The more than 2 mile long water tunnel was built in 1915 above the 210 freeway in Sylmar and sent water from the Los Angeles Aqueduct to the now closed Maclay Reservior. It closed 30-years ago.
Now, following a record winter of precipitation, the Department of Water and Power wants to rehabilitate the Maclay Highline and put it back into use.
"If we didn't have this particular asset in place, we would have a difficult time dealing with all the excess water that we have right now," said Mike Grahek, the LADWP manager overseeing the project.
The tunnel has been damaged by several earthquakes. One portion, 75 feet below the mountain, collapsed several years ago. It took work crews two months to repair.
But now, the $3.3 million rehabilitation project is nearly complete.
"We're going to use it this year for sure," Grahek said. "In the future, if we have another plentiful year in the Sierra Nevada, we will be able to utilize it again."
The LADWP said within the next few months the Maclay Highline will begin transferring up to 42 million gallons of water per day from the overflowing L.A. Aqueduct to the Pacoima Spreading Grounds.