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Current measurements in Knight Inlet, 1956. Rodgers, George Keith 1958

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CURRENT MEASUREMENTS IN KNIGHT INLET 1956 by GEORGE KEITH RODGERS B.A.Sc, U n i v e r s i t y of Toronto, 1956 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of PHYSICS We accept th i s thes i s as conforming to the required standjard THE UNIVERSITY OF BRITISH COLUMBIA May,1958 ABSTRACT Current measurements were made i n Knight In le t during the per iod , Ju ly 4 t h to 1 1 t h , 1956 . A current drag, designed at the Chesapeake Bay I n s t i t u t e , was employed for current measurements i n the upper 20 meters of the water column. An Ekman 'current : meter was used at depths below 20 meters. Corrections fo r ship motion were applied to the Ekman current meter readings . This i n v e s t i g a t i o n consis t s ofj (1) a general analys i s of the techniques used i n the c o l l e c t i o n and treatment of the data, (2) a d e s c r i p t i o n of the currents obtained from the above treatment of the data . Currents at every depth of measurement showed o s c i l l a t i n g or f l u c t u a t i n g components superimposed on a net current . T i d a l forces appear to act at a l l depths. The d i r e c t e f fect of wind stress on currents i s apparent to depths of at l ea s t 10 meters. Indirect wind effects are indicated at greater depths. I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d without, my w r i t t e n p e r m i s s i o n . Department o f ~Pf4 Y^S, l£S The U n i v e r s i t y o f B r i t i s h C o lumbia, Vancouver 3 , Canada. Date ACKNOWLEDGEMENTS The author wishes to express his grat i tude t o : D r . G .L .P ickard under whose d i r e c t i o n and advice t h i s study was ca r r i ed out, D r . R.W. Stewart whose c r i t i c i s m and suggestions have been most he lpfu l ,and fe l low graduate students at the Ins t i tu te of Oceanography fo r t h e i r i n t e r e s t and comments during the preparat ion of th i s t h e s i s . TABLE OF CONTENTS Page I INTRODUCTION 1 II INLET DESCRIPTION . . . . . . . . 4 III EXPERIMENTAL PROCEDURE 9 General D e s c r i p t i o n 9 Current Measuring Devices 12 1) Ekman Current Meter 12 2) C .B . I .Current Drag 14 IV DATA TREATMENT 18 Ship Motion 18 Current Measurements 22 V RESULTS. 23 Ship Motion . . . 23 Descr ip t ion of Currents 26 1) S ta t ion &/2, Ju ly 6th to 8th, 1956. . . . 26 2) S ta t ion 5, Ju ly 4th to 6th, 1956. . . . . 30 3) S ta t ion 5, Ju ly 8th to 11th,1956. . . . . 33 VI DISCUSSION 38 Technique. . 38 1) Design of the experiment 38 2) Ship motion 40 TABLE OP CONTENTS (CONTINUED) Page VI DISCUSSION continued 3) Comparison of Ekman meter and C . B . I . drag measurements at the same depths . . 42 Currents 47 1) S ta t ion 3V2 4 7 •2) S ta t ion 5 52 3) Tides and t i d a l currents 54 4) Wind effects 56 5) Hourly transport 58 6) Fresh water transport 61 7) Net transport 62 8) Internal waves 64 VII CONCLUSIONS . . . . . . . . . . . 67 VIII RECOMMENDATIONS. . 69 REFERENCES . 72 LIST OF FIGURES Figure 1. Schematic representat ion of the s a l i n i t y d i s t r i b u t i o n and net c i r c u l a t i o n i n an i n l e t . 2. Knight In le t - map, l o n g i t u d i n a l depth p r o f i l e and s a l i n i t y p r o f i l e s of Ju ly , 1956. 3. Transverse sections at the current s t a t ions . 4. Shorel ine and bottom contours near s t a t i o n 3"*"/2. 5 . The C.B . I , current drag. 6. Pos i t i on ing of shore s t a t ions . 7. The extent of ship motion. 8. D i s t r i b u t i o n of ship speed at the two current s t a t i o n s . 9. Comparison of uncorrected and corrected Ekman current meter readings. 10. Longi tudina l component of currents at s t a t i o n 31/2, Ju ly 6th to 8th, 1956. LIST OP FIGURES (continued) Figure 11. Transverse component of currents at s t a t i o n 3 1/2, July 6th to 8th, 1956. 12. Hourly p r o f i l e s of currents at s t a t i o n 3 1/2, Ju ly 6th to 8th, 1956. 13. Net current p r o f i l e s at s t a t i o n 3 1/2, Ju ly 6th to 8th, 1956. 14. Longi tudina l component of currents at s t a t i o n 5, Ju ly 4th to 6th, 1956. 15. Transverse component of currents at s t a t i o n 5, Ju ly 4th to 6th, 1956. 16. Hourly p r o f i l e s of currents at s t a t i o n 5, Ju ly 4th to 6th, 1956. 17- Net current p r o f i l e s at s t a t i o n 5, Ju ly 4th to 6th, 1956. 18. Longi tudina l component of currents at s t a t i o n 5, July 8th to 11th, 1956. 19. Transverse component of currents at s t a t i o n 5, Ju ly 8th to 11th, 1956. LIST OP FIGURES (continued) Figure 20. Hourly p r o f i l e s of currents at s t a t i on 5, Ju ly 8th to 11th, 1956. 21. Net current p r o f i l e s at s t a t i o n 5, Ju ly 8th to 11th, 1956. 22. Comparison of Ekman meter and C . B . I , current drag readings . 23. The ef fect of the wire drag c o r r e c t i o n . 24. Calculated and observed t ransport s . 25. Progressive i n t e r n a l waves. I INTRODUCTION The In s t i tu te of Oceanography of the U n i v e r s i t y of B r i t i s h Columbia has c a r r i e d out a study of the coas ta l Inlets of B r i t i s h Columbia over several years . These i n l e t s are deep indentations In the shore l ine . They are long and narrow with steep s ide s . The bottom topography i s character ized by a deep bas in that Is often two to three times the depth of the outside passages and coas ta l she l f regions through which they have access to the sea. The deep bas in of the i n l e t and the shallower passages beyond the i n l e t mouth are u sua l ly separated by a s i l l , or shallower sec t ion where the depth i s about one h a l f that of the outside passages. In these i n l e t s the d i s t r i b u t i o n of propert ies such as s a l i n i t y , temperature and oxygen content has been determined. The s a l i n i t y d i s t r i b u t i o n provides some information about" c i r c u l a t i o n i n the i n l e t s . The c i r c u l a t i o n or water movements w i t h i n the i n l e t s , i f f u l l y understood, would help i n understanding the sources and movement of nutr ients for b i o l o g i c a l a c t i v i t y . I t a l so would a s s i s t i n determining the d i s t r i b u t i o n of par t i cu la te mater ia l and poss ib le p o l l u t a n t s . - 1 -- 2 -The f i r s t f a c t provided by observation of the s a l i n i t y d i s t r i b u t i o n i s that a l l f r e sh water emptied in to an i n l e t by r i v e r s ( p r i n c i p a l l y at the head of the i n l e t ) stays i n the surface l a y e r s . The f re sh water flows out over higher s a l i n i t y sea water. The s a l i n i t y of the surface layer increases from the head to the mouth. Therefore s a l t water must be mixed upward in to the surface layer and carr ied seaward. In order that there be cont inu i ty of the f re sh water f low, the speed of the down-inlet flow of the surface layer must increase towards the mouth. In order to replace the s a l t c a r r i ed seaward In the surface l ayer there must be u p - i n l e t flow of sea water at depths below the surface l ayer (see f igure 1 ) . Extensive surveys of a shallow east coast estuary (Pr i tchard , 1952) where the water Is 3 l i g h t l y less s t r a t i f i e d bears out these ideas . Dynamical studies of deep i n l e t s are based on t h i s (Cameron, 1951 and Stommel, 1 9 5 1 ) . However, i n deep i n l e t s the d i s t r i b u t i o n of net currents (non-periodic) and also of t i d a l currents (per iodic) i s unknown and these can be obtained only by d i r e c t measurements. There are some d i f f i c u l t i e s i n carry ing out a current measurement programme i n these deep i n l e t s and experiments were made i n 1952 , 1953 and 1955 i n order to f i n d a su i tab le p o s i t i o n for measurements; to determine the best technique for anchoring; to determine the magnitude of currents to be measured, and to experiment wi th current measuring devices . - 3 -The 1956 data from Knight I n l e t , with which t h i s thes is i s concerned, represents the most recent experiment i n t h i s s e r i e s . The data serves as the basis for an analys i s of the techniques employed and fo r an analys i s of the currents i n order to determine the inf luence of t i d e , wind and runof f . II INLET DESCRIPTION The data treated In th i s thes is was obtained i n Knight I n l e t . In general c h a r a c t e r i s t i c s t h i s i n l e t i s t y p i c a l of those i n B r i t i s h Columbia (see f igure 2 ,3 and 4 ) . I t i s a long , narrow deep coas ta l indenta t ion with a length of 102 kilometers (55 n a u t i c a l miles) and an average width of 3 kilometers (1.6 n a u t i c a l m i l e s ) . The average m i d - i n l e t depth i s 420 meters (1380 feet) and the maximum i s 550 meters (1800 f e e t ) . I t has two s i l l s i n i t s l ength , 74 and 110 kilometers from the head of the i n l e t . The bas in (designated as the outer basin) between these two s i l l s has I r regular topography but does not exceed 250 meters i n depth. The inner bas in Inside the inner s i l l i s deeper and contains the maximum depth (Pickard, 1956). The outer s i l l depth i s 67 meters and the Inner s i l l depth i s 63 meters. This i n l e t i s a p o s i t i v e , f jord-type estuary (Pr i tchard , 1952) i n cons iderat ion of Its depth, s i l l s and average s a l t content (less than the adjacent sea) . The freah water i s supplied l a r g e l y by r i v e r runoff introduced at the head by the K l i n a k l i n i R i v e r . - 4 -- 5 -This r i v e r runoff i s at a maximum i n June or July due to melt ing of the snow and i ce at higher a l t i t u d e s . An estimate of the mean monthly runoff has been made from r a i n f a l l and watershed data (Pickard and T r i t e s , 1 9 5 7 ) • For June and July the values are 790 and 616 cubic meters per second r e s p e c t i v e l y . A ser ies of s a l i n i t y p r o f i l e s down the length of the i n l e t i s p lot ted i n f igure 2. These are taken from data obtained during the two days fo l lowing the l a s t current measurement. The i n l e t begins as a h igh ly s t r a t i f i e d , two-layer system at the head and grades to near homogeneous i n the outer ba s in . The f re sh water i s concentrated i n the upper 20 meters, though there i s s t i l l a gradient i n s a l i n i t y below t h i s . The f r e sh water has s a l t water mixed upward in to i t as i t moves down the i n l e t . The upper l ayer eventual ly reaches a s a l i n i t y close to that of the sea water at the mouth. A 3 indicated In the in t roduct ion t h i s implies an outflow i n the surface layer to provide cont inu i ty of f r e sh water f low, and inflow at depth to balance the s a l t c a r r i e d out with the f re sh water. Just where th i s inflow takes place Is undetermined. However, i n view of the f a i r s t a b i l i t y of the upper 50 meters of water and the fact that s a l t i s being supplied at the lower boundary of the surface layer ( at a - 6 -depth of about 15 meters) i t seems l i k e l y that u p - i n l e t flow w i l l be concentrated just below the upper l a y e r . Tides i n th i s reg ion are of the semi-diurnal mixed type with a maximum range of about 5 meters. The nearest continuously recording t ide s t a t i on to Knight In le t i s at A l e r t Bay, about 40 miles from the reg ion where t h i s data was obtained. A l e r t Bay Is i n the network of channels i n t o which the i n l e t empties. The two current s tat ions at which measurements were made were 5 and 3 1 / 2 . The nearest t ide s t a t i on re fer red to the A l e r t Bay t i d e predic t ions i s Glendale Cove, about 5 miles up-In le t from s t a t i o n 5 (see f i gure 2 ) . Por Glendale Cove there Is no time di f ference from A l e r t Bay i n high or low water, but there i s a mean r a t i o of r i s e for high t ide given as 1 .15 (Tide tab les , 1 9 5 6 ) . The predicted t ides for A l e r t Bay are those which are indicated on the various graphs. The state of the t i d e at s t a t i on 5 from Ju ly 4 t h to 6 t h was i n the t r a n s i t i o n from neap to spring t ides with marked i n e q u a l i t y . The range of t ide fo r successive high to low waters d i f f e red by a factor of two, while the range of t ide fo r successive low to high waters was very near ly the same. For the period from Ju ly 6 t h to 8 t h on s t a t i on 3"**/2 the t i d e was near spr ings , s t i l l with the fac tor of 2 between successive high to low water ranges. The time spent on s t a t i o n 5 from - 7 -July 8th to 11th was during spr ing t ides with the f ac tor defined before being only 1.6. The two stat ions on which current measurements were made are i n the s t ra ight reach^of the i n l e t (see f i gure 2 ) . A s t ra ight reach was chosen f o r . t h e current measurements because previous measurements i n a sinuous i n l e t (Bute In le t i n p a r t i c u l a r ) were d i f f i c u l t to i n t e r p r e t . S ta t ion 31/2 was on the inner s i l l , or s l i g h t l y u p - i n l e t from the shallowest part (see f igure 4 ) . S ta t ion 5 was s i tuated 15 kilometers ( 8 n a u t i c a l miles) u p - i n l e t from s t a t i o n 3^/2 over the deeper bas in ins ide the inner s i l l . Transverse p r o f i l e s of the i n l e t at these s tat ions are shown i n f igure 3. Apart from the depth di f ference between these two s tat ions there Is a d i f ference i n the symmetry about the cent re - l ine of the i n l e t . The anchoring p o s i t i o n corresponds roughly with the c e n t r e - l i n e . At s t a t i o n 5 there are steep sides and a l e v e l bottom and l i t t l e asymmetry about the