The Altered Laguna: A Conceptual Model for Watershed Stewardship

Final version (November 26, 2007)

Table 1-1  Summary of estimated pollutant loadings during winter by land uses

A synthesis of current data on sedimentation, water quality, and ecosystem impairments, for planning and management of the Laguna de Santa Rosa watershed, Sonoma County, California.

Executive Summary

Project goals

The Laguna de Santa Rosa watershed embodies a complex system of physical, hydrological, chemical and biological processes that are closely linked to many direct and indirect impacts from the largest concentration of human settlements in Sonoma County. The Laguna is wedged between five expanding urban centers: Cotati, Rohnert Park, Sebastopol, Santa Rosa, and Windsor. Much of the Laguna de Santa Rosa and its watershed tributaries have been altered, and now reflect numerous historic and contemporary human caused modifications to natural processes. Many of these alterations have rendered the watershed as impaired, with negative impacts to natural hydrology, sedimentation, flood capacity, water quality and valuable ecosystem services for wildlife and humans. This degraded system, historically extremely rich and diverse, now performs at a sub-optimal level and active restoration is needed to turn the tide for improvement of “Beneficial Uses” identified in the North Coast Regional Water Quality Control Board Basin Plan.

The Laguna de Santa Rosa Foundation, in collaboration with Philip Williams and Associates (PWA) and Tetra Tech, and with guidance from North Coast Regional Water Quality Control Board and a Technical Advisory Group developed a conceptual framework to address the following goals:

  1. Improve our understanding of the Laguna system for basin scale planning and management;
  2. Gather and analyze available data;
  3. Identify data gaps, appropriate system indicators, monitoring regimes, and restoration targets; and
  4. Specify further modeling efforts focused on the watershed.

Table 1-2  Nutrient concentration trends for the upper, middle, and lower Laguna

The impetus to this process is the project’s important role in launching the Laguna Total Maximum Daily Load (TMDL) study to address water quality concerns, and to ensure that the appropriate watershed-scale scope is used for the TMDL-related work. This report addresses the following project objectives:

  • Prepare a list of detailed management objectives to guide future restoration, model development and data collection activities;
  • Establish a comprehensive project database to consolidate and organize existing information to support assessment and model development;
  • Develop a suite of conceptual models to identify key factors and processes driving existing and future conditions within the basin with regard to hydrology and sedimentation, water quality, and ecosystem processes;
  • Perform data gaps and uncertainties analysis to identify the information needed to complete an assessment and modeling analysis of the basin, including those assessments and tools needed for TMDL development;
  • Develop model selection and development recommendations to ensure that the chosen approach addresses the needs of all of the modeling objectives;
  • Prepare monitoring recommendations to provide a basis for data collection prioritization.

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