakad mudbank.
H A R V E S T F R O M M U D B A N K
PLATE IV. A. Oilsardine; B: a mixed catch; C: prawns spread out for drying; D: Shelling of
prawns, after drying; E: a mixed catch of prawns, crabs and fishes; and F: Fishvans
at Purakad waiting for transporting prawn and fish catch from mudbank.
of the fishery aspects of the mudbank at A l l e p p e y w i t h some considerations on the physico chemical features. Dora et al (1968) carried out i n v e s t i g a t i o n s on the texture of Narakkal mudbank sediments.
Varma and Kurup (1969) opined that the formation of the mudbank is t h e result of the interaction between the inshore and offshore transport of sediments in suspension, the former by waves and the latter by r i p - f l o w s . According to Kurup ( 1 9 7 2 ) , the c o n v e r g i n g l i t t o r a l currents in the inshore waters of the Kerala coast have influence on the s h o r e -
line changes along the coast and play an important role on the f o r m a t i o n o f t h e mud- bank s o u t h of A l l e p p e y . Iyer and M o n i (1972) evaluated the effects of mudbanks on the s h o r e - l i n e stability. Gopinathan and Qasim (1974) have investigated the f o r m a t i o n and characteristics o f the Alleppey mudbank.
The organic carbon of the mudbank sediments of Alleppey have been studied by Jacob and Qasim ( 1 9 7 4 ) . T w o recent fairly exhaustive works are; first, a detailed i n v e s t i g a t i o n o n the meiobenthos and macrobenthos of the mudbanks on the s o u t h - w e s t coast of India by Damodaran ( 1 9 7 3 ) and, s e c o n d , a s t u d y of the physical aspects of the mudbank i n c l u d i n g the texture of sediments, by Kurup ( 1 9 7 7 ) . M a t h e w et al (1977,) have studied the diurnal variations in the d i s t r i b u t i o n of zooplankton in relation t o currents and other e c o l o g i c a l parameters of the mudbank of A l l e p p e y . Recently, McPherson and Kurup (1981,) postulated a mathematical model t o explain the w a v e damping at the mudbank.
I n f o r m a t i o n was gathered from several sources, including statements by inhabitants in the f i s h i n g v i l l a g e . A fisherman (70 years o l d ) of Punnapra stated that he had never seen mud cones at Punnapra area in his l i f e - t i m e ; but he remembered that there was a w e l l -
f o r m e d mudbank at north Punnapra during 1950. A n o t h e r person stated t h a t , in the late f i f t i e s , the seat of the mudbank was at south
Punnapra w i t h its southern end at Nirkunnam, and t h i s was so u n t i l 1968. Then it shifted t o Valanjavazhi in 1969 and Nirkunnam and Ayyancoil became respectively t h e northern and southern ends of t h e mudbank. Local fishermen also stated that mud cones were observed on the land at Nirkunnam in 1969.
In 1971 and 1972 the northern periphery of the mudbank w a s observed at Kakkazham, w h e r e the mud cones were observed in 1972 on the beach and in the i n t e r - t i d a l zone. In 1973, there was no proper mudbank formation at Karoor-Ayyankoil, and the s i t u a t i o n has re- mained so in subsequent years, w h e n only ' i n c i p i e n t ' mudbanks or 'evanescent' mudbanks have occurred. Thus Purakkad was the l o c a t i o n of mudbank in 1974 and 1975. In 1976 it m o v e d further s o u t h t o appear b e t w e e n Pura- kkad and Thottappally. Since 1976, until the mudbank season in 1980, the mudbank a p p e - ared at T h o t t a p p a l l y , n o r t h of the s p i l l w a y .
In 1981 t w o mudbanks w e r e observed in the A l l e p p e y r e g i o n , one at Punnapra and the other at Thottappally-Pallana r e g i o n . However, all the post-1973 mudbanks south of Alleppey have been very evanescent ones of not any great consequence.
TYPES OF M U D B A N K S
Studies thus far carried out indicate that the mudbank c o u l d result from d i f f e r e n t f a c t - ors, such a s :
a) e r o s i o n , accretion and transport of sediments,
b) t r a n s p o r t a t i o n of sediments through u p w e l l i n g or currents in the coastal waters,
c) transport of sediments t o the river m o u t h ,
d) f o r m a t i o n of m u d cones due t o pressure in the lake site ; and
e) dredged sludge w h i c h is dumped into the inshore sea.
