I constantly refer to "the mesa" when talking about my den. The mesa is an escarpment that rises 50-100' above the back of my house. It's the edge of a lava flow that blanketed the area many thousands of years ago. When I take Anubis on walkies we get to the top of the mesa by walking through a small gully that cuts a path through the basalt at the top. I know this is an active channel. I have seen water flowing down it a couple of times before during torrential downpours. If you look down from the top of the mesa at my house you can see that there is a broad alluvial fan that spreads out toward my back yard as well as my neighbor's. On the other side of my neighbor there is a concrete channel which would carry flood water brought down by the gully. This sets the stage for what happened yesterday.
Just before I left work I checked out the National Weather Service website to see if there were any storms heading our way. The radar showed a nice red blob to the north of the house heading south. On the drive home there was lightning all around including a few *FLASH! BOOMs!* At one point I could see the road ahead become a nice shade of silver. When I hit the change in color I was thrust into a driving rainstorm. By the time I pulled into my driveway it was coming down in sheets and hail began to pelt the car. I decided to wait out the storm in the truck. I had visions of tenax's vehicle after a hailstorm in Socorro last year. Windshields were smashed during that storm.
I noticed that there were rivulets of water starting to run down the mesa. I realized that I had better get back there to see what was happening. I ran from the truck to the house, quickly changed into swim trunks, grabbed a towel, and headed out into the back yard to see what was going on. Sure enough, the little gully was flowing at a pretty good volume for its small size. It had already downcut 2-3' in places. I hopped over the cinderblock fence and found myself ankle-deep in water and hail. Crap! The little gully was carrying most of the water towards the concrete channel, but a few small channels had started to form that carried water right up to the back of my fence. I grabbed a shovel and started digging a diversion channel to carry the flow back to the main gully. *FLASH! BOOM!* Damnit! I was not going to get hit by lightning. Retreat! The flow in the gully soon subsided. I went to survey the damage and found a considerable amount of sand had been deposited in back of my fence. The neighbor also had a fair amount of debris stacked up against his wall, and there were seeps at the bottom sending little rivulets into his yard. The sand was supersaturated in some places forming little pools of quicksand. Yes, for all of you WAM people, I did frolic a bit in them *grins*
It looks like I need to dig some sort of pilot channel to better divert flow away from my wall and towards the concrete channel. I know storms like the one we had are somewhat uncommon, but they will happen again. I'll have to go out there tonight and survey how much work it will be to dig the trench. Since it is technically National Park Service land, I'll have to be discreet.