c e n t r e - l i n e . At s t a t i o n 3^/2 there i s a steep side and a l e v e l bottom to the south of the c e n t r e - l i n e . To the north i t i s shallower and the grade Is less than that of the steep southern s lope . During the period of these observations the p r e v a i l i n g winds arid the strongest winds were westerly , or up-i n l e t . The one exception was the f i r s t 24 hours on s t a t i o n 5 when a steady 10 knot wind blew down the i n l e t . The u p - i n l e t wind3 followed approximately a d i u r n a l cycle with a minimum from 0600 to 1200 hours and a maximum at 1600 to 2000 hours . The maximum u p - i n l e t wind i n each case was over 20 knots . I l l EXPERIMENTAL PROCEDURE General D e s c r i p t i o n Measurements were taken from the research ve s se l , H.M.C.S . Cedarwood, a wooden ship of 51 meters length , 9,2 meters beam and 4*5 meter d r a f t . A s ing le anchor was used as previous attempts i n 1952 - 3 to anchor bow and s tern were unsuccess ful . The ship motion was, monitored during current measurements (In a way which i s described below) to permit c o r r e c t i o n for the swing of the vesse l on i t s anchor cab le . Current p r o f i l e s were obtained from the surface to 20 meters every h a l f hour with a C . B . I , current drag (descr ip t ion i n sec t ion on instrumentation) fo r the f i r s t and second anchorages and every hour on the t h i r d anchorage. Measurements with the Ekman current meter were taken i n the remainder of the water column every hour. At s t a t i o n 5 the Ekman current meter measurement depths were 50, 100, 200 and 300 meters. At s t a t i o n 3 1 / 2 t n e depths were 10, 20, 40, 60 and 70 meters. I t w i l l be noted that there - Is an overlap of C . B . I drag and Ekman meter measurements at the 10 and 20 - 9 -- I O -meter depths on s t a t i on 3^"/2. These measurements served to compare the two instruments. The periods of observation consisted of 48 hours on s t a t i on 5 from Ju ly 4 t h to 6 th ; 48 hours on s t a t i o n 3^/2 from Ju ly 6th to 8th and another 68 hours on s t a t i o n 5 from Ju ly 8th to 11th. The fo l lowing table summarizes the amount of data obtained. S ta t ion 5 3V2 5 Durat ion of anchorage 1500 July to 1500 Ju ly 4th 6 th 1800 1800 July to July 6th 8th 2100 Ju ly to 1600 Ju ly 8th 11th No.of C .B . I .d rag p r o f i l e s to 20m. 90 96 64 No.of Ekman meter p r o f i l e s 48 48 63 A ' bathythermograph cast to 270 meters was made hourly at s t a t i o n 5 and to 75 meters hourly at s t a t i o n 3 1 / 2 . The occas ional 20 meter cast was made to determine the surface temperature s tructure i n more d e t a i l . Hourly meteorological observations included the wind v e l o c i t y , a i r temperature (wet and dry bulb thermometers), barometric pressure, cloud type and cloud c o v e r , v i s i b i l i t y and sea s t a te . - 11 -At the beginning and end of each Ekman current reading a 3-point f i x with a sextant was taken on shore s t a t i o n s . The p o s i t i o n of these shore s tat ions were determined severa l times during the anchorages with radar ranging and gyro compass bear ing . These shore s tat ions were u s u a l l y prominent racks whitewashed for dayl ight v i s i b i l i t y and marked by o i l lanterns at n i g h t . Only when r a i n was heavy were these s tat ions not v i s i b l e . On the two days fo l lowing the l a s t current s t a t i o n , oceanographic s tat ions were taken along the length of the i n l e t to determine the water s t ruc ture . In numerous instances below there w i l l be reference to a ' c a l c u l a t e d 1 t i d a l current as opposed to the observed current s . This ' c a l c u l a t e d ' current i s deduced from predicted t i d e s , several assumptions being made, namely: (1) that the r e a l t ide was as pred ic ted , (2) that the whole water surface of the In le t r i s e s and f a l l s uni formly, (3) that the t i d a l current necessary to provide the water fo r f i l l i n g (or emptying) the t i d a l prism i s uniform across the ent i re sec t ion of the i n l e t , (4) that the t i d a l current var ies s i n u s o i d a l l y . The close correspondence of the ac tua l t ide records and predicted t ide heights at A l e r t Bay lend support to the - 12 -f i r s t assumption. E a r l y inves t iga t ions by Dawson (1920) support the second. There i s less j u s t i f i c a t i o n fo r the f i n a l two assumptions. A more de ta i l ed account of t h i s t ide current c a l c u l a t i o n appears i n the d i s cu s s ion . Current Measuring Devices 1. The Ekman Current Meter. The Ekman current meter i s an in teg ra t ing , p r o p e l l o r -type device which i s act ivated and deactivated by messengers. During the a c t i v a t i o n period the number of revolut ions of the prope l lo r i s metered. A l so , f o r every 33 turns of the p r o p e l l e r , a small phosphor-bronze b a l l i s re leased to f a l l in to a compass-directed trough d i r e c t i n g the b a l l in to a 1 0 ° segmented cup. After deac t iva t ion the meter Is r a i s e d . Both the number of revolut ions made by the p r o p e l l o r , and the number of b a l l s i n each 1 0 ° segmented cup are noted. The number of revolut ions made, combined with the a c t i v a t i o n period gives the average revolut ions per minute. Comparison with a c a l i b r a t i o n curve gives the current measured. A weighted mean of the angles indicated by the b a l l 3 determines the current d i r e c t i o n . - 13 -The period of a c t i v a t i o n was us u a l l y 2 minutes, though periods of 1 and 4 minutes were used when the current was very large or very small, r e s p e c t i v e l y . For the meter used i n t h i s experiment the threshold v e l o c i t y required to overcome f r i c t i o n was 1.8 centimeters per second. Experience with c a l i b r a t i o n of these instruments shows a possible error of about 3 per cent i n readings. The accuracy i n the d i r e c t i o n i n d i c a t i o n i s about * 5 degrees f o r reasonably large currents, but there i s a larger uncertainty i n small currents ( Tabata and G r o l l , 1956). Error i n i n d i c a t i o n of the water current i s introduced by horizontal ship d r i f t during the current measurement. The Ekman meter reads the vector sum of the water current r e l a t i v e to the earth and the ship v e l o c i t y r e l a t i v e to the current. Since the ship v e l o c i t y i s a s i g n i f i c a n t percentage of t h i s reading ( see discussion of ship motion) the ship's movement was monitored to correct f o r t h i s . The major disadvantage i n using the Ekman current meter i s the slowness with which measurements are made. This i s because the meter has to be recovered a f t e r each measurement. It takes approximately one h a l f hour to take 4 measurements at 50, 100, 200 and 300 meters. - 14 -2. The C.B.I. Current Drag: Currents i n the upper layer ( zero to 20 meters ) are of sp e c i a l i n t e r e s t i n estuaries. Experience has indicated that they vary markedly with depth and time. This d e t a i l must be provided by frequent readings at several l e v e l s . Preferably the readings f o r a l l depths should be made simultaneously. As indicated before, the Ekman current meter i s too slow f o r t h i s , even though the depth i s only 20 meters. Another objection i s that the magnetic effects of the ship may appreciably a f f e c t current d i r e c t i o n indications at these small depths ( Sverdrup, et a l , 1942). A C.B.I, current drag can provide the type of measurement required. The design used was that described by Burt and Pritchard (1951) of the Chesapeake Bay Ins t i t u t e ( hence C.B.I, drag). Readings can be obtained at one depth i n about 15 seconds and the drag can be quickly lowered or raised to successive depths. This device i s a negatively buoyant, weighted biplane (see figure 5) suspended by a l i g h t , s t e e l wire. The current exerts a force on the biplane, and the wire angle from the v e r t i c a l i s a measure of the magnitude of the current. The d i r e c t i o n of the current i s given by an estimate of the angle at which the wire streams away from the ship, combined with the ship's heading. - 15 -The s izes of the biplane and weights used are determined by the magnitude of the currents to be measured, i n cons iderat ion of the optimum, angle-measuring range ( 3 degrees to 45 degrees) and the Reynolds number r e s t r i c t i o n f o r the equation used to ca l ib ra te the drag* The r e s t r i c t i o n on the Reynolds number i s that I t be greater than 1000 for flow past the drag, i n order that the drag c o e f f i c i e n t -for the biplane be constant. In t h i s experiment a 1.5 by 1.0 foot biplane was used with 10, 20 or 40 pound weights. With these combinations the lower l i m i t of a speed measurement .is 0.3 centimeters per second. This i s h igh ly s a t i s f ac tory In the current range of zero to 150 centimeters per second, encountered. The equation of the C . B . I , drag i s v = ( 2W / CdA<>)^ (tan 0 fz= k f tan 0,)%. as a consequence of the balance of forces shown i n f igure 5. The symbols represent the f o l l o w i n g : 8 = angle measured from the v e r t i c a l W = weight of the drag i n water Cd = drag c o e f f i c i e n t of the plane A = plane area ^ = f l u i d densi ty The drag c o e f f i c i e n t used by Burt and Pr i t chard was 1.2 . - 16 -A check of th i s formula was made by Burt and Pr i tchard by simultaneous current measurements with the drag and a von Arx recording meter. They show good agreement to a depth of 25 feet and have indicated successful use to 50 f e e t . The use of t h i s drag to 20 meters or 65 feet i n B r i t i s h Columbia i n l e t s required a further check on i t s accuracy at such depths. A l s o , s ince currents i n the B r i t i s h Columbia i n l e t s appear to be twice those used by Burt and Pr i tchard fo r t h e i r check, there i s further reason to inves t iga te i t s accuracy. Sources of error i n us ing the above formula i n c l u d e : (1) neglect of drag on the suspending wire (2) neglect of l i f t on the wire (3) neglect of wire curvature . Er ror i n the d i r e c t i o n est imation may be caused by current d i r e c t i n g of the sh ip ' s h u l l i f the h u l l does not l i n e up p a r a l l e l to the surface current . The fac t that part of the d i r e c t i o n measurement involves an eye est imation of angle probably introduces an average error of * 10 degrees even with the most experienced operator. In reading the wire angle there was a poss ible error of i 1/2 degree. The accuracy i n angle required for a 0.05 knot (2.5 centimeters per second) accuracy In current i s g iven by Burt and Pr i tchard as : - 17 -Measuring Angle at 3 ° at 1 0 ° at 2 0 ° 15 lb .weight 1 ° 1 1 / 2 ° 2 e 30 lb.weight 1 / 2 ° 1 ° 1 1 / 2 ° '.A point of d i s t i n c t i o n between drag measurements and Ekman meter measurements Is that the Ekman measurements are values integrated over 2 minutes ( i n most cases) whereas drag measurements are obtained i n about 15 seconds. The l a t t e r more c l o s e l y approximate Instantaneous readings . IV DATA TREATMENT Ship Motion: The sextant headings on shore s tat ions and the data determining the shore s t a t i on pos i t ions were used to ca l cu la te the sh ip ' s v e l o c i t y during current measurements. These were a lso used to determine the large scale movements of the ship from hour to hour. The shore stat ions were arranged as "shown i n f igure 6, so that one angle ( 0^) was measured between two stat ions on one shore, and the other ( 82) on two stat ions one on e i ther shore. The r e l a t i v e pos i t ions of these s ta t ions were determined from the gyro compass f ixes and radar ranging . A three-armed protractor i s u s u a l l y used to p lo t ship movement or p o s i t i o n , but for short period movements the proctractor i s not as sens i t ive as the accuracy of the sextant readings warrants. By short term i s meant the ship movement i n the period of a current measurement (usual ly 2 minutes) . The fo l lowing describes the manner i n which the ship movement was determined. - 18 -- 19 -A change i n 6-^ i s a measure of the c r o s s - i n l e t movement and a change i n i s a measure of the a long- in le t movement. The movement, AS, i s re la ted to the mean of the two f ixes on the same s ta t ions , © , the distance between the two shore s ta t ions , L , and the change i n angle, A 0 , by the fo l lowing equation: A S = i (cosec 2 | ) ( AG) This equation appl ies to only one of the components of movement (ei ther cross or along the i n l e t ) and i s based on two assumptions: (1) that Z\S i s small compared to L , and (2) that the ship (point of observation) Is f a i r l y c lose to the r i g h t b i sec tor of the l i n e jo in ing the two shore s t a t i o n s . Any more rigorous formula to f i t the ac tua l s i t u a t i o n of s tat ions requires an uneconomical amount of labour for reducing the data . The sh ip ' s v e l o c i t y during current measurements was determined from the time between sextant f i x e s , ( the a c t i v a t i o n time of the current meter) and the distance the ship had moved as determined from the f ixes i n the above manner. The formula above was used to determine each component of the movement and these were combined to give a v e c t o r i a l displacement. Some information regarding the extent of ship movement or the long-period movement i s presented i n t h i s t h e s i s . For t h i s purpose the three-armed protractor was s u f f i c i e n t l y - 20 -accurate to present the p i c