What is a Bajada (or Alluvial Fan) ?
|Source: Structural Geologist Mike Norton|
Alluvial fan in the Cirque d'Estaubé, French Pyrenees
Great Definition Source: http://en.wikipedia.org
"An alluvial fan is a fan- or cone-shaped deposit of sediment crossed and built up by streams. If a fan is built up by debris flows it is properly called a debris cone or colluvial fan. These flows come from a single point source at the apex of the fan, and over time move to occupy many positions on the fan surface. Fans are typically found where a canyon draining from mountainous terrain emerges out onto a flatter plain, and especially along fault-bounded mountain fronts. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial fan."
The above definition by Wiki aptly describes what most around the world, but especially those in drier locations have observed at one time or another with regards geologic features which emerge from most mountain canyons. If you notice the picture above of the alluvial fan in the Pyrennes Mountains which border France and Spain, take note that there is generally one main channel in which the stream or river flows out, and yet, there appears to be a greater historical pattern spread all across this Bajada. In actuality this main channel can oscillate back and forth depending on heavier flow patterns brought about by a wetter than normal rainy period. But there have always been a number of questions that plagued my mind over the years. For the purpose of simplicity (my wife says I write too much text), let's restrict this post to Southern California and in particular Riverside County (although San Bernardino Co fits in nicely as well). There are several Bajada land formations which define most of the inland empire cities from San Bernardino to Los Angeles. Most people don't even realize they are living on many of these alluvial fans or flood plains. Many while commuting never give them any thought or second look. Most river or stream beds have been straightened and channelized for commercial convenience sake. But there are several tree establishment puzzles that took place decades ago which question beg. How did such large examples of old growth Sycamores and Cottonwoods become so well established when they appear to be so far away from the stream bed channel ? From what I always knew of such riparian species, they need generous amounts of water to survive the early years of their life, so what gives with these examples on dry locations ? Cyclic wet periods are extremely key to establishment and should be studied as such and remember not for their destructive potential, but for habitat establishments in the wild.
This next photo below is of a Bajada or Alluvial Fan which emerges from what I thought was once labeled as Portrero Wash or Creek at the bridge on Gilman Hot Springs Rd, but the sign is now removed. It's source is the city regions of Beaumont and Banning CA and in particular the Sun Lakes Country Club and Golf Course. As you may see from this Google Satellite map link Here , the Alluvial Fan was at one time much wider than now. It is restricted by an eastern Earthen barrier or Levee on the east which protects the Scientology Military Compound and the raised easement of Hwy 79 on the western edge. What is left can be seen with several lines of stream channels which fan out at massive flood stages which are characteristic of most alluvial fans, and hence the name.
|Photo Credit: Mine|
|Image - hvrc.com|
Hemet & San Jacinto Valley looking north towards the foothills of the San Bernadino Mountains. Porptrero Creek and the alluvial fan which ran all year would be over on the far right of the photo.
Historical Annual Rain Totals of a wetter period
1978 - 26.60 inches
1979 - 13.47 inches
1980 - 18.86 inches
1981 - 08.29 inches
1982 - 16.90 inches
1983 - 21.03 inches
Historical Annual Rainfall Totals Same Period
1978 - 12.92 inches
1979 - 12.87 inches
1980 - 15.77 inches
1981 - 08.10 inches
1982 - 15.07 inches
1983 - 22.91 inches
Historical annual Rainfall same period as above
1978 - 46.99 inches
1979 - 29.62 inches
1980 - 45.65 inches
1981 - 15.81 inches
1982 - 49.47 inches
1983 - 56.87 inches
All these figures above are of the rainfall averages for the wetter "El Nino" years. That was an amazing time period of wet. Too bad the officials didn't take advantage of it to rebuild several important ecosystems.
|Credit: Riverside Flood Control|
"Flooding in the vicinity of State Street (Highway 74) and Ramona Expressway, February 21, 1980, as a result of the breach of the San Jacinto River Levee."Again, keep in mind please and burn into your memory if you can, this six year heavier than normal time frame which has valuable learning potential aside from destructive forces which often are the result of human poor planning anyway.
Major construction of San Jacinto River
bridge on Hwy 79 in Riverside County 1994
View looking in the direction of the Scientology Compound and the mature Cottonwood trees well established which had not existed prior to the flooding period.
|Photo Credit: Mine|
|Photo Credit: Mine|
|Photo Credit: Mine|
|Photo Credit: Mine|
For the moment, this is what I have and my personal account of what physically took place at this geographical location called Portrero Creek & it's Bajada particularly during the 1980s. This was of course a major part of my work route in commuting for many years. But I did promise to discuss what lessons could be learned from this, so what are they ? Well I always had personal questions in my mind about isolated tree establishments of large solitary trees which existed on dry locations for no apparent logical reasons, especially water loving riparian tree species. Numerous areas like Waterman Canyon in San Bernardino or Cable Wash in Devore or Lytle Creek, all have similar riparian tree establishment puzzles which have clear explanations for their presence if time, observation and experience are taken into account over a period a couple decades. My good fortune was to have seen the Portrero Creek Bajada (alluvial fan) when it was at it's driest barren state and to be observant when the transformation took place especially towards the middle 1980s.
