Currents, Tides and Undertows

Water can move around a person or vessel, carrying it towards or away from a chosen destination. The direction someone faces, the direction in which they act and their resulting movement relative to the shore may differ.

The language of currents and tides often describes changing circumstances, collective activity and the effort involved in proceeding with or against a prevailing movement.

Physical Background

Tides are changes in water level associated with the gravitational influence of the Moon and Sun. Currents are flows of water. Tidal changes can generate currents, while winds and differences in water density also drive ocean circulation. Density differences arise through variations in temperature and salinity. NOAA: Tides and Currents

Types and Characteristics

River currents: Carry water along a channel, with speed and direction varying around bends and obstacles.
Tidal currents: Accompany tidal changes in coastal waters, channels and estuaries.
Wind-driven currents: Move water at or near the surface in response to wind.
Eddies: Circulating movements within a larger flow.
Undercurrents: Flows beneath the surface or below another current.
Undertow: A return flow near the seabed generated by breaking waves.
Rip currents: Concentrated flows travelling away from shore through the surf zone.

Undertow and rip currents are separate processes. The National Weather Service describes undertow as a near-bed return flow and distinguishes it from the concentrated outward movement of a rip current. National Weather Service: Rip Current Science

Movement Relative to the Shore

A boat can make progress through the water while making little progress past a fixed point on land if the water is moving the other way. Conversely, a drifting object can change its position substantially without generating its own propulsion.

These relationships make the reference point important. Remaining beside a buoy, moving with a floating object and approaching the shore are different measures of movement. A changing tide can also alter access to a landing place without changing the traveller's destination.

Literary Examples

In Shakespeare's Julius Caesar, Act IV, Scene III, Brutus uses a tide and voyage to argue that an opportunity should be taken while circumstances favour it. He links the image to the decision to advance towards Philippi. Folger Shakespeare Library: Julius Caesar, Act IV, Scene III

The speech uses moving water to describe timing and opportunity. It expresses Brutus's judgement at that moment in the play, rather than establishing that going with a current will always produce a favourable result.

Close reading: a current used to persuade

Brutus concludes his maritime comparison by presenting action as urgent:

And we must take the current when it serves
Or lose our ventures.

Brutus, Shakespeare’s Julius Caesar, Act 4, scene 3, lines 254–255.^[1]

The conditional timing matters: Brutus argues that present conditions favour movement and will not remain favourable indefinitely. Cassius has offered a different calculation, preferring to let the enemy advance and expend resources while their own forces rest. The current is therefore part of an argument between commanders, not a neutral measurement both already accept. Brutus’s concluding alternatives narrow the decision to using the opportunity or losing the undertaking, and Cassius agrees to proceed. Attending to the exchange shows how a movement metaphor can make one proposed action feel necessary while another speaker has described a reason to remain in place.

Idioms and Figurative Expressions

Go with the flow: Adapt to events or follow what others are doing.
Swim against the tide: Act against a prevailing opinion, practice or movement.
Turn the tide: Change the direction in which a situation is developing.
Stem the tide: Check or reduce an unwelcome developing trend.
At a low ebb: In a weakened or depleted condition.
An undercurrent of resentment: Resentment that influences a situation without being openly expressed.
Swept along: Carried into activity or events with little opportunity for independent direction.
Tide someone over: Provide enough assistance or resources to get through a temporary difficulty.

Homophones

Tide / tied: Tide concerns changing water levels. Tied describes attachment or restraint, as well as an equal score.

Current / currant: A current is a flow. A currant is a small fruit or, in another culinary use, a small dried grape.

Video

This National Weather Service demonstration uses green dye to make a rip current visible. It illustrates water moving away from the shore, supporting the article's distinction between rip currents, tidal movement and undertow. NOAA's explanation and original embed.