t u r e . Unfortunately, due to the rugged nature of the coas t l ine i n th i s i n l e t , there i s not too much choice i n the pos i t ion ing of shore s t a t i o n s . Thus the condit ions stated above are not exact ly met. For th i s reason the error i n the a long- in le t d i r e c t i o n i s put at 5 to 10 per cent . For the same type of reason the error invthe cross-i n l e t component of the ship motion must be put at 15 to 20 per cent . The reason for the large poss ible error i n the cross-i n l e t component l i e s i n the shorel ine i r r e g u l a r i t i e s . The s tat ions had to be placed so that , at times, the ship was f a r off the i d e a l r i g h t b i s e c t o r . Thus any cross-stream currents deduced from currents corrected fo r ship motion may include an error of the above proport ion (15 to 20 per cent) of the ship v e l o c i t y . There Is the assumption i m p l i c i t here that the meter moves with the sh ip . This i s an assumption that i s often made, but seldom j u s t i f i e d . The fo l lowing i s an attempt to put an upper l i m i t on the poss ible error that might be incurred by making the above assumption. I f the assumption does not ho ld , then there w i l l be r e l a t i v e movement between the meter and the sh ip . This would r e su l t i n a change i n the suspending wire angle from the v e r t i c a l or a change i n the angle at which the wire streams away from the - 21 ship ( provided the sh ip ' s heading i s not changed). Only the change i n wire angle from the v e r t i c a l w i l l be considered. During current measurements th i s wire angle was checked. A change i n angle of 5° would probably have been no t i ced . This angle i s used as a l i m i t of noticeable meter movement with respect to the sh ip . The maximum angle which would have gone unnoticed, combined with an average ship movement of 11 meters ( s ta t ion 5) over a meter a c t i v a t i o n i n t e r v a l of 2 minutes, shows that the meter must partake of at l eas t J5% of the ship movement when i t i s at a depth of 50 meters; or at leas t 50$ at a depth of 100 meters. At greater depths the above l i m i t of detect ion of wire angle change (5°) gives no guarantee that the meter w i l l move with the sh ip . Nevertheless the f u l l c o r r e c t i o n fo r the ship v e l o c i t y has has been applied throughout th i s data . Due to poor v i s i b i l i t y i t was not always poss ible to monitor ship motion. Por t h i s reason some of the data presented i s not corrected for ship motion. The Ekman reading i t s e l f was used i f no cor rec t ion was a v a i l a b l e . The percentage of uncorrected data for the f i r s t period at s t a t i o n 5 was 31%; at s t a t i on 3 1 / 2 i - f c was 2% and i n the second period of observations at s t a t i on 5 i t was 1%. These f igures give some reason to consider the data of the f i r s t period on s t a t i o n 5 as less r e l i a b l e than the data for the second period at the same s t a t i o n . 22 -Current Me astir erne nt s The currents obtained from the C . B . I , drag and from the deeper measurements were separated into a long-Inlet (conveniently east-west) and c r o s s - i n l e t components. For the C . B . I , drag measurements, r e s o l u t i o n in to components was ca r r i ed out only for d i rec t ions greater than 2 0 ° from the east-west l i n e because of the — 1 0 ° poss ible error i n the d i r e c t i o n estimate. The C . B . I , drag measurements were f i r s t p lo t ted as p r o f i l e s to determine the current at standard depths of 2 ,4 ,6 , 10, 15 and 20 meters, "Ekman meter readings were taken at set depths, .When the wire-angle was l a rge , r a i s i n g the meter above the set l e v e l , adjustment was made by paying out more wire . The ser ies of component values f o r each depth were then p lot ted on a time scale along with the t ide and wind cond i t ions . From these p lots and a smooth curve drawn through the currents obtained, a v e r t i c a l current p r o f i l e forvthe along-i n l e t component was constructed for each hour and the hourly p r o f i l e s p lot ted as a s e r i e s . The net current at each depth was determined by a 25 hour average of the above hourly va lues . The 25 hour average was used to eliminate the t ida l - currents . V RESULTS Ships Motion; A p lo t of the ships p o s i t i o n fo r successive f ixes on shore stat ions shows marked di f ferences between anchorages (figure 7)» Though movements may have been pecu l i a r to that p a r t i c u l a r ship they w i l l be a guide for future measurements and, of course, they are of s i gn i f i cance i n t h i s set of measurements. During the f i r s t period of observation on s t a t i on 5, the wind was zero or down-inlet and the surface current predominantly down-inlet . The ship moved on an arc of about 500 meters length, thus descr ib ing predominant shearing (side to s ide) motion. On two occasions i t sheared and surged (moved up on the anchor) v i o l e n t l y of f i t s s table a rc . These two periods were i n i t i a l l y associated with transverse, a l ternate bands of s l i c k and ru f f l ed surfaces moving up the i n l e t . I t i s bel ieved that these bands are due to progress ive, i n t e r v a l waves i n the lower boundary of the surface l a y e r . When the ship moved off the arc i t required one to three hours to r e t u r n to i t . - 23 -- 24 -During the second anchorage on s t a t i o n 5 , the wind and surface current conditions were d i f f e r e n t . The wind was always up-inlet, and the surface current reversed f a i r l y r e g u l a r l y . In t h i s instance the extent of ship motion was large, covering an e l l i p t i c a l region of 950 by 550 meters. The e l l i p t i c a l pattern was formed by two arcs and paths between them. The arc on the up-inlet end of thi s pattern i s of smaller length and of greater density of p o s i t i o n than the i l l - d e f i n e d arc on the down-inlet end. When the wind and surface currents are i n the same d i r e c t i o n the ship moves on the\smaller arc. The down-inlet end where wind and surface current were opposed showed an i l l - d e f i n e d arc as well as large movement from hour to hour. The frequency d i s t r i b u t i o n of the ship' vs speed f o r the two stations has been plotted In fi g u r e 8. The d i s t r i b u t i o n s are skewed as the ship's speed can apparently be great i n some cases. Here, again, a difference can be seen between stations 3^/2 and 5 . The mean ship speed at sta t i o n 31/2 was 4 . 5 centimeters per second and at s t a t i o n 5 about 7«5 centimeters per second. These two means have significance i n evaluating the necessity f o r monitoring ship motion during current measurements. In fi g u r e 9 there are plotted the Ekman readings as well as the corrected readings f o r both longitudinal and transverse components of a part of the series at stations 3^/2 - 25 -and 5. The cor rec t ion at s t a t i o n 3/2 i s r e l a t i v e l y sma l l . The cor rec t ion at s t a t ion 5 i s l a rger and predominantly i n the transverse component, A comparison of mean ship speed i n d i f f e rent wind, surface current and anchorage condit ions suggests that the mean ship speed increases w i t h : (1) increased wind, (2) decreased surface current , (3) increased depth at the anchorage, (4) l i g h t cross stream breezes ( markedly), (5) opposing wind and surface current . Cer ta in of these are obviously i n t e r r e l a t e d . In p a r t i c u l a r , i n estuaries where t i d a l currents are present at the surface, a shallow reg ion presents a smaller depth for the anchorage and usua l ly Increases the t i d a l currents . Both of these act i n the d i r e c t i o n towards decreased ship motion. When the wi nd and surface current tend towards the same d i r e c t i o n there w i l l a lso be a decrease i n the ship movement. In view of the large ef fect of wind stress on surface currents there i3 an increased tendency for the wind and the surface current to be i n the same d i r e c t i o n . - 26 -Desc r ip t ion of Currents . (1) S ta t ion 31/2, Ju ly 6 t h to 8th, 1956 A time ser ies p lo t of the l o n g i t u d i n a l component of the current (figure 10) shows strong o s c i l l a t i o n s up and down i n l e t . The times of peak currents and s lack water are h igh ly correlated with what might be deduced from the predicted t ide height curve. The o s c i l l a t o r y currents do not show a smooth s inuso ida l v a r i a t i o n . There are large i r r e g u l a r i t i e s at a l l depths of measurement. Though a mean amplitude of o s c i l l a t i o n cannot have much s ign i f i cance since the t ide i s a semi-diurnal mixed type , I t can be said that there was a mean range i n current of about 140 to 150 centimeters per second. Comparison of the range i n current at d i f f e rent depths shows that they were near ly constant at a l l depths with two exceptions and one dubious case. The dubious case involves the depth of 2 meters where the ef fect of the wind d i s tor ted the o s c i l l a t i n g currents making an estimate of current range d i f f i c u l t . The current range at 70 meters was reduced to about 105 centimeters per second or 70% of currents above I t . The f lood current at 40 meters during the second h a l f of the anchorage was remarkably reduced (figure 10 (b) ) to 30 or 40$> of the f i r s t f lood peaks In general I t appeared that the maximum f lood current was more subject to large f luc tua t ions wi th in one f lood than was the ebb. - 27 -The transverse component of the current p lot ted as a time ser ies ( f igure 11 ) shows asymmetry about a mean current at a l l depths. In general , the south component on the f lood was greater than the north component on the ebb. This statement does not apply to the measurements at 10 meters wherenet flow was n o r t h e r l y . The currents on the f lood and ebb did not d i f f e r i n d i r e c t i o n by 180 degrees. The mean ebb d i r e c t i o n at a l l depths over a f u l l 25 hours was between 270 and 2 8 5 ° true fo r the whole anchorage. The mean f lood at 10 meters was i n the d i r e c t i o n of 1 0 4 ° t rue . At 20 and 40 meters I t was about 1 2 5 ° , and at 60 and 70 meters i t was 1 3 5 ° t r u e . The l a s t 25 hours showed some change i n mean d i rec t ions of the f l o o d s . D i rec t ions at both 10 and 20 meters were 1 0 3 ° . At 40 meters i t was 1 5 5 ° , at 60 meters i t was about 1 3 5 ° (as before) and at 70 meters i t was 1 2 9 ° t r u e . The fo l lowing table summarizes t h i s data : F i r s t 25 hours Last 25 hours mean d i r e c t i o n Flood Ebb Flood Ebb depth  10 m. 1 0 4 ° true 2 8 6 ° 1 0 3 ° 278' 20 125 278 103 282 40 127 273 155 274 60 135 277 136 271 70 134 283 129 273 28 Deal ing now with only the l o n g i t u d i n a l component, i t i s seen that the p lo t of the ser ies of hour ly p r o f i l e s ( f igure 12) Is n a t u r a l l y d iv ided in to two per iods . The f i r s t const i tutes a period of no wind, and the second a period of varying u p - i n l e t winds. During the f i r s t period the column of water below 20 meters appeared to move as a un i t with a smaller amplitude of motion at 70 meters. The region above 20 meters appears more complicated. This may be an a r t i f a c t of observation s ince there was more de ta i l ed coverage i n th i s r e g i o n . Above 10 meters the f lood current was markedly less than that of the water below 20 meters. The ebb current i n the upper 20 meters was somewhat larger than the ebb below. There was a minimum i n the ebb at 4 to 6 meters. This was less evident on the f l o o d . During the second period there were varying u p - i n l e t winds with a maximum speed of 23 knots . There was considerable di f ference between the flow at the surface and at 40 meters. The near-surface current (2 meters depth) was reduced to zero on the ebb and was more than twice the deep current on the f l o o d . On the hour between the period of zero wind and the f i r s t recorded wind a reduct ion appeared i n the f lood current at 40 meters. There appeared to be no ef fect on the ebb current at t h i s depth. < 29 -There also appeared a minimum or down-inlet tendency for flow at about 10 meters which was most marked on the f l o o d . This ' d i r e c t i o n " of flow at th i s depth could be the cause of the apparent u p - i n l e t flow at 4 to 6 meters as described for the f i r s t pe r iod . This l a t t e r flow was ob l i t e ra ted by the wind currents during the second ha l f of the anchorage. The 25 hourly-value mean f o r each depth i s p lo t ted i n p r o f i l e for the f i r s t and l a s t 25 hours of the anchorage (f igure 13 ) . These two p r o f i l e s are quite d i f f e r e n t . Consider f i r s t the i n i t i a l mean p r o f i l e for which there was an average wind of 4 knots . There was net outflow at a l l depths of measurements down to 40 meters. The net flow at 60 and 70 meters was u p - i n l e t . There was a s i g n i f i c a n t minimum i n the outflow at 4 meters or a l t e r n a t i v e l y , a maximum i n the outflow at 15 meters. Turning to the f i n a l 25 hour period i t should be noted f i r s t that the mean wind fo r th i s period was 12 knots u p - i n l e t . The superimposed i n i t i a l mean flow shows the great change that took p lace . The surface flow to 6 meters was completely reversed. The outward flow at 10 and 15 meters was v i r t u a l l y unchanged, but at 20 and 40 meters the outflow had increased . The inflow at 60 and 70 meters had also been reduced. This resul ted i n a depth of no net