Tuesday, March 15, 2016

A Far Too Rare Scene in These Parts in Recent Years: Flooding on Dry Creek

The latest storm to pass through Central California dropped 1.28 inches of rain in my backyard gauge, giving us 4.26 inches for the month of March, and about a third of a normal year's precipitation in the space of just ten days or so. By the time this last storm arrived, the watershed was saturated, and so Dry Creek...was not dry. It reached a peak flow of about 3,000 cubic feet per second yesterday.
 Unlike the Tuolumne River, there are no reservoirs like Don Pedro Dam to catch the runoff from the storms, so Dry Creek rises and falls quickly with the storms. The runoff shows two peaks, as there were a pair of storms over the weekend and Monday. The blue bars on the top show the amounts and timing of precipitation in the watershed, and the dotted line records the runoff. Notice the lag between the timing of the storms. This is the delay between the water falling from the sky, and the peak flow miles downstream. By analyzing the pattern and amounts of precipitation, predictions can be made as to the amount of runoff (the pink dotted line). If the storm is immense, graphs like this can be used to warn downstream residents to prepare for flooding, in terms of both the timing, and the discharge (water flow/height) of the river.

The rainy season is drawing to a close, although a few more storms will no doubt blow through. The drought is not over, but it is nice that all the precipitation arriving for the rest of the year is adding to the above-normal yearly rainfall total. If it could only be true of the snowpack too!

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