SILTING IN NAVIGATIONAL CHANNELS OF THE COCHIN HARBOUR AREA

Transcription

1 /. mar. bil. Ass. India, 1971, 13 (1): SILTING IN NAVIGATIONAL CHANNELS OF THE COCHIN HARBOUR AREA C. K. GOPINATHAN AND S. Z. QASIM Central Marine Fisheries Research Institute, Cchin-ll ABSTRACT Suspended material in the Cchin Backwater varies cnsiderably with the state f tides and seasns. The water clumn has maximum suspended material during the mnsn perid, but its quantity declines prgressively during the pst-mnsn and pre-mnsn mnths. Shrt term changes induced by the tidal currents are quite large and during the pre- and pst-mnsn mnths the ttal material transprted frm the sea int the backwater amunts t apprximately 900 tnnes/day. The ttal amunt f material dredged annually frm the navigatinal channels is abut 2 X10* m'. Of this, nearly 1.2 x 10 m'/year is dredged frm the apprach channel t the harbur. At ne pint, where much f the silting takes place during the mnsn mnths, the bed f the apprach channel rises m every year. In the adjining backwater, where silting ccurs during the pre- and pst-mnsn mnths, mst f the silted material gets resuspended during the mnsn mnths, and with the strng ebb currents, gets transprted int the sea. Thus the tw prcesses transprtatin f the material frm the sea int the backwater during the pst- and pre-mnsn mnths and its retransprtatin frm the backwater int the sea during the mnsn mnths seem t alternate with each ther. The peculiar pattern f circulatin in the estuary influences the transprtatin f material int ne f the inner channels where heavy silting ccurs. INTRODUCTION THE distributin f suspended material and sedimentatin rate in estuaries, especially in thse where engineering wrks have been undertaken, is f much practical value. Burt (1955) discussed the distributin f suspended material in the Chesapeake Bay, while Biggs (1970) develped mdels f the sedimentatin prcess fr the upper and middle sectins f the same bay. Krey (1961) bserved that 40-90% f the suspended material present in the Nrth Sea was in the frm f detritus. The general mechanism assciated with the transprt f sediments int the estuaries has been explained by Pstma (1967). A few reprts n the sedimentatin prcess and ther related aspects in estuaries and castal waters f India are available frm the Centenary Cnference n Prt and Harbur Management, which was held at Calcutta (Institute f Prt Management, 1970). In recent years the hydrgraphy f the Cchin Backwater has been studied intensively (Qasim and Gpinathan, 1969 ; Qasim et ah, 1968 and 1969; Sankaranarayanan and Qasim, 1969). A few investigatins n the prblems assciated with the rate f sedimentatin have been made earlier (DuCane, Bristw, Brwn and Keen, 1938 ; Das, Hariharan and Varadachari, 1966 and Sundararaman, unpublished).