The need of the hour is a critical study of the various types of mudbanks and the mecha- nisms w h i c h are responsible for them under different situations.
Remote sensing and satellite imagery technique for studying mudbanks
It is necessary t o o b t a i n synoptic pictures of the river discharges in the inshore waters and the i n d i c a t i o n o f f o r m a t i o n or b u i l d up of sediments t o f o r m mudbank, and the related features b e t w e e n Q u i l o n and Mangalore. The manpower and facilities required for m o n i t - oring such a long stretch of coast w i l l be CMFRI BULLETIN 31
tremendous and, as such, the time has come for techniques such as remote sensing and s a t e l l i t e imagery t o be taken advantage of t o record t h e events synoptically. This w i l l also facilitate m o n i t o r i n g the water shed of the rivers t o assess the run off and t h e amount of i n f l o w in the inshore waters. Because of t h e m u l t i f a r i o u s uses to w h i c h river waters are presently put it is only a short time before major imbalances may d e v e l o p in t h e coastal regime, affecting its f e r t i l i t y as w e l l as the other associated natural phenomena. Fortuna- tely, intensive m o n i t o r i n g systems can be d e v e l o p e d and t o d a y we are aware of the magnitude of the problems and h o w t o a p p r o - ach the same.
Some priorities for consideration in future inte- grated investigations on mudbanl(
1. The s t a b i l i s a t i o n of the coastal track by use of appropriate vegetation is an area w h i c h needs i n v e s t i g a t i o n s . This is necessary on account o f the considerable erosion along l o n g stretches o f the coast. The importance of rehabilitation of mangrove vegetation as w e l l as other plant c o m - munity for stabilizing the beaches and the
s u b l i t t o r a l s h o u l d be g i v e n priority.
2. The f l o c c u l a t i o n of cohesive sediments in suspension and the a g g l o m e r a t i o n of p a r t i , cles added by b i o l o g i c a l organisms and the subsequent rate of s e d i m e n t a t i o n , is area w h i c h is yet t o be u n d e r s t o o d . S i m i l - arly the i n t e r - a c t i o n between various b i o l o g i c a l and physical processes i n v o l v e d and accretion and f i n e - g r a i n sediments in the areas adjacent to the mudbanks is practically u n k n o w n .
3. To-date w e have no idea o f the role of epiphytic m i c r o f l o r a and d i a t o m s w h i c h produce mucus and thereby accretion of intertidal mud d e p o s i t i o n .
4. We k n o w l i t t l e about a c t i o n of inverte- brates on sediment d e p o s i t i o n .
5. Normally, suspended sedimentary material should be a repository of trace metals as w e l l as heavy metals. We have practically no i n f o r m a t i o n as t o the extent that m u d - banks c o n t r i b u t e t o w a r d s this.
6. The role o f m i c r o - b i o t a in organic d e g r a - dation and process of recycling is yet another area where i n f o r m a t i o n is lacking.
7. We have no i n f o r m a t i o n on sediment o x y - gen demand and the rate of oxygen t r a n s - ference in the mudbank.
8. The " c r i t i c a l l i m i t " or " c r i t i c a l d e p t h " f o r d e f i n i n g the boundary based on the s u s - pended or s i l t d i s i r i b u t i o n in t h e mudbank has not been properly d e f i n e d . This is important as the outer boundary may be o s c i l l a t i n g , depending on the load of suspended matter. Our present p r o j e c t i o n s in t h i s are arbitrary.
9. The question may be asked as t o whether w e have any idea of the mudbank s e d i - ments as c o n c e n t r a t i n g mechanisms of organic and inorganic materials. The answer is n o ! S i m i l a r l y , w e lack in i n f o r m - ation on entrainment, d e p o s i t i o n and transport of fine grain sediments in the mudbank.
10. Is there a w a y of estimating annual/sea- sonal total budget of substances of the mudbank, w h i c h separate f r o m mud t o the water? Particularly suspended materials and trace metals? The answer at present is no.
1 1 . A b s o l u t e l y no i n f o r m a t i o n is available from the mudbank studies on the b i o - g e o ~ chemical cycles taking place there.
12. We have no i n f o r m a t i o n on the role of microbial metabolism in t h e m u d sedi- ments and the role it may play in m o b i l i - s a t i o n of phosphorus.
