Tides

On p. 378 of the 1st volume of the work ‘Zargo’s Islands’ (Ilhas de Zargo) there is the following information, which we take the liberty of transcribing word for word:

“

On the movement of the tidal currents of Madeira, the Hydrographic Mission of the Adjacent Islands (Ilhas Adjacentes) has kindly supplied us with these reliable notes:

During the flood tide the waters come from the southern quadrants; during the ebb, from the north-east quadrant.

The flood waters divide on the south coast of Madeira, running west and east from the stretch between Ponta do Sol (‘point of the sun’) and Ponta do Jardim do Mar (‘point of the garden by the sea’). From this point to Ponta do Pargo (‘sea bream point’), the sea currents generally set from the north-west close to the coast. These currents run parallel to the coast or slightly inclined towards it, and are at times quite strong offshore (in the zone of approximately 500 m depth). Near the headlands they become stronger, sometimes producing a meeting of waters, as can be seen at Ponta do Pargo and above all at Ponta de São Lourenço, where their speeds reach about 2 miles at spring tides.

The flood currents are felt chiefly on the south coast, at Ponta do Pargo and Ponta de São Lourenço, and also on the north-west coast, at Ponta do Tristão (‘Tristão’s point’) and near Ilhéu Mole (Porto Moniz).

The ebb waters produce strong currents towards the south-south-west at Ponta de São Lourenço, towards the west at Ponta de São Jorge and towards the south-west at Ilhéu Mole and Ponta do Tristão. The waters run almost parallel to the coast from Ponta de São Jorge to Ilhéu Mole, that is, on the north coast; on the north-east coast the currents are nil or very weak, except in the deep waters off Ponta do Barlavento (‘windward point’).

The ebb currents are felt chiefly on the north coast, above all at Ponta de São Lourenço and Ilhéu Mole, where at spring tides they reach speeds of 1.5 miles.

At neap tides the currents are generally nil or very weak. These currents are influenced by the prevailing winds and the barometric conditions of the North Atlantic.

At Funchal it is chiefly the flood currents that are felt; they run slightly inclined towards the coast (east-north-east) and at spring tides reach speeds of about 1.2 miles at around half-flood. The ebb currents are generally nil or very weak, the waters running east-north-east and at other times west.

At Porto Moniz, both the flood and the ebb currents are felt at spring tides, but chiefly during the flood counter-currents and surges of water arise at first inside the harbour, the waters running more directly during the ebb at a speed of 1 mile. At Porto da Cruz (‘harbour of the cross’) the currents are generally quite weak or nil.

Around the island of Porto Santo (‘holy harbour’) the sea currents reach their greatest speeds at spring tides, running from the southern quadrants during the flood and from the north-east quadrant during the ebb. They are felt chiefly at the southern point of Ilhéu de Cima (‘upper islet’), where at spring tides the waters run north-east at a speed of 1 mile during the flood and 1.5 during the ebb. At the point of Ilhéu de Baixo (‘lower islet’), during the flood, they run west or east at a speed of 1 mile, at spring tides, during the ebb.

The tides are very regular, with two high waters and two low waters every day. The values of the harmonic and non-harmonic constants are those of the tables drawn up by the Hydrographic Mission of the Adjacent Islands (Ilhas Adjacentes). By comparing the values of the establishments of the port (time of high water at full and new moon), one obtains the differences between the times of high and low water at the respective ports’. These tables are printed on p. 380 ff. of ‘Zargo’s Islands’.

Since 1939 the ‘Junta Autonoma dos Portos do Arquipélago da Madeira’ has published every year an interesting booklet entitled Tabela das Marés no Porto do Funchal, which gives precisely, from 1 January to 31 December and at stated times, the heights of the high and low waters, taken morning and afternoon within the harbour of Funchal (Porto do Funchal). These data are preceded by the following notes: ‘This table was calculated by the Hydrological Mission of the Adjacent Islands from the records of 1937 supplied by the same Mission’s tide gauge, installed on the Molhe da Pontinha (‘little point breakwater’). The heights in the tide table refer to the plane of hydrographic zero, which lies 1.40 m below mean sea level (1937) and 4.138 m below the level mark of the Hydrographic Mission of the Adjacent Islands on the upper rim of the well of its tide gauge. – The times are Funchal legal time (Greenwich Mean Time minus one hour).

The ‘tidal elements’ for the port of Funchal given there are as follows: unit of height 1.06 m, maximum observed range 2.58 m, mean deduced range 1.53 m, minimum observed range 0.55 m, maximum diurnal inequality in height 0.25 m, and the ‘establishment of the port’ 0 h 32 min.

The establishment of the port, or the time of high water at spring tides, is at Funchal, according to the geographical map of General António Pedro de Azevedo, 12 h 48 min, the rise of the tide being 2.28 m’.