2 SILTING IN COCHIN HARBOUR NAVIGATIONAL CHANNELS 15 The Cchin Harbur (Lat. 9 58'N and Lng 'E) is situated alng the suthwest cast f India. It has a dredged apprach channel, 6 km lng, which is riented alng an east-west directin fr the entry f ships int the harbur. The extensin f the apprach channel int the backwater gets frked and frms the Ernakulam and Mattanchery Channels, because f the presence f 'V\'illingdn Island in between (Fig. 1). Dredging is being undertaken at regular intervals as the Channels get silted up fairly quickly. T get sme idea, therefre, f the silting prcess, several series f bservatins were made n the rate f sedimentatin and n the distributin f the suspended material in the harbur area,. These bservatins frm the basis f the present cmmunicatin. We are grateful t the authrities f the Cchin Prt Trust fr making us available the data n sunding in the backwater and the data n dredging arund the harbur area. A part f this wrk was carried ut while we were n the staff f the Natinal Institute f Oceangraphy. We thank Dr. N. K. Panikkar lr the facilities we enjyed. PROCEDURE AND METHODS Water samples frm 6 statins in the Cchin Backwater were cllected using a Van Drn sampler. These were frm the surface, mid-depth and 1 m abve the bttm. Statins 1 and 2 were almst perpendicular t the castline, while the ther 4 statins were nearly parallel t the castline (see Fig. 1). The depth at statin 3 and 6 was abut 5 m, whereas at the ther statins it was abut 10 m. Seasnal changes in the quantity f suspended material in the water clumn were studied by cllecting water samples at frtnightly intervals thrughut the year, nrmally during the slack tide, either at HLW r at LHW. These samples were thrughly shaken and then a knwn vlume f water was filtered thrugh Whatman 42 filter pads (pre-size l.l/u) f knwn weight. After filtratin the pads were washed t remve traces f seawater. These were then dried in a desiccatr and reweighed. The difference in weight gave the amunt f suspended material in a given vlume f water. The methd used was very similar t that f Krey (1961) fr the estimatin f sestn. The temperature f the water was measured by reversing thermmeters and salinity by an inductin salinmeter r by the cnventinal titratin methd. The distributin f suspended material in relatin t tides was studied by cnducting fur surveys at tw statins, each f which lasted 12 t 24 hurs. During these surveys the estimatin f suspended material was dne at 1 t 2 hurly intervals in relatin t tidal heights, which were determined by cnstructing marigrams using the Indian Tide Tables published by the Gedetic and Research Branch, Survey f India. The depth sunding data which frmed the basis f further analysis f the silting prcess in the backwater were supplied by the Cchin Prt Trust. GENERAL HYDROGRAPHIC FEATURES Accrding t Bristw (1938) the surface currents in the nearshre areas ff Cchin is sutherly frm February t September and nrtherly frm Octber t January. The predminant wave perid at Cchin is generally less than 5 secnds (Srivastava et al., 1967 and 1968). The waves are nrtherly frm Nvember t February, nrth-westerly frm April t July and westerly frm August t Octber. The average significant wave height is abut 1.5 m in July. This cincides with the rugh weather cnditins prevailing in the Arabian Sea at Cchin during this mnth.

3 16 C. K. GOPINATHAN AND S. Z. QASIM The annual meterlgical and hydrgraphical cnditins f the area can arbitrarily be divided int three well marked seasns, each f 4 mnths : (1) mnsn, -9*55N 76'15E FIG. 1. Map shwing the Cchin Backwater with the lcatins f 6 statins, the dredged apprach channel t Cchin Harbur and the dredged Mattanchery and Ernakulam Channels. The area measuring 0.26 km", where seasnal variatins in the bed prfile were studied, has been marked and indicated by arrw. O-bar in the apprach channel gives the psitin f the uter sand-bar which was cut acrss when the apprach channel was cnstructed. frm mid-may t mid-september (2) pst-mnsn, frm mid-september t mid- January and (3) pre-mnsn frm mid-january t mid-may. The average meterlgical cnditins (air temperature, relative humidity and rainfall) tgether with sme hydrgraphical features (water temperature, salinity and the ttal transprt f water thrugh the harbur entrance) pertaining t the three seasns have been given in Table 1. The pre-mnsn perid in the backwater is marked by a unifrmly high salinity ( t32%j and high temperature (29-32 C). The freshwater discharge int the backwater during this perid is very little and hence there is n stratificatin in the water clumn. Fllwing heavy rainfall and runff during the mnsn seasn, a pycncline develps in the water clumn, with clder seawater at the bttm and warmer freshwater at the tp. In the beginning, the seawater zne at the bttm remains shallw, but gradually it gets enlarged and reduces the freshwater clumn abve int a thinner zne (see Sankaranarayanan and Qasim, 1969). During the mnsn seasn the temperature and salinity variatins are f the rder f C and 0-30 % respectively. In the pst-mnsn perid bth temperature

4 lo TABLE 1 ; Average meterlgical and hydrgraphical cnditins f the Cchin Backwater area during the three seasns Seasn Pie-mnsdn Mnsn Perid Mid-Jan. 32 C t Mid-May Mid-May t Mid-Sept. Pst-mnsn Mid-Sept. 25 C t Mid-Jan. Mean air temperature Percentage relative humidity Average rainfall (mm/mnth) Average surface temperature Average Range in near surface bttm salinity temperature Average,near bttm salinity Average water transprt thrugh the harbur entrance, between MLLW and MHHW Ebb Fld C 30-32%e 30 C 33 % 83xlO«85xlO» 27 C C 1-18% 25 C 25 % 182xlO«36X10«m' m' C % 28 C 30 % 82xl0«90xl0«m' m z g c < H 2: r 2: 2: tn r

5 18 C. K. GOPlNATHAN AND S. Z. QASlM and salinity shw a prgressive increase. The average temperature and salinity during this perid is apprximately 30 C and 30%, respectively. RESULTS Distributin f suspended material with tides The tides in the backwater play an imprtant rle in the transprtatin f sediments in the area. The tides are f a mixed type, predminantly semidiurnal (Qasim and Gpinathan, 1969). Fig. 2 gives three marigrams representing the three seasns E 0 u PRE-MONSOON DAYS Fi. 2. Marigrams representing an apprximatin f tidal rhythm in the Cchin Backwater during pre-mnsn (March 1970), mnsn (July 1970) and pst-mnsn (Nvember 1970).

