It shall not be necessary to obtain a permit to repair any structure mentioned in this article if such structure is now or may be hereafter maintained under a grant as provided in this article; provided, that the repair provided for in this section shall not affect or change the drift of sands, or alter the current of waters in a manner different from the effect such structure had on the current or drift of sands, or alter the current of the waters in a manner different from the effect such structure had on the current or drift prior to the arising of the condition necessitating such repair, and providing such repair shall only restore the structure to its original condition.