(2) A person shall not be guilty of an offence under sub- section (1), by reason only of having done or caused to be done any of the following acts, namely:-
constructing, improving or maintaining in or across or on the bank or bed of any stream any building, bridge, weir, dam, sluice, dock, pier, drain or sewer or other permanent works which he has a right to construct, improve or maintain;
depositing any materials on the bank or in the bed of any stream for the purpose of reclaiming land or for supporting, repairing or protecting the bank or bed of such stream provided such materials are not capable of polluting such stream;
putting into any stream any sand or gravel or other natural deposit which has flowed from or been deposited by the current of such stream;
causing or permitting, with the consent of the State Board, the deposit accumulated in a well pond or reservoir to enter into any stream.