[Bonds considered additional to other bonds; authority to

issue; limitations.] The bonds authorized to be issued under the terms hereof shall not in any manner impair the original construction fund bond issue, but shall be considered as additional securities authorized to be issued by conservancy districts, and full legislative authority is hereby granted to said districts to sell tax anticipation bonds, refunding bonds, debentures and other negotiable securities, pledging the full faith and credit of such districts, and power is hereby granted to such districts for the levy of special assessments to pay the same, but in no event shall the assessments or outstanding obligations of such districts exceed the amount of the benefits confirmed and approved.