From such observation, one can glean from such experience that not only riparian, but even several other plant community ecosystems can become establish anew when these cyclical wetter periods emerge. Although with climate change it is doubtful that such periods will reveal themselves any longer. Still, much can be learned and practical application be created artificially in an urban landscape setting, or habitat restoration project, or with simple home gardening projects. During such unique wetter periods, plants are babied and nurtured during these times of plenty, then gradually the system tapers off in it's generous abundance and allows the earlier established plants to fend for themselves. The stronger plants/trees with the deeper root systems will become the winners, while the weaker ones fail and naturally thin out as the natural program demands. I have used this technique in replication, not only in urban landscape establishment, but in remote habitat restoration and it does indeed prove successful over time. Of course for me, I always inoculate with a good blend of mycorrhizal mix at time of planting. I found myself the last week before I left to come back to Sweden in a disagreement with this inoculating at planting time with a Native Plant nursery person who said that the micro-biological activity is everywhere floating in the atmosphere and it was not necessary. Why yes, there are spores everywhere in the air. But there is also more and more damning evidence that microbiological ecosystems in the ground are suffering some decline just as everything else above the ground. Toxic acid rains and many more chemical and GMO Plant contamination are having an effect on mycorrhizae. I've actually inoculated trees in wild out-plantings and had surrounding Chaparral like Scrub Oak and other trees make drastic improvement through the interconnections, which indicates to me all is not well in the wild. As time goes on, more and more researchers will come to the conclusions that Nature alone cannot function as it normally once did and that some major artificial assistance to speed things up will become necessary. I not only do not like hearing this, but hate having to say it as well. One more important side note about Bajada Basins and Alluvial Plains. Throughout the western North America, they have been huge storage components for water. Many streams or rivers that emerge from mountain canyons will often be seen disappearing deep into the alluvial fan. This is not the result of evaporation, but the looseness of the course rock and sand which allows water to easily filter and percolate deeply into the earth inside these geological forms. The best place to store water is underground, not behind dams or any other surface lake. It's also the best place for the plant world to access water during lean times. (See footnote @ bottom)
Now as far as the urban landscape goes, most ecosystems or plant communities you install should only have surface drip irrigation for the first few years at most. This replicates the cyclic flooding events that in times past made their appearance and created the wild landscapes centuries ago. Now unfortunately while visiting here, I had the opportunity to observe several public and professional landscape systems installed for development utilizing Native plant settings or themes, but employing a method of irrigation that employed large rainbird sprinkling systems which created large surface soil coverage over vast areas which has allowed massive amounts of weeds to grow to 3 or more foot of height and often times out competing the native plants. The goal is to merely establish the plants are the beginning with just enough regular water for root development and later as I have written about before, installing a method of Deep Irrigation Methods for Training Deeper Rooting networks and then later updating this with IRRIGATION ISSUES: Why Isn't Nature Replicated more often ? The bottom line is that people just don't get the gist of allowing plants to maintain health and vigor without forcing new growth during hotter months through excessive watering and fertilizing which not only encourages weeds, but attracts all manner of insect pests and fungal diseases and/or other blight. Go out into the wild and you don't see this. This is because they are in maintenance mode by means of sustenance from a deeper underground hydrological system which works well when properly established.
A prime bad Big Brother Government example is of a Cal-Trans Landscaping Project under and around the Interchange on and off ramps of Hwy 52 & Hwy 67 between El Cajon and Santee employing the wrong irrigation techniques of massive Industrial Strength Rainbird displays, though I was happy to see Natives being used. They'll eventually have killed off what they had set out to accomplish with the utilizing of Native Plants.
In the Rattlesnake Mountain chain far above this Freeway Interchange where the Sky Ranch Development was established, they have followed the same identical flawed pattern as that of the Cal-Trans Native Plant Landscaping Project. We're talking Mega-Overkill with regards another industrial sized Rainbird Irrigation System which has a double daily watering regimen which has not been changed since the initial installation. The photo to the left here is on the top ridge of the development which buffers between the neighbourhood housing and the wild Conservation No Trespassing protected area. While I applaud the use of Coast Live Oak and other ornamental chaparral shrubs, there are weeds overwhelming the system everywhere, especially in the lower valley near Pepper Drive Elementary School. If they were worried about some naturalized Torrey Pines potentially causing brushfires and insisted they had to be chopped down, then they have almost guaranteed fire disaster by the multiple hectares of weed infested landscape which now encircles this entire Private Rich Folk Community Habitat. The really sad part is when Government, which everyone assumes knows better, pulls blunders like this terrible landscape layout, then to be followed by a large commercial Landscaping firms, what chance is there that your average home and/or land owner will ever get the message ? I'm telling you, this simple basic fundamental stuff about nature needs to be taught long before College or even High School level learning. It should be elementary School teaching.
|Photo Credit: Mine|
While it is commendable they have established some Coastal Live Oak trees and other native chaparral plants, they will ruin it all if they don't change a flawed irrigation system that has existed for over 8 years now.
Further Interesting Reading:
I'll have a series of posts dealing with Juan Bautista de Anza's Journal and Natural World documentation experiences and divide them into three or four parts. They are seriously important to what nature once was and how it functioned. They were also detailed in such a way as to report on the local Natural resources which were present and potential money making Ventures for the Empires for who these expeditions were funded for in the first place. Anza's description was almost dead on accurate for the region I'll be relating to between Western Arizona all the way to Riverside California. Keep close watch.
Side note on Alluvial Basin Water Storage: Arizona Geology Blog