Interesting tidal flows – Tidal Diamonds

Tidal diamonds are invaluable sources of information in relation to the speed and direction of tidal streams.  They are essential when working out bearings to follow on a crossing, by drawing tidal vectors.  Whilst away on a paddling trip earlier this year I came across, what must be an almost unique tidal diamond?  It is Tidal Diamond C on Admiralty Chart 808, East Guernsey, Herm and Sark.

49°27.5 N
2°31.4 W
Hours
Dir
Rate (kn)
  Sp           Np
-6
-5
-4
-3
-2
-1
HW
+1
+2
+3
+4
+5
+6
213
213
213
213
033
033
033
033
033
033
213
213
213
5.1            2.2
4.1            1.8
2.7            1.2
1.2            0.5
1.2            0.5
3.9            1.7
5.2                  2.2
 4.9            2.1
 3.3            1.4
 1.5            0.5
 1.3            0.5
 4.0            1.7
 5.2            2.2

The first observation is that the streams only flow in two directions, exactly opposite each other.  The tide is flowing approximately SSW and then it changes abruptly and goes NNE.  An exact 180° change.
Something else to note is that maximum rate occurs at high and low water, with slack water, if it can be called that, occurring at mid tide.  Many a sea kayaker and other water users have been caught unawares because they assume that maximum rate must occur at mid tide and have set out to cross the Little Russel on what they thought was high water slack.
The advice is to always double check your data and to keep your eyes open for interesting and possibly unique items of information as shown by this tidal diamond.

Tidal Diamond
The location of the diamond is in line with the two towers on the photograph and to the right of Brehon Tower, which is in the middle of the channel between Guernsey and Herm, the Little Russel.


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