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Interesting Drainage Design

Interesting Drainage Design

Interesting Drainage Design

Check out the drainage facilities at Google Earth Coordinates 32 degrees, 47 minutes, 09.46 seconds North and 117 degrees, 08 minutes, 24.19 seconds West, and downstream.

What were they trying to accomplish? Why did they size these facilities unrelated to their drainage areas? Why did they apply rip rap to a stream bed that will further bank erosion? Why did they ignore some areas of erosion?

Who "designed" this drainage.


RE: Interesting Drainage Design

Very interesting and, as they used to say on Laugh-In, "but stupid." smile BTW, there is one additional new drainage feature north of your coordinates (at 32°47'13.46"N, 117°08'26.80"W) in addition to the several that are south. A company that I used to work for has an office about two miles from there. Maybe it was them.

It appears that four of the drainage features are designed to protect the service road for a line of large power poles. Two of the drainage features handle runoff from the adjacent electrical substations. The drainage feature at your coordinate handles an apparently large watershed to the north consisting of developed and undeveloped land (and then discharges into the obviously eroded and erodable channel that you noted). The drainage feature that I found handles runoff from Dalewood Avenue in the adjacent residential neighborhood. Downstream of these four are two expensive fence crossings and then the final discharge into a basin across the I-805 that doesn't look very big compared to how large the total watershed appears to be. One thing I found interesting is that the drainage feature serving the larger substation is proportionately much larger than the one serving the smaller substation, yeat it appears to me that their respective watersheds are almost equal in size and runoff potential. In addition, the first fence crossing seems to be flatter, yet smaller, than the one just downstream, which doesn't make sense.

While there may be perfectly valid reasons (and calculations) for this design, I suspect that the electrical utility had money to spend on concrete and riprap, but not enough to stabilize the eroded channel, and that they did the design in-house with an EIT.

"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Interesting Drainage Design

It was financed with government grant money.

Mike McCann
MMC Engineering

RE: Interesting Drainage Design

Oooh! I'll take a stab at Google armchair engineering from the other side of the continent! The real question is what was the goal of this project? I believe the goal is more related to Security.

If one uses the Historical Imagery available in Google Earth, one will note that the narrow channel from the northern substation has been lined with concrete since at least 2002. The other locations of these improvements were existing depressions and discharge points which probably had erosion compromising the security of the fences. So, the owner hardened the channels upstream of the fences in hopes of stabilizing these points and put outlet protection/energy dissipation downstream of each hardened area.

Before these improvements, the photos indicate there were considerable amounts of large stone already in much of the channel downstream of the coordinates and upstream as well.

While it would be quite neighborly and philanthropic for the owner to improve existing problems in the entire channel, most folks don't have those kind of budgets.

According to Streamstats, it also doesn't appear to be THAT big of a watershed either - 0.2 square miles. Streamstats flows are not valid for areas less than 0.5 miles, but it calculates them anyway... which yields only 53.5 cfs for the 100 year storm event south just south of I-805.

RE: Interesting Drainage Design

They do stormwater in San Diego? I lived there for about 2 years when I was younger, I can't recall it raining once.

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