6 SILTING IN COCHIN HARBOUR NAVIGATIONAL CHANNELS 19 (pre-mnsn, mnsn and pst-mnsn). A clse examinatin f the tidal cycle will reveal that generally there is a steep rise in the water level frm LLW t HHW in abut 6 hurs. This is fllwed by a fall in the water level and again a rise frming a smaller peak, the LHW (Fig. 2). The time taken fr the water level t fall t the initial LLW is nearly 18 hurs. It can als be seen frm Fig. 2 that the tidal scillatins in the mnsn mnths are f a lwer range (20-8C' cm) than in the ther seasns ( cm). Observatins n the tidal currents at statin 1 shwed that the change in the tidal current frm ebb tfldstarts near the bttm which gradually mves up t the surface. The change frm fld t ebb, n the ther hand, takes place in a reverse manner, that is, the ebb current starts at the surface and then prgressively reaches the bttm. The frce f the fld current is maximum near the bttm, but that f the ebb is maximum near the surface. During the mnsn mnths, because f large influx f freshwater, the ebb currents frm surface t bttm are very strng. The maximum speed f the fld current varies frm 1 t 1.5 knts, while the ebb current has always a greater intensity and during the mnsn mnths it varies frm 2.5 t 3.5 knts. E100 t 80. i2 60 US I 40- < 20 Q s STATION A \, STATION A '».. 0 « A 8 12, T I Me HOURS 21/ ;i ^i-^s Tt TIME HOURS FIG. 3. Changes in the cncentratin f suspended material in relatin t the state f tides. Tp drawings represent the tidal heights as a functin f time n respective dates. The lwer drawings shw changes in suspended material at different depths. Clsed circles, surface ; pen circles, mid-depth ; crsses, 1 m abve bttm. The quantity f suspended material in the estuary varies markedly with the state f the tides (Fig. 3). At statin 4, the variatin in the suspended material was small, but there was a clear increase in the values with the fld during the pstmnsn mnths. A similar increase was nticed with the ebb during the mnsn mnths. At statin 1, the increase was cnsiderable (Fig. 3), particularly during the pre-mnsn mnth (January). Distributin f suspended material with seasns Mn thly values f the suspended material at different depths f all the 6 sta-

7 20 C. K. GOPINATHAK AND S. Z. QASIM tins have been shwn in Pig. 4. The values fr each frtnight were cmbined t give the mnthly averages shwn in the figure. During the pre-mnsn mnths, the suspended material at all the statins was relatively lw. At statins 2 and 3 the values were abut 10 mg/1 at the surface and with little change these cncentratins cntinued t ccur till abut mid-may. At the ther statins, the values at the surface were still lwer (lmg/1). Such lw values were recrded in February at statin4,in March at statin 5, and frm February t May at statin 6. The values near the bttm at all the statins were higher than thse at the surface. In the backwater, maximum transparency f water has been reprted during the pre-mnsn perid (Qasim et ah, 1968). During the mnsn mnths the suspended material increased sharply thrughut the water clumn at all the statins. Values as high as 30 mg/1 were fund at the surface; mg/1 at mid-depth, and mg/1 near the bttm. At statin 6, the maximum cncentratin was recrded in August. As cmpared t the ther statins, the suspended material was maximum at statin 1 and the values near the bttm were as high as 100 mg/1 in August (Fig. 4). During the pst-mnsn mnths the suspended material at all the statins was far less than during the mnsn mnths. Silting in navigatinal channels -' The navigatinal channels f the Cchin Harbur area cnsist f an apprach channel and tw inner channels the Ernakulam Channel and the Mattanchery Channel (Fig. 1). These are apprximately 6 km, 3 km and 4 km lng respectively. A gradual rise in the bed f these channels ccurs every year and the quantity f material remved frm the channels is f the rder f 2 x 10* m^/year. Nearly 70 % f this material is taken ut frm the apprach channel, 28 % frm the Mattanchery Channel and the rest frm the Ernakulam Channel. The data n silting in the apprach channel fr the different mnths during and the average mnthly silting fr the last 15 years, frm the data made available t us by the Cchin Prt Trust, have been shwn in Fig. 5,, Nrmally, January and February are the mnths when the apprach channel is dr^ged and therefre n data n silting fr this perid are available. Silting starts in March sn after the dredging is ver. It increases cnsiderably during the mnths pf July, August and September (Fig. 5). Frm Octber it decreases and prbably n silting ccurs in the apprach channel in December. The data n silting in the apprach channel fr shwed cnsiderable variatin as cmpared; t the average values f silting fr the past 15 years. During , silting in the apprach channel was f the rder f 30xlO*m*/ mnth fr the mnsn perid. Fr the same perid, the average f the past 15 years wrks ut t be 18 x 10*m*/mnth. The rise in the level f bed, based n the average f 15 years, was 1.37 m/year. Hwever, large variatins frm this value were nticed in certain years. Transprtatin f material thrugh the entrance The changes in the suspended material during the fld in the pre-mnsn and pst-mnsn mnths were very large. Fr instance, n 12/13 December 1966 (see Fig. 3), the suspended material in the water clumn was f the rder f 25 mg/1 at the lw tide. It became apprximately 75 mg/1 within 3 hurs during flding. The increase at each hur frm the initial value was fund t be 8.8 mg/1, 25 mg/1 and 53 mg/1. Taking the crss sectinal area: at statin 1 as 4700 m* belw LWOST and the average current velcity at each hur as 30, 50 and 70 cm/secnd, the ttal

