Fast-Track Dredging to Save the Delta

Governor Newsom’s priority constituency is now located outside of California and shaded purple, and a new team occupies the White House that is as red as red can be. So it is probably safe to say that even here in deep blue California, many of the policies governing energy and water are about to be reviewed and revised. One of these policy shifts, we may hope, will be to fast track expanded dredging operations in the Sacramento-San Joaquin Delta.

Compared with most water project proposals, the price tag to resume dredging in the delta is surprisingly low. At about $10 million per mile, dredging 75 miles of delta channels comes in at $750 million, and these days, any big water project that comes in under $1.0 billion is a bargain.

The immediate benefit of dredging choke points throughout the delta is more reservoir storage. Most of California’s reservoirs are never filled, in order to always leave them with the capacity to absorb heavy rainfall or rapid snow melt to prevent downstream flooding. But if dredging were to restore the capacity of the delta channels to safely allow heavier storm and snowmelt flows to make it into the San Francisco Bay without breaching the levees, California’s reservoirs could retain an additional million acre feet per year. In terms of construction cost divided by annual yield, at $1,000 per acre foot, nothing comes close. The financial case for dredging is compelling.

Another reason to dredge the delta channels is to increase the volume of water in those channels. This has multiple benefits. With many of the silted up channels only 3-4 feet deep, when the delta pumps operate it can easily overwhelm the downstream flow. Water exports using the pumps can lower the water level by 1-2 feet. But if these channels are 10-12 feet deep, there is so much more water in them that it takes commensurately more pumping to lower the water level or reverse the flow.

Increasing the volume of water in the delta channels via dredging is also a way to reduce salinity. During high tide, salt water from the San Francisco Bay pushes into the delta, but if there is a higher preexisting volume of fresh water in the delta channels, as the level of fresh water upstream rises, it increases the capacity to withdraw water from the delta for urban and agricultural use. And, in general, if the flow capacity of delta channels is increased, heavy winter and spring flows can more efficiently flush out salinity coming from municipal discharge and irrigation runoff.

Ever since the delta levees were constructed over a century ago, and islands and channels replaced a vast marshland, local agencies and private landowners routinely dredged the channels and maintained the levees to preserve navigation and prevent flooding. But starting in the 1970s, two things happened.

First, by then the State Water Project and the federally-owned Central Valley Project were pumping millions of acre feet every year out of the delta and into aqueducts to serve farms and cities in the San Joaquin Valley and Southern California. Second, and less discussed in terms of the impact it has had, is that with only a few exceptions, regular dredging ceased.

The impact of delta pumping on fish populations is a topic of fierce debate. The impact of silted up, shallow channels throughout the delta on fish populations, on the other hand, rarely comes up as a topic for discussion. This needs to change, because dredging is not only a way to guarantee a more reliable supply of water for farms and cities, and help prevent flooding, it is also likely to benefit the environment and the fish.

An obvious example of this is if another million acre feet per year can be stored in California’s reservoirs, some of that water can be reserved for releases at critical times to maintain environmental flows. But the depth of the delta channels affects how productive those releases may be in protecting fish. If the center of delta channels is dredged to a depth of 10-12 feet, the temperature of the water down there will be much cooler than it is today when a channel is only 3 feet deep. This helps salmon that prefer cold water, and it may also help salmon avoid bass that prefer warmer, shallower water.

Simply by deepening delta channels and increasing the volume of water in them, dredging creates more habitat. It also improves seasonal flows which reduces algal blooms, reduces hot spots, improves water quality, and lowers salinity.

The decline in salmon populations began about the same time as the delta pumps were completed and started exporting water out of the delta, and hence the decline of that species is often attributed to the pumping. But regular dredging ceased at around the same time, significantly altering delta habitat. And during nearly a century of regular dredging, salmon and bass populations both thrived.

It would seem that amid the ongoing debate over how much water exports may or may not be a major factor in the decline of salmon and other delta species, we might try dredging again. It is a cost effective way to get more water, reduce flood risk, and restore habitat. And who knows, it might be the best thing that happened to California’s salmon population in many years.

Edward Ring is the director of water and energy policy for the California Policy Center, which he co-founded in 2013 and served as its first president. He is also a senior fellow with the Center for American Greatness, and a regular contributor to the California Globe. His work has appeared in the Los Angeles Times, the Wall Street Journal, the Economist, National Review, City Journal, and other media outlets.