motion at 55 to - 30 -60 meters rather than 40 to 45 meters as occurred during the f i r s t 25 hours. (2) S ta t ion 5 , Ju ly 4th to 6th, 1956 The time ser ies p lo t of the l o n g i t u d i n a l components of the current w i l l be considered f i r s t ( f igure 14). At 300 meters the o s c i l l a t o r y current was predominant but there were sporadic bursts super-imposed on i t . The o s c i l l a t o r y current was what one might deduce from the t ide height v a r i a t i o n . At 200 meters the same held true with regard to the o s c i l l a t o r y motion and i t s c o r r e l a t i o n with t i d e . I t appears that the I r r e g u l a r i t i e s i n the flow occur u s u a l l y on the f lood current . At 100 meters the i r r e g u l a r i t i e s near ly ob l i t e ra ted the systematic o s c i l l a t i o n s and at 50 meters the f luc tua t ions were incoherent but just as large as the systematic o s c i l l a t i n g currents at 100 meters. The mean range of currents was about 30 centimeters per second at 200 and 300 meters. This was s l i g h t l y reduced to about 24 centimeters per second at 100 and 50 meters. Before continuing with the currents i n the upper 20 meters the wind condit ions should be descr ibed. The anchorage can be d iv ided into two per iods ; the f i r s t period character ized by a 10 knot down-inlet wind and the second period by no wind. - 31 -Currents measured i n the upper 20 meters were much l a rger than those at the greater depths, ranging from 120 centimeters per second down-inlet to 45 centimeters per second u p - i n l e t . I t i s apparent that the net flow was down-i n l e t at a l l depths, the magnitude decreasing with increas ing depth. At the 2,4 and 6 meter-depths during the f i r s t h a l f of the anchorage there were u p - i n l e t surges i n current of 60 to 90 centimeters per second, l a s t i n g from 1/2 to 1 hour i n the hour before predicted high water. During the second h a l f of the anchorage th i s same feature resembled a step funct ion with the u p - i n l e t surge l a s t i n g 2 to 3 hours In the 3 hours before predicted h igh water. At 10, 15 and 20 meters there was an increas ing frequency of zero currents measured as depth increased. Currents at these 3 depths were sporadic, although they tended to coincide with the extremes i n current at the 2, 4 and 6 meter depths. The current range at the 2 meter depth was l a rger than at other depths. At 4 and 6 meters the range was about 75$ of that at 2 meters. At 10, 15 and 20 meters i t was 50$ of the range at 2 meters. The current range at lower depths i s only 25$ of that at 2 meters. - 32 -Turning to the transverse components at 50, 100, 200 and 300 meters (f igure 15) i t i s seen that the currents were h igh ly i r r e g u l a r and of the same magnitude as the l o n g i t u d i n a l components at the same depth. Inspection of the ser ies of hour ly p r o f i l e s of the l o n g i t u d i n a l components (f igure 16) reveals some i n t e r e s t i n g features . At the depths of 50 or 100 meters the f lood current appeared to s tar t e a r l i e r and then spread downward. This ea r ly f lood u s u a l l y s tarted after predicted high water and would not extend to 300 meters u n t i l predicted low water. There were two features associated with the period between low and high water. At 300 meters i n the middle of t h i s period a down-inlet surge i n the current of 1 to 2 hours durat ion took place i n 3 cases out of 4. In the smaller depths of 5 to 15 meters there appeared an u p - i n l e t current surge i n the 1 or 2 hours before predicted high water. Again th i s happened i n 3 cases out of 4. In th i s four th case an u p - i n l e t surge took place , but was observed at depths of 5 to 10 meters greater . The p r o f i l e s g iven by 25 hour means for the f i r s t and l a s t 25 hours are shown i n f igure 17. The f i r s t p r o f i l e corresponds to a period when there was an average down-inlet wind of 10 knots . The second period was one of no wind. - 33 -The f i r s t p r o f i l e shows net currents at 100, 200, and 300 meters which were barely s i g n i f i c a n t . An u p - i n l e t flow took place at 50 meters. There was a net flow down-Inlet at a l l depths to 20 meters with a p a r t i c u l a r l y strong flow down-inlet from the surface to 5 meters. There was a s i g n i f i c a n t minimum i n the down-inlet flow at 10 meters, or a l t e r n a t i v e l y , a maximum at 15 meters. The f i n a l period of 25 hours showed several changes. Net down-inlet currents from the surface to 20 meters were reduced. The minimum i n the down-inlet flow observed at 10 meters i n the f i r s t 25 hours had disappeared i n the l a s t 25 hours. The u p - i n l e t flow evident only at 50 meters during the f i r s t 25 hours, showed also at 15 and 20 meters i n the l a s t 25 hours . Net currents at 200 and 300 meters were again i n s i g n i f i c a n t , but at 100 meters there appeared a s i g n i f i c a n t net current ..down-inlet. (3) S ta t ion 5, Ju ly 8th to 11th, 1956 The time series p lo t of the l o n g i t u d i n a l component of currents (f igure 18) shows the o s c i l l a t i n g currents observed at the other s t a t i o n s . The currents at 50 meters and below were much l i k e those measured during the f i r s t anchorage with perhaps a somewhat greater range. The o s c i l l a t i o n s were more coherent i n the second h a l f of the period than i n the f i r s t . Again the currents at 100 meters were s l i g h t l y less coherent - 34 -than at 200 and 300 meters. Currents at 50 meters were, however, just as coherent as those at 100 meters i n contrast to the f i r s t anchorage. Currents at 200 and 300 meters were those one might deduce from the predicted t i d e , both In magnitude and phase; that i s , u p - i n l e t flow from predicted low water to high water and down-inlet flow from predicted high water to low water. The magnitude was i n reasonable agreement with the t i d a l prism, t ide r i s e s and the c ros s - sec t ion at the s t a t i on assuming that the t i d a l flow was uniform over the whole s e c t i o n . Before considering the currents i n the upper 20 meters, the wind condit ions should be i n d i c a t e d . During th i s complete period there was an u p - i n l e t wind, with the d i u r n a l c y c l e , to maximum speeds of 25 knots . Along with th i s change i n wind condit ions from the f i r s t anchorage there was a change i n the character of the currents i n the upper 20 meters. The o s c i l l a t i o n s were more near ly symmetrical about the mean current than before (compare f igures 18 (a) and 14 (a)) . The mean current i s also seen to reverse during about 24 hours i n the middle of the per iod . The o s c i l l a t i o n s were not those one might expect from the predicted t i d e , i f these are defined as above. The magnitude i s to great and there i s a 9 0 ° phase l a g . The range of current i n the l o n g i t u d i n a l d i r e c t i o n var ied with depth. I f the range at 2 meters i s taken as 100 - 35 -per cent, then at 4 meters i t was 100 per cent,, at 6 meters i t was 90 per cent ,at 10 meters 75 per cent, at 15 and 20 meters 50 per cent and about 25 per cent at 50 meters and below. The transverse component at depths of 5 0 , 100 , 200 and 300 meters (figure 19) was i r r e g u l a r with poss ib ly a l arger amplitude at 50 meters than at the greater depths. In contrast to the f i r s t period of measurements the amplitude of f luc tua t ions of the transverse ( c ro s s - in le t ) component was one h a l f or less that of the l o n g i t u d i n a l component. This di f ference between the two periods of observation may be due to the fac t that a greater percentage of measurements f o r the second period had data ava i l ab le to correct for ship motion. Turning to the hourly p r o f i l e s (f igure 20) of the l o n g i t u d i n a l component there i s seen to have been a f a i r l y consistent pattern for the f i r s t h a l f of the p e r i o d . Any time during the three hours before predicted high water there appeared a strong f lood current from the surface to 20 meters. The water at 200 and 300 meters was i n the l a s t stage of f lood when t h i s surface flow began. At the same time as th i s f lood took place at the surface there occurred a down-inlet current at 50 and 100 meters. As the predicted t ide passed h igh water the down-inlet current spread to the 200 and 300nne te r depths and the surface u p - i n l e t flow deepened to about 50 meters. Midway between high and low water the surface u p - i n l e t flow - 36 -stopped or reversed to a small dow-inlet flow so that fo r the remainder of the predicted ebb the whole column was moving down the i n l e t . There was a f a i r l y consis tent flow for the remainder of the predicted ebb at depths of 50 meters and more. During th i s l a s t per iod , though, the surface down-i n l e t currents had speeds from zero to 75 centimeters per second. During the second h a l f of the period the flow at 50 meters depth and greater followed the above pat tern , but i n the surface 20 meters the flow deviated from that described above. The u p - i n l e t flow was l a te and at a greater depth. I t a l so pers i s ted into the second ha l f of the ebb as ca lcula ted from the predicted t ide he ights . Three 25 hour means are p lot ted i n f igure 21. These cover the f i r s t , middle and l a s t 25 hour per iods . Since there were only 68 hours of observation there i s some small overlap of data i n these means. In a l l three p r o f i l e s there was a s i g n i f i c a n t u p - i n l e t flow at a depth of 300 meters. At 200 meters a net down-inlet flow became s i g n i f i c a n t i n the middle and l a s t p r o f i l e s . At 100 meters there was a marked down-inlet flow i n a l l 3 p r o f i l e s . At 50 meters the net flow was not s i g n i f i c a n t . At some depth between 50 and 20 meters there was a 'depth of no mot ion ' . It was probably c loser to 50 meters. This 'depth of no motion' separated the net down-inlet flow at - 37 -100 meters and the net u p - i n l e t flow at 20 meters. The upper boundary of t h i s u p - i n l e t flow cannot be placed too accurate ly as i t appears that the wind has a d i r e c t ef fect on flow down to perhaps 15 meters, thus penetrat ing to the reg ion of th i s boundary. The f i r s t 25 hours was a period with a mean up-i n l e t wind of 14 knots . Here there was s t i l l a net down-i n l e t flow from 2 to 15 meters, though the flow at 20 meters was u p - i n l e t . In the middle p r o f i l e the average wind had increased s l i g h t l y and had been blowing for a longer period of time. The flow i n the upper 20 meters was a l l u p - i n l e t although there appeared to be two flows separated by a minimum u p - i n l e t flow at 6 meters. Turning, then, to the l a s t p r o f i l e i t i s seen that the surface flow was down-inlet despite a continuing average wind of 16 knots up the I n l e t . The maximum down-inlet flow i n th i s l a s t p r o f i l e was at 4 and 6 meters rather than c lose to the surface ( 2 meters ) as was noted i n the net currents of the f i r s t 25 hours . VI DISCUSSION Technique; (1) Design of the experiment: P r i m a r i l y th i s experiment was ca r r i ed out to determine the general c h a r a c t e r i s t i c s of the currents i n the i n l e t . For a given amount of time, manpower and instrumentation an optimum programme was designed. A balance was struck between the number of depths of measurement and the frequency with which measurements at one depth could be made. There was the choice of e i ther making frequent measurements at c l o s e l y spaced depths i n some layer of p a r t i c u l a r i n t e r e s t , or of spreading the number of depths of measurement over the whole column of water. Since a general p ic ture was desired the l a t t e r course was taken i n the deeper waters. In the surface layer the former course was undertaken for two reasons. I t was recognized that water i n th i s l ayer often showed large var i a t ions i n current w i t h i n ; a small depth. The sharp gradients i n water propert ies appear to be re l a ted to these v a r i a t i o n s . Perhaps the greatest impetus towards the more deta i led study of the surface l ayer was the fact that the C . B . I - 38 -- 39 -current drag could provide the information e a s i l y and q u i c k l y . In support of the large separat ion between measuring depths i n the deeper water (100 meters at s t a t i o n 5) i t may be said that the small and smooth gradient of water propert ies argues fo r some uni formity i n water movement. The choice of the s tat ions to be occupied for current measurements and the choice of the p o s i t i o n i n the width of the channel present two other problems i n the experiment des ign. S ta t ion 5 was chosen to give information about the water movement at depth behind the s i l l . S ta t ion 3^/2 Is the s i l l p o s i t i o n and represents a markedly d i f f e rent i n l e t charac-t e r i s t i c from s t a t ion 5. With a s ingle ship to cover a whole cros s - sec t ion of the i n l e t , i t was l o g i c a l to anchor close to mid-channel. With the choice of a long, s t r a ight reach i t was hoped that eddy structures or any current pat tern showing asymmetry about the i n l e t cent re - l ine would be avoided. This was not e n t i r e l y r e a l i z e d . The current data suggests that the ship, p o s i t i o n was not representing the whole c ro s s - s ec t ion . In add i t ion , from observations of debris and foam f l o a t i n g