8 r H 5 w c < H r 2; w r FIG. 4. Seasnal variatins in the cncentratin f suspended material at 6 statins in the Cchin Backwater fr the perid September 1965 t Octber Clsed circles, surface ; pen circles, mid-depth ; crsses, 1 m abve bttm.

9 22 C, K, OOPINATHAN AND S. Z. QASIM silt transprted int the backwater wuld be f the rder f 880 tnnes/day. The transprt f water int the backwater during flding between MLLW and MHHW Fi. 5. Mnthly variatins in the rate f silting in the apprach channel. Open histgrams repreent the perid September 1965 t August 1966 ;filledhistgrams give the mnthly averages fr the last 15 years, is nearly 85 x 10* m^. The abve calculatin takes int accunt the water transprted int the backwater as 25 x 10* m*. This is an average value and therefre, the value f the sediment transprt given abve is a cnservative estimate. If a similar cmputatin is made fr the bservatin n 21/ (see Fig. 3), the sediment transprted int the backwater by the fld tide wuld be f a much greater magnitude. Frm Fig. 3 it can als be deduced that very little f the transprted material will escape int the sea during the ebb tide. Thugh the ebb current is strnger than the fld, the material is nt stirred up and s the ebb water carries very little material with it. This cnditin seems t prevail during the pst-mnsn and the pre-mnsn mnths. During the mnsn mnths, n the ther hand, the sediments get stirred up and are transprted frm the backwater t the sea (see belw). Silting in the adjining backwater T give a cmprehensive picture f the rate f silting in the backwater, the bathemetry f an area measuring 0.26 km^, which has been indicated in Fig. 1, was

10 SILTING IN COCHIN HARBOUR NAVIGATIONAL CHANNELS 23 FIO. 6 (A-L). Bathemetry f an area in the Cchin Backwater indicated in Fig. 1 during the different perids f the year Cnturs shw the depths 5-10 m. A part f the area where dredging tk place in January 1966 has been indicated in E. The dates during which sundings were taken have been given in A-L.

