A. For the accomplishment of the official plan, the board of directors of any district shall have full power and authority to improve in alignment, section, grade, location or in any other manner, any watercourse, and they may remove, widen, lengthen, lower, raise or otherwise change any public or private road bridge or railroad bridge, or any flume, aqueduct or telephone, telegraph, gas, oil, sewer, water or other pipelines or any other construction, over, across, in, into, under or through any such watercourse, or may require the same to be done, and the foregoing shall apply to all such changes specified by the official plan, or reasonably necessary for the accomplishment of the same; provided, however, that whenever any such change is made necessary in any construction because of the failure of the same to permit the free flow of the water in such stream in time of flood, or to permit the necessary enlargement or protection of the channel, then the owner of such construction shall make such change and all adjustments of grade, roadway, track, approach or other construction incidental thereto, without cost to the district, and without any claim for damages against the district; except that the district shall pay the cost of excavating the earth for the enlargement of any channel, or for placing earth for the filling of any channel, where such excavation or filling is required as a part of the official plan in making the changes outlined in this section; but the district shall not be required to make such fill or excavation unless the same would be necessary to the official plan if the construction or work so changed did not exist. Before the removal, change or modification of any work or construction outlined in this section, the board of directors shall give notice to the owner thereof, requiring that the same be adapted to the official plan. In case such removals, changes or adjustments are not commenced and completed by the owner within the respective times specified therefor in such notice (which time shall be reasonable under all the circumstances) such removals, changes or adjustments may be made by the district, at the expense of the owner.