Directional current structures occurring in the intertidal zone of the Minas basin at Five Islands, Nova Scotia, include sand waves, megaripples, current ripples, cross-stratification, micro-cross-laminae, scour striae, and flute markings. Their orientation is controlled either by ebb tidal currents or by sheet runoff at low tide. Depth of water, local topographic obstructions, and presence or absence of strong winds exert local influences on the orientation of these directional current structures.

Tidal currents flow at an average velocity of 1.3 knots during flood stage and 1.5 knots at ebb stage. Flood currents flow in an average direction of 60°, whereas ebb currents flow toward an average direction of 255° (readings given in azimuths). Locally, however (such as on the northwestern side of some east-west-oriented islands), ebb currents continue to flow toward the northeast for 2 hours after the shift from the flood to the ebb phase. Such a time lag in shift of flow direction is reflected in the orientation of primary structures. In the northwest lee of these islands, sand waves were observed to be face-oriented toward the northeast. Because sand-wave migration occurs at maximum water depths during the 2 hours before and after the shift from flood to ebb stage, they continue to be face-oriented toward the northeast at the northwest sides of islands. The megaripples and current ripples are formed by ebb tidal currents at lower water depths and are oriented southwestward. In open reaches where change in flow direction coincides with the change from the flood to ebb phase, sand waves as well as superimposed megaripples and current ripples are oriented southwestward.

During the 15 minutes preceding emergence of the intertidal zone, slope-controlled sheet runoff and channel flow in sand-wave troughs dominate the flow systems and form current ripples and flute markings. Their orientation reflects local slope changes. The depth of reworking of such sheet runoff seldom exceeds 1 inch. Consequently, although current ripples formed by sheet runoff may be superimposed on sand waves and megaripples, the internal micro-cross-laminae so produced are, in very few cases, of any consequence in box cores or trenches. Preserved internal cross-stratification, oriented in the same direction as steep faces of sand waves and megaripples, is produced by ebb currents of considerable velocity.

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