How rising sea levels could impact Delta, Sacramento Valley

03.25.19

 

As the sea level rises, it could impact more than the California coastline. The rising water could impact the Sacramento region.

Some researchers said the rise could threaten levees in the area and increase the risk of flooding throughout the Delta and the Sacramento Valley.

“Essentially, the Delta is the product of sea level rise,” he said. “The sea level rose to drown the confluence of the Sacramento and San Joaquin rivers to create this marsh.”

How high the sea level will rise and how quickly is debatable, but Lund said the implications are already clear.

When it comes to the many islands that make up the Delta, the sea level rise will increase pressure on levees surrounding the islands and put the islands in jeopardy.

“For the islands that are below sea level, that tide is coming through twice a day and it’s working those levees,” Lund said. “That pressure is coming on and off twice a day. So, that could accelerate the compaction of some of the levees.”

Making matters worse, in many places the land behind the levees has been sinking. That makes levees more vulnerable and harder to fix after flooding.

“In the main part of the Delta, the land level is between 5 and 25 feet below sea level,” Lund said. “So as the sea level rises, you can see the potential for, for increased flooding and for flooding that is more expensive to repair.”

Lund points to cases where levee breaks in the Delta have already led to serious flooding. Frank’s Tract, which was once acres of farmland, now looks like a large lake after the levees failed in 1938. Mildred Island is no longer an island after it flooded in 1983.

“There are all kinds of things which can cause these islands to fail once that difference between the land level and the sea level is big enough,” Lund said.

A 1990 UC Davis study suggests the sea level rise could impact as many as 30 islands in the Delta.

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