13. The optimum/maximum of trace metals in this natural ecosystem of mudbank is s t i l l u n k n o w n . There is hardly any i n f o r m - ation to assess trace metal uptake in sediments and suspended metals—to un- derstand the modus operandi—whether it is through p h y s i c o - c h e m i c a l absorption or t h r o u g h physical accumulation of metal enrichment of particulate matter. Or t h r o u g h b i o l o g i c a l uptake.
14. There is a lack of information on b i o l o g i - cal uptake; the role of bacterial p o p u l a t i o n in this process and the m i n e r a l i s a t i o n of MUDBANKS
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algal matter by bacteria are practically u n k n o w n .
15. The earlier w o r k s clearly indicate that nematodes c o n s t i t u t e n u m e r i c a l l y t h e most important component of the meiofauna o f t h e mudbanks. However, w e have no i n f o r m a t i o n on the nematodes-bacteria i n t e r a c t i o n . The burying and f e e d i n g a c t i - v i t y of nematodes may help in i m p r o v i n g exchange o f m e t a b o l i t e s and other essen- t i a l nutrients f o r bacteria to maintain the latter at the p o i n t o f maximum g r o w t h . Nematodes also assist in the process o f b i o - t u r b i n a t i o n . A c c o r d i n g t o Piatt and W a r w i c h (1980), nematodes are primary consumers of f o o d f o r higher organisms and t h e y play a v i t a l subsidiary role in organic d e c o m p o s i t i o n and in m o d i f y i n g the physical stability o f sediments. More w o r k on the nematodes in the mudbank area is necessary.
16. Often large quantities of benthic animals, such as t u b e - w e l l i n g polychaetes and bivalves, are f o u n d accumulated in the intertidal area w h e n the mudbank exists.
The causative factors for their displace- ment from natural beds in the mudbank area needs study.
17. Examination of core samples f r o m the mudbank and adjacent areas is necessary to understand as t o h o w l o n g this p h e n o - menon in the A l l e p p e y region has been in existence.
In the f o l l o w i n g reports stress has been made t o study some aspects of the physico- chemical and b i o l o g i c a l aspects of the m u d - bank. It is h o p e d that t h i s w i l l stimulate more
intensive studies o f an integrated nature in future by c o l l a b o r a t i o n and c o o r d i n a t i o n of
w o r k w i t h other interested agencies.
Coastal zone management—need for a national policy
The mudbank is a phenomenon of the coastal zone. The management problems c o n n e c t e d w i t h it during a year of successful mudbank f o r m a t i o n , particularly b e t w e e n Quilon and Cochin, are up t o n o w tackled on an ad~hoc or temporary basic. There is an imperative need for a national coastal m a n a - gement strategy to be d e v e l o p e d t o l o o k c o n s t r u c t i v e l y at these and other phenomena and shape public policy. A large share of t h i s responsibility w i l l rest w i t h the Department of Environment, Government of India, w h i c h s h o u l d develop a strategy, that w o u l d also improve the q u a l i t y o f l i f e of the people i n v o l - ved in various a c t i v i t i e s along the coastal zone. This w o u l d i n v o l v e also a j u d i c i o u s development o f aquaculture practices in the sea and in the adjacent inundated brackish- water areas; the interest o f the artisanal fisher- men and fisheries; the development of harbour and other infrastructure; the proper m a n a g e - ment o f the mangrove eco-systems; and the p r o t e c t i o n and s a f e t y of the estuarine areas f r o m industrial p o l l u t i o n ; besides m o n i t o r i n g o f human interference on the rivers and water- sheds, w h i c h eventually upsets run o f f i n t o the sea and thereby affects d e l e t e r i o u s l y the coastal eco-systems, problems o f erosion and accretion, and special phenomena such as mudbanks and their importance in i n f l u e n c i n g the coastal zone management.
It is hoped that p r i o r i t y w i l l be g i v e n t o e v o l v i n g a coastal zone management p o l i c y for the c o u n t r y taking also into account an integrated approach of demographic and environmental problems o f the coastal zone.
No d o u b t , the Department of Environment, Government of I n d i a , has to play a nodal f u n c t i o n in close liaison w i t h the concerned maritime States and U n i o n Territories. W e hope that this Report w i l l create an awareness in this d i r e c t i o n and stimulate p o s i t i v e a c t i o n .
CMFRI BULLETIN 31
