User:Shelbyyyw/California aqueduct

Plan/Outline:

To add a section to the article 'California Aqueduct".

Section will be called Land Subsidence

This section will discuss how the land around the California Aqueduct and surrounding areas has had subsidence.

This article does not have a section about this so instead of contributing to sections of this article or creating a new article, I would rather add more information not listed to this article. So this article will have another section to it discussing only the land subsidence.

Background
Land subsidence is when the land gradually or suddenly sinks or settles due to movement or removal of natural materials such as water, minerals, oil and natural gases. More often than not, subsidence occurs when groundwater is removed from sediment or rocks in a large quanity. This often occurs due to human interference, but can also happen from natural phenomenons. Subsidence can happen over very large areas or small little sections of land. This has occurred along the California Aqueduct of the State Water Project since construction.

Human causes include; pumping, mining and fracking.

Natural causes include; earthquakes, erosion, glacial movement, soil compaction and the formation of sinkholes.

Groundwater use and pumping in the area was the major water use for farmers and agriculture in the 1920's and overtime this over pumping resulted in land subsidence and a decline in groundwater-level resources. In time, this resulted in major land subsidence by the 1970's with local areas having 1 to 28 feet of subsidence. With the creation and use of the California Aqueduct along these regions, surface water being transported put a halt on significant compaction and a recovery in ground water levels now with less ground water pumping. The California Aqueduct has been increasing in subsidence rates rapidly, even though it was relatively stable for many years after being constructed.

Measurement
Measurement of this subsidence is done in a few ways. Originally, subsidence was recorded based on land surveying, repeating the surveying, and along with monitoring compaction by recording the data from extensometers at multiple sites. Since then, Global Positioning Systems (GPS) has been used along with land surveying to record subsidence and compaction. More recently, interferometric synthetic aperture radar (InSAR) has been used to monitor subsidence along with GPS. InSAR is being used to recreate maps to closely watch the progression of the land around the California Aqueduct.

Consequences
Subsidence can put land, both private and public, at risk of infrastructure damage. Bridges, levees, roads, and groundwater wells are either at risk of damage or have been damaged already. With subsidence progression, underground aquifers could be at risk and water storage from them could be threatened. Damage and sinking of the canal of the California Aqueduct has already occurred from subsidence which has made the canal less reliable. Capacity has been compromised due to damage to the canals and therefore has caused problems and delays with delivering the water across the state, as well as higher rates and costs for power and operation.