Explanation (2) In the following cases, that is to say (a) Whenever owing to any sudden change in the channel of any navigable river or other unforeseen emergency, it becomes necessary for any Railway Administration to acquire the 'immediate possession of any land for the maintenance of their traffic or for the purpose of making thereon a river side or ghat, station or of (1) 876 providing convenient connection with or access to any such station; (b) Whenever in the opinion of the Collector it becomes necessary to acquire the immediate possession of any land for the purpose of any library or educational institution or for the construction, extension or improvement of any building or other structure in any village for the common use of the inhabitants of such village, or any godown for, any society registered under the (Act 11 of 1912), or any dwelling house for the poor, or the construction of labour colonies or houses for any other class of people under a Govermnent sponsored 'Housing Scheme or any irrigation tank, irrigation or drainage channel, or any well, or any public road; (c) Whenever land is required for a public purpose which in the opinion of the appropriate Government is of urgent importance, the Collector may, immediately after the, publication of the notice mentioned in sub section (1) and with the previous sanction of the appropriate Government enter upon and take possession of such land, which shall thereupon vest absolutely in the Government free from all encumbrances.