MINUTES. >>> SANTA CLARA COUNTY HAS A NEW TUNNEL, NOT FOR CARS OR PEOPLE, BUT FOR WATER. IT COULD PREVENT FLOODING IN THE FUTURE. AS OUR LEN RAMIREZ REPORTS, IT'S PART OF A HUGE PROJECT TO REBUILD ANDERSON RESERVOIR. >> Reporter: DESPITE ALL THE RAIN THAT WE'VE HAD THIS YEAR, THE ANDERSON RESERVOIR LEVELS HAVE HAD TO BE KEPT ARTIFICIALLY LOW BECAUSE THE DAM ITSELF IS NOT EARTHQUAKE SAFE, BUT THIS NEW TUNNEL, THIS OUTLET TUNNEL THAT THEY'RE BUILDING RIGHT UNDERNEATH MY FEET, IS THE FIRST MAJOR MILESTONE IN THE RETROFIT OF THE DAM WHICH WILL MEET THE WATER NEEDS OF SANTA CLARA COUNTY FOR MANY YEARS TO COME. RYAN MCCARTTER IS WALKING THROUGH A TUNNEL BORED DEEP INTO THE SIDE OF A MOUNTAIN AT ANDERSON RESERVOIR. >> WE'RE BASICALLY TOUCHING A RESERVOIR WITH THIS TUNNEL. WE'RE BELOW WATER. >> Reporter: THE TUNNEL IS ALMOST HALF A MILE LONG AND 200 FEET BELOW THE ANDERSON FLOOR. IT'S PART OF A $2.3 BILLION PROJECT TO RETROFIT SANTA CLARA COUNTY'S LARGEST RESERVOIR TO PREVENT FLOODING DURING WENT YEARS AND SURVIVE A MAJOR EARTHQUAKE. >> SO THIS IS A SPRAY-APPLIED CONCRETE THEY SHOOT IN. WE'VE GOT ABOUT EIGHT INCHES OF CONCRETE BEHIND HERE PLUS THESE STEEL RIBS EVERY THREE TO FIVE FEET. >> Reporter: THIS IS THE ORIGINAL OUTLET BUILT IN 1950 AT THE BASE OF THE DAM. THE NEW TUNNEL WILL DISCHARGE 15 TIMES MORE WATER. IT'S ALL DESIGNED TO PREVENT THE DAM FROM SPILLING OVER. IN 2017 TORRENTS OF WATER GUSHED OVER THE SPILLWAY AND LED TO MAJOR FLOODING IN COYOTE CREEK IN DOWNTOWN SAN JOSE. >> IF THIS PROJECT HAD BEEN IN PLACE IN 2017, HE WOULD NOT HAVE SEEN THE FLOODING WE DID THERE. THIS PROJECT IS SO IMPORTANT AND SO BIG IT REACHES ALL THE WAY INTO AL VISO. >> Reporter: THE TUNNEL WILL ALSO ALLOW THE SANTA CLARA WATER DISTRICT TO BETTER MANAGE WATER RESOURCES FOR WILDLIFE HABITAT AND DROUGHT PREVENTION. RYAN SAYS COMPLETING THE PROJECT IN A YEAR AND A HALF IS PART OF A MAJOR MILESTONE. >> REALLY PASS FASCINATING TO ME TO SEE SOMETHING ON PAPER WE'VE PLANNED AND DESIGNED FOR SO LONG AND SEEING IT BUILT. >> Reporter:
