As reported in the Sacramento Bee, the cost of a single-tunnel Delta conveyance is now estimated at $15.9 billion. In a previous 2018 analysis to support a short-lived proposal to stage the twin-tunnel WaterFix proposal, DWR estimated the single-tunnel 1st stage of WaterFix at $11.1 billion in 2017 dollars, which is equivalent to $11.7 billion in 2020 dollars. This is a 35% increase in constant dollars, and should lead the Governor and the dwindling number of water agencies that still support the single-tunnel delta conveyance facility (DCF) to reevaluate the investment.
That 2018 analysis wildly overstated the economic benefits of a single-tunnel to participating water agencies, but for now let's accept their estimate of benefits. The image below shows the results of that analysis (Table 5, with no federal subsidy).
Simply updating the costs to this latest estimate ($15.9 billion in 2020 dollars is equivalent to $15 billion in the 2017$) reduces the benefit-cost ratio for SWP urban agencies from 1.23 to 0.92, and for agricultural agencies from 1.17 to 0.87 in the trading scenario.
That's a bad investment, but it is actually much worse than that. The 2018 analysis assumed the project would be operational in 13 years, whereas the new cost estimates a 20 year delivery period. I didn't incorporate the extra 7 year wait for benefits in the above recalculations of the b-c ratio, but it would make it even lower.
At some point, we might see a revised economic analysis that manufactures new benefits to magically get the benefit-cost ratio over 1. Readers of this blog know that DWR and MWD already have an established track record of inventing new benefits as new information reveals the delta tunnel(s) to be a worse and worse investment.
P.S. Thanks to Restore the Delta for archiving the 2018 analysis online for the public record. DWR has wiped their previous links, and I couldn't find a saved copy in my files.