How Valley Water Helped Stop the Ground from Sinking in San José

July 15, 2025

Valley Water employees stand beneath a benchmark marker illustrating 13 feet of land subsidence in San José from 1912 to 1969. The pole, placed in front of the historic U.S. Post Office building in Downtown San Jose, highlights dramatic ground level changes due to groundwater overpumping before Valley Water began managing groundwater sustainably.

Did you know that parts of downtown San José used to be up to 14 feet higher than they are today? Due to a phenomenon called subsidence, the ground actually sank. Thanks to Valley Water’s long-standing efforts to protect and manage our groundwater, subsidence is no longer an issue in Santa Clara County. Since our founding in 1929, we’ve made huge strides to protect the region’s most precious resource: water.

What is subsidence?

Subsidence is the gradual sinking or sudden settling of the Earth's surface. While it can be triggered by natural events like sinkholes, earthquakes, or volcanic activity, it’s most often caused by human actions, especially the excessive removal of underground resources like water.

In Santa Clara County, the biggest cause of subsidence has been the overpumping of groundwater from clay and silt-rich basins faster than it can be replenished naturally.

What problems can subsidence cause?

Subsidence isn’t just about losing elevation. It can have serious consequences for people, infrastructure and the environment. Subsidence can lead to seawater intrusion, a higher flood risk in low-lying areas, damage to infrastructure, economic losses, and long-term impacts on groundwater aquifers and the ecosystems that rely on them.

Critical infrastructure vulnerable to subsidence includes:

Levees
Pumping stations
Sewer and storm systems
Water supply wells and pipelines
Roads, bridges, and railroads

Has there been permanent subsidence in Santa Clara County?

Yes, and in fact, our region was the first place in the U.S. where subsidence due to groundwater overpumping was officially observed. It was first detected in 1915 and eventually affected more than 100 square miles in northern Santa Clara County.

The worst impacts were seen in the heart of the valley, covering areas like Sunnyvale, Santa Clara, and San José, where the land sank as much as 14 feet. Interestingly, no permanent subsidence has been observed in southern Santa Clara County.

How did Valley Water stop subsidence?

By around 1970, Valley Water had successfully stopped permanent subsidence through a combination of smart investments and water management strategies. These included:

Building reservoirs
Diversifying water sources
Enhancing groundwater recharge efforts
Establishing long-term groundwater management programs

What is being done to prevent more subsidence?

At Valley Water, we continue monitoring and managing groundwater to prevent subsidence from returning. Our proactive measures include:

Recharging aquifers using 285 acres of recharge ponds and approximately 100 miles of streams with local and imported surface water.
Delivering surface water to retailers from three treatment plants to reduce groundwater pumping.
Promoting water conservation and recycling programs to cut overall demand.

Subsidence may have shaped Santa Clara County's past, but thanks to Valley Water’s innovative and proactive approach, it doesn’t have to define our future. By investing in long-term water management solutions and continuously monitoring groundwater levels, we have not only halted the sinking of our land but also continue to protect the region’s infrastructure, environment, and water supply.

Valley Water manages an integrated water resources system that includes the supply of clean, safe water, flood protection and stewardship of streams on behalf of Santa Clara County's 2 million residents. Valley Water effectively manages 10 dams and surface water reservoirs, three water treatment plants, an advanced recycled water purification center, a state-of-the-art water quality laboratory, nearly 280 acres of groundwater recharge ponds and 350 miles of waterways. We provide wholesale water and groundwater management services to local municipalities and private water retailers who deliver drinking water directly to homes and businesses in Santa Clara County.