Welcome to the Montonoso Bioswale! Bioswales are becoming more common in suburban areas as they provide local streams and rivers a natural way to filter out runoff and other pollutants in addition to reduce flooding and erosion during storms. There's plenty of public parking here at the above coordinates. This earthcache will focus more on the geology side of the Montonoso bioswale and the above coordinates will lead you to an informational sign about the geology here. Make sure you read the plaque as well as use your own observations to answer the questions correctly. Don't forget to do the traditional cache nearby as it's one of the best in town. Now let's talk about geology!
Oso Creek is one of the many tributaries that end up in the larger San Juan Creek which empties at Doheny State Beach in Dana Point. Oso Creek Begins at the Oso Reservoir near El Toro Road and California State Route 241. Before Mission Viejo existed, the creek was seasonal meaning it only flowed when during the rainy season. Today, it flows year round thanks to runoff from nearby lawns, golf courses, and street drains.. The term "environmental geology" will come up often in this discussion as its the study of the local geology and how humans can change it. Whether its good or bad is up for debate, but either way environmental geology helps describe the lasting impacts that humans can create.
This section of Oso Creek (from Marguerite Parkway to Oso Parkway) was converted into a bioswale recently in order to prevent runoff from the city streets to enter the Pacific Ocean and to prevent erosion from occurring in mass flooding events during the rainy seasons. A bioswale works to minimize these impacts in order to maximize the productivity of these streams and their resources they offer to the city. Here, you will see a few erosion and water filtration techniques. Let's start with the geology (erosion).
Geology
The hills of Mission Viejo were created in part due to tectonic up lift of seabeds with the many segments of the Christanos Fault. Most of the hill's compositions are sedimentary rocks such as sandstone or limestone, which provides more evidence that this area was underwater recently. Sedimentary rocks form slowly, but erode fast due to their irregular particle size. Conglomerate, for example, formed along rivers or areas known to have tsunamis, has different sized cobbles stone within clay, siltstone, or sandstone. Sandstone rocks are formed closest to the land, while silt and clay are formed further out in calmer waters.
The canyon you see before you here was formed by erosion during large storms ever since the creek was formed and accelerated with the grade being increased by a few millimeters every year. The rocks, placed here artificially, along the banks help slow rushing water along the banks. This in turn reduces the effects of erosion along the canyon tops. These rocks are a type of granite, similar to ones that make up the jetties in Dana Point Harbor. Granite is an igneous rock, formed when molten magma cooled underground, giving the rock enough time to form crystals and become stronger. Oso Creek is part of the San Juan Creek Watershed, with the Oso Creek Watershed highlighted in orange. I marked where this earthcache site is on the map with the red arrow for reference.
Erosion is a major factor along the Oso Creek as it runs behind homes, businesses, and other infrastructures. There are four main types of transportation materials in rivers. The first is suspension which is like sand that is being suspended in the later. The next is solution which is dissolved minerals on the atomic scale like salt. The next two are traction and saltation which are big enough to see from afar. Traction are large boulders which are moved only during large flooding events, while saltation are smaller rocks and pebbles which are moved periodically. The way you can tell the difference between tractions and saltations are their lectures. Tractions, only being moved in floods, are quite jagged and rough to touch. On the other hand, saltations are smooth and round as they have bounced down stream frequently.
Some ways to reduce erosion is to control the velocity of the flow. This can be done by making the grade, or angle of decent, low. An angle that is 5 degrees below the horizontal will make the river flow slower than that of a river with a 20 degree angle from the horizontal. Another factor is the type of riverbed. Is it natural or manmade? A natural one is more susceptible to flooding, while a manmade one better prevents them. A few man-made flood prevention techniques include turning the creek bed into a catch basin, to elimination the effects wave cutting on the sides of the channel or the bottom. Another technique is making the channel somewhat both natural and artificial by adding a series of boulders or large rocks along the channel to slow the velocity of the river the closer you are to the shoreline. Lastly, if the channel is a V-shape or a U-shape will cause erosion to occur at different rates depending on what section you are observing the creek at.
Hydrology
The Oso Creek Watershed begins its journey in the Santa Ana Mountains, above Oso Reservoir. Snow melt in the spring along with rain fuel the creek into a raging river, occasionally creating flooding. This section of the creek often will flood during heavy rains. Flash floods are notorious for moving boulders the size of cars downstream from the mountains. Although this is extremely rare, it can still happen. That being said, during flash floods, Oso Creek is susceptible to large amounts of sediment being washed away from the bottom of the river where it cuts through the soft sedimentation layers like a hot knife on butter.
During the dry season, the creek flows very slowly and sometimes will build up in some areas giving off sulfur dioxide gas. This is from bacteria in the creek builds up and will start to decompose any organic matter such as dead animals or trees and plants that have fallen in the stream. The smell helps identify if the stream is stagnate or flowing, or recently has flowed. One thing that accelerated bacteria and algae growth in the creek is runoff from homes, gardens, and golf courses. Here, fertilizer can make it's way down to the creek and will literally feed the bacteria and algae accelerating it's growth. A way that a bioswale can help stop the influx of runoff from entering the watershed is the plants that grown along the countless entrances to the river.
Plants have complex, and sometimes very large root systems. As water flows towards the creek, some of it will seep just below the surface. The lowest point it seeps two is called the "water table". The water here still is contaminated with runoff, but is soon filtered through the roots of the many flora species along the rivers edges. In addition to reducing the risk of contaminates in the river, the plants use these fertilizers for themselves and grow faster, better, and stronger which in turn lowers the risk of more fertilizer contamination in the river and so on. This occurrence is called a positive feedback loop.
Works Cited
https://www.geocaching.com/geocache/GC720TN_waterfront-trail-series-ajax-bioswale
https://www.geocaching.com/geocache/GC5X4V8_newport-boulevard-bioswale
http://dudek.com/services/stormwater-planning-and-design/
http://chubbyrevision.weebly.com/river-landforms.html
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
Note: You will only receive an email from me if I need clarification on your answers. You are free to log the cache as a find whenever you like.
1. "Montanoso Bioswale" on the first line of your email AND list all geocaching names of your party so I can match your answers to them.
2. Look at the bioswale and determine if there is any water flow. If so, estimate the velocity (how fast it's moving). If not, where is it collection or non-exisitant?
3. Name at least one type of erosion transportation materials that you can see. Explain why you can see it here and why you can't see the others. Use the chart above to help you located them.
4. Estimate the (a) width AND (b) depth of the bioswale channel.
5. Is this a U-shape or V-shape channel? How would this help during a flash flood event?