Step 1: Understanding the Concept:
The question asks for the legal doctrine that was prominently applied and evolved by the Supreme Court in the Kamal Nath case. The case is M.C. Mehta v. Kamal Nath.
Step 2: Detailed Explanation:
In the case of M.C. Mehta v. Kamal Nath (1997), a PIL was filed regarding the unauthorized construction of a motel on the banks of the River Beas in Himachal Pradesh, which involved diverting the river's course. The family of the then minister, Kamal Nath, was involved.
The Supreme Court, in its judgment, invoked the Public Trust Doctrine. This doctrine, rooted in common law, posits that certain natural resources like rivers, forests, and air are held by the government in trust for the free and unimpeded use of the general public. The state, as a trustee, has a legal duty to protect these resources for the enjoyment of the public and cannot permit their use for private or commercial purposes in a way that harms the public interest.
The Court held that the government had committed a breach of public trust by leasing this ecologically fragile land and ordered the motel to pay compensation for the restoration of the environment ('Polluter Pays Principle') and to hand over the land to the government.
Step 3: Final Answer:
The Supreme Court in the Kamal Nath case evolved and applied the Public Trust Doctrine.