on the water, i t was found on occasion that the surface currents could be quite d i f f e rent across the i n l e t . In one instance i t seemed that the flow across two th i rds of the i n l e t was one d i r e c t i o n while i n the other t h i r d i t was i n the opposite d i r e c t i o n . - 40 -(2) Ship Motion: In previous data i t had been recognized that ship motion might contr ibute a large proport ion of the current meter read ing . The 1956 data bears t h i s out _ e s p e c i a l l y f o r the deep s t a t i o n , number 5« I f the mean speed for ship motion i s compared with the maximum h a l f range of currents measured at each s t a t i o n , some idea of i t s importance can be determined. Por s t a t i o n 5 the mean ship speed during current measurements was 7»5 centimeters per second compared with a h a l f range i n current of 15 centimeters per second. Here, then, was a mean ship speed that was 50 per cent of the maximum currents measured . C l e a r l y cor rec t ion must be made and the cor rec t ion must also be determinded accurate ly . In the case of s t a t i o n 3^/2 more favourable condit ions existed which put the mean ship speed at only 4»5 centimeters per second compared with a h a l f range i n currents of about 70 centimeters per second. The ship speed, therefore , averaged 7 per cent of the current speed, a f ac tor of 7 bet ter than the cor rec t ion for s t a t i o n 5« These two comparisons give r i s e to three conclus ions . F i r s t , the Ekman current meter readings at s t a t i on 3"^ /2 are l i t t l e affected by ship motion. Therefore the accuracy of determination of the ship movement i s not so c r i t i c a l . A l so , data taken at th i s s t a t i o n i n previous years can be used wi th - 41 -confidence even though no ship movement was determined. Secondly, currents indicated by the Ekman meter on s t a t i o n 5 must be viewed c r i t i c a l l y . Then i t i s noted that only 6 9 $ of Ekman measurements were corrected fo r the f i r s t anchorage on s t a t i o n 5 compared with 9 9 $ on the second anchorage, i t i s c lear that the data for the second anchorage i s more r e l i a b l e . T h i r d l y , as mentioned i n the preceding paragraph, the ship movement at s t a t i o n 5 i s a large proport ion of the Ekman meter readings . Therefore the accuracy of the currents obtained by cor rec t ing the Ekman readings i s l a r g e l y determined by the accuracy with which the ship movement i s known. C e r t a i n l y the accuracy i n the ship v e l o c i t y c a l c u l a t i o n i s much less than the Ekman current meter accuracy. In p a r t i c u l a r , the cross-stream components of currents at s t a t i o n 5 are i n greater doubt than the l o n g i t u d i n a l components. For t h i s reason, l i t t l e s i gn i f i cance was placed i n i n d i v i d u a l values or means of the c r o s s - i n l e t component at s t a t i on 5 . For the reason just stated i t seems advisable to attempt to improve the technique of determining the ship movement when anchored at stations;: such as s t a t i o n 5* At such a s t a t i o n the speed of ship movement i s of the same order as the currents to be measured. - 42 -(3) Comparison of Ekman and C . B . I , drag readings at the same depths: As mentioned i n the d e s c r i p t i o n of the instruments, i t was not advisable to use the Ekman meter above 20 meters depth due to . the poss ible magnetic effects of the ship on the d i r e c t i o n i n d i c a t i o n . A l so , the C . B . I , drag was'used i n currents and depths for which the device has not been c a l i b r a t e d . Por these reasons i t was deemed advisable to check one device against the other . While anchored at s t a t i o n 3 1 /2 , both Ekman meter and C . B . I , drag measurements were made at 10 and 20 meters. These measurements were not made simultaneously but merely i n the regular schedule of operations as out l ined i n the procedure. That i s , a current p r o f i l e to 20 meters was taken every h a l f hour on the hour with the C . B . I , current drag, and the Ekman meter was used at 10 and 20 meters shor t ly after the C . B . I , drag current p r o f i l e taken on the hour. The p lo t of both Ekman and C . B . I , drag measurements (the along- i n l e t component) are shown i n f igure 22. In general , the peak currents indicated by the Ekman meter were less than those indicated by the drag. Since current i n the upper 20 meters i s u sua l ly u n i d i r e c t i o n a l , i t appears that drag on the wire has introduced an appreciable e r r o r . That i s , the formula based on just the drag on the biplane does not - 43 -represent the t o t a l drag on the system. The above conclus ion was reached from cons iderat ion of the t ime-series p lo t of the two sets of current data , however, an ef fect re la ted to th i s was apparent i n another c a l c u l a t i o n . In order to determine the mean current p r o f i l e s , a 25 hourly-value running mean was ca lcula ted for currents at a l l depths. This included both Ekman meter and G.B . I , drag readings separately fo r the 10 and 20 meter depths where these overlapped. There was a di f ference i n the trend of the means indicated by the C.B . I , drag and Ekman meter measurements (see f igure 2 3 ) . I t i s seen i n the measurements at 20 meters that the trend of the means fo r the Ekman meter measurements were i n opposite d i r e c t i o n s . Any conclus ion as to the depth to which the wind e f fect had d i r e c t l y penetrated w i l l perhaps hinge on which trend i s the correct one. There Is no way i n which to carry out any systematic error c o r r e c t i o n In Ekman meter readings as poss ib le errors recognized cannot be evaluated. The di f ference between the Ekman meter and C.B . I , drag averages was i n a d i r e c t i o n indicated by the d i r e c t i o n of the mean flow above the p a r t i c u l a r depth, at which measurements were compared. The wire on which the C.B . I , drag i s suspended Is i n th i s flow above the depth of measurement. There i s a drag on the wire due to th i s - 44 -f low. I f th i s drag on the wire i s s i g n i f i c a n t then the C . B . I , drag measurement means would deviate from the true average i n the d i r e c t i o n of the mean flow above the depth of measurement. This i s the d i r e c t i o n i n which the means of the C . B . I , drag measurements deviate from the means of the Ekman meter measurements. A cor rec t ion for th i s wire drag can be appl ied to the C . B . I , drag measurements. A formula d i r e c t l y r e l a t i n g the current at one depth to the angle measured at the surface cannot be simply stated i f drag on the wire i s s i g n i f i c a n t . This i s because the drag on the wire depends on the strength of the current between the surface and the depth of measurement. The currents given by the equation developed by Burt and Pr i tchard (1951) were f i r s t p lot ted for each p r o f i l e , Then a non-uniform gr id of rectangles based on an equation developed below, provided a c o r r e c t i o n to the square of the v e l o c i t y given by the s imp l i f i ed equation deduced by Burt and P r i t c h a r d . This c o r r e c t i o n was applied every 5 meters to success ive ly correct the p r o f i l e i n 5 meter in te rva l s from the surface down to 20 meters. The development of the formula on which the g r i d was constructed i s out l ined below. F i r s t , the equation developed by Burt and Pr i tchard i s reviewed. Referr ing to the force diagram i n f igure 5. - 45 -tan 0 = P/W (1) where P i s the drag force on the b ip lane , W i s the weight of the drag i n water and 0 i s the angle measured at the surface . Now, 2P = C D P A Q> v (2) where C D P i s the drag c o e f f i c i e n t of the b ip lane , A i s the area of the b ip lane , Is the densi ty of the f l u i d and v i s the actual v e l o c i t y at the depth of measurement. Henee the v e l o c i t y , V, g iven by cons iderat ion of only the drag on the biplane i s , V= ( 2 W / C D P A p q ) ) ^ (tan e) ' y* (3) This i s not the ac tua l v e l o c i t y because the drag on the wire has not yet been considered. In considering the drag force on the wire , there i s added to P another force N, g iven by, 2 N = c d w ^ d r v z 2 d - z ( 4 ) where N i s the force due to the drag on the wire , C D W i s the drag c o e f f i c i e n t of the wire, d i s the diameter of the wire , h i s the depth of measurement and z i s depth measured downward from the surface. Only the v e r t i c a l p ro j ec t ion of the wire, perpendicular to the current , i s considered here . - 46 -Then as f a r as the angle measured at the surface Is concerned the angle i s g iven by the balance of T,W and P plus N. Hence, P + N tan 6 = — ^ — (4) Subs t i tu t ion of equations (2) and (4) in to equation (5) produces, ? t a n e = 2 w + T T \ a? ( 6 ) o Now © was the angle measured and i s r e l a t ed to V by equation ( 3 ) . Therefore, Cdp A o V 2 9 h o o ^dw^ r n p '.This equation provides the c o r r e c t i o n . The-drag c o e f f i c i e n t for the 3/32 i n c h , stranded, s t ee l wire used i s not p r e c i s e l y known. However, i t i s known that for currents of the magnitude measured the drag c o e f f i c i e n t fo r a smooth cy l inder i s between 1 .0 and 1.1. The f ac t that the s t e e l wire was stranded and therefore rougher may ind ica te a s l i g h t l y higher drag c o e f f i c i e n t . Lacking exact measurements, the value was put at 1 .2 fo r the purpose of c a l c u l a t i o n s . This Is the same value as that used for the b ip l ane . This c o r r e c t i o n was ca r r i ed out f o r the C . B . I , drag measurements and the r e su l t s are shown i n f igure 23 - 47 -There s t i l l remains some discrepancy between the Ekman averages and the corrected C.B . I , averages, though agreement i s considerably improved. Other errors can pos s ib ly account for these d i screpancies . I t i s poss ible that the drag c o e f f i c i e n t fo r the wire may be appreciably d i f f e rent from 1.2 . Weights are added to the drag and the area which they present to the current i s not considered. A twenty pound weight has a c ros s - sec t ion of 97 square centimeters compared with 1,390 f o r the b i p l a n e . This i s a poss ible 6% e r r o r . L i f t on the wire has also been neglected. I t has a tendency to reduce the weight, W. An estimate of t h i s error can be made considering an average angle measurement of 30° for measurements at s t a t i on 3^/2. Assuming a uniform v e l o c i t y from the surface to the depth of measurement the l i f t i s found to be about 7$ of the weight of the drag. Currents . (1) S ta t ion 3V2 Currents at a l l depths at s t a t i o n 31/2 showed an o s c i l l a t i n g component superimposed on a mean f low. These o s c i l l a t i n g currents were of the same range at a l l the depths of measurement with the poss ib le exception of the depth nearest the bottom, where i n s u f f i c i e n t data provides room for uncer t a in ty . - 48 -The o s c i l l a t i n g currents showed peaks at times midway between predicted h igh and low water and, apart from net f low, showed s lack water or zero current near times of predicted high and low water. These facts are strong evidence that flow at fche s i l l i s t y p i c a l of channel flow and that the o s c i l l a t i n g currents are due p r i m a r i l y to the r i s e and f a l l of the t ide i n the i n l e t . Further evidence for th i s l a s t statement w i l l be presented below i n the d i scus s ion of transport through the s e c t i o n . The general c h a r a c t e r i s t i c s of the mean flow on which the o s c i l l a t i n g currents were superimposed did not remain the same throughout the period of observat ion. Large changes took place as indicated i n f igure 13. In comparing the f i r s t and l a s t 25 hours of the anchorage, s i g n i f i c a n t changes are seen to have taken place at a l l depths except 10 and 15 meters, the flow was completely reversed, changing from down-inlet to up-i n l e t . This change i s a t t r ibuted d i r e c t l y to the wind stress exerted at the surface. At 20 meters and a l l greater depths the change i n flow was i n a d i r e c t i o n opposite to the change i n surface l a y e r . I t appears that t h i s may be an i n d i r e c t ef fect of the wind s t re s s . The magnitude of the change at depth i s s u f f i c i e n t to compensate for the flow r e v e r s a l i n the surface . Further evidence po int ing to these changes at greater depths, as an - 49 -effect r e l a ted to the wind, i s the fac t that the marked change In the f lood current noted at 40 meters was h igh ly corre la ted with the onset of the wind. There i s no obvious reason why th i s marked change i n the character of the f lood current sho-gld take place at 40 meters. The net currents at the greatest depths (40 , 60 and 70 meters) changed i n the same d i r e c t i o n with a s l i g h t l y l a rger change at 40 meters. Thus, although the ef fect at 40 meters was more not iceable , the change i n the net current i s comparable at a l l 3 of these depths. From th i s period of observation i t appears that there i s inflow at the bottom and outflow at mid-depths. In the surface the mean current i s down-inlet when there Is no wind but can be reversed i f a strong u p - i n l e t wind i s blowing. When one considers the net flow deduced from the s a l i n i t y s tructure i n the i n l e t , i t i s seen that the observed net flow d i s t r i b u t i o n with depth i s not the same. From the s a l i n i t y s tructure I t was deduced that outflow must take place In the low s a l i n i t y upper l ayer and inflow at some depth below t h i s . The point at which th i s and the observed net flow diverge i s i n the fac t that outflow pers i s t s down to a depth of 45 to 50 meters - - w e l l below the low s a l i n i t y upper l a y e r . I t i s quite poss ible that the mean flow i n th i s reg ion near the s i l l , , i s not p r i m a r i l y determined by the densi ty d i s t r i b u t i o n , - 50 -but more by the jet ef fects of a c o n s t r i c t i n g cros s - sec t ion and attendant ampl i f i ca t ion of t i d a l currents . Topography may also inf luence the flow i n th i s r eg ion . The d i scus s ion so far has deal t with only the a long- in le t components of the current . However, there are large c r o s s - i n l e t components of the current which, when averaged, ind ica te new flow towards the side of the i n l e t . The best demonstration of th i s feature i s In the mean d i rec t ions of the f lood and ebb at the depths of 10, 20, 40, 60 and 70 meters (see table i n d e s c r i p t i o n ) . The current d i rec t ions on f lood and ebb do not d i f f e r by 1 8 0 ° . Ebb d i rec t ions at a l l depths l ay between 271 and 2 8 6 ° t r u e . At 10 meters on the f lood i t was very close to 1 0 4 ° ( i . e . 