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TIDAL STREAMS THE DOWNS
Tidal Streams – The streams in the fairway of the English channel, off the northern coast of France, and off the southern coast of England, have, up to the present, been called “east-going” and “west-going.” Off the coast between South Foreland and North Foreland, in the Downs and round the Goodwin sands, the Channel east-going stream is more nearly north-going, and the Channel west-going stream is more nearly south-going; the designations of the streams have been changed accordingly. This alteration is specially required because the north- and south-going streams of the Downs meet with and separate from the east- and west-going streams of the Thames estuary off the coast between North Foreland and Foreness.
The streams run northward and southward through the Downs, usually in about the direction of the channel, but the times at which they begin to run become appreciably later from south to north. At a position 5.4 miles 082° from South Foreland lighthouse, south-westward of South Sand head, the southern extremity of Goodwin sands, the north-going stream, spring rate 2.3 knots, neap rate 1.3 knots, mean direction 035°, begins -0200 Dover; the south-going stream, spring rate 2.2 knots, neap rate 1.2 knots, mean direction 214°, begins +0400 Dover. The north-going stream when strongest runs in a direction 039°, just clear westward of South Sand head (see “Caution” below).
At a position 159°, 3.5 miles from the entrance to Ramsgate harbour, the north-going stream, spring rate 3.2 knots, neap rate 1.7 knots, mean direction 020°, begins -0135 Dover; the south-going stream, spring rate 2.8 knots, neap rate 1.5 knots, mean direction 197°, begins +0435 Dover (Lat. 51° 08’ N., Long. 1° 19’ E.).
At a position on the north-western side of Gull stream about one mile west-north-westward of N. Goodwin light-buoy, the north-going stream, spring rate 2.8 knots, neap rate 1.6 knots, mean direction 030°, begins -0120 Dover; the south-going stream, spring rate 2.6 knots, neap rate 1.4 knots, mean direction 215°, begins +0440 Dover.
At a position about 3.2 miles 141° from North Foreland lighthouse, the north-going stream, spring rate 2.5 knots, neap rate 1.3 knots, mean direction 019°, begins -0120 Dover; the south-going stream, spring rate 2.2 knots, neap rate 1.3 knots, mean direction 200°, begins +0440 Dover. The stream at this position is more or less rotatory; the north-going stream begins in a direction about 340°, when strong runs in directions between about 005° and 025°, and ends in a direction about 060°; the south-going stream begins in a direction about 135°, when strong runs in directions between about 190° and 205°, and ends in a direction about 230°.
At a position, about 2½ miles northward of Goodwin knoll, the north-going stream, which is slightly rotatory, begins, in a direction about 357°, -0120 Dover, runs when strong (over 2 knots at springs) in directions between 010° and 045° attaining its greatest rate, 3.2 knots at springs 1.8 knots at neaps, in a direction 023°, +0100 Dover, and ends, in a direction about 060°. The south-going stream, which is more nearly rectilinear, begins, in a direction about 180°, +0500 Dover, attains its greatest rate, 3.1 knots at springs 1.7 knots at neaps, in a direction 208°, -0400 Dover, and ends in a direction about 230°.
The streams in the neighbourhood of the Downs and Goodwin sands are more or less rotatory in a clockwise direction but the °ree of rotation varies in different parts; at all positions, however, though at the beginning of the stream, either north-going or south-going, its direction may be considerably to the left, and at its end considerably to the right, of its mean direction, the direction changes quickly near the beginning and end of the stream, which, when at all strong, always runs within a few °rees of its mean direction. As a rough general rule it may be assumed that, except off the northern side of Goodwin knoll and the sand westward of it, half an hour after the stream begins it is running in a direction about 5° to the left of its mean direction, and that this direction changes gradually to the right till, half an hour before the stream ends (or before the stream in the opposite direction begins), when its direction is about 5° to the right of its mean direction.
Northward of Goodwin knoll and the sand westward of it, the streams are more rotatory, and about one hour after the stream in either direction begins its direction is about 10° to the left, and about one hour before it ends about 10° to the right, of its mean direction.
Between South and North Forelands the streams run strongly along the coast between South Foreland and Deal; the north-going stream begins about -0150 Dover, the south-going stream begins about +0415 Dover (Lat. 51° 08’ N., Long. 1° 19’ E.).
In the bay formed by the coast between Deal and Ramsgate the streams are weak. Definite information regarding the streams in the River Stour is not available; the in-going (flood) stream probably begins about -0450 Dover and runs at first in the channel through the flats; later, as the flats cover, it runs inwards towards Shellness from all directions. The ebb stream probably begins about +0020 Dover and runs at first across the flats towards Ramsgate; later, as the flats dry, it runs in the channel.
Off Ramsgate pier heads the north-going stream, direction north-eastward, begins about -0210 Dover; the south-going stream, direction south-westward, begins about +0400 Dover; spring rate in both directions about 3 knots.
Between Ramsgate and North Foreland the north-going stream begins about -0140 Dover, the south-going stream begins about +0420 Dover; the streams are strong off the southern part of this coast, but lose strength and become irregular as North Foreland is approached (see below).
Caution. – At certain positions, and at certain times, the streams set strongly towards and across the Goodwin sands, as follows:
Southward of South Sand head, between about -0100 and +0300 Dover, the north-going stream sets strongly towards and across the southern part of the sands in the direction of its length; this set is specially dangerous, for it occurs near high water when the sands are covered.
Observations have not been obtained between South Sand head and the Fork, or in Trinity bay. It is, however, probable that the north-going stream sets north-eastward into Trinity bay and through Kellett gut, and north-north-eastward into the channel which runs towards the drying sand westward of Goodwin knoll. This set, if it occurs, is dangerous, for it occurs near high water when the sands are covered.
In the southern part of Gull stream the streams run about in the direction of the channel.
About 2½ miles northward of Goodwin sands the south-going stream sets at first towards Goodwin knoll, but changes direction quickly and when strongest sets towards the western part of the drying sand westward of Goodwin knoll; the strongest set occurs about one hour before low water, when, at springs, the sands are beginning to dry and probably deflect the stream. In order to ascertain the set, the streams have been observed at two positions northward of the sands, in 51° 18.3’ N., 1° 34.4’ E., and in 51° 18.2’ N. 1° 31.8’ E.
At the first of these positions the north-going stream, spring rate 2.4 knots, neap rate 1.4 knots, begins -0135 Dover and runs in directions which change gradually from about 340° to about 015°, the greatest rate being attained in a direction 002°. The south-going stream, spring rate 2.1 knots, neap rate 1.1 knots, begins -0400 Dover, in a south-easterly direction, but changes quickly, runs when strong in directions from 180° to 200°, and ends in a south-westerly direction. At this position, therefore, the south-going stream when strong runs directly towards the sands, but this set occurs near low water.
At the second position the north-going stream, spring rate 2.3 knots, neap rate 1.3 knots, begins, in a northerly direction, -0120 Dover; the direction changes quickly and, when strong, the stream runs in a direction about 045°, and ends in an easterly direction. The south-going stream, spring rate 2.3 knots, neap rate 1.3 knots, begins, in a south-south-easterly direction, +0440 Dover; the direction changes quickly, and when strong the stream runs in directions 220° to 230°, and ends in a west-south-westerly direction. At this position, though the south-going stream runs towards the sand at first, when strong it runs in about the direction of the Gull stream.