Infrastructure v. Public Works 6: The through-Delta component

All of the discussion about a possible Peripheral Canal has taken focus away from the so-called “through-Delta” component of the PC proposal.

The through-Delta element was until a few years ago the “preferred alternative” of CALFED. While the precise location and construction of the through-Delta system is not entirely specified, a few of its characteristics can be construed from available evidence.

Geographically, the through-Delta infrastructure would occur along the length of the Large Owner Axis, a string of islands that connect the two primary bits of in-Delta water redistribution infrastructure, the Delta Cross Channel and the SWP/CVP pumping facilities. This island chain is so named because most of the links are (or until recently were, I haven’t checked in several years) owned by large, non-agriculture-first landowners like the Nature Conservancy (Staten Island), the Hilton Family (Venice Island), something called the Tuscany Institute (Mandeville Island), and the Delta Wetlands Project (Bouldin, Bacon, two others), an in-Delta water development proposal.

Physically, the through-Delta infrastructure would widen the existing river and slough channels flanking the LOA. This would increase their channel carrying capacity, reduce flood risk, and create tidal zone habitat that is being lost to the relentless riprapping of the water sides of Delta levees. These three objectives synthesize the agendas of several contentious interests, and are accomplished through another example of a hybrid infrastructure—a setback levee—which is basically a much thicker, stepped levee.

Of course, widening the waterways means turning agricultural land into infrastructure. There are roughly 1,000 miles of levee in the Delta. If all were to receive setback levees of 400 feet in total cross section, doubling in volume, then approximately 25,000 acres of Delta farmland would become hybrid infrastructure.

More likely is determining which levees/islands are most at risk, and upgrading those. One anti-PC scenario being promoted is to “restore” the most vulnerable islands by making their levees capable of withstanding a seismic event.

This is no small undertaking, despite its minimization by the promoters of this scenario. To fortify existing levees to a “no-fail” capability would require at minimum 25% as much new levee material as indicated in the setback levee diagram. Keep in mind that an average Delta island is surrounded by something like 25 miles of levee. West- and central Delta islands are most vulnerable to seismic failure, and include at least 10 islands, despite the PPIC estimate. These fortified, and with through-Delta conveyance islands setback leveed, yields approximately 250 miles of levee upgrades and perhaps 7 to 12,000 acres turned into infrastructure. That is a lot of fill.

This order of magnitude scope of work is an approximate apples-to-apples comparison with the costs of a Peripheral Canal, which may be “as long as the Panama Canal,” as its critics like to say, but it is still only 50 or so miles long, not 125 (half the total levee length), like the “fortified Delta” solution. Of course, all of the big-ticket items, like siphons, etc., would not be needed in the fortified Delta solution. So, perhaps the cost is a wash.

Fortifying the Delta’s levee system will in the short (50-year) term profoundly change the perception of much of the Delta estuary’s remaining beauty and uniqueness—and perhaps this is the best solution. On the other hand, as a riparian/tidal estuary landscape takes hold on the setback benches, it will become beautiful. But it will take time.