1 8 0 ° d i f f e rent ) but at 20 and 40 meters i t was 1 2 5 ° and at 60 and 70 meters i t was about 1 3 5 ° t rue . There i s an increas ing southward set of the f lood current as the depth increases . The s l i g h t northward set of the ebb currents was consistent with the southern shorel ine of the i n l e t from the east to Prominent Point (see f igure 4 ) « The topography may expla in the southward set of the f lood currents and pos s ib ly i t s v a r i a t i o n with depth. The axis of the outer bas in i s i n c l i n e d to the axis of the inner bas in A current f lowing u p - i n l e t i n the outer bas in reg ion i s p a r t i a l l y trapped i n the shallow of Hoeya Sound and L u l l Bay (see f igure 4) . Water escaping from t h i s reg ion must flow around Boulder Point with a southward component. This would def lec t the f lood - 51 -currents to the south* There was a b ig di f ference between f lood current d i rec t ions i n the f i r s t and l a s t 25 hours at depths of 20 and 40 meters. At 20 meters i t changed from 1 2 5 ° to 1 0 3 ° t r u e . Thus i t was al igned p a r a l l e l to the current d i r e c t i o n at 10 meters i n the l a s t 25 hours. This could poss ib ly be an i n d i c a t i o n that the wind stress at the surface has a d i r e c t inf luence to a depth of 20 meters. The change In the magnitude of the mean current between the f i r s t and l a s t 25 hours indicated a near ly s i g n i f i c a n t change i n the d i r e c t i o n opposite to that of the wind s t ress , which would seem to contradic t the above statement. However, the mean current applies to a complete t i d a l c y c l e , while the" angles were ca lculated only from e i ther the f lood or ebb current v e l o c i t i e s . I t i s poss ib le that the wind stress could penetrate deeper during currents which were p a r a l l e l to i t (flood i n th i s case) than during currents which opposed i t . At 40 meters the change i n the flow i s marked i n the d i r e c t i o n of the f lood current aa we l l as i n the increase i n magnitude of the mean flow down the i n l e t . Both of these appear to be due to only one phenomenon, a decrease i n magnitude of the l o n g i t u d i n a l component of the current on the f l o o d . This means that the ef fect was probably not an i n t e n s i f i c a t i o n of the southward set of the f lood , but another e f fect d i rec ted down-inlet along the axis of the Inner bas in to the west and operating only - 52 -during the f lood per iod . There i s no obvious explanation fo r t h i s type of e f f e c t . (2) S ta t ion 5: As at s t a t i on 3 1 / 2 , the currents were character ized by an o s c i l l a t i n g current superimposed upon a mean current . At th i s s t a t i o n , however, the currents were not near ly as r e g u l a r . The magnitude of the o s c i l l a t i n g currents at 50, 100, 200 and 300 meters were only one quarter the magnitude at 2 meters. The currents at d i f f e rent depths did not occur with the same phase. In general there appears to have been two d i f f e r i n g regions , surface and deep, separated by a broad boundary reg ion from 20 to 100 meters. The confused nature of currents at 50 meters may be due to the fac t that th i s depth i s i n t h i s t r a n s i t i o n reg ion . As noted i n the d e s c r i p t i o n , the currents at 50 meters were of the same magnitude as those at greater depths, but d id not show any systematic o s c i l l a t i n g component. The deeper region w i l l be deal t with f i r s t . The fo l lowing comments apply to currents at 300 and 200 meters, and to a le s ser degree to those at 100 meters. At these depths the currents were o s c i l l a t o r y and superimposed on a very small net current . The s lack water coincided with predicted high and low tlde^ suggesting that these currents were caused by t i d a l f o rce s . Further^'support fo r th i s idea i s found i n the magnitude of the o s c i l l a t i n g currents . These magnitudes are i n agreement with t i d a l currents ca lcula ted assuming l a t e r a l uni formity and - 53 -and uni formity with depth for t i d a l flow to f i l l or empty the In le t according to the predicted t i d e he ights . Turning to the upper l a y e r , there was found to be an o s c i l l a t i n g current , but the current had a range at 2 and 4 meters four times l a rger than the t i d a l currents ca lcula ted as above. The range i n the o s c i l l a t i n g currents decreased with depth. These o s c i l l a t i o n s were not i n phase with movements at depth, but d id occur i n a systematic fashion re la ted to the predicted t ide he ights . Whatever mechanism or mechanisms were present to cause the flow i n the surface l ayer , there was c e r t a i n l y a strong component with a t i d a l p e r i o d . The v e r t i c a l p r o f i l e s of the net currents show three consistent features that are d i s t r i b u t e d In depth and may be re l a ted to the two flow regimes of o s c i l l a t o r y current s . S ta r t ing at the surface there was found to be outflow except when a strong u p - i n l e t wind was blowing. There was inflow below th i s surface layer extending to below 50 meters and at 100 meters there was a down-inlet flow that slowly but s t e a d i l y increased over the course of the week of measurements. The f i r s t two have an explanation as described i n the i n t r o d u c t i o n . The runoff must escape i n the surface l ayer and the r e t u r n (up- inlet ) flow of s a l t water below t h i s apparently extends just to about 50 meters. The average transport for the two periods of current measurements fo r depths down to 50 meters, - 54 -i s d i s t r i b u t e d as f o l l o w s : Fresh water i n the upper 10 m. - 600 cu.m./se;c, down-inlet Sa l t water i n the upper 10 m. - 1700 " " " " " Sa l t water at 10 to 50 m. - 1200 " " ° up- i n l e t I t i s seen that there was not s t r i c t balance of s a l t water. There was, however, a l ack of adequate coverage by measurements at depths between 20 and 50 meters where a large part of the u p - i n l e t moving s a l t water appeared to be. I t i s f e l t that errors due to l i n e a r i n t e r p o l a t i o n between these points may e a s i l y account for the apparent unbalance of s a l t . There i s no explanation for the we l l developed down-i n l e t flow observed at 100 meters. I t can only be pointed out that th i s flow was corre la ted with a complete change i n the wind stress at the surface, from down-inlet to u p - i n l e t . There was also a c o r r e l a t i o n with the t r a n s i t i o n from neap to spr ing t i d e s . (3) Tides and t i d a l currents , No t ide s tat ions were set up i n conjunct ion with these current measurements. For th i s reason currents have been re la ted to the predicted t ide at A l e r t Bay. Comparison of the ac tua l t ide record at A l e r t Bay with the predicted t ides shows excel lent agreement. - 55 -Previous studies i n i n l e t s have shown v i r t u a l l y no time lead or l ag i n the t i d a l r i s e along the whole length of an i n l e t , though there may be a d i f ference i n the t ide range (Dawson, 1920). This study i s r e f l e c t e d i n the present t ide tables which give no time di f ference between A l e r t Bay and Glendale cove ( see f igure 2 f o r i t s pos i t ion) and a mean r a t i o of r i s e of 1.15 f o r high t i d e s . For these reasons i t i s f e l t that any current that i s p r i m a r i l y t i d a l i n character w i l l be d i r e c t l y re la ted to the r i s e and f a l l of the t ide as p red ic ted . This was the case at a l l depths of measurement at s t a t i on 3^/2 and at the greater depths at s t a t i o n 5. A s i g n i f i c a n t r e s u l t of these experiments was the discovery of t i d a l currents wel l below the depth of the Inner s i l l (67 meter s i l l depth) i n the inner ba s in . The currents at s t a t i o n 5 i n the 20 meter surface l ayer appear not to have been a d i r e c t e f fect of the r i s e and f a l l of the t ide i n the i n l e t i f the assumption of cross-sec t ion uni formity of t i d a l currents i s c o r r e c t . They were out of phase with the ca lcula ted t i d a l currents , though the var i a t ions were systematic and had a t i d a l p e r i o d . Estimates have been made of the depth of t i d a l inf luence by only considering the amplitude of currents at the surface ( T r i t e s , 1955)* This data suggests that th i s i s not a v a l i d procedure at such stat ions as Knight 5. - 56 -There i s the question of whether t i d a l currents should be a smooth funct ion of t ime. Tide height curves appear to be smooth i n most cases, but t i d a l currents , ( the rate of the change of t ide height curve) are not neces sar i ly so. A check was made of the slopes of the ac tua l t ide records fo r th i s period of observat ions . The smallest time i n t e r v a l over which a slope could be accurate ly obtained was 10 minutes and even with this. ' 10 minute slope i t was evident that t i d a l currents are not smooth functions of time and c e r t a i n l y do not adhere to a s inuso ida l curve . Peaks tend to be f l a t tened and " s lack water" i s a period of sharp current burs t s . The data show th i s c l e a r l y , e s p e c i a l l y the data taken ha l f -hour ly with the C.B . I , drag ( see f igures 10 (a), 14 (a) and 14 (b) ). (4) Wind E f f e c t s : There were long periods of wind during a l l three anchorages. I t i s obvious from the v e r t i c a l p r o f i l e s of net currents that the wind stress had a large d i r e c t e f fect on the surface current s . The flow of water at the surface wa3 both accelerated and impeded - even reversed- during the period of these observat ions . Reversal of the surface current i s shown i n a comparison between the f i r s t and l a s t 25 hours on s t a t i o n 3 -^/2 (f igure 13) and between the f i r s t and middle 25 hours of the second anchorage on s t a t i o n 5 (f igure 21). The acce lera t ion of near-s'urface flow i s c l e a r l y shown - 57 -i n the period of down-inlet wind ( f i r s t 25 hours) on the f i r s t anchorage at s t a t i o n 5 ( f igure 17). A comparison of the net currents at the surface i n the middle and l a s t p r o f i l e s f o r the second anchorage at s t a t i o n 5 shows a l i m i t to which wind can af fect surface current s . Apparently between these two periods the flow near the surface has returned to the down-inlet d i r e c t i o n despite the fac t that a strong u p - i n l e t wind was s t i l l blowing. Here i s evidence that the wind stress can only reverse surface flow for a l i m i t e d time. It appears from the data that there was a pressure gradient b u i l t up w i t h i n 30 hours to balance the wind stress due to an average wind of 16 knots . The data suggests that the depth of d i r e c t inf luence of the wind can be quite v a r i a b l e . When the magnitudes of mean currents are considered, i t i s found that the wind appears to have had a d i r e c t inf luence down to only 6 meters at s t a t i o n 3^/2. Current d i r e c t i o n data at the same s t a t i on suggests that th i s d i r e c t e f fect may have penetrated to 20 meters, though the change i n magnitude of mean current at th i s depth, i f s i g n i f i c a -nt , was i n the opposite d i r e c t i o n to the wind s t re s s . Since the d i r e c t i o n data was obtained by consider ing f lood and ebb currents separately and the mean currents i n a 25 hour per iod , the apparent cont rad ic t ion may not e x i s t . I t seems poss ible that the wind stress could have had an inf luence to a greater - 58 -depth on the flood than on the ebb. This could be due to a change i n the water structure (density gradients) with the state of the t i d e . Turning to data from s t a t i o n 5, there i s seen to be large d i r e c t effects down to at least 20 meters. The reason f o r the difference between stations 3^/2 and 5 i s l i k e l y the difference i n water structure at the two stations. There i s evidence f o r i n d i r e c t effects of the wind stress. Some flows, such as those at 40 meters on s t a t i o n 3^/2 and at 100 meters on st a t i o n 5 underwent changes that were correlated with changes i n the wind stress at the water surface. The change i n the flood flow