Pacific Southwest Research Station

Realigning the Lake Tahoe Interagency Monitoring Program for use as a monitoring tool

Principal Investigators:
Robert Coats, Hydroikos Ltd.
Jack Lewis, Consultant
John Reuter, University of California-Davis

Proposal [pdf]

Final Report [pdf]
Final Report Appendices [pdf]

LTIMP Station Loads [xlsx]

Please contact Dr. Robert Coats with questions regarding the final report.

Project Summary

Since 1980, the Lake Tahoe Interagency Monitoring Program (LTIMP) has measured discharge and sampled water quality at up to twenty stations in Tahoe Basin streams. Measured constituents have included suspended sediment and various forms of nitrogen and phosphorus.

In order to improve the usefulness of the program and the existing data base, this project:

1. Identified and, to the extent possible, corrected for two sources of bias in the data base.
2. Generated synthetic data sets using turbidity, discharge, and time of year as explanatory variables for different forms of nitrogen, phosphorus, and suspended and fine sediment.
3. Resampled the synthetic data sets and part of the historic record in experiments to compare the accuracy of different load calculation models.
4. Identified the best load calculation models for estimating each constituent load.
5. Using the best models, recalculated total annual loads for all constituents and stations over the period of record.
6. Regressed total loads against total annual and maximum daily discharge, and tested for time trends in the residuals.
7. Developed a spreadsheet showing the relationships between sample size and confidence limits for estimated loads of the constituents.

The time series analyses show significant long-term downward trends in some constituent loads and some streams, which are attributed to long-term recovery of watersheds from historic disturbance. The confidence-limit spreadsheet will be a useful tool for managers in modifying LTIMP to make it a streamlined and effective tool for future water quality monitoring in the Tahoe Basin.