Soil Stratigraphy and Erosion Potential on the American and Sacramento Rivers

Science Center Objects

Much of the Sacramento region is protected from flooding by levees constructed on the American and Sacramento Rivers, which join near downtown Sacramento before flowing to the Sacramento-San Joaquin River Delta.

A large dam at Folsom, on the American River, constructed by the U.S. Army Corps of Engineers (USACE) in the 1950s is also part of the region’s flood protection scheme. Like all flood control dams, it helps regulate peak discharges, but in extreme cases, a large volume of water would have to be discharged from the dam and carried by the rivers below. These large flows have the potential to erode the riverbed and compromise the levees.

To ensure the integrity of the levees, the U.S. Geological Survey (USGS) is working with the USACE The U.S. Department of Agriculture’s (USDA) National Sedimentation Lab, and Texas A&M University (TAMU) to investigate potential problems. The role of the USGS in this project is to document soil characteristics and perform borehole erosion tests in order to compute erosion rates. Results will be presented in a report that will be prepared by USGS.

map of proposed erosion test drill sites

Map of proposed erosion test drill sites along American and Sacramento rivers.

Objectives and Scope

  1. Perform site reconnaissance at 11 proposed drilling sites on the American River, and 10 proposed sites on the Sacramento River.
  2. Perform drilling at 11 sites on the American River and 10 sites on the Sacramento River. Where possible, two holes will be drilled at each site. One hole will be drilled to obtain samples for laboratory testing, and to reveal stratigraphy, which will be documented on field sheets, with the second hole being drilled to perform the Borehole Erosion Test.
  3. Produce a report describing the testing procedure and results, and provide some interpretation of the results, including vertical and longitudinal variability, comparison of the Borehole Erosion Test results to the results obtained by the USDA team, and assessment of potential equilibrium cross-sectional area should extreme flow conditions persist.
  4. Participate in periodic project meetings to describe progress.

Relevance and Benefits

This project is clearly a natural hazards issue, specifically flood-related, targeted at an area that is both at risk of flooding and important to the state and nation. The subject of water-related hazards is a priority for the USGS Water Mission Area. Results of this proposed study could guide future investments in flood control efforts for the Sacramento region and the project includes input from local partners including the California Department of Water Resources and Sacramento County.