Where "the plan for reclamation" of the drainage district is found insufficient to reclaim in whole or in part any or all of the land of the district, the board of supervisors shall have the right to formulate new or amended plans containing new ditches, levees or other works, and additional assessments may be made in conformity with the provisions of section thirteen, the same to be made in proportion to the increased benefits accruing to the lands because of the additional works. If it should be found at any time that the amount of total tax levied under the provisions of section eighteen is insufficient to pay the costs of the works set out in "the plan for reclamation," or additional work done under the provisions of this section, the board of supervisors may make an additional levy to provide funds to complete the work, provided the total of all the levies of such tax does not exceed the total amount of benefits assessed.