Storage Capacity and Sedimentation Characteristics of Loch Lomond Reservoir, California, 2019

Scientific Investigations Report 2021-5081
Water Availability and Use Science Program
Prepared in cooperation with the city of Santa Cruz
By: , and 



In May of 2019, Loch Lomond Reservoir was surveyed by the U.S. Geological Survey (USGS) in cooperation with the city of Santa Cruz to assess the current storage capacity and sedimentation rates in the reservoir. Survey methods combined sonar soundings to measure bathymetry and lidar scans with GPS data to measure near-shore topography and sediment bed samples to understand reservoir bed-material
size. The survey data produced a bare-earth digital elevation model (DEM) of the reservoir at a resolution of 1 square meter or better to elevations at or above the reservoir spillway elevation, providing the coverage needed to estimate storage capacity. Additionally, the USGS compared the current survey to storage estimates from historical surveys—particularly the most recent survey in 2009—to evaluate storage capacity trends. Lastly, a hindcast estimate of scaled sediment yield using sediment yields from the San Lorenzo River (USGS station 11160500)—where the San Lorenzo River watershed encompasses the Loch Lomond Reservoir watershed—were used to compare indirect estimates of storage loss to direct storage loss.

The 2019 survey resulted in a measured storage capacity of 8,770±50 acre-feet. The differences in storage between 2009 and 2019 varied substantially by depth. In shallow areas with depths less than 30 ft (at full reservoir), such as the very upstream end of the reservoir, storage loss (sediment deposition) dominated with a loss of about 68 acre-feet from 2009 to 2019. In areas deeper than 30 ft, persistent small storage gains over a wide range of depths totaled 82 acre-feet from 2009 to 2019.

Storage loss estimates derived from estimated watershed sediment yields and reservoir characteristics were similar to storage losses computed from past surveys. This hindcasting produced an estimate of about 500 acre-feet of total storage loss for the history of the reservoir, or an average of about 8–9 acre-feet/year during the 60-year period. For the period 2009–2019, the hindcast produced an estimated total storage loss of 42 acre-feet, which is broadly consistent with the 68 acre-feet of storage loss computed for shallow areas based on the repeat surveys.

Suggested Citation

Whealdon-Haught, D.R., Wright, S.A., and Marineau, M.D., 2021, Storage capacity and sedimentation characteristics of Loch Lomond Reservoir, California, 2019: U.S. Geological Survey Scientific Investigations Report 2021-5081, 28 p.,

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments  
  • Abstract  
  • Introduction  
  • Methods  
  • Data Availability  
  • Results  
  • Discussion of Storage-Capacity Changes from 2009 to 2019  
  • Discussion of Long-Term Reservoir Storage and Watershed Sediment Yield  
  • Conclusions  
  • References Cited  
  • Appendix 1. Bowman and Williams 2012 Memo to the City of Santa Cruz  
  • Appendix 2. Bowman and Williams 2017 Memo to the City of Santa Cruz 
Publication type Report
Publication Subtype USGS Numbered Series
Title Storage capacity and sedimentation characteristics of Loch Lomond Reservoir, California, 2019
Series title Scientific Investigations Report
Series number 2021-5081
DOI 10.3133/sir20215081
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) California Water Science Center
Description Report: vii, 28 p.; Data Release
Country United States
State California
Other Geospatial Loch Lomond Reservoir
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details