Currents General remarks

Direction. Currents in the Black Sea, which in general are weak and inconsistent, consist of a main circulation setting anti-clockwise along its shores, with several branches connecting in various parts. Counter currents, setting in a direction contrary to that of the main current, occur between the main current and the shore in many places. These counter currents are very irregular. There is also an almost constant flow of water from the Black Sea through Marmara Denizi to the Mediterranean.

Causes. Currents in the Black Sea are due to two causes: the outflow of the rivers, the bulk of which enters the NW part of the sea, and the influence of the wind. Variations in the amount of discharge from the rivers, and variations of the wind distribution due to the passage of depressions and other causes may effect the normal currents to a very large extent, and in some areas, may even reverse their direction.

Strength. The strength and consistency of this anti-clockwise circulation is greatest after the melting of the snows in late spring and early summer, when the discharge from the rivers is greatest. In late summer and autumn, when the volume of water discharged by the rivers is relatively small, the circulation is generally weaker and more subject to changes due to the influences of the wind. The largest variations in the current are found in the NW part of the sea; here, especially during the spring, the outflow of the River Danube is often felt well offshore, causing a considerable E, or even NE, set.

Local current systems are found off the mouths of rivers. As a rule river water flow out of the mouth in a direction at right angles to the trend of the coastline, thence it gradually turns to the right and may even turn so much towards the shore as to produce an eddy returning towards the mouth.

Sea level. The annual range in Mean Sea Level due to the meteorological pressure effects is about 5 cm; exceptionally a rise of 15 cm and a fall of 18 cm have been recorded. Superimposed on this are variations resulting from changes in the amount of water entering or leaving the Black Sea of from 50 cm to 1.5 m.

Winds exercise a considerable effect on the water level. In general, onshore winds tend to raise, and offshore winds to lower the level. The range of level thus caused depends largely upon local conditions, being much more marked in bays and inlets than in more open places, and may be as much as 30 cm.

Seiches, which occur with little or no warning, can raise or lower the sea level by about 1 m over wide areas. The seiches may be the result of seismic disturbances some distance away or the consequence of changes in atmospheric pressure.

Tidal ranges. Tidal influence has virtually no effect on water levels in the Black Sea. The average spring range in the W part of the Black Sea is only 8 cm.

Currents and tides

Currents tend to be monsoonal in origin, generally setting W during the NE monsoon (January to March) and E during the SW Monsoon (May to October); during the intervening months the currents are variable. The rate of the current in the E/W channels may attain 5 knots. Local Observations:

In February 1960 a W set, with a rate of 1 ½ kn, was reported to have been experienced between a position 25 miles E of Vaadhoo Atoll (0030 N, 7315 E) and Vaadhoo Kandu, 220 miles N.

In October 1960 a S set with a rate of about 1 kn, was reported to have been experienced off the E side of the atolls lying between Male Island (410N, 7330E) and latitude 230N, 100 miles S.

The N fringe of the Equatorial Counter-current is the main influence both near Addoo Atoll and in Equatorial Channel, the predominant Direction appears to be E or NE throughout the year, but observations in the area are scantly and marked variations no doubt occur. Observations suggest the current increases in strength within 50 miles from the atoll.

Local Observations:

In December 1965, a vessel approaching Addoo Atoll from W in an approximate latitude of 045S, reported the counter-current to have a rate of 1 kn or less; thence when E of meridian 72E the set was observed to be ENE with the rate increased to an estimated 3 kn, and subsequently possibly to 5 kn when 30 miles W of Gan Kandu. There a strong set across the entrance to Gan Kandu is frequently experienced usually in an E direction, but changing to SW when the wind has been E for a period.

The ingoing stream sets strongly into the lagoon through Viligili Kandu and out of the lagoon through Gan Kandu. The outgoing stream sets out through both channels; thus, the stream through Gan Kandu is continuously out of the lagoon. In Kuda Kandu the sets are into the lagoon with the in-going stream and out with the out-going stream; but in Maa Kandu it sets continuously out of the lagoon. The tidal stream in Maa Kandu is reported to attain a rate of 5 kn.

Strong sets, both E or W, with rates up to 5 ½ knots have often been reported in Equatorial Channel, but in its S part the E-going counter equatorial current with a rate up to about 4 kn seems to prevail.

Tidal streams setting E when in-going and W when out-going are negligible near Foammulah except for the effect of retarding and accelerating the current.

Currents setting E with a rate of up to 3 ½ kn have been experienced in October and November but during the NE monsoon (December and March) a W set with a rate of nearly 4 kn was reported to have been experienced in the middle of the channel.

Tidal streams in this channel attain a rate of 2 kn at springs; this rate may be increased or reduced by the current prevailing.

