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The rule states that over the first period the quantity increases by 1/12. Then in the second period by 2/12, in the third by 3/12, in the fourth by 3/12, fifth by 2/12 and at the end of the sixth period reaches its maximum with an increase of 1/12. The steps are 1:2:3:3:2:1 giving a total change of 12/12.
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. [1] Tide heights at intermediate times (between high and low water) can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal ...
The first tide predicting machine (TPM) was built in 1872 by the Légé Engineering Company. [11] A model of it was exhibited at the British Association meeting in 1873 [12] (for computing 8 tidal components), followed in 1875-76 by a machine on a slightly larger scale (for computing 10 tidal components), was designed by Sir William Thomson (who later became Lord Kelvin). [13]
The sluice gates applicable to tidal power are the flap gate, vertical rising gate, radial gate, and rising sector. Only a few such plants exist. The first was the Rance Tidal Power Station , on the Rance river , in France, which has been operating since 1966 and generates 240MW.
Head of tide, tidal limit [2] or tidehead [3] is the farthest point upstream where a river is affected by tidal fluctuations, [4] or where the fluctuations are less than a certain amount. [5] The river section influenced by tides and marine forces but without salinity is a tidal river , while downstream areas are brackish and termed estuaries .
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Tidal mill at Olhão, Portugal. A tide mill is a water mill driven by tidal rise and fall. A dam with a sluice is created across a suitable tidal inlet, or a section of river estuary is made into a reservoir. As the tide comes in, it enters the mill pond through a one-way gate, and this gate closes automatically when the tide begins to fall.
A tidal atlas or a tidal stream atlas is used to predict the direction and speed of tidal currents. A tidal atlas usually consists of a set of 12 or 13 diagrams, one for each hour of the tidal cycle, for a coastal region. Each diagram uses arrows to indicate the direction of the flow at that time.