81
The small circles in the tide tables
indicate moon stages (see page 82 for tide tables in Oct/Nov): - October 9th is a full moon, Oct 17th is a half moon, Oct 25th is a new moon. Whenever you see the moon you learn a bit about the tide. See a half moon and it’s neaps - see a full moon and it’s springs. The range of the tide is worked out by deducting the height of a low water from the height of a subsequent or preceding high water. When you study a tide table, make sure you adjust the times of tides for British Summer Time. Some tide tables do this but not all e.g. the tide tables in this magazine require you to add 1 hour for BST. But remember these are tide predictions as barometric pressure and wind will influence both tide times and heights. Unusually high pressure will depress tidal heights and unusually low pressure has the reverse effect. A 34mb difference from the average can cause differences in height of up to 0.3m. Strong winds also have an effect.
Sea levels are raised on a lee shore with lower levels on a weather shore. Winds under about force 5 will have little effect. These effects are very variable and depend on the topography of the area but does explain why places on the river such as Bayards Cove can flood when spring tides are unusually high and/or when low pressure storms and high winds prevail. Bayards Cove is arguably a lee shore to a south westerly storm coming up the river. In Dartmouth, when there are spring tides, it is normal for the
time of high tide to be roughly 8am and 8pm, plus or minus an hour or two. You won’t get a spring high tide at lunchtime. A neap tide is always high about lunchtime. This is a local rule, it would not apply in other harbours. The time of high tide gets later each day (by roughly 50 minutes). Why? If you are directly under the moon now you won’t be in 24 hours’ time because the moon will have moved on a bit (by 1/28th of its orbit).
The strength of the current is fastest in the centre of
the river and will be slower if you are close to the edge
It’s important to understand the 1/12 rule of tides. The rule states that in the first hour after low tide the water level will rise by one-twelfth of the range, in the second-hour two-twelfths, and so on. The sequence of steps being 1 : 2 : 3 : 3 : 2 : 1 across the approx 6 hours between the tides. The tide is, therefore, running fastest in the middle of the tide i.e. half the volume of water moves in the middle two hours. The tide is strongest where
the river is narrowest, eg near Dittisham and between the castles at Dartmouth. Typically, a Spring tide will be running as fast as 2 knots at full strength in the middle of the river. This explains why falling in the river from e.g. the Darthaven visitors pontoon on a dark winter’s night on an ebbing Spring tide can easily prove fatal as the poor victim is quickly transported out to the castles. If you have to paddle a board
or kayak against the tide it is always better to stay really tight close to the side of the river. The strength of the current is fastest in the centre of the river and will be slower if you are close to the edge - a boat’s length or two from the side is often best. If paddling a board or piloting a small boat it is tempting to go where the depth of the river is lowest. At spring tides, however, there are large areas of mud that appear at low water. Dragging a board across mud or being marooned on a small boat waiting for the tide to return can easily spoil your day out. The river areas where you can get stuck on the mud are at Old Mill Creek, just upriver from the Naval College and Flat Owers, an area in the widest part go the estuary between Dittisham and Galmpton. A large triangular mud island appears at low tide which is notorious for ensnaring unwary owners of yachts and motorboats and keeping them firmly in its clutches until the tide comes back in hours later.
Sources: DHNA, DYC, South Devon AONB
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108