The tidal streams in the channel are very strong; the in-going stream sets E and the out-going stream sets W. During the monsoons the stream is accelerated by the prevailing current, setting W during the NE monsoon and E during the SW monsoon attaining a rate of up to 4 kn and causing severe tide-rips.

Local observations: In February 1960, a current, with a rate of 2 kn in a direction of 255, was experienced in the channel; and in October 1996 an E set with a rate of 1 ½ to 2 kn was experienced at the E end of the channel.

From the few observations which have been made near Male, it seems likely that water movement there is influenced by the monsoon currents far more than by the tidal streams. When the currents are flowing strongly tidal streams are probably only strong enough to increase or decrease the flow of the currents, but rarely strong enough to reverse their direction. Therefore, because they depend on the current, sets are often strong and unpredictable.

In Gaadhoo Koa the streams from Vaadhoo Kandu set across the channel, and may achieve rates up to 6 kts; during the NE monsoon a component of the current sets NW through the entrance setting a vessel towards the reef fringing the E side of Male; within the entrance the flow then turns W between Male and Funadhoo. Strong sets have been reported during the NE monsoon within Male Harbour.

In February 1972 the NW flow started 1 ½ hours before HW and continued until 1 ½ hours before LW, attaining a maximum rate of 2 ½ to 3 kn N of Male Breakwater. At about the time of HW, the flow sets strongly along the N face of the breakwater; at the same time the flow E of Funadhoo was weak and variable.

During the SW monsoon a component of the current enters Male Lagoon through Giraavaru Kandu, 6 miles W of Male, flowing principally through the channel E of Viligili and between Male and Funadhoo into Vaadhoo Kandu.

Local observations: In August (1972) and E-going set was experienced SE of a line joining Male and Hulule; within this line, slack water was found between Funadhoo and Dhoonidhoo then a strong E-going set was encountered to the anchorage. It was also observed that four hours after low water, with the in-going stream tending to oppose the current, a moderate NE flow was experienced in the lagoon.

At the change of monsoon it was reported (1991) that the current in the approaches of Gaadhoo Koa had an E set of about 1 kn. At the same time, the tidal streams inside the lagoon were weak and variable, never exceeding ½ kn.

Currents in the N part of the Maldive Group set W and NW from December to March inclusive; from May to October they set E and Se but are subject to much variability at all seasons. April and November are months of transition.

Tidal streams at the N end of the Maldive Group attain a rate of about 1 ½ kn but are very irregular and always influenced by the prevailing winds and currents; thus during the NE monsoon the out-going stream seems to run longer than in the opposite season. With strong W winds the in-going stream sets E for most of the day but when the wind eases the out-going stream takes its turn to set W in the same way when the water may fall 0.1 m lower than it usually does at springs.

Tidal streams at I. Atoll do not appear to follow any regular pattern and currents are only experienced occasionally, probably entirely under the influence of local weather conditions. The following isolated observations have been made previously:

In the offing. During December and January, the current generally sets N or W but it is irregular.

Offshore. In December, about 50 miles E of the atoll, the current was once observed to set N with the rate of 2 kn; but one month later there was no almost current in this position.

Currents within 2 miles of the coast and W of Dondra Head are irregular; there is often an indraught into Matara Bay.

The currents E of Dondra Head are generally weak and set parallel with the coast. During the survey, in 1908-19909, the currents were found to be weak and, although sometimes variable in direction, to set generally with the prevailing wind. The greatest rate observed was less than 1 kn; the average rate was ½ kn.

Currents farther offshore; a report (1994) from sea indicated a W-going current during the NE monsoon of between 1 and 3 kn whilst on passage S of Sri Lanka.

The tidal Streams in Palk Strait and Palk Bay are generally irregular, being influenced by the prevailing winds. However, during February, March and April they are more predictable, changing about every 6 ½ hours at HW and LW in the bay. In Palk Strait the tidal streams set WSW on the falling tide and ENE othe rising tide at Trincomalee.

Within Palk Bay tidal streams follow the general direction of the coast in a broadly anti-clockwise movement on the rising tide, setting NE west of Delft Island and NW through Delft Channel, and clockwise, reversing direction, on the falling tide.

Spring rates of nearly 1 kn in Delft Channel and about ¾ kn in West Channel may be found.

The current in Palk Strait generally sets with the wind, except in May and October when it is variable. During February, March and April, in a calm, there is no current in the strait. A set out of Palk Strait usually occurs when the current outside the strait is setting N; the reverse may take place with a S offshore current.

The rate and direction of the inshore tidal stream varies the strength of the current near Middle Banks. In the middle of Palk Bay the current sets to leeward in both monsoons.

