Pacific Southwest Research Station

Development of an Online Watershed Interface to predict the effects of forest and fire management on sediment and phosphorus loads in surface runoff in the Lake Tahoe Basin

Principal Investigators:
William Elliot and Randy Foltz, USDA Forest Service-Rocky Mountain Research Station
Erin Brooks and Jan Boll, University of Idaho
Michael Hogan, Integrated Environmental Restoration Services, Inc.

Proposal [pdf]

Final Report [pdf]

Agenda and Presentations from October 2014 Stakeholder Meeting:
Agenda [pdf]
Project Overview [pdf]
Rainfall Simulators Comparison [pdf]
Current Draft Interface & Incorporating Base Flow and Phosphorus [pdf]

Project Summary

Lake Tahoe, widely known for its clear waters, has started to experience during the last 50 years problems related with reduced transparency. Long-term water quality monitoring at the outlet of the Lake’s main tributaries suggested an increase in sediment (fine particles < 16 µm in diameter) and nutrient (nitrogen and phosphorus) delivery to the Lake, which has contributed to the decline in water clarity. Urban development and changes in land use and land cover are the main sources of direct pollutant input to the Lake, but other factors such as atmospheric deposition have also been responsible for the Lake’s nutrient enrichment.

In the absence of disturbance, forest hillslopes erode very little, and water leaving forested watersheds is generally subsurface lateral flow or interflow and groundwater. When a forest is disturbed, surface runoff may increase, generating surface runoff and sediment delivery. In some cases, such disturbance can also release nutrients like phosphorus to runoff and subsurface lateral flow, adversely affecting offsite water quality. If there is no forest management, then the risk of wildfire is increased, as is the probability of elevated erosion rates much greater than those associated with disturbances from forest management.

There was a need for a tool that could predict the impacts of wildfire and compare that to the impacts of fuel management activities. This project was designed to provide such a tool at a sub watershed scale.