By pipes above and under floor, Hetch Hetchy Reservoir water flows 150 miles via a collection of tunnels, energy vegetation and reservoirs earlier than reaching the Bay Space’s native water system 32 hours later. Benefiting from slope adjustments from the Sierra Nevada to the Bay Space, the unique engineers had been in a position to assemble a possible path for water to journey fully by way of one of the vital climate-friendly vitality sources obtainable: gravity.

By the top of the present mission, water will nonetheless circulate via the Mountain Tunnel by gravity, however there will even be some modernization enhancements: pipes that management the quantity of water flowing out and in; bigger tunnel entrances that may accommodate building gear; grout sealants to guard the tunnel lining from chipping as shortly as doable.

We need to get one other 100 years out of this useful resource, stated mission supervisor Randy Anderson.

Fifteen years in the past, SFPUC thought-about constructing a brand new tunnel to exchange the Mountain Tunnel, which on the time was estimated to price greater than $500 million, or possible a billion {dollars} immediately, Miller stated. As a substitute, the company determined to restore the prevailing tunnel over the course of six winters beginning in January 2021 at a complete price of $238 million.

The prices for constructing the mountain tunnel come from retail and buyer income, SFPUC spokesman Joseph Sweiss stated. SFPUC is at the moment proposing to extend water and sewer charges over the following three fiscal years, beginning in July, by $12.69 per 12 months for the common San Francisco single-family residential family.

The speed will increase are to pay for important providers and improve outdated techniques to stop outages, meet regulatory necessities, enhance seismic security, and adapt to droughts and storms because the local weather adjustments, in keeping with Sweiss. SFPUC will maintain a public listening to on Might 23 on the proposed charge improve.

SFPUC is utilizing low-interest loans from California’s Clear Water State Revolving Fund program to assist fund the Mountain Tunnel Enchancment Venture, which is able to save taxpayers greater than $100 million, Sweiss stated.

We’ve extra work to do than we may afford, Miller stated. However we have to get this important work performed so we will proceed to ship dependable water to individuals.

About 85 % of the water provide for two.4 million individuals in San Francisco, Santa Clara and San Mateo and Alameda counties comes from snowmelt from the Sierra Nevada saved within the Hetch Hetchy Reservoir. The opposite 15 % comes from native reservoirs in Calaveras and San Antonio within the East Bay, and Pilarcitos and Crystal Springs within the peninsula, Sweiss stated. There’s additionally a small quantity of groundwater for San Francisco prospects, Sweiss stated.

Repairs can solely occur in the course of the winter, when water demand is low and the Bay Space can get by with its native reservoirs, which retailer water from Hetch Hetchy and native rainfall, Miller stated.

One already accomplished aspect of the mission is the brand new circulate management construction, referred to as the guts of the rehabilitation mission, Anderson stated. From the floor, the circulate management facility is a big gap within the floor 150 toes deep, sufficient to carry a 15-story constructing.

Underground, the circulate management facility is at mountain tunnel degree, with two bypass pipes that can have valves put in to handle the quantity of water flowing inside the tunnel. This may give operators higher operational flexibility and shield the mountain tunnel from deterioration, as fixed adjustments within the quantity of flowing water can put on down its lining, Anderson stated.

(The valves) can open, have the tunnel crammed with water and keep good strain contained in the tunnel always, Anderson stated.

One other main addition is a brand new 1,000-foot entrance to the tunnel, as lots of the current entrances couldn’t accommodate the gear wanted for upkeep. On the finish of the brand new entrance is a brand new 30,000-pound door that may stand up to the extreme strain of the water flowing via the tunnel on the opposite facet, Anderson stated.

The brand new entrance will even stop SFPUC from having to decrease the Priest Reservoir, into which the mountain tunnel water discharges, to entry the tunnel and carry out upkeep work. This may enable SFPUC to increase outages from 60 days to 100 days, as upkeep will not influence the native water provide in Tuolumne County, which is available in half from Priest Reservoir, Anderson stated.