Correct Option
The correct option is 1, 2, 3 and 4.
Explanation
Tides are the periodic rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth. These vertical movements of water generate tidal currents, which have significant geomorphological, ecological, and economic applications.
Statement-wise Analysis
- Statement 1 is Correct: Tides play a crucial role in desilting river estuaries. The strong tidal currents, particularly the outgoing ebb tide, help scour sediments and silt from the river mouth and transport them into the deeper sea. This natural flushing mechanism prevents the clogging of estuaries.
- Statement 2 is Correct: Tides assist in removing polluted water from estuaries. The cyclic inflow of clean seawater during high tide and the outflow of water during low tide create a flushing effect. This process dilutes pollutants and carries sewage or industrial waste away from the coast, thereby aiding in the self-purification of estuarine ecosystems.
- Statement 3 is Correct: Tides are a source of renewable energy. The potential energy difference between high and low tides, as well as the kinetic energy of tidal currents, can be harnessed to generate electricity. Tidal power plants (e.g., tidal barrages) utilize this energy, making it a viable non-conventional energy source.
- Statement 4 is Correct: Tides are vital for navigation in harbours with shallow bars or riverine ports. High tides raise the water level, allowing large ships to cross shallow sandbars and enter harbours safely. Ports like Kandla (tidal port) and Kolkata (riverine port) in India depend on high tides for the movement of heavy vessels.
Key Takeaway
Tides are essential for navigation (raising water levels for ports), energy generation (tidal power), and ecological maintenance (desilting sediments and flushing pollutants from estuaries).