The department shall, after hearing, determine whether it will be of public use and benefit to grant the rights asked for, and in such determination, shall give due consideration to the effect upon scenic and recreational values and upon fish and wildlife and upon the natural flow of the water in the stream below the dam and any hazards to navigation, fishing, bathing and other public uses. The department shall, in all cases, investigate the question whether the cutting clean and removal of all timber and tree growth from all or any part of the flowage area is reasonably required in the public interests, and in such cases as it shall find that such cutting clean and removal of all timber and tree growth from all or any part of the flowage area are so required, such cutting clean and removal of all timber and tree growth shall be a condition to the exercise of such rights. The department shall embody all its findings in its permit.