When the establishment of such lines in accordance with sections 22a-342 to 22a-348, inclusive, requires that they be placed through portions of or so as to include entire existing structures within the regulated area, such structures or portions thereof shall be considered as a nonconforming use of the area, except that, if the structure is destroyed or damaged to the extent of more than fifty per cent of the fair market value, such structure shall be replaced or repaired only through a permit from the commissioner, provided the commissioner may define types of structures which may be reconstructed within such lines without a permit. Whenever the commissioner finds that existing structures or encroachments within the lines established constitute a hazard to life and property in the event of flood, he is empowered to take such land and structure as provided by part I of chapter 835 and cause removal of such encroachment.