California Levee Failures: 6000 BC to 2000 AD.
This topographic map, from the 1950s, provides most of the clues for predicting levee failures in the Marysville area. The yellow areas are floodplains, mostly covered by sand washed down from gold mining in the last century. The levees (orange lines) have been built here. The three great levee breaks of the past few decades are shown in red.
The yellow floodplain areas have been used as orchard lands for a century of more. During floods, water seeps under the levees and appears in the yellow areas as springs, sand boils, and sinkholes. The orchards pond water, sometimes killing the trees. This problem has been known and complained about by farmers for decades and is well documented by the Department of Water Resources in many reports.
Old river channels can be found at depth beneath the yellow areas, especially where the levees rudely pinch into the river or cut off its sweeping curves. These are the most dangerous areas from the standpoint of levee underseepage.
Perhaps the ancient pagans had it right. The river knows its haunts; when it gets angry it
takes them back.
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