Laguna de Santa Rosa Foundation

Management Plan

Sustaining Our Water Resources

The Laguna watershed has a complex and diverse hydrology—cool water, high-gradient creeks in the upper watershed flow down the hillsides to the broad, flat, vernal pool-dotted Santa Rosa Plain, meeting the warm, slow-moving Laguna main channel, that flows northward to join the Russian River. The diversity of Laguna wetlands is a central reason for the Laguna’s biological diversity. Vernal pools and swales, sedge-dominated high marshes, tule-dominated low marshes, seasonal floodplains, and perennial creeks and streams all support different plant and wildlife communities.

Alluvial Fans

Historically, streams flowing down from Sonoma, Taylor and the Mayacama Mountains formed broad alluvial fans as they deposited sediments over the east side of the Santa Rosa Plain. Today though, these alluvial processes are constrained because of our need to protect property from damaging floods. But flooding, erosion and sedimentation are natural, desirable processes in a well-functioning stream ecosystem and are thought to be essential for maintaining biological diversity.

Alleviating the Detrimental Effects

Over the long term, flooding and the detrimental effects of sedimentation can be alleviated through a combined set of practices, including: stabilizing stream banks, reducing upland sources of erosion, restoring riparian forests, retaining aquifer recharge areas, protecting the floodplain from encroachment, wisely managing vegetation in urban creeks, and selectively removing accumulated deposits of sediment from key areas.

Sedimentation

Coordinated, watershed-scale studies and modeling are a critical first step for developing a baseline characterization of the watershed and predicting future changes in year-round water dynamics. The Sonoma County Water Agency (SCWA) and US Army Corps of Engineers (USACE) are evaluating flooding patterns in different parts of the watershed. Together they co-sponsored the Sedimentation Study, which provides a predictive model for the rate and fate of sediment delivery in the Laguna, showing the contributive levels of sediment expected from each of the Laguna’s sub-watersheds.

Sediment Transport

Currently SCWA and USACE are working with the US Geological Survey to model sediment transport through portions of the Laguna main channel: when complete, this model will provide an understanding of how water-borne silt is moving (or not moving) through the middle and lower reaches of the Laguna from Highway 12 to the Russian River.

Flooding

Accelerated changes in flood levels and water retention on the floodplain will affect the long term viability of restoration projects: areas that are constantly inundated will not be suitable for riparian plants. The recent rapid changes to the surface and sub-surface water table has triggered large changes in the middle reach of the Laguna: many acres of former riparian forest have died from overly-saturated soils and have been replaced by the invasive exotic Ludwigia.

In order to understand these changes to floodplain dynamics and to plan for successful restoration of impacted sites, better data is needed. As a start, a more comprehensive set of stream gauges for collecting stage and discharge readings is essential: these would help in the development and calibration of predictive hydrology models.

Rainfall Guages

Similarly, a comprehensive set of rainfall gauges, especially ones distributed over the mountainous portions of the watershed, would be valuable for water budget models. Together with these proposed data collection stations, a better survey and analysis of topography, canopy cover, impervious surfaces, and land use patterns is called for; these will yield valuable information that can be applied towards many different kinds of restoration efforts.

Pollution

Water quality in the Laguna has been a challenge for decades. Although pollution levels in the Laguna today are a vast improvement over the days when regulations were lax or non-existent, more progress is needed. The most recent Environmental Protection Agency 303(d) list of impaired water bodies, prepared in 2004, includes listings for the Laguna de Santa Rosa, Santa Rosa Creek, and Mark West Creek sub-basins—which collectively form the working definition of the greater Laguna watershed.

Sub-basins

These sub-basins are considered to be legally impaired for having excess nitrogen, excess phosphorus, elevated water temperature, low dissolved oxygen, and excess sediment/siltation.
Although we have a general understanding of the Laguna’s water quality concerns, we have yet to quantify either the sources or the effects of particular pollutants. A Total Daily Maximum Load (TMDL) process should be initiated to address the Laguna’s water quality impairments. This process should work towards the initial goal of developing a basic understanding of pollutant sources, and should work towards the subsequent goal of developing policies and management practices that can eliminate, or reduce to acceptable levels, these impairments.

Storm Water Management Program

Part of the solution will come through implementation of the Storm Water Management Program, developed by the City of Santa Rosa, the County of Sonoma, and the Sonoma County Water Agency. Part of the solution will come through better nutrient management systems put in place through the Resource Conservation Districts working in partnership with local livestock operators. And part of the solution will come through open space acquisitions and habitat restoration of riparian areas.

Incremental Recycled Water Program

The IRWP, or Incremental Recycled Water Program, is the Laguna Subregional Wastewater Treatment Facility’s plan for disposing treated wastewater during the next fifteen years. For the past couple of decades, agricultural and urban irrigation has been an innovative and important method for reusing this water. The Geyser’s pipeline, since it came online in 2004, has added a second important endpoint for this resource. When winter rains eliminate the need for irrigation, and when the Geyser’s daily capacity to receive water is met, excess water is pumped to storage ponds for later summertime use. But when this wintertime storage capacity is exceeded, treated wastewater needs to be discharged into either the Laguna or the Russian River. Direct discharges of wastewater to the Laguna should be phased out as soon as possible.

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