David Lewis - Watershed Management Advisor

The Watershed Management Program provides scientifically based education to maintain viable natural resource management and agricultural production while conserving, protecting, and restoring watershed functions. Specific areas of program research and education include:

• Point and nonpoint source pollution management
• Links between agricultural and natural resource management practices and watershed beneficial uses

Know Your Watershed

A watershed is a geographic unit that collects, stores, and releases water. Collected water comes in the form of rain, snow, and in our coastal watersheds fog. It is stored in lakes, ponds, and subsurface soils and geologic formations.  Rivers and streams, as well as groundwater flow, then release this water.

The United States Geological Survey formally catalogues the nation’s watersheds into Hydrologic Unit Codes. These codes are used by resource agencies to identify specific watersheds in which they are conducting research or setting policy. You can locate your watershed and obtain its code through this U.S. Environmental Protection Agency resource (www.epa.gov/surf/locate/). With the code you can obtain watershed specific information available for California watersheds through the State Water Resource Control Board (www.swrcb.ca.gov/watershed/index.html) and the California Rivers Assessment (endeavor.des.ucdavis.edu/newcara).

Total Maximum Daily Loads

One of the most prominent and far reaching water quality policy tools that exist for watersheds are Total Maximum Daily Loads (TMDL). These are used the Regional Water Quality Control Board and US Environmental Protection Agency to identify watersheds with impaired beneficial uses and develop plans to mitigate impairments.  Resource and regulatory agency staff use the term TMDL to refer to a definition, a process, and a document.

The definition of a TMDL is “sum of the individual wasteload allocations for point sources, load allocations for nonpoint sources and natural background pollutants, and an appropriate margin of safety (USEPA).”

As a process, TMDLs serve to identify impaired water bodies, determine the sources for this impairment, and implement mitigation measures to reduce those sources and remove impairments.  This process has several formal steps including Problem Statement, Source Allocation, and Implementation Plan development.  Public input and comment is sought at each of these steps.

TMDL documents include “Technical Support Documents” such as that sediment and temperature in the Navarro River Watershed and the reference document and Action Plan for sediment in the Garcia River Watershed.  These documents were the result of a TMDL development process during the last five years and provide the problem statements, source analysis, and implementation plans that were developed.

Additional description of TMDLs are provided by the North Coast Regional Water Quality Control Board (http://www.swrcb.ca.gov/rwqcb1/Program_Information/tmdl/tmdlprogram.html) and Region 9 of the US EPA (http://www.epa.gov/region09/water/tmdl/fact.html). A summary of water quality regulations and role of TMDLs for California’s future water policy is available through the California State Library (http://ferguson.library.ca.gov:80/crb/99/05/99005.pdf).

Water bodies scheduled to TMDLS developed and implemented are listed on the California 303(d) List and TMDL Priority Schedule.  This list is updated and revised every two years.  To learn the TMDL status of a specific water body contact the relevant regional board (http://www.swrcb.ca.gov/regions.html) or check the 303(d) by region (www.epa.gov/region09/water/tmdl/fact.html).

Research Projects

• Paired Watershed Research
• Garcia River Temperature Study

The team's goal is to develop an understanding of the complex interactions of soil, geology, vegetation, and land use management with watershed function within these watersheds.  The team includes Barbara Allen-Diaz, range ecology professor at UC Berkeley; Ken Tate, rangeland watershed specialist at UC Davis; Randy Dahlgren and Mike Singer, soil science professors at UC Davis; Rob Atwill, environmental health specialist with the School of Veterinary Medicine at UC Davis; and David Lewis.  The network of coastal and sierrain watersheds, dominated by oak woodland, was established with the support of the University of California Integrated Hardwood Range Management Program, and respective staff at the University of California Sierra Foothill and Hopland Research and Extension Centers.

Stream flow is monitored at flumes installed at the outlet of each watershed.  Water samples are collected throughout the winter at 1-2 hour intervals during storms and 3-4 hour intervals between storms.  In addition, vegetation composition, structure, and pattern are being documented at the watershed scale.

Currently, baseline data is being collected in order to ‘calibrate’ the watersheds before implementing  treatments.  During this calibration phase, the UC team is documenting relationships between the watersheds by comparing water quality (e.g. nitrate concentration) and yield measurements from each. Once the calibration phase is complete, the team plans to change grazing intensities and implement controlled burning within a subset of the watersheds, while maintaining current management in the others.   The interactions of a treatment will be measured by detecting a significant change in the previously established relationship between the treated and control watershed.