Federal Study Compares Different Size Delta Tunnels: Larger Delta Tunnel Costs More but Doesn’t Deliver More

Last week, federal participants in the Bay Delta Conservation Plan process presented their analysis of the water yields and costs of different size tunnels to divert water from the Sacramento–San Joaquin Delta. After examining different size tunnel options, they found that a 3,000 cubic feet per second (c.f.s.) tunnel in the North Delta could divert virtually the same amount of water as all other tunnel sizes up to the maximum capacity studied of 15,000 c.f.s. The reason for this is clear: there is a limited amount of water available for diversion from the North Delta. The group concluded that making the tunnel bigger does not make any more water available for diversion; however a larger tunnel would cost over $5 billion more than the equally effective smaller one.

There are two critically important caveats for these findings. First, the essential information on how much water must remain in the Delta to support a healthy ecosystem has not yet been established. The first estimates will come from the State Water Resources Control Board this August, and it is likely that they will show less water available for export under any alternative. Second, some water exporters are likely to push for a 6,000 or 9,000 c.f.s. tunnel. However the potential for future misuse of a larger tunnel will generate fierce opposition and decades of delay. After the Delta flow needs are established and guaranteed, it is possible that a 3,000 c.f.s. conveyance would have significantly reduced opposition.

The PowerPoint presentation on conveyance sizing, cost and water yields presented by Ron Milligan, Executive Manager of the Federal Team at last week’s BDCP Steering Committee is available online.