2. Learn by heart the following terms relating to tidal levels, various limits and depths. Be ready to decipher the abbreviations.

Tidal levels

1.	CD	Chart Datum Datum to Sounding Reduction	Нуль карты Нуль карты, к которому приведены глубины
2.	LAT	Lowest Astronomical Tide	Самый низкий теоретический уровень возможный по астрономическим условиям
3.	HAT	Highest Astronomical Tide	Наивысший теоретический уровень возможный по астрономическим условиям
4.	MLW	Mean Low Water	Средняя малая вода
5.	MHW	Mean High Water	Средняя полная вода
6.	MSL	Mean Sea level	Средний уровень моря
7.	MLWS	Mean Low Water Springs	Средняя малая сизигийная вода
8.	MHWS	Mean High Water Springs	Средняя полная сизигийная вода
9.	MLWN	Mean Low Water Neaps	Средняя малая квадратурная вода
10.	MHWN	Mean High Water Neaps	Средняя полная квадратурная вода
11.	MLLW	Mean Lower Low Water	Средняя низкая малая вода
12.	MHHW	Mean Higher High Water	Средняя высокая полная вода
13.	MHLW	Mean Higher Low Water	Средняя высокая малая вода
14.	MLHW	Mean Lower High Water	Средняя низкая полная вода
15.	Sp/Spr.	Spring Tide	Сизигийные приливы
16.	Np	Neap Tide	Квадратурные приливы
17.	HW	High Water	Полная вода
18.	LW^	Low Water	Малая вода
19.	MTL	Mean Tide Level	Средний Уровень Прилива
	OD	Ordnance Datum	Картографический уровень, уровень государственной нивелировки (Бр.)

Various limits

	Symbols and legends on charts	English Explanation	Russian Explanation
1	Graphic symbols only	Limit of fast ice, ice front Limit of sea ice (pack ice) - seasonal	Граница неподвижного льда (припай), ледяной барьер (черный цвет) Граница сезонного дрейфующего морского льда (паковый лед) (фиолетовый цвет)
2	Log pond Booming ground Timber	Log pond	Ограниченный бассейн (для различных целей, например, лесосплавный рейд)
3	Spoil ground	Spoil ground	Район свалки грунта
4	Spoil ground (disused)	Spoil ground (disused)	Район свалки грунта (недействующий)
5	Dredging area	Dredging area	Район дноуглубительных работ
6	Cargo Transshipment Area	Cargo Transshipment Area	Район перевалки груза
7	Incineration area Area for burning refuse materials	Incineration area	Район сжигания мусора

Depths – General

1	ED † (ED)	Existence doubtful	Существование сомнительное
2	SD	Sounding of doubtful depth	Глубина сомнительная
3	Rep † Repd	Reported but not confirmed	Имеется неподтвержденное сообщение
4	Rep (1973) † Repd (1973)	Reported with year of report but not confirmed	Имеется неподтвержденное сообщение ( с указанием года)
5		Reported but not confirmed sounding or danger (on small-scale INT charts only)	Имеется неподтвержденной сообщение глубины или опасности) (только на международных мелкомасштабных картах)
6	Unexam † unexamd	Unexamined	Необследованный

3. Match the definitions with the terms given below

Age of the tide; Equinoctial tides; Chart Datum; Lowest Astronomical Tide (L.A.T.); Neap tides; Amplitude; Duration of rise or fall; Quadrature; Slack water; Range of tide; Rise of the tide

1.The time, usually given in days, between the new or full moon and the time of the next maximum spring range.

2. The distance between the high and low points of any tide or constituent.

3. The level to which soundings on a nautical charts and tidal predictions are referred. The level of the Lowest Astronomical Tide is generally used.

4. The time interval between low and high water or between high and low water

5. These are tides with particularly large ranges, which occur at ports, where the tides are semi-diurnal at about the time of the equinoxes

6. The lowest level predicted to occur under any combination of astronomical conditions and under average meteorological conditions.

7. Tides with lower high waters and higher low waters, which occur at semi-diurnal ports at about the times of the Moon’s quadrature.

8. When the sun and the Moon are 90 degrees apart

9. The vertical distance between high and low water

10. The height of the tide above chart datum

11. The period when the horizontal movement of the water is nil, regardless of the height of the tide.

12. Tides with the highest high waters and lowest low waters during a period of about 14 days at a port where the tide is semi-diurnal. Usually about the time of New or Full Moon

5. Give synonyms to:

Stream, velocity, abeam, to commence, to alter, to permit, to berth; eddy

6. Give antonyms to:

Ebb; early; weak; under water rocks; foul ground; rapid; falling water; low water.