Reimbursement for work commenced by non-Federal public bodies no later than one year after August 13, 1968, to carry out or assist in carrying out projects for beach erosion control, may be made in accordance with the provisions of section
426f of title
33. Reimbursement for such work may, as an alternative, be made in accordance with the provisions of this section, provided that agreement required herein shall have been executed prior to commencement of the work. Expenditures for projects for beach erosion control commenced by non-Federal public bodies subsequent to one year after August 13, 1968, may be reimbursed by the Secretary of the Army, acting through the Chief of Engineers, only in accordance with the provisions of this section.