11 - 24 C. K. GOPINATHAN AND S. Z. QASIM examined in detail. The depth cnturs in this area fr the different perids f the year have been given in Fig. 6, A-L. The areas bund by the depth cnturs 5-10 m were measured by a planimeter and the ttal amunt f material depsited r remved was calculated fr the different perids. These have been shwn in Fig. 7. As can be seen frm Figs. 6 and 7, maximum silting tk place frm September t December. This was in cntrast t the apprach channel where maximum silting ui u Z S = 0 9. I u Fi. 7. Average rate f silting in different mnths calculated frm the changes indicated in Fig. 6. The histgrams represent the perid September 1965 t August ccurred during the mnsn mnths (see Fig. 5). The remval f material bserved between January and February and indicated in Fig. 7, belw zer, was as a result f dredging which tk place in January 1966 (see Fig. 6E). Silting again ccurred in March and April (Fig. 7). Frm these data it can be assumed that unless dredging takes place, silting cntinues t ccur, with varying degrees, frm September t abut April. By May, when the mnsn seasn starts the material depsited during the earlier mnths gets stirred up by the strng freshwater utflw and is remved int the sea and perhaps gets depsited in the apprach channel. Thus in the backwater the tw prcesses during the year maintain a state f balance and the verall effect f silting and desilting gives rise t almst cnstant depth in the backwater (see Fig. 6 A-L). n ^ ^ u I s 0 N 1965 D J F M 1966 A M J J A DISCUSSION The apprach channel at Cchin was cnstructed in Befre that, there was a sand bar at a distance f 1.6 km west f the cast. The depth f water ver this dme-shaped bar was abut 3 m belw LWOST, increasing n either side, alng the east and west. The apprach channel was cnstructed by cutting the bar acrss. The psitin f the frmer bar is shwn as O-bar in Fig. 1. The material which gt silted up after the cnstructin f the channel was dredged ut next year, during January and February (1929), when the sea became calm. Since then the tw prcesses, silting and the remval f the silted material by dredging, have been ging n alternately. The main regin in the apprach channel, which is subjected t heavy silting, is a 140 m wide and 4.3 km lng area, west f the pint O-bar. This area gets silted up t a level f 1.2 t 1.8 m every year. The material remved frm the channel in the frm f fluid mud is dumped abut 600 m away alng the sides f the channel. Frm 1928 t 1937, the dredged material frm the apprach channel was dumped alng the nrthern side f the channel and frm 1937 t 1962 alng the suthern side. Since 1962, the dumping started n the nrthern side again.

12 SILTING IN COCHIN HARBOUR NAVIGATIONAL CHANNELS 25 Presumably the idea f changing the dumping site arbitrarily was t have an effective dispersin f the dredged material int the sea. DuCane et al. (19.38) indicated that the heavy silting bserved in certain years was definitely influenced by the appearance and mvements f the mud banks in clse vicinity f the channel. In recent years, sme studies n the silt mvement in the area were cnducted by the Cchin Prt Trust in cllabratin with the Bhabha Atmic Research Centre, Trmbay, and the Central Water and Pwer Research Statin, Pna (Cle and Tarapre, 1966 ; Sunderaraman, unpublished). The silt mvement in the area was studied by the radiactive-tracer technique. Three experiments were cnducted during the pst-mnsn and pre-mnsn mnths f and a furth experiment was carried ut during the mnsn mnths f The results f these experiments shwed that the material dumped abut 850 m away, either n the suthern r nrthern sides f the apprach channel, fund its way int the channel. It subsequently came thrugh the bifurcated channels int the backwater. The material dumped abut 2 km suth f the apprach channel als fund its way int the channel. The experiment which was carried ut in the mnsn mnths f 1970 shwed that the material dumped at a pint, 2 km nrth f the channel, and 5 km west f the cast, did nt find its way int the channel. One f the factrs affecting the silting in the channels is the sedimentatin f the suspended material in the estuary during the pst- and pre-jnnsn mnths. An area just utside the dredged channels will experience maximum sedimentatin f the suspended material during the pst-mnsn seasn, whereas in the upper reaches f the estuary, sedimentatin wuld be maximum during the pre-mnsn seasn. As a result f typical estuarine circulatin as indicated by Pstma (1967), the material frm the sea may find its way int the lwer parts f the rivers where seawater hardly ever penetrates. Thus it seems likely that the prtin f the backwater which is nearer t the harbur will receive larger quantities f marine mud during the pst- and pre-mnsn mnths than the ther parts f the backwater. The high values f the suspended material in the backwater duiing the mnsn mnths suggest that the sedimented material is prbably resusperided by the freshwater runff. The tidal actin and the strng ebb currents during the mnsn mnths further accelerate the resuspensin f the bttm sediment. This suspended material seems t mve slwly twards the entrance f the estuary in an scillatry fashin. High values f the suspended material recrded at statin 1 during the mnsn mnths seem t signify such a mvement which leads t what has been termed as the ' turbidity maximum ' at the estuarine entrance (Psitma, 1967). Seawater is always present in the apprach channel, even during the mnsn mnths, when the freshwater discharge frm the backwater is maximum. In the apprach channel, the freshwater, which is heavily laded with suspended material, mixes with the denser seawater at the bttm. Because f sme electrstatic prperty f the material in suspensin, while such a mixing is taking place, the fine particles aggregate int larger particles and quickly sink t the bttm (DuCane et al., 1938 ; Ippen, 1966). Althugh such a mechanism wuld seem t perate all alng the apprach channel during the mnsn seasn, because f strng currents near the entrance, its settlement there seems t be prevented. Prbably because f the slackening f the currents in sme parts f the apprach channel, the material settles mre readily alng the west f O-bar, which is a well-knwn area f maximum silting. Of the tw channels encircling the Willingdn Island, the Mattanchery Channel is subjected t a much greater silting than that f the Ernakulam Channel. Nearly 1 /3 f the reprted silting in the three dredged channels during the year ccurs in the

