What is Double Tide? How it is formed?

A tidal regime wherein the tide rise to a max., falls slightly, and then rises to a 2nd max is known as Double Tide.

If the harmonic curves of a semi-diurnal and quarter-diurnal tide are combined, they produce a double high tide if the initial phase difference between the constituents is near 180 degrees. If the initial phase difference is near zero degrees, it results in a double low tide.