New Orleans voters Saturday overwhelmingly approved a measure to raise property taxes to provide more money for the struggling New Orleans Public Library system.

The request for a 25-year, 2.5-mill tax that would raise a projected $8.25 million a year for the library system — money that city and library officials say is necessary for the system to continue operating its 14 branches and to reopen one that has been closed for nearly 10 years — cruised to an easy victory, with about 75 percent of voters in favor.

The tax will be in addition to the 3.14 mills now dedicated to the library. That tax expires at the end of 2021.

The new millage will give the system enough money to extend the hours and days of operation at all its branches, library system Executive Director Charles Brown has said. It also will allow the system to purchase more books, e-books, music and videos for its permanent collections. The tax increase also can support additional outreach efforts and services, like a mobile library and computer classes.

If the measure had failed, the library system would not have been able to reach those goals, and half of its 14 branches might have had to be shut down, Brown said.

The library has been supporting itself over the past three years by joining the money raised from the existing millage with funds drawn from a reserve account accumulated when many of the city’s libraries were closed after Hurricane Katrina. That surplus will be exhausted by mid-2016, officials have said.

The library system’s budget for 2015 is about $13 million. About $9.5 million of that will be funded by the existing millage. Another $530,000 will come from the city’s general fund, state grants, donations, fines and fees. The balance, about $3 million, will be pulled from the reserve account. The City Council contributed $200,000 from the general fund after learning of the library’s plight during budget hearings last fall.

The system needs about $18 million annually to operate at an optimal level, Brown has said.

With the new tax, the library system intends to increase its hours of operation and to keep the six largest branches open seven days a week and the others open six days a week.

With the exception of the Latter Memorial Library on St. Charles Avenue, which is open seven days a week, and the Martin Luther King Library in the Lower 9th Ward, which is open Monday through Friday, all of the libraries have been closed on Fridays and Sundays. Most close at 7 p.m. during the week.

If the tax proposal had failed, the system would have had to reduce those already skimpy hours of operation by 35 percent. It also would have had to close seven of the 14 libraries and drop plans to reopen the Nora Navra branch, which has been closed since flooding in 2005.

Six of the system’s 13 locations were destroyed following the storm. Twelve of those branches are now open, and two new ones have been added, for a total of 14 active branches. The Nora Navra branch on St. Bernard Avenue in the 7th Ward is the only one that remains closed.