Explanation
Option (a) is incorrect: Tidal phenomena are influenced by the shape of coastal features. A common misconception is that gulfs with narrow openings and wider interiors experience amplified tides. In reality, the opposite is true. Gulfs characterized by wide entrances and narrowing interiors, like a funnel, tend to exhibit higher tides. This occurs because the incoming tidal surge is compressed as it moves into the narrowing gulf, forcing the water level to rise. Options (b), (c) and (d) are correct:
Tidal currents, on the other hand, are generated when a gulf or bay is connected to the open sea through a narrow channel, as the water flows in and out with the tides. A tidal bore occurs when an incoming tide moves into a narrow, shallow, and funnel-shaped estuary, creating a sudden upstream surge of water. The narrowing estuary amplifies the tide’s height and velocity, while the shallow depth slows the river’s flow, allowing the tide to push upstream forcefully. This phenomenon is common in areas with a high tidal range, such as the Hooghly River in India and the Qiantang River in China. The tidal influence on the Hooghly River’s mouth is critical for the Kolkata Port as it facilitates navigation despite the river’s shallow depth. The semi-diurnal tides, with a range of up to 5 meters, help maintain water levels, enabling large vessels to access the port. Additionally, tidal currents assist in flushing out silt and sediments, which would otherwise accumulate and obstruct navigation channels. This natural tidal mechanism, combined with dredging efforts, ensures year-round operability of the port.