13 26 C. K. GOPINATHAN AND S, Z. QASlM Mattanchery Channel. Certainly this channel seems t be greatly influenced by the peculiar pattern f circulatin prevalent in the Cchin Backwater. It has been bserved that the fld currents, during the mnsn mnths, flw mainly thrugh the Mattanchery Channel int the backwater, suth f the Willingdn Island. Observatins n the synptic distributin f salinity within the area during the same perid have clearly shwn that the near bttm circulatin arund the Willingdn Island is anti-clckwise. Thus, the sediment-laded bttm water entering the Mattanchery Channel during the fld tide seems t leave behind a part f its sediment lad as it passes the Mattanchery Channel. REFERENCES BIGGS, R. B Surces and distributin f suspended sediment in nrthern Chesapeake Bay. Marine GeL, 9 : BRISTOW, R. C Histry f mud banks. Vls. 1 and 2, Cchin Gvernment Press, 174 pp. and 55 pp. BURT, W. V Distributin f suspended material in Chesapeake Bay. J. mar. Res., 14 : DAS, P. K., HARIHARAN, V. and VARADACHARI, V. V. R Sme studies n wave refractin in relatin t beach ersin alng the Kerala cast. Prc. Indian Acad. Sci., A 64 : DUCANE, C. G., BRISTOW, R. C, BROWN, J. C. and KEEN, B.A. 1938, Reprt f the special cmmittee n the mvement f mud banks. Cchin, Cchin Gvernment Press, 57 pp. GLE, C. V. and TARAPORE, Z. S Radiactive tracer studies at Cchin (Abstract) IIOE Newsletter, A-.2%. INSTTTUTE OF PORT MANAGEMENT Papers n develpment and maintenance f navigable channels in estuaries and castal areas. Centenary Cnference n Prt and Harbur Management, 19-21, Octber 1970, 86 pp. IPPEN, A. T Ssdimentatin in estuaries, pp /«A. T. Ippen (ed.) '.j/«r;'a«rf Castline Hydrdynamics. McGraw Hill Bk C., Inc., New Yrk. KREY, J Der Detritus in Meere. J. Cns. perm. int. Explr. Mer, 24 : POSTMA, H Sediment transprt and sedimentatin in the estuarine envirnment, pp In G. H. Lauff (ed.) Estuaries. Pbl. 83, American Assciatin fr the Advancement f Science, Washingtn D.C. QASIM, S. Z., BHATTATHIRI, P. M. A. and ABIDI, S. A. H Slar radiatin and its penetratin in a trpical estuary. /. exp. mar. Bil. Ecl., 2 : and GpiNATHAN, C. K Tidal cycle and the envirnmental features f Cchin Backwater (a trpical estuary). Prc. Indian Acad. Sci., B 69 : SANKARANARAYANAN, V. N. and QASIM, S. Z Nutrients f Cchin Backwater in relatin t envirnmental characteristics. Marine Bil., 2 : SRIVASTAVA, P. S., NAIR, D. K. and KARTHA, K. R. R Departmental Reprt N. PR. 13/67. Indian Naval Physical Labratry, Cchin. and Mnthly wave characteristics f the Arabian Sea. Indian J. Met. Gephy., 19 : SuNDERARAMAN, C. K. (Unpublished) Methd f determining sand and silt mvements alng the cast in estuaries and in maritime rivers. Use f mdern techniques and methd adpted at Cchin Prt by using radiactive tracers. Natinal Cnference n Prt and Harbur Management, Calcutta, January 12-16, 1968.