Six on Saturday: Mudslide

 

With all the rain, it was no surprise. Mudslides are somewhat common here, and they sometimes close roads. In fact, we were sort of expecting a small mudslide almost in this particular spot right when we got the call about it. The only slight surprise was that it was right next to where we expected it to be. The cliff that we expected to make this sort of mess was still intact under the tarps put over it to deflect some of the rain.

Fortunately, it was a small mudslide that blocked only one lane. We were able to direct traffic through the other lane while the blocked lane was cleared of debris by a small bulldozer.

The top of the cliff slid to the bottom along with a stump of a Douglas fir that was cut down many years ago. The Douglas fir was cut down so that it would not destabilize the soil that it was rooted into as it moved in the wind. However, The soil was destabilized as the Douglas fir roots that held it together decayed. This is actually a common dilemma, since trees sometimes need to be cut down before they cause such problems, but the death and decay of the roots of such trees ultimately cause the same problems.

The sorts of trees that could be coppiced do not do so well in the dry soil on top of cliffs. Otherwise, we could plants willows, cottonwoods or something of the sort, and cut them down as they get too big, without killing the roots. They would be happy to regenerate and continue the process. The sorts of plants that prevent surface erosion do not do much to stabilize the soil. Otherwise, we could put something as simple as freeway iceplant (Carpobrotus chilensis) on top, and let it cascade downward over the unstable area.

1. It was nothing too serious, but just enough to block the inbound lane. Tarps over the cliff that we expected to make this sort of mess are visible above the retaining wall just beyond. My work pickup in the lower right corner of the picture blocked the inbound lane with its headlights and hazard flashers on. I directed incoming traffic around it into the clear outbound lane as it was available. The young man off in the distance moved his pickup out of the outbound lane, and also directed traffic accordingly. When necessary, he stopped traffic while incoming traffic used the outbound lane. We communicated by radio and hand signals.P90309

2. This is the stump of the Douglas fir that was cut down so that it would not dislodge the soil and cause a mudslide. A decayed stump of a smaller madrone tree is to the right. Their rotting roots and the English ivy were insufficient to stabilize the top of the cliff.P90309+

3. These significant mudstone boulders on the far side of the road could have done some serious damage to a car if one had gotten in their way.P90309++

4. That is where the Douglas fir stump came from, just to the left of the drainage pipe. It did not get very far. That is it at the lower left corner.P90309+++

5. We arrived about ten. By noon, there was not much evidence of what had happened. We left the cones because the road was slippery with mud.P90309++++

6. This is supposed to be a gardening blog, so here is an unidentified fern that witnessed the whole ordeal from a stable portion of the same cliff. There is slightly more flora to this story than two dead stumps and a bit of ivy.P90309+++++

This is the link for Six on Saturday, for anyone else who would like to participate:

https://thepropagatorblog.wordpress.com/2017/09/18/six-on-saturday-a-participant-guide/

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Creeping Myoporum

80912The familiar sandalwood, Myoporum laetum, that is such a resilient small tree or big shrub in windy coastal climates, might make the wrong impression for the less familiar creeping myoporum, Myoporum parvifolium. Creeping myporum does not get much more than a foot high unless it climbs over stones or other obstacles, and it might stay less than six inches deep in exposed spots.

The evergreen foliage is dense enough to prevent most weeds from getting through. The tiny and narrow leaves are only about half an inch or an inch long, perhaps a bit longer. Clustered white starry flowers that begin to bloom late in spring continue to bloom through summer. Although tiny, and neither profuse nor remarkably showy, they are a nice accent to the rich green of the foliage.

Creeping myporum prefers full sun and occasional watering. It rots easily if watered too much. Its other weakness is that it does not tolerate traffic well. Creeping myoporum is a low growing shrub with woody stems that can break if trampled on. Individual plants can get ten feet wide if they get the chance. They are typically planted much closer together so that they cover the ground faster.

Rain Is Necessary But Messy

10914Water is no more scarce in California than it has been in recorded history. The problem with it is that it is a limited resource that must be shared amongst too many people. Likewise, rainstorms are no more torrential than they have ever been. Floods, erosion and wind are only more destructive now because there is so much more infrastructure that can be damaged than ever before.

Rain and wind are perfectly natural. Furthermore, it is natural for the weather to knock down limbs or entire trees. It only seems unnatural when these limbs or trees fall on houses, cars or anything else that gets in their way. Plants actually enjoy rainy weather much more than we do. Some like to be rinsed of dust and debris left from former infestations of mites, aphid, scale or sooty mold.

What plants do not like about rain is erosion. It is bad enough that so many plants in refined gardens are deprived of their own litter to insulate the surface of the soil. It is even worse if the bare soil gets eroded away from fine feeder roots at the surface of the soil. This is something that the rest of us would agree on. We do not want gullies carved into slopes, or drains clogged with mud.

Trees, shrubs and some stout perennials with aggressive roots are useful where the potential for major erosion is a concern, but might not do much for annoying surface erosion. Sprawling and spreading plants that form dense networks of low branches and surface roots are more effective. They soften the splatter of rain, slow the flow of drainage, and catch much of any dislodged silt.

Groundcover plants like ivy, gazania and iceplant are probably the best option for controlling surface erosion. Dense and low shrubbery that spreads over the ground and holds its own debris probably work just as well. These include low junipers, trailing rosemary and dwarf coyote brush. Larger shrubbery can help if it can drag its lowest limbs on the ground, and no one rakes below it.

Mulching limits erosion while new plants grow. Although new mulch needs to be added annually as old mulch decomposes, less will be necessary as plants grow and cover more area. Mulch is also effective where no plants are desired. For large areas, especially where plants are not expected to fill in, landscape cloth below ornamental bark inhibits weeds. However, coarse bark slowly shifts downhill, so replaces one kind of erosion with another, and will eventually need to be raked back uphill.