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Land Subsidence in Arizona

 

 

In the News...

Recently the Department has begun working with NASA's Jet Propulsion Laboratory to collect data  through NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) program in Cochise County to improve data collection and to complement the Department's satellite-based Inteferometric Synthetic Aperature Radar (InSAR) data.  The Arizona Department of Water Resources has been collecting and processing InSAR data since 2002 to monitor land subsidence throughout Arizona.  The Department has identified more than 25 land subsidence features that cover more than 1,100 square miles.

 

NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar News Release

Radar Plane Scans South American Landscapes (Yahoo! News)

 
NewInteractive Arizona Land Subsidence Map
Arizona Land Subsidence Areas
   

 

 

What is Land Subsidence
Arizona Land Subsidence Interactive Map

Active Land Subsidence Areas in Arizona
Based on ADWR InSAR Data

Land subsidence has been occurring across Arizona since the early 1900’s. Millions of people around the world live in active land subsidence areas and are unaware. Most of the time, there is no clear and identifiable sign that land subsidence has occurred in an area. Areas in Maricopa and Pinal Counties have subsided more than eighteen feet since the early 1900's.

Land subsidence in the basins of Arizona is generally due to compaction of the alluvium caused by lowering of the water table. As the water table declines, pores in the alluvium once held open by water pressure are no longer supported and collapse. Collapse and subsequent lowering in elevation of the land surface is defined as land subsidence. This subsidence is generally not recoverable. If this subsidence occurs over areas of bedrock, differential subsidence can occur.

Differential subsidence is when adjacent areas subside at different rates. Bedrock will not compress like the surrounding alluvium, creating a subsurface platform. Differential subsidence occurs where shallow bedrock and deep bedrock are adjacent to each other, creating a zone of differential change in surface elevation. Because of these different amounts of subsidence, tension can build in the alluvium layer at this differential subsidence zone, forming an earth fissure.

ADWR Land Subsidence in Arizona Fact Sheet pdf (<1 MB)

 

 

Earth Fissures

 

Earth fissures are cracks at or near the earth’s surface that are the result of differential subsidence. Earth fissures start out as small cracks and may not be visible on the surface. They grow and widen from surface water flowing into the crack, eroding material from the sides.

Earth fissures have caused millions of dollars in property and infrastructure damage, damaging pipelines, roads, canals, flood retention structures, bridges, buildings, and private property. There are unanswered questions about how earth fissures interact with groundwater pollution.

Earth Fissure in Queen Creek

The Y Fissure in Queen Creek Area after

a Monsoon Storm in August 2005

 

 

Impacts of Land Subsidence and Earth Fissures

There are many consequences of land subsidence and earth fissures: Elevation and slope change affecting the natural flood plain drainage, flow within canals and drains, damaging intermodal infrastructure (roads, bridges, railways, etc), damaging water retention and retarding structures (dams, levees, floodways, etc), and damaging private property(homes, driveways, fences, etc).

Earth fissures are identified by using on the ground and aerial monitoring techniques. The Arizona Geological Survey (ASGS) started an intensive earth fissure mapping program in 2006. The goal of this program is to survey and record each known earth fissure around the State and provide this data to the public.

 

 

Land Subsidence Monitoring
Hawk Rock InSAR Interferogram

Hawk Rock Subsidence Feature

2004 - 2008 Interferogram

 

Land subsidence has been detected over the years using surveying techniques such as differential leveling and high accuracy Global Positioning System (GPS) surveying. In the early 1990’sscientists began to use Synthetic Aperture Radar (SAR) and interferometric processing (InSAR) to detect land surface elevation changes. InSAR has been developed into a highly reliable land subsidence monitoring technique that has been utilized by ADWR since 2002. ADWR has identified numerous subsidence features around the State and continues to monitor the extent and rates of these features on an annual basis.

Land subsidence maps were developed by ADWR using archived and current InSAR data with the goal of providing hydrologists, geologists, water managers, and the public the most accurate land subsidence data.

ADWR is also part of the Arizona Land Subsidence Group which was jointly created by the geological and engineering communities as a venue for discussing the state of knowledge regarding subsidence of Arizona’s alluvial basins.

 

 

 

 



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