The time gap between spring and neap is approximately 7 days. The neap tides refers to a period of moderate tides when the sun and moon are at right angles to each other. The spring tides are high tides.
Plunge pool or waterfall lake is a deep depression in the stream bed at the base of the waterfall. It is created by the erosional force of the cascading water. They occur at the youthful stage of the river development.