at 40 meters on s t a t i o n 31/2 i s thought to be strong evidence f o r i n d i r e c t influence of the wind. The flow at 100 meters on s t a t i o n 5 i s not considered to be as strong evidence f o r t h i s phenomenon. I f flows at these depths were influenced by the wind, i t appears that the flows were of a compensatory nature. That i s , t h e y changed i n the d i r e c t i o n opposite to that of the change i n the wind. (5) Hourly Transports: The hourly current p r o f i l e s obtained were used to calculate a transport through the i n l e t cross-sections at the stations. The assumption of l a t e r a l uniformity was made i n order to calculate t h i s . This i s related to the assumption made i n cal c u l a t i n g t i d a l currents. In the l a t t e r case i t was - 59 -assumed that the t i d a l current would be uniform across the whole s e c t i o n . Then the hour ly p r o f i l e s plus the best c ros s - sec t ion p r o f i l e obtainable (see f igure 3) provided an estimate of the transport at every hour. A table method was used to ca lcu la te the transport from the currents at the p a r t i c u l a r depths. L inear In terpo la t ion between observed currents i s implied i n th i s method. The re su l t s for a l l three anchorages are shown i n f igure 24. In add i t ion to the observed points there i s p lot ted a s o l i d l i n e denoting a ca lcula ted transport with which to compare the observed t ransport s . This ca lcu la ted transport was determined from the predicted t ide heights , the t i d a l prism,and assuming that the t i d a l current was uniform across the sect ion and that i t var ied s i n u s o i d a l l y . There has been support fo r these assumptions i n the magnitude of o s c i l l a t o r y currents observed (see d i scus s ion of t ides and t i d a l currents above) and there i s further support for them i n the observed transports at s t a t i o n 3^/2, Observed transports at s t a t i on 5 do not support the above assumptions. The f igure shows a d i f ference i n agreement of observed and ca lcula ted transports between data at s t a t i o n 3 1/ 2 a n d 5* For s t a t ion 3 1 / 2 there was very close correspondence between ca lcula ted and observed t ransport s . This i s interpreted as a reasonable assurance that currents - 60 -near mid-channel at s t a t i o n 3^ /2 are representat ive of the t o t a l c ro s s - sec t ion . The i r r e g u l a r i t i e s that showed i n the currents at i n d i v i d u a l depths were not evident i n the observed t ransport s . This i s due to averaging over the whole water column. The transports at s t a t i o n 5 are f a r from agreement with the ca lculated curve. Periods of f lood and ebb can be recognized, but that i s about a l l . The v a r i a t i o n i s not s inuso ida l and shows large f l u c t u a t i o n s . This i s taken as evidence that flow across the sect ion i s not l a t e r a l l y uniform. There may have been concentrations of the current (to one side of the i n l e t or at some p a r t i c u l a r depth) w i t h i n the cross s e c t i o n . There has been some further evidence for both l a t e r a l uniformity and l a t e r a l non-uniformity i n surface currents . Experiments with photography of l i n e s of dye stretched across i n l e t s (Pickard,1953) have shown a f u l l range of condi t ions . Some resu l t s show a f a i r l y uniform flow across the i n l e t with the exception of regions close to shore. In other instances smal l , l o c a l i z e d jets have appeared. The l a t t e r could complicate transport ca lcu la t ions based on current measurements taken at just one p o s i t i o n i n the i n l e t . I f current measurements are taken i n one p o s i t i o n i n the i n l e t there i s considerable doubt whether they w i l l be - 61 -representat ive of currents to e i ther side of that p o s i t i o n . I t has been noted that there were large l a t e r a l movements of the ship , encompassing about one quarter of the width of the i n l e t , during the second anchorage on s t a t i on 5. I t i s therefore poss ible that the ship was moving i n and out of current pat terns . The attendant complications i n the i n t e r p r e t a t i o n of current measurements are obvious. (6) F re shwater Transport : An estimate has been made of the f re sh water transport i n the surface layer from the net currents and the f re sh water por t ion of th i s l a y e r . D a t a from both s ta t ions were used. Seven 25-hour periods were chosen respresenting the ent i re durat ion of the current measurements with as l i t t l e time overlap as po s s ib l e . I t was found that the mean f r e sh water transport was 310 cubic meters per second down-inlet although i t var ied from 2000 cubic meters per second down-i n l e t to 1000 cubic meters per second u p - i n l e t depending on the durat ion and d i r e c t i o n of the wind s t re s s . This net f resh water transport should represent approximately the r i v e r flow into the i n l e t unless there i s a deepening of the brackish surface l a y e r . I t i s not bel ieved that such a deepening can take place over any great period of time as evidenced by the rapid r e turn of outflow near the surface at s t a t ion 5 (second anchorage) despite a strong contrary wind. - 62 -Estimates of a mean monthly transport of f resh water into the i n l e t have been made (Pickard and Tr i te s ,1957) • These are based on p r e c i p i t a t i o n and watershed data . The values given i n this paper are : June: 27.8 x 10 3 c u . f t . / s e c . ( 790 cu.m./sec) J u l y : 21.7 x 10 3 " " " ( 615 " » » ) I t i s to be noted that these are mean monthly values , and d a i l y or weekly values could d i f f e r appreciably from these. I t i s f e l t that the value of 310 cubic meters per second obtained, i s i n reasonable agreement with these f i g u r e s . (7) Net Transport : The only net transport to be expected through any sec t ion of the i n l e t i s the f resh water component of the surface l a y e r . As noted i n the previous sec t ion , t h i s was about 300 cubic meters per second down-inlet when ca lcula ted from just the f re sh water component of the surface l a y e r . The net transport through the whole column should just equal th i s 300 cubic meters per second with the transports of s a l t water at various depths c a n c e l l i n g each other. Under the assumptions made i n the transport ca l cu la t ions i t was found that the net transport d id not equal the f r e sh water component of the surface l ayer t ransport . At both s tat ions there was ca lcula ted a down-inlet transport i n - 63 -every 25 hour per iod . At s t a t i o n 3/2 i t was 3,700 cubic meters per second and at s t a t i on 5 i t was 8,500 cubic meters per second. The net transport i s i n the r i g h t d i r e c t i o n , b u t , i s an order of magnitude greater than the f r e sh water t ransport . I f these values were true values , the water l e v e l i n the i n l e t would have f a l l e n at the rate of 2 to 3 meters per day. However, i t has already been remarked that the assumptions under which these transports were ca lcula ted are In doubt. There i s the question of just how s i g n i f i c a n t t h i s net transport was i n terms of the accuracy of measurements and the assumptions made i n the c a l c u l a t i o n s . I t should be noted that despite the fact that the net transport ca lcu la ted above i s 10 to 20 times the f re sh water t ransport , the net transport i t s e l f i s only one tenth of the average transport required to f i l l or empty the t i d a l prism during a f lood or ebb. Nonetheless, the net transport ca lcula ted was always i n one d i r e c t i o n and i t i s f e l t that i t may have been s i g n i f i c a n t . R e a l i z i n g that i t was based on currents measured i n mid-channel, two poss ible explanations for t h i s net transport are suggested. I t may have been that the ebb flowed p r e f e r e n t i a l l y i n mid-channel, and the f lood at the s ides . There may also have been a h o r i z o n t a l closed c i r c u l a t i o n with i t s down-inlet por t ion i n mid-channel. - 64- -At s t a t i o n 5, i t i s seen that the net flow developed at the 100 meter depth i s s u f f i c i e n t to account fo r the net down-inlet t ransport . I f the cause fo r th i s flow could be determined, the problem may be so lved . (8) Internal Waves: One feature of the i n l e t s which has been noted on several occasions i s the existence of i n t e r n a l waves or waves at density d i s c o n t i n u i t i e s i n the water s t ruc ture . A l t e rna t ing bands of s l i c k and r u f f l e d water surface observed moving up an i n l e t have been observed (Pickard,1954) and explained as a progressive i n t e r n a l wave t r a v e l l i n g on the sharp densi ty gradient at 10 to 15 meters which i s present i n these 2-layer i n l e t s . There i s some evidence to suggest that i n t e r n a l waves are also present at greater depths. During t h i s set of current measurements, bathythermogram casts were made r e g u l a r l y to a depth of 270 meters at s t a t i o n 5. Prom these i t appears that isotherms o s c i l l a t e d v e r t i c a l l y with a t i d a l p e r i o d . In p a r t i c u l a r there was a temperature minimum which o s c i l l a t e d between the 75 and 150 meter depths. The minimum i s thought to be the residue of severe winter coo l ing ( G . L . P ickard , pr iva te communication). This ser ies of bathythermograms i s , at present, the subject of a separate study. The o s c i l l a t i o n of these isotherms may be due to i n t e r n a l waves. - 65 -The existence of i n t e r n a l waves may expla in one feature of the net current p r o f i l e s . This feature i s present i n the mean current p r o f i l e s f o r the f i r s t 25 hours on s t a t i o n 3I/2 and for the f i r s t 25 hours on s t a t i on 5 ( f i r s t anchorage) which are shown i n f igures 13 and 17 . In the surface layer at s t a t ion 3^/2 there was a minimum at 4 meters and a maximum at 15 meters i n the down-inlet f low. At s t a t i o n 5 the minimum was at 10 meters and the maximum at 15 meters. This feature has been noted before i n current measurements taken at s t a t i o n 4 i n Knight In le t (Tr i t e s ,1955 ) . This pattern of a minimum and maximum can be regarded as e i ther a minimum alone, a maximum alone, or both a minimum and maximum superimposed on a net current which monotonically decreases with depth. There i s no way of d i f f e r e n t i a t i n g between these poss ib le i n t e r p r e t a t -i o n s . A s imp l i f i ed p ic ture of an i n t e r n a l wave w i l l demonstrate the poss ible ef fects of i n t e r n a l waves on current measurements. In the f i r s t instance, for progressive i n t e r n a l waves of f i n i t e amplitude there i s a small transport of f l u i d i n the d i r e c t i o n i n which the wave t r a v e l s . The second ef fect i s an apparent net flow i n the d i r e c t i o n of wave t r a v e l when current measurements are taken at a depth between the cres t and trough of an i n t e r n a l wave which per s i s t s over any great percentage of the t ime. - 66 -The second ef fect i s the one considered here . In f igure 25 i s shown an i n t e r n a l wave at a dens i ty d i s c o n t i n u i t y . I t can be seen that measurements taken continuously at l e v e l A w i l l show a net flow i n the d i r e c t i o n i n which the wave'is t r a v e l l i n g . I t must be emphasized that th i s i s just a simple presentat ion . The ef fect of a dens i ty gradient (which i s the usual case In an i n l e t ) ra ther than a sharp densi ty d i s c o n t i n u i t y , i s that there w i l l be severa l modes of o s c i l l a t i o n pos s ib le . A complex s i t u a t i o n could develop i n r e a l i t y . Applying th i s to the net current p r o f i l e , and i n p a r t i c u l a r to the minimum and maximum near the surface, i t seems poss ible that these may be due to i n t e r n a l waves i n the boundary between the brackish surface l ayer and the denser sea water below. The fac t that strong Interna l waves observed (by the s l i c k and r u f f l e d bands) have been moving up the i n l e t may suggest that the minimum i n the down-inlet flow i s the apparent flow due to a progressive i n t e r n a l wave. VII CONCLUSIONS The character of currents at a l l depths of measurement was that of an o s c i l l a t i n g current or a f l u c t u a t i n g current superimposed on a net current . There i s reason to bel ieve that the o s c i l l a t i n g component at a l l depths at s t a t i o n 3 1 / 2 on the s i l l , and at 200 and 300 meters at s t a t i on 5 i n the inner bas in was determined p r i m a r i l y by t i d a l fo rces . The combination of forces producing the flow at the surface at s t a t i o n 5 i s undetermined but did contain a period re l a ted to the t i d e . The wind stress exerted at the surface has a large: d i r e c t ef fect on surface currents to at leas t a depth of 10 meters, and poss ib ly to 20 meters or more. I t i s recognized that t h i s depth of penetrat ion may depend on the densi ty s tructure of the water and i t s changes with p o s i t i o n and state of t i d e . There i s also evidence that there may be i n d i r e c t inf luences of the wind as i t affects deeper f lows. These flows appear to be of a compensatory nature. - 67 -- 68 -In regions such as that at s t a t i o n 3 / 2 i t i s recognized that bottom topography and an i r r e g u l a r shorel ine may have a large effect on the d i r e c t i o n and strength of cur rent s . There i s