STORM RUNOFF
The decorative bridge in the Japanese style garden in my front yard normally
spans a dry cobblestone "fake stream." However, in a storm, the stream
rapidly becomes very real, as these five pictures show (taken Dec. 28, 2002).
They were taken in sequence within about an hour just before peak runoff
for the shot on the left, at peak for the next three, and less than an hour
after peak for the last, when rain was still falling but moderately instead
of at downpour levels.
I live at the bottom of a "swale" (short and shallow valley) among the
sand dunes on which Los Osos is built. There are no publicly maintained
storm drains in Los Osos. Each owner must allow storm water in the upper
end of his property and out the lower end at the points where it always entered
and left. So I get all the drainage from our swale coming down my stream,
into the "sump" (a rect
angular structure with sandy soil at the bottom) where some sinks in
and the rest runs off through a 6-inch pvc pipe to the back of my property,
thereafter the problem of my downsteam neighbors. In a downpour, the water
rushes in filling the 
sump amazingly fast, yet the slightest slowing of the rain and the water
level also drops fast. There is a shallow overflow area just above the
drainage pipe (picture at left) taking water down the side of the house
in case the 6-inch pipe can't quite handle the volume. Less than an hour
after the peak flow, with rain still moderately heavy but no longer at
downpour levels, the sump and pipe were absorbing the runoff so well that
the soil in the bottom of the sump is showing again (picture at right). I
have to dig soil out after such big storms and find somewhere else in the
gardens for it in order to make room for dirt washed in with future storms.
That's where the hill in the middle of the backyard came from, also dirt
for several very large containers, including the whiskey barrel in the above
left picture, and I'm starting a new hill in another part of the back yard.
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