San Francisco Bay Area - East Bay (BALT1) Site near Castro Valley, CA

Science Center Objects

Recent Conditions

The instruments for this site were installed in the spring of 2009 and are used to monitor and detect changes in local conditions.  Soil water content and ground water pressure are monitored at two nests on the same hillslope.  Data for the site include:

Data are recorded and updated every 5 minutes and displayed on graphs.

Project Background

Landslides in the San Francisco Bay area (SFBA) of California impact people, infrastructure, and the environment, and are commonly induced by intense or prolonged rainfall associated with strong winter storms.  Both shallow (<3 meter) and deep (≥3 meter) landslides can occur.  Typically, shallow landslides occur as a result of high-intensity precipitation when the ground is already nearly saturated with water from previous storms.  These types of events can occur during the height of the rainy season, from December through February.  Deep-seated landslides can also occur during these times, but are also often triggered during the spring months (March through May), when water from rainfall has had a chance to make its way to deeper soil and bedrock.

The U.S. Geological Survey, in cooperation with local and state government organizations, operates several shallow landslide monitoring sites in the SFBA for research purposes.  The goal of this research is to identify thresholds for widespread shallow landsliding and related high-mobility debris flows based on in-situ soil moisture conditions.  This information is being used to develop landslide warning criteria with the National Weather Service.  Monitoring data includes cumulative rainfall, rainfall intensity, soil water content, groundwater pressure, air temperature, and relative humidity.  Infiltration of water from rainfall increases soil water content, cumulatively saturating the soil profile.  However, periods without rainfall can lead to drying of the soil.  If the soil profile is nearly saturated, additional intense precipitation can increase groundwater pressures which can, in turn, induce landslide movement.

landslide monitoring equipment inside small fence on grassy slope

The USGS “BALT1” site is located in the San Francisco East Bay and consists of a cattle-protected enclosure with dataloggers monitoring the hillslope in the central part of the image.  This slope is typical for many in the East Bay region that have generated mobile debris flows in the past.  The area consists of grasslands over an approximately 1-meter-deep sandy soil layer, underlain by sandstone. (Public domain.)

landslide monitoring equipment inside small fence on grassy slope

The USGS “BALT1” monitoring site showing datalogger enclosure, solar panel, air temperature sensor, and rainfall gage.  The contents are contained within a fence enclosure to protect the instrumentation from grazing cattle. (Public domain.)