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Changes in soil moisture, characterized by infiltration and evapotranspiration, are impacting watersheds in the Sierra Nevada Mountains and the quantity and quality of water for downstream communities. To better understand soil moisture conditions, the USGS, in cooperation with the California Department of Water Resources, initiated a monitoring study to provide enhanced soil moisture data to be incorporated into a hydrologic model used to predict runoff and retention.

An essential part of this project is the installation of soil moisture monitoring stations. Each monitoring station has five sensors that detect the amount of water in the soil profile to a depth of about three feet. The remote stations are solar powered and transmit the data via a satellite or cellular uplink, allowing the data to be monitored in real time. The plan is to install a total of 30 stations over the next two years. (Right: map showing locations of planned stations.)

To begin this effort, scientists and technicians from the California Water Science Center’s Watershed Sciences Program, accompanied by soil scientists from the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service – Soil and Plant Science Division, traveled to a study area in the Upper Feather River Watershed in Plumas County California. Here, during the week of July 8-13, 2024, they installed seven soil moisture stations.

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The soil monitoring station installation team included personnel from the USGS and USDA. From left to right: Theresa Kunch (USDA), Darren Pinnegar (USDA), Diana Zamora-Reyes (USGS), Jim Howle (USGS), Nate Smalley (USGS), Michelle Stern (USGS), Mimi Payne (USGS), Justin Clause (USGS), Gianna Mantel (USGS), Jessica Castiblanco (USDA), Elias Tejeda (USGS), and Jeff Gronemyer (USGS).

After determining an undisturbed site for the soil pit, the next step is digging a pit 100 cm (or 3.3 feet) deep. If on a slope, the “face” of the soil pit is on the upslope side of the area. The sensor depths are installed at five depths: 5 cm, 10 cm, 25 cm, 50 cm, and 100 cm. 

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Jessica Castiblanco (USDA) helps dig the pit for the soil moisture sensors. Inset: close-up of soil removed from Squirrel Creek pit. She also analyzed the soil for soil characteristics, including color and texture.

Each sensor, or probe, was connected to long wiring with exposed wires at the end that are connected to the datalogger.

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Soil moisture sensors positioned in pit at different depths. Inset: close-up of sensor showing the two probes that gather the data.

While the pit was being dug and sensors were being placed, other members of the team worked to position a support mast and assemble the data logging and satellite transmitting components. The structure was placed in a sunny area in an exposed south-facing direction to allow for the datalogger to transmit data and ensure the solar panel has access to adequate power. 

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Shown from top left are: 1] setting up the mast support, 2] installing the datalogger. (Justin Clause is shown providing insight on basic wiring.) 3] attaching solar panel and directional antenna, 4] the final install of the standalone site.

Bringing the station online

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Once the mast was installed, and the enclosure, the solar panel, and antenna were all secured, the soil moisture sensors were then wired up to the datalogger. Once all wiring of the sensors were connected, the datalogger received power.  

Data from the satellite uplink will eventually be available to the public on the USGS National Water Information System (NWIS).

At left, USGS Hydrologist Jim Howle checks data logging and transmission components using a laptop computer.