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.
You are not doing enough the stop subside. The the creeks and streams are a mess with the homeless occupying too many of the areas.
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