I read your report where “The authorities are continuing to monitor the effects of spring tides…” (December 31, 2009).
Spring tides are regular, easy to predict, fortnightly occurrences known the world over. The average citizen should just need a calendar with the phases of the moon.
Sea defence engineers at the Public Works Ministry should know additionally that:
1. The chief theoretical effects are at full moon, new moon, and perigee. The effects are reinforced when perigee, when the moon is closest to the earth in the lunar month, is near. This time, full moon was December 31, 2009, and perigee was January 1, 2010, only one day apart.
2. The times of the maximum gravitational influence of the moon on the tides is approximately 4 hours after its zenith on either side of the earth. The moon was fullest at 15:14 Guyana Standard Time on December 31, 2009, three-and-a-quarter hours after zenith on the other side of the earth, just about when the highest spring tides are due here.
3. There are resonances that reinforce the gravitational effects of the moon and sun. There is a maximum resonance when the sun and the moon are 0 and 180 degrees away in any surface dimension. On December 31, 2009 the sun and moon were on opposite sides of the earth in both the surface dimensions of latitude and longitude: double maximum resonance!
There are also other resonances and effects, eg, the shape of the coast and the nature of the beaches. These change with time and sometimes with effort.
I am sure the tide tables published by the T&HD would take the above three effects into consideration. However, if they are still compiled by the British Admiralty based on old data from when they were in authority here (and merely copied by the T&HD), then it is high time the present authorities get their own data from a properly based tidal gauge, and compile accurate tide tables. I was made to understand that even one inch of shipping is of economic significance.
I first brought this to the attention of the authorities about 1980. Nothing was done. I brought it also to public attention in 2000. Now at the turn of this new decade I am asking that “monitoring” take place not only during disasters, however mild, but that it be compulsorily ongoing, so that we can learn from the data.
Yours faithfully,
Alfred Bhulai
