Section 16. In any case where the commonwealth, or a county, city, town or district thereof, has been or shall be authorized by provisions of general or special law to take real estate or any interest therein by eminent domain under chapter seventy-nine, the officer or board of officers thereof authorized to exercise such power may, unless otherwise provided, elect to take such property or interest under this chapter and, if betterments are to be assessed, to assess the same hereunder.