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TIDAL STREAMS PORTSMOUTH HARBOUR
Tidal streams – In the narrowest part of the entrance, as springs, the flood stream begins +0515 Portsmouth (+0530 Dover); the ebb stream begins +0025 Portsmouth (+0040 Dover). The flood stream runs in two periods; in the first the rate increases to a maximum of one knot – 0500 Portsmouth (-0445 Dover), then decreases to a minimum of 0.6 knot -0400 Portsmouth (-0345 Dover), then again increases, and the greatest rate, 3.3 knots, is attained -0130 Portsmouth (-0115 Dover). The ebb stream, unlike the stream off Victoria pier, runs in one period only; its rate increases rather slowly at first, till about +0130 Portsmouth (+0145 Dover), and then rapidly, and the greatest rate, 4.9 knots (corresponding to 6 knots or more with tides of the greatest range), is attained +0300 Portsmouth (+0315 Dover).
From the entrance inwards, the streams do not change appreciably, though there is some small decrease in the rates, especially that of the ebb stream, till off The Point. Above this position the times at which the streams begin become gradually, but very slightly, later, and the rates decrease considerably; in mid-channel about west-south-westward of North Corner jetty, the flood stream begins +0545 Portsmouth (+0600 Dover) and attains a rate of 1.7 knots at springs, 0.6 knot at neaps; the ebb stream begins +0030 Portsmouth (+0045 Dover) and attains a rate of 1.5 knots at springs, 0.8 knot at neaps; the flood stream is very weak till after about -0330 Portsmouth (-0315 Dover).
As, from The Point (Lat. 50° 47’ N., Long. 1° 06’ W.), the harbour is ascended, the rate of the ebb stream decreases more rapidly than the rate of the flood stream, and above about Portsmouth Harbour railway station the rate of the flood stream is a little greater than the rate of the ebb stream.
The flood stream runs north-westward, and the ebb stream south-eastward, across the entrance to Haslar lake. There is little stream in Haslar lake, Cold harbour, and Weevil lake.
Eddies are to be expected on both sides of the harbour entrance, and off the piers and jetties on both sides of the harbour, when the streams are running strongly.
Above North Corner jetty the flood stream divides and runs into Fountain, Porchester and Fareham lakes; the Porchester and Fareham lake flood streams also divide and run up the various subsidiary channels; the ebb streams from all the channels meet in the main channel above North Corner jetty.
The streams are very weak in Fountain lake and do not exceed about 0.5 knot at springs in a mid-channel position northward of North Corner jetty, or 0.3 knot at springs between North wall and Whale island. In Fareham lake, in mid-channel southward of the entrance to Porchester lake, the flood stream begins +0545 Portsmouth (+0600 Dover), but is very weak till after -0330 Portsmouth (-0315 Dover) and attains its greatest rate, one knot at springs, 0.5 knot at neaps, -0115 Portsmouth (-0100 Dover); the ebb stream, which is again stronger than the flood, begins +0100 Portsmouth (+0115 Dover), and attains its greatest rate, 1.6 knots at springs, 0.9 knot at neaps, +0300 Portsmouth (+0315 Dover).
The rates of the streams decrease rapidly as Porchester and Fareham creeks are ascended. The ebb stream begins off Porchester castle about +0035 Portsmouth (+0050 Dover), and off the upper town quay at Fareham about +0025 Portsmouth (+0040 Dover); the ebb stream ceases at both places about +0500 Portsmouth (+0515 Dover), after which the stream is probably slack for some 3 hours more before the flood stream begins.