A two-year study published by ASU shows parts of Phoenix are sinking. This is not a new issue to the valley but the study shows new information about which parts of the Phoenix-metro area are sinking most rapidly.
The problem is caused by the overuse of Phoenix's groundwater, the water stored in underground aquifers. When water is pumped more rapidly than it is recharged subsidence occurs.
"When we pum
p it out of the ground, the water is originally in pore spaces between the grains of an aquifer and when we pump it out it puts more stress on the grains that remain. Once you reach a level of stress the pore can collapse," said Megan Miller, ASU Geological studies PHD candidate leading the study.
Some of the problems that come with subsidence include fissures or cracks in the ground. That can cause cracks in home foundations, canals and any other structure laid on a location where a fissure occurs.
Using satellite images, for the last two years Miller compiled data on the rate of sinking.
"Phoenix is sinking in some areas and rising in others due to our groundwater use," said Miller.
MIller said research shows a pocket in the West Valley is sinking .5 centimeters a year, in the North Valley 1.5 centimeters a year and the most significant drop in Apache Junction at 2.5 centimeters per year. On the contrary it seems aquifer recharge efforts are working in Scottsdale since the study shows that area is actually rising.
"Usually we see rapid subsidence from outside a metro area and this is right below the city," said Dr. Machoochehr Shrrzaei, the study's supervising professor.
Shrrzaei said the information he and his student gathered has been passed along to the Arizona Department of Water Resources. From there the professor said it now will be up to individual communities to turn around the groundwater overuse.
"I think regionally it's important to note that we live in a semi-arid environment and there are only a few places to get our water," said Miller.
To put it into perspective while any subsidence is bad the two centimeter drop annually here is small compared to the 5 centimeter drop per month in central California.