Tidal Stream Atlas: Strait of Gibraltar, 1st Edition

The Atlas includes background information and supporting notes on tidal streams in the Strait, followed by charts covering each hourly interval from 5 hours before HW Gibraltar to 6 hours after HW Gibraltar. A notes section is also included for reference.

The introductory information explains the semidiurnal tidal pattern within the Strait, the average tidal ranges during spring and neap tides, the direction and timing of flood and ebb streams, and variations in stream rates. It also describes the complex two-layer current system, including the predominant easterly surface current flowing into the Mediterranean and the denser westerly sub-current known as the Mediterranean outflow.

This Witherbys’ Tidal Stream Atlas for the Strait of Gibraltar contains tidal stream information for the sea area from West of Cape Trafalgar to East of Gibraltar. Tidal stream charts are provided for hourly intervals relative to HW Gibraltar, commencing at 5 hours before HW until 6 hours after HW. The rate values shown on the charts are in knots.

Tides

Tides within the Strait of Gibraltar are semidiurnal, meaning there are two high tides and two low tides in every 24 hours (usually of comparable height). During springs, there is a maximum average range of 1.4 m between low and high water. During neaps, the minimum average is reduced to 0.6 m.

The flood tide is Westerly moving, and the ebb is Easterly.

The Easterly flood commences around the time of HW Gibraltar and runs until approximately 6 hours after HW, at which point it turns and begins to flow Westerly on the ebb. During springs, the rates may exceed the predictions shown on the charts. At neaps, the rates will be weaker than those shown.

Currents

The Strait of Gibraltar contains a complex two layer current system where the surface currents act independently of the deeper sub-currents. This is driven by the difference in salinity between the waters of the Mediterranean Sea and the North Atlantic Ocean.

Generally, there is a predominant Easterly surface current that moves inwards from the Atlantic. This Easterly current typically has a velocity of 1–2 knots across the Strait.

Below the surface, the sub-current is much denser and runs Westerly out into the Atlantic. This outflow does not have much navigational impact, however it can be a contributory factor to surface turbulence within the water. This sub-current is referred to as the Mediterranean outflow.

Background and Supporting Notes to the Tidal Atlas

5 hrs before HW Gibraltar
4 hrs before HW Gibraltar
3 hrs before HW Gibraltar
2 hrs before HW Gibraltar
1 hr before HW Gibraltar

HW Gibraltar

1 hr after HW Gibraltar
2 hrs after HW Gibraltar
3 hrs after HW Gibraltar
4 hrs after HW Gibraltar
5 hr after HW Gibraltar
6 hrs after HW Gibraltar

Notes

Witherbys

Witherbys titles are developed using scripts developed by technical experts that are peer reviewed within work groups. Typically, they seek to improve understanding of the regulations, recommendations and guidelines issued by Industry.

Witherbys staff have significant expertise in the fields of navigation and hazardous cargoes as well as in the presentation of complex subjects in a graphic and easy to understand manner.