SFBWR Salt Pond Levee Earthcache EarthCache
SFBWR Salt Pond Levee Earthcache
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As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
This is one of a set of earthcaches that are part of the hiking trail system at Don Edwards San Francisco Bay National Wildlife Refuge. You may park at the visitor center to begin your journey. BE SURE that you have downloaded a copy of the trail map (visit link)
before beginning your hiking journey.
Logging Requirements:
Send the answers to #1-#5 to me through my geocaching profile.
1.List the name “GC2EV6X SFBWR Salt Pond Levee Earthcache” in the first line of your email. Also, list the number of people in your group.
2.Examine the sediment that has been deposited onto the levee. What is the size and consistency of this sediment? (See “Geology” section below)
3.Based on the description below, has the levee you are standing next to been retrofitted?
4. Post a picture of yourself and/or your GPS with your log that shows the river/marsh behind you. DO NOT show any of the pertinent information panels in your picture, OR tell me whether you are HIGHER or LOWER than the trails "observation deck" when at the earthcache cords.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
A map of the hiking trails is available at: (visit link)
Construction of Levees:
A levee is a type of dam that runs along the banks of a river or canal. Levees reinforce the banks and help prevent flooding. By confining the flow, levees can also increase the speed of the water.
Levees can be natural or man-made. A natural levee is formed when sediment settles on the river bank, raising the level of the land around the river.
To construct a man-made levee, workers pile dirt or concrete along the river banks, creating an embankment. This embankment is flat at the top, and slopes at an angle down to the water. For added strength, sandbags are sometimes placed over dirt embankments.
Levees protect the land in many parts of the world. In the United States, you will find important levee systems along the Mississippi and Sacramento Rivers.
In our area, the Sacramento and the Sacramento-San Joaquin Delta’s risk for flooding is the highest in the country because of the city’s aging levee system that has been inadequately maintained. Sacramento has even less protection than that of New Orleans despite spending $300 million to strengthen the Sacramento and American rivers levees that has taken place for the past 20 years.
Governor Arnold Schwarzenegger declared a state of emergency for California’s levees in February 2006. He executed Executive Order S-01-06 directing agencies to identify, evaluate and repair critical systems. As a result, some critical erosion sites were repaired in 2006, but the underlying structural problem for the Sacramento & Bay regions (and the rest of the state) remains.
According the Governor’s office, 104 levees have been redone, though hundreds of others are still “scheduled” for maintenance, though most have been placed on hold because of the state’s current economic crisis. These repairs essentially retrofit the levees with rocks on its water side to rebuild its slope to original flood level protection.
Geology:
The dirt here has been dredged from the bottom of the river channel and thus contains sediment (and gravel) from the complete river watershed, which means that you can potentially find sediment that originated in the Sierra Nevadas, over 100 miles away!
How does this happen? Well, the force of the rivers and streams in the watershed tear rock fragments from the parent rocks, and erode the soil as it streams “downstream.” The speed and quantity of the water both affect how much sediment and the size of the sediment that it can carry. Once the water slows down, sediment drops out of solution and lands on the bottom of the river. This can be good (sediment is very agriculturally rich) and bad (it can change the course of the river, cause flooding, and destroy shipping channels). One of your logging requirements will ask you to examine the sediment. Is it mostly dirt and fine sediment and thus probably indicating a slowly moving river, or does it contain pieces of sandstone, granite, and other minerals that speak of a quickly moving river that has rapidly carried deposits of rock from the east?
Park Information:
“Don Edwards San Francisco Bay National Wildlife Refuge, the first urban National Wildlife Refuge established in the United States, is dedicated to preserving and enhancing wildlife habitat, protecting migratory birds, protecting threatened and endangered species, and providing opportunities for wildlife-oriented recreation and nature study for the surrounding communities.”
Resources:
Alt & Hyndman, Roadside Geology of Northern and Central California. Mountain Press Publishing. Missoula: Montana. 2000.
Don Edwards SF Bay Wildlife Refuge – (visit link)
About.com -- (visit link)
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