I work at the Monterey Business Center in Yucca Valley, California, which is about 250,000 square feet of flat roofs and cement parking lot. I’d been wondering what all that would look like in a rain event and on August 29, 2013 I found out.
Monterey Business Center arial from Google Maps
Jackie is not as excited about the rain as I am.
Roof water pours onto the sidewalk and into the parking lot
The parking lots have channels to direct water to the street
Onto the street
Down the street
Off the end of the street
Into a gully. (The blue-topped pipe in the gully says “water” on it. I thought that was hilarious.)
Down the gully
And through the desert
Until it hits the berm of a road
Until it breaks through onto the road
And starts to flow down the road
This is where it ran out of steam. The water puddled up here and then mostly evaporated, “To rain again on someone else, east of us,” as Buck from Transition JT says. If there had been more water, it would have poured down this road and into a slightly more intentional gully at the end of it:
It would eventually hit the big wash in front of those mountains in the distance and flow east to the dry lake bed that is just west of Copper Mountain, maybe 18 miles away. That’s the lowest point in our watershed.
Copper Mountain, Sunfair lake bed in front.
Nathen's Miraculous Escape 
September 3, 2013 at 6:17 am
Is that really only 2,500 square feet? I make an inch of rain over that area as around 10 gallons, which seems very low.
September 4, 2013 at 8:06 pm
Hmm. Well, that’s my very rough estimate based on Google Maps foot legend. Maybe I’m miscalculating. It’s on Indio and Yucca Trail in Yucca Valley, CA, if you want to check. It was way, way more than 10 gallons. There is an adjoining property to the north that probably contributed, too, though I didn’t notice much compared to ours. And I doubt we got a full inch in that Yucca Valley event.
September 5, 2013 at 12:53 pm
Oh, you are so right! I was off by two zeros. Should be 250,000 square feet. Good to have math teachers for friends! I’ll correct that number above.
September 5, 2013 at 6:13 pm
That makes more sense, so here’s a second question…on dry Vermont clay, a flow like the one you’re showing would get sucked into the ground in about thirty seconds. It takes a very long rain event to saturate the clay and make it water-tight. So what kind of soil is that, where it can be completely dry and the water runs on top like it’s on wax paper?
September 5, 2013 at 7:45 pm
Well, a lot of it soaks in and it does take a downpour to get it to run across the ground. But the “soil” is sand made from granitic rock eroded off the nearby hills. Very little of it is clay or organic matter.
September 5, 2013 at 8:07 am
I love that you did this.
July 5, 2014 at 9:36 am
[…] This is looking down into Sunfair from the north tip of the Bunker Mountains. Sunny Sands is the road heading off into the east. The microconfluence is close to where Sunny Sands ends. You can see the dry lake to the right, where all the washes in the area empty to. You could call our valley the Sunfair Dry Lake Drainage Basin. […]