The Delta Levees (You are Driving On!)

Did you know that there are some levee roads with burning peat beneath them?  Did you know that there are over 1,100 miles of levees in the Delta?

Before the levee was repaired with money from the Department of Water Resources subvention program (funded by voter-approved bonds), the levee looks like the one above and is vulnerable to tidal wave action, wind erosion and subsidence.  After the Reclamation District repairs and improves the levee it looks like the example below.  (on Bouldin Island)

Recently, I was able to join a tour of Delta levees hosted by the Association of California Water Agencies (ACWA).  I learned a lot about levees for flood protection and saw much of the Delta in a day.

At the time of the Gold Rush, the Sacramento-San Joaquin Bay Delta was a giant swamp full of tules.  These tules, along with ocean tidal action, and the inflow of two great river systems, created a myriad of shifting islands and sloughs.  From the late 1800s to the 1930s, local special districts, mainly Reclamation Districts, were formed and land was drained of “excess water” and “reclaimed” for agricultural use.  The islands once drained and cleared of tules were rich with peat soil.  At various times there have been booms of potatoes, asparagus, and pears.  Now wine grapes and blueberries are being planted.  And some of the land is being returned to wildlife habitat.

Much of the roads through the Delta are atop levees that protect the various tracts and islands.  The local Reclamation Districts are responsible for maintaining the levees and  work with the County to maintain the roads.

The cost of maintaining levees has risen and the value of agricultural income has not kept pace, so the State of California created a subvention program to cost share with the Reclamation Districts to maintain the flood protection.  A levee break is expensive both in terms of emergency response and subsequent recovery to the California taxpayer.  Preventive care may be the most affordable option in some cases.  It is complicated, though, as the exposed peat soils emit greenhouse gases and some of the islands have subsided so much that they are structurally compromised.  The structure of levees is hostile to native fish and redesign or removal may be necessary in some situations to restore more natural conditions for native species to recover.  Thus any discussion of levees quickly becomes controversial.  It is possible that Delta levee priorities and policies will be clarified by the Delta Stewardship Council’s sixth (and final?) Delta Plan.

As you travel east to west in the Delta, you will notice that the levees change.  The Delta around Interstate 5 is still a riverine system, and these levees are designed to meet the Army Corp of Engineer specifications and are called “project levees” due to a federal project that helped pay for them.  As you drive toward the San Francisco Bay, the levees change shape and you gradually drop to sea level.  Tidal action becomes predominant.  These levees are “non-project” levees maintained without any federal funding.

The western levees are some of the most fragile because of the subsidence of the peat soils.  You may notice as you drive along that the river on one side is only 5 feet below the top of the levee (depending on low/high tide), whereas the farmland can be more than 50 feet below the top of the levee on the other side.  Over time the peat has been used up, or blown away, or back in the day–burned off.  Without the tule marsh to renew it, it will continue to subside.  In some cases the subsidence is so great that it has compromised the levee as water bubbled up through the bottom.

Peat soil is also combustible and can burn for days, months and even up to a year, if lit accidentally by a spark or a match.  So be carefully out there.  There is one stretch of road that Caltrans believes has a peat fire beneath it but they have not yet figured out a way to put it out.  The bottom line:  do not take your levee for granted.

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