reason,from the re su l t s of transport c a l c u l a t i o n s , to th ink that there i s l a t e r a l non-uniformity of currents across an i n l e t . The fact that the net transport was found always to be d i rected down-inlet for these mid-channel s tat ions suggests that the l a t e r a l non-uniformity may be systematic i n o r i g i n . The values obtained for the net f re sh water transport down the i n l e t are i n good agreement with monthly means determined independently from p r e c i p i t a t i o n and watershed data . VIII RECOMMENDATIONS The above conclusions about currents and the problems encountered i n the i n t e r p r e t a t i o n of current measurements, as we l l as comments made about the tfeohnique, lead to recommendations for future work. These recommendations are made p r i m a r i l y to help reduce errors i n measurements and to provide more information with which to in te rpre t the current data . Despite the fact that monitoring of the ship motion gives a c o r r e c t i o n for currents measured, i t s t i l l seems advisable to attempt to use a mul t ip le anchoring scheme i f the time and equipment are a v a i l a b l e . The large poss ible e r ror i n the c o r r e c t i o n current plus the f ac t that the c o r r e c t i o n current ( ship ' s speed) may be a large proport ion of currents measured are the reasons why i t i s f e l t that mul t ip le anchoring should be undertaken whenever p o s s i b l e . I f there i s the manpower ava i lab le there are several observations that could be made to f a c i l i t a t e the i n t e r p r e t a t -i o n of current measurements. A t ide gauge should be placed on the shore near the ship p o s i t i o n . I f pos s ib le , there should be - 69 -- 70 -more of these placed at various pos i t ions i n the i n l e t . One person i n charge of a cutter or other small boat could carry out surface current measurements across the width of the i n l e t to determine i f the flow i s uniform across the i n l e t or not . Often the structure of the water near the surface i s of in tere s t when surface current measurements indicate the accumulation of f re sh water i n the i n l e t . Subsequent deepening of the surface layer and the l o c a t i o n of such a deepening could be determined by measurements taken from a small boat . There i s , of course, the p o s s i b i l i t y of a m u l t i -ship operat ion (apart from use of a sh ip ' s c u t t e r ) . Both add i t iona l simultaneous current s tat ions across one sec t ion of the i n l e t , and simultaneous oceanographic data fo r dynamic studies would provide considerably more information about currents and t h e i r d i s t r i b u t i o n . Instrumentation can be improved. Notably, use of a deck-reading current meter would cut down time requirements, thus providing a more deta i led and more near ly synoptic p i c t u r e . Prom the ca lcu la t ions of drag on the wire of the C . B . I , current drag, i t i s obvious that the smallest wire poss ib le should be used to improve accuracy at the depth at which i t has already been used, and to make i t poss ib le to use the drag at even greater depths. - 71 -The marked Influence of wind stress on surface currents suggests the necess i ty for more d e t a i l concerning wind f a c t o r s . Frequent wind measurements at two or more heights above the water surface would f a c i l i t a t e ca l cu la t ions of wind s t res s . REFERENCES. BURT, W.V. , " and D,W.PRITCHARD. 1951. An inexpensive and rapid technique, for obtaining current p r o f i l e s i n estuarine waters. Jour. Mar. Res. V o l .14, No. 2, pp. 180 - 189. CAMERON, W.M. 1951. On the dynamic's o f " i n l e t c i r c u l a t i o n s . Doctora l d i s s e r t a t i o n , Univ . of C a l i f o r n i a , Los Angles, C a l i f . CANADIAN HYDROGRAPHIC SERVICE. 1956. P a c i f i c coast t ide and current tab les , 1956. DAWSON, W.B. 1920. The t ides and t i d a l streams wi th ' i l l u s t r a t i v e examples from Canadian waters. King ' s P r i n t e r , Ottawa. PICKARD, G . L . 1953. Oceanography of B r i t i s h Columbia mainland i n l e t s . I I , Currents . Prog.-Rep. P a c i f i c Coasts Stations F i s h . Res. Bd. Canada, No.97, pp. 12 - 1 3 . -w~ 1954. Oceanography of B r i t i s h Columbia i n l e t s , I I I , Internal"waves. Prog. Rep. P a c i f i c Coast Stations F i s h . Res. Bd. Canada, No.98, pp. 13 - 16. -.1956. Phys i ca l features of - B r i t i s h Columbia i n l e t s . Tran. Roy. Soc. Canada, V o l . 50, Ser. 3 , pp. 47 - 58. PICKARD, G. L . , and R.W.TRITES. 1957. Fresh water t r a n s p o r t determination"from the"heat budget w i t h a p p l i c a t i o n s to B r i t i s h C o l u m b i a ' i n l e t s . Jour. F i s h . Res. Bd. Canada, V o l . 14, No.4, PP. 605 - 616. PRITCHARD, D.W. 1952. Estu a r i n e hydrography. Advances i n Geophysics, Vol.1, pp. 243 - 280. Academic Press Inc., New York, N.Y. - 72 -- 73 -STOMMEL,H. 1951. Recent developments i n the study of -t i d a l e s tuar ie s . Tech. Rep. , Ref. No. 51 -33, Woods Hole"Oceanographis I n s t i t u t i o n , Woods Hole, Mass. SVERDRUP, H . U . , M.W.JOHNSON and R.H.FLEMING. 1942. The Oceans. Chap. 10. P r e n t i c e - H a l l , I n c . , New York, N.Y. TABATA, S. , and A.W. GROLL. 1956. The ef fect of sh ip ' s r o l l oh the Ekman current meter• T r a n s . , ' American Geophysical Union, V o l . 37, No.4, pp. 425 - 428. ' TRITES,R.W. 1 9 5 5 . A study of the oceanographic s tructure In B r i t i s h Columbia i n l e t s and some of the determining f a c t o r s . D o c t o r a l ' d i s s e r t a t i o n , the U n i v e r s i t y of B r i t i s h Columbia, Vancouver B r i t i s h Columbia. SCHEMATIC SALINITY DISTRIBUTION Salinity increasing » 3 0 % , 3 0 3 0 3 0 3 0 % ! ' 1 ^i 1. o SCHEMATIC NET CIRCULATION RSver SCHEMATIC REPRESENTATION OF THE SALINITY DISTRIBUTION AND CIRCULATION IN AN INLET Figure I m - SALINITY PROFILES 6 0 -Figure 2 STATION 3 '/2 N 2 3 0 0 M e t e r W i d t h • \ — 5 0 m e t e r s STATION 5 \ 2 4 0 0 M e t e r W i d t h \ — 1 0 0 • • S O U T H V \ ~ 3 0 0 m e t e r s /•'.'•' N O R T H TRANSVERSE SECTIONS AT CURRENT STATIONS THE Figure 3 SHORELINE AND BOTTOM CONTOURS NEAR STATION 3 '/2 Y/7\ The extent of ship motion t Principal current directions - P L O T T E D F R O M CANADIAN H Y D R O G R A P H I C S E R V I C E F IELD S H E E T NO. 2 4 8 — L S C A L E : 0.5 n m . I—•• L -1.0 km. D e p t h c o n t o u r s in 2 0 meter in terva l s Figure 4 STATION POSITIONING OF SHORE STATIONS Figure 6 down- in let up- in let — tl STATION 5 July 4 th to 6 t h inlet width is 12.5 inches . STATION 5 July 8th to II th THE EXTENT OF SHIP MOTION Figure 7 I 35 4 -30 25 H 20 A 15 H io J 5 H 0 0 0 I _ L _ STATION 3 \ i — i — r 0.2 6 1.2 36 ft./sec. cm/sec. SHIP SPEED DISTRIBUTION OF SHIP SPEED AT THE TWO CURRENT STATIONS Figure 8 STATION 3V2 D E P T H 20 60 H m. 1800 - 6 JULY TO 1 5 0 0 - 7 JULY 30 A Longitudinal Component V 30-cm./sec. 30-\ / Transverse Component 30 H ~p4 •\ / +-9 / o STATION 5 DEPTH 100 m. 2 2 0 0 - 8 JULY T O 1 7 0 0 - 9 JULY + 15 A Longitudinal Component 151 cm./sec. •I-o. t Flood —: y-o o \ Ebb \ . * 15 A Transverse Component 15 J * • \ + A *. + o—o— 0 o + \ + ? + f +• South 0 North I + 4-1- Uncorrected Readings o o o Corrected Readings CORRECTED AND UNCORRECTED READINGS COMPARED Figure 9 TIDE { M E T E R S ) 5 -Measurements Taken With The C.B.I. Current Drag. UP - INLET D O W N - INLET - 10 (KNOTS) 0 - 10 PDST I i i i i i—i— 18 00 ' i I l_l I i i 06 J I 1 L 12 J—I—I I I I I I I I I I I i i i I i i i i i I i i 18 00 06 12 18 150 100 50 0 50 . 50 / • V .A/ V \ / v DEPTH OF MEASUREMENT ( METERS) 2 \ cc UJ a. 50 -A u i ^ \ / •\ .A • • • \ / \ \ A/ V. / \ \ /V • *— ••• — • V 50 -cc A /v. Ul 2 iZ 50-T77 5 \~t . A' - V _ L v \ • Ul o / • 50 -t 50 50 0 50 50-0 • 50 A / o - • •'VAA .'\/ v. v\./ T/\ . / \ / \ \/ \ / \i \ A \i\ r\ iV L o n g i t u d i n a l C o m p o n e n t o f C u r r e n t s S T A T I O N July 6th to 8th , 1956 10 15 20 Figure 10(a) TIDE (METERS) I I I I l I l l l l l I J I I I I I I I I I I I I I i i I l I l P D S T 18 00 06 I I I I 1 I I I i- i i i I - 20 WIND . | Q (KNOTS) - 0 - 10 12 18 0 0 06 12 18 Measurements Taken With An Ekman Current Meter U P - I N L E T DOWN— INLET . . . CORRECTED READINGS. o o o UNCORRECTED READINGS . O o CO cr a. z 3 50 -i 0 / 50 H 50 H \ V . V -t 50 H 50 -\ 0 V 7 9 1 \ \ \ T 50 H 50 H 0 / 50 H 50 ^ 0 50 H \ • 7— ~7 \ \ 7 DEPTH (Meters) 10 20 40 60 70 Longitudinal Component of Currents STATION . 3 l/z July 6th to 8th , 1956. Figure 1 0 (b) 5 -TIDE ( METERS) Measurements Taken With An Ekman Current Meter NORTH SOUTH . * . CORRECTED READINGS o o o UNCORRECTED READINGS o Z O o Ul in cr UJ a CO cr UJ I-UJ 2 t-Z UJ o z 3 20 10 L_i i i i i I i i—i i i_J i i i i i I i i i L_J I i i i i \ I I_J i i i I i i' i i i I t i i i i I 18 00 06 12 18 00 06 12 18 - 0 - 10 WIND (KNOTS) 50 -0 50 -DEPTH (Meters) 10 •-• \ • / \ 50 H 0 \ / 50 -50 -0 50 50 0 \ / \ / 50 -T \ t • 20 40 60 70 Transverse Component of Currents STATION 3 l/2 July 6th to 8th , 1956. Figure I I i c CD ro KN 3'/2 0 20 DEPTH 40 (M.) 60 H 7 JULY 1956 WIND (KNOTS) TIDE (FT.) 0 20 DEPTH 40-(M.) 60 WIND (KNOTS) 20-10-8 JULY NET CURRENT S C A L E 4 2 0 2 4 ft/sec. at\Ys»c. 100 0 100 UP DOWN INLET INLET (FLOOD) (EBB) PROFILE FOR FIRST 25 HOURS PROFILE FOR LAST 25 HOURS FIRST AND LAST PROFILES SUPERIMPOSED Units of cm./sec. UP-INLET DOWN — INLET 20 40 60 80 meters 20 40 J L 20 -o NET CURRENT PROFILES AT STATION 3V 2 J U L Y 6 T H T O 8 T H , 1956 Figure 13 5 — TIDE (METERS) t UP INLET DOWN INLET POST o o UJ CO ct UJ CO CC UJ 2 CO I-WIND (KNOTS) Longitudinal Component STATION Ju ly 4 th to 6 th , 1956 Depth (meters) Measurements Taken With A C.B.I. Current D r a g . Figure 14(a) TIDE ( METERS) —10 WIND (KNOTS) -10 J—I—I—I—I—I—I—I—I—I—I—I—I—I—L_l 1—l_J l_l I L_l I I I I I I I l_l l l l l l I l I I I I 1 i i i i PDS T 18 00 06 12 18 00 06 12 Longitudinal STATION 5 Measurements Taken With Component J u l y 4 t h t 0 6 t h * 1 9 5 6 A C ' B J ' C u r r e n t D r a g -Figure 14 (b) . . • C O R R E C T E D READINGS o o o UNCORRECTED READINGS Longitudinal Component STATION 5 July .4th to 6th , 1956 Measurements Taken With An Ekman Current Meter. Figure 1 4 ( c ) Figure 15 KN 5 0 •-20-50-DEPTH IOO-200 • 300-WIND 10-(KNOTS) 0-L TIDE 10-(FT.) 0--4 JULY 5 JULY WIND 10-(KNOTS) 0-^  TIDE 10-(FTJ NET o 1.0 ft./ see. 20 40 era/sec. ft./SGC. cm./sec. CURRENT SCALE 3 2 1 0 1 2 3 T i I I 100 50 0 50 100 UP DOWN INLET INLET (FLOOD) (EBB) G.K.R. JULY 1957 Units of c m . / sec. 0 20 40 1 1 I I L_ V PROFILE FOR FIRST 2 5 HOURS 60 _J L up-inlet —I— down-inlet 0 100 -- 200-- 3 0 0 -m. 20 40 j i i i 60 j i PROFILE FOR L A S T 25 HOURS c m . / s e c . 0 20 40 60 1 ) 1 1 I j . _ I 1 _ L 100 -200-300-m. V FIRST AND L A S T PROFILES S U P E R I M P O S E D NET CURRENT PROFILES FOR STATION 5 J U L Y 4 T H T O 6 T H , 1956 Figure 17 - 2 0 - 10 WIND (KNOTS) Longitudinal Component STATION 5 July 8th to Nth , 1956 Depth (meters) 4 Measurements Taken With A C.B.I. Current Drag. Figure 18(a) PDST 00 06 12 18 00 06 12 18 00 06 12 L o n g i t u d i n a l S T A T I O N 5 Measurements Taken With C o m p o n e n t July 8th to N t h , 1956 A C B I - Current Drag. Figure 18 (b) I I I I I I I I I I" I I I I I I I ' I • I • I I 1 I I I I I I L I I I I 1 I I I I I I I I I I i I I I I I I I i i i i i j i i i i POST 00 06 12 18 00 06 12 18 00 06 15 15 ^.y V TT Depth (meters) 50 Q NO 15 -o UJ cn o -cc UJ a. 15 -CO cc UJ ET 15 -2 \-UJ 0 -o u. o 15 -tn \-z 15 -r\ -u 15 -\ V / \ \ v./ \ \ r 100 1Z1 \ / / \ J / •v / y / V v / y-y % 200 / / \ / J \ \ T 9 300 v/ UP INLET I DOWN INLET Longitudinal Component STATION 5 July 8th to I Ith , 1956 • • . CORRECTED READINGS o o o UNCORRECTED READINGS Measurements Taken With An Ekman Current Meter. Figure 18 ( c ) I—I I 1 I—I I I I I I I I I 1 I 1 I I I I—1 I I I—I I I I—I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I 1 I I I I 1 POST OO 06 12 18 00 06 12 18 00 06 12 Depth (meters) I . . . CORRECTED READINGS NORTH I oooo UNCORRECTED READINGS SOUTH Transverse Component STATION 5 July 8th to Nth , 1956 Measurements Taken With An Ekman Current Meter. Figure 19 Units of cm. / sec 0 20 » \ up- inlet 20 PROFILE FOR FIRST 25 HOURS 100 -- 2 0 0 -- 3 0 0 -mete rs cm. / s e c 20 0 20 100 -200 -300 -m. PROFILE FOR L A S T 25 HOURS down - inlet 20 PROFILE FOR MIDDLE 25 HOURS NET CURRENT PROFILES FOR STATION 5 J U L Y 8 T H T O IITH , 1956 Figure 21 STATION 3'/ 2 J U L Y 6 T H T O 8 T H , 1 9 5 6 L O N G I T U D I N A L C O M P O N E N T Depth of 10 meters o o o E K M A N READINGS • • • C.B.I. DRAG READINGS COMPARISON OF EKMAN METER AND C.B.I. CURRENT DRAG READINGS Figure 22 The following points are 25 —hour running means — data from station 3V2 Mean Current in Upper 10 meters • • • • 1 2 -• • • • 6 -• • • • • • up-inlet • • Second 6 -• . « ' 12-• down - inlet • Current Means at 10 meters . * * • «x 6 -• • • • • . • • + + 0 . • • • *• + + 9 • • * + + • 2 o o 0 0 • • • 6 * s * veters »2 - J ? ° 0 • * • * * „ S ° O 0 ° ? ? • «; Current Means at 20 meters 0 0 0 0 0 • • + . • 1 2 - ' 0 0 0 • • • • • • • * + * + * + + + + + + * + MEANS FOR EKMAN METER READINGS MEANS FOR C.B.I. DRAG READINGS UNCORRECTED FOR WIRE DRAG • • • • + + + + 0 0 0 0 + + + MEANS FOR C.B.I. DRAG READINGS CORRECTED FOR WIRE DRAG THE EFFECT OF THE WIRE DRAG CORRECTION Figure 23 STATION 3 1/2 July 6th to 8th , 1956 • Calculated STATION 5 July 4th to 6th , 1956 - 6 V - 6 STATION 5 July 8 th to llth , 1956 CALCULATED AND OBSERVED TRANSPORTS Figure 24 AIR - S E A BOUNDARY DISCONTINUITY DIRECTION IN WHICH WAVE IS TRAVELLING HORIZONTAL COMPONENT OF PARTICLE MOTION A PROGRESSIVE INTERNAL WAVE Figure 25 

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