Will The Tule River Flood This Winter?

As I make my way to and from home along Globe Drive, I enjoy looking in the river bottom to see what I can spot.  Yesterday I noted the rather dense undergrowth below the Sycamores and other trees.  Many of the trees are 12 to 15 inches in diameter, towering high in the air.  But it is not the trees that are the "root" of the problem (pun thoroughly intended).  It is the proliferation of little growth that will start the flooding problem.

Nature has a way of cleaning out the river channel which She calls flooding.  This starts high on the slopes of the Sierra Nevada, usually because a nice warm rain has come in on the heels of a cold storm.  The snow-level is down around 3,500 feet altitude, just above the Upper Powerhouse on Highway 190.  Then what's known as the "Pineapple Express" comes barreling in, straight out of Hawaii, and is both wet and warm.  You know it's going to get sloppy down here when you hear it's raining at 10,000 feet.

This brings all that snow down in a great rush.  It is this combination of events, the cold storm out of Alaska, and the warm rain behind it from Hawaii, that have precipitated many of the more destructive floods in the Tule River Canyon.

When the water level in the river channel begins to rise, smaller plants along the side get uprooted, washing along in the rushing muddy water.  When sufficient little stuff is uprooted, it begins to build up around the trunks of the trees.  When the accumulation of small stuff exceeds the holding ability of the roots of a tree, down it comes.

When one tree comes down, others are sure to follow.  Soon there will be a log-jam of trees exactly like the bunches of little stuff hanging up on the trees.  As the logs accumulate, water builds behind the temporary dam.  But ... the downward flow of water will not be denied.

At some point the collection of trees and rocks holding the log-jam give way to the inexorable pressure of the river at flood stage.  Now a channel-wide floatilla of uprooted trees, tightly packed with small brush and other lighter plants, goes bounding downstream cleaning the channel as it goes.

As effectively as a giant bulldozer, this jam of logs and plants will scour the river bottom, removing all dirt, roots, and plant material from the channel.  When the river recedes, and returns to its quieter form, there are only bare rocks shining in the sunshine once covered by thick, lush brush and plants.

The underbrush and plants under the trees seem to repeatedly flourish and grow, constantly fed by the river, until the flood cycle scrubs the river bottom the next time.  The process of regrowth can take 15 to 20 years or more before the right set of conditions come along to cause a flood.

So, will the Tule flood this year?  If the storm conditions create a high flow of water, the undergrowth and mature trees are there waiting to become a huge floating bulldozer and scour the river channel most of the way to Lake Success.