SPAWN’s Sediment Load Reduction Project in the Lagunitas Creek Watershed has been well underway this past month and will be wrapping up shortly. Here’s the latest update on how this project has developed:
By Ayano Hayes | California
This summer has been all about construction and restoration, addressing one of the main sources of pollution that impacts water quality within the Lagunitas Creek Watershed. Based on the Total Maximum Daily Load (TMDL) Assessment for the Watershed, fine sediment is one of the main pollution sources that affects juvenile salmon in the freshwater streams. A TMDL sets the maximum amount of a pollutant that a water body can receive while still meeting water quality standards. For restoration projects to be effective, science-based criteria and studies, such as what’s emphasized in the Lagunitas Creek Sediment TMDL, are referenced, and incorporated into design to meet objectives towards fine sediment control.
SPAWN has completed several Instream and Floodplain Habitat Restoration Projects over the years, but this summer, sediment load transport was addressed on nearly 1 mile of priority sections of impaired dirt road. Following rain events in the winter, dirt roads would become saturated, soft, and easily moldable when driven on, unraveling the stability of the roads over time. Add any steep elevation to a road, and any ruts with improper drainage outlets act as easy transport lanes for sediment to naturally run off during a rain event. This run-off would find its way to stream crossings or smaller drainages that would ultimately end up into Lagunitas Creek, contributing to water quality impairments from fine sediment. Therefore, working up in the hills on McIssac and Zanardi Ranches, on Golden Gate National Recreation Area land, road sections were repaired, upgraded, improved, and stream crossings were restored.
Pacific Watershed Associates designed the project while Bohan & Canelis General Engineering implemented the design. The road treatments that were prescribed ranged from rolling dips, crossroad drains, to out sloping, widening, resurfacing, and decommissioning sections of road. Most of the treatments were rolling dips and crossroad drains to manage run-off by diverting water off the road in strategic locations. The major road sections were resurfaced with road rock material as a final touch to allow all year driving. Two stream crossings that faced head cuts and significant erosion were regraded with gentler slopes, while grade controls and armored fill were put in place. Another stream crossing was decommissioned and fully restored by removing the road and culvert within an ephemeral stream. Multiple roads sections fit the bill for decommissioning and were either re-worked into the natural landscape or received other treatments that would help divert water.
Sediment load reduction was also focused at the closed Redi-Mix concrete plant on Black Mountain Ranch. A private ranch, in the Agricultural Production Zone, under a rolling 20-year Williams Act contract, and a MALT Easement. SPAWN conducted Phase 1of floodplain restoration in 2016 with the final phase to be completed this year. Approximately 0.6 acres of the cement plant staging area has been removed (around 500 cu. yds) to revegetate and expand the floodplain riparian corridor along 350 linear feet of Lagunitas Creek. This site is known to flood during large storm events. Now, instead of road run off and water spreading across impervious surfaces and entering back into Lagunitas creek, water will be able to supply a native landscape, recharge, and filter through the soil.
Construction may have ended, but SPAWN is preparing for the revegetation stage, where volunteers can get involved with restoration! Stay tuned for more updates on this project and opportunities to volunteer. Contact SPAWN’s Conservation Project Manager, Ayan Hayes, ahayes@tirn.net to learn more.
Funding for this project has been provided in full by the United States Environmental Protection Agency under the Federal Nonpoint Source Pollution Control Program (Clean Water Act Section 319) through an agreement with the State Water Resources Control Board.
