The controversial water diversion tunnels proposed in California’s Sacramento-San Joaquin Delta may be the biggest waterworks up for review anywhere in the world. And this $17 billion project requires a variety of permits and approvals before construction can begin.

Gov. Jerry Brown hopes to start building in 2018, but there are many steps ahead before a single bucket of dirt can be shifted. There are environmental impact studies, federal and state endangered species permits, federal dredging permits and an eminent domain process to acquire land – all still in the works.

One of the most important is a state permit to divert water at three new locations on the Sacramento River. It sounds pretty basic, but in reality, this is one of the most complicated steps.

The State Water Resources Control Board is the agency charged with issuing the new diversion permit – essentially a new water right. The board has already held 53 days of public hearings on the matter. It has collected some 11,000 pages of transcripts and 2,600 exhibits, a tally that does not include computer modeling done on the project that is also part of the record.

All this for a hearing process that isn’t even half over yet.

“This could go down to be the biggest hearing we’ve had,” said Les Grober, the water board’s deputy director for water rights. “It’s not possible to know how many additional days of hearings we’ll need. It’s just a very, very, very big project.”

The tunnel project, dubbed WaterFix by the state Department of Water Resources, calls for the building of two 40ft (12m) diameter tunnels, each bored at least 150ft (46m) below the surface. They would divert a portion of the Sacramento River’s flow at three massive new intakes on the riverbank near Courtland, on the north edge of the estuary.

The tunnels would then shunt that water 35 miles (56km) south to existing diversion pumps near Tracy, where it will be fed into state and federal distribution canals that serve 25 million people and 3 million acres (1.2 million hectares) of farmland.

The goal of the project is to avoid reverse flows in the estuary now caused by the powerful south-Delta pumps, which kill and confuse fish and alter water quality. The three new diversions near Courtland will have modern fish screens, potentially allowing them to operate with fewer interruptions – thereby making water deliveries more reliable.

While all the other permits and studies are essential to understanding the tunnels’ impact on water and wildlife, it may turn out that the water diversion permit is the single most important bit of procedure.

That’s because when, where and how the tunnels divert water affects everything else in the Sacramento-San Joaquin estuary, from fish breeding to recreational boating.

The board is considering not just a new permit for the three intakes, but also major revisions to existing water use permits held by DWR and the United States Bureau of Reclamation. That’s because once the intakes are built, the two agencies plan to change how their existing upstream reservoirs are operated to work in concert with the tunnels.

The process is also significant due to the broad public participation allowed.

All the other permits are largely administrative: They’re issued primarily by lone government officials after reviewing extensive studies. The water board process is the only step in which a decision is made by a public body in a public meeting.

“This is really the only public hearing process that we’re going to see on this project. I think the wider public may not get that,” said Osha Meserve, a Sacramento attorney representing a variety of North Delta landowners at the hearings. “It’s the most important water-rights change petition that we’ve ever had in the state, and it’s sort of flying under the radar.”

Due to the prolonged and complicated nature of the hearings, public attendance has been light. Grober said the first few days were well attended, and a number of average citizens offered spoken testimony. Since then, fewer than a dozen people have been in attendance. The hearings are webcast live, but the board does not monitor how many people are watching.

The water board process is more complicated than a typical government public hearing. On water-rights matters like this, its hearings are similar to a court proceeding. Witnesses are called by one side to give testimony, then they can be cross-examined by the other side. Board members oversee the process like a panel of judges.

Eventually, the water board will weigh the evidence and vote on a draft order that will either reject the new water intakes or allow them to be built – most likely with a variety of operating conditions.

In the meantime, observers and participants face a difficult task keeping up with the firehose of information. New witness testimony and seemingly obscure documents submitted as evidence must all be watched carefully to avoid surprises or sudden shifts in strategy.

“It’s taken up a tremendous amount of my time for the past year,” said Meserve. “You can’t really be partway in it. Trying to present scientifically reported information as evidence is harder than I would have thought. But somebody has to do it, or it won’t be in the record.”

Among the issues Meserve is trying to illuminate for the board are the potential effects on Delta water-rights holders and groundwater users if the new intakes are built.

Each of the intakes would completely transform nearly a mile of riverfront, where there are now hundreds of existing private water diversions vital to farmers and homeowners. How will these be affected by the intakes?

The tunnels are also expected to bisect many groundwater wells along their 35-mile (56-km) path, and may affect aquifer function even for wells that aren’t in the way, Meserve said.

Nicki Suard is also tracking the hearings, as a private business owner. She owns Snug Harbor, a small marina on Steamboat Slough, a tributary of the Sacramento River near the proposed intakes. While Suard is also an attorney, she has no background in water law and said following the process has been challenging.

“I’m a novice like anybody,” said Suard, who has attended most of the 53-day-long hearing dates in person. “It’s been a huge learning experience for me. It’s very hard to run a business and attend the hearings and read documents. I would say it’s a full-time job.”

A top concern for Suard is how the intakes might affect water flow in Steamboat Slough. She worries the volume of diversions could be enough to drop water depth in the slough, harming water quality as well as boating access.

Suard has tried to read all the evidence submitted concerning water quality in the North Delta. But even that has been taxing, she said.

“You’ve got to understand the volume of documents that are involved in this. It’s just amazing,” she said. “I don’t know if there is anybody who has read all the documents.”

The water board is nearing the end of the first half of the hearing process, which focuses on potential project impacts to other legal users of the delta. This final phase of part one involves two to three weeks of rebuttal hearings, in which DWR is allowed to challenge claims that the project will cause harm. Then comes two to three weeks of “sur-rebuttal,” in which critics of the project get to challenge DWR’s rebuttal.

After a break of several months, part two of the hearings will begin, which will focus on potential harm to the Delta’s fish and wildlife.

After that, probably sometime in early 2018, Grober said, the board will consider voting on a draft order.

“We don’t have the details of how much time that would involve,” he said. “But this is a big order on a big issue. There will probably be a number of days involved in that.”

Asked if she has any advice for the water board as it wrestles with the issues in this long hearing, Suard had a simple suggestion.

“I would like to see them base whatever they do on the truth, on facts,” she said. “And to not ignore it when they’re told, ‘Hey, you made a mistake here.’”