Habitat Enhancement

Habitat Enhancement 

Since its founding, Friends has designed, implemented, managed, or overseen a dozen or more habitat enhancement projects in the watershed. Thanks go to our partners, students, teachers, volunteers, and the local communities for their invaluable contributions.  

College of Marin Ecology Study Area  

This woodland site covers two acres adjacent to the multi-use path that links the college and Bon Air Road and is bounded by Corte Madera Creek and a tidal slough. We initiated the project in 1998 and has as its goal the eventual replacement of all eucalyptus and acacia trees on the site with a diverse woodland of native species.  

In early 2005 a large area was cleared of non-native trees and replanted with nearly 400 native plants. A survey of birds using the area was conducted previously, and trees were retained to ensure that roosting herons, especially egrets, would be disturbed as little as possible. The most successful native tree species planted are: coast live and valley oaks; box-elder; and black walnut. The main understory plants are whiteroot sedge (Carex barbarae), introduced by Friends, and the pre-existing native creeping wild rye (Elymus triticoides). Both spread rapidly given the opportunity.  

In the summer of 2021, the College of Marin cleared an illegal BMX track from a large portion of the ESA and in the process removed many acacia trees. With donations and the help of volunteers, Friends planted native shrubs and 85 trees. 

Whenever funds are available, more eucalyptuses and acacias are removed. Friends’ volunteers continue to remove periwinkle and other invasives to expand the native plantings. A berm currently protects most of the area from tidal intrusion, however there is an opening in the southern corner, where several salt-marsh plant species are found. Rising sea level will jeopardize the riparian plants unless preventive action is taken.   

Lower COM Corte Madera Creek Habitat Restoration 

The State Coastal Conservancy provided funding to develop 65% designs to remove part of the concrete channel at its downstream end. The Marin County Water Conservation and Flood Control District funded 100% designs and specifications. All the permits are in place and construction is fully funded.  

The project will create approximately 0.6 acres of new tidal wetland and 0.8 acres of new transitional and upland riparian habitats by removing or lowering 625 lineal feet of concrete flood channel wall. Importantly, the new habitats would use appropriate native vegetation and be designed at elevations that would accommodate sea-level rise so they would be resilient to climate change.  

Other notable project elements include:  

• Hydraulic analysis to confirm that the project would not increase flood water surface elevations  
• Retention of paths and Improvements to an existing pocket-park adjacent to the creek 
• New vegetated basins and bio-swales for stormwater run-off to replace existing storm drains that feed directly into the creek  
• Re-use or recycle all materials removed for the project  

Hal Brown Park Culvert Replacement and Tidal Marsh Restoration 

With funding from Marin County Parks and the Regional Water Resources Control Board through the mechanism of a Supplemental Environmental Project, we implemented a two-part project. First, the under-sized culvert at the downstream end of the marsh was replaced to increase tidal flow to the marsh. Second, completely bare soil with high salinity, high pH, and too much gravel was excavated from some locations and replaced with Young Bay Mud. This area quickly met revegetation criteria in the permits. However, because the supply of Young Bay Mud was overestimated, we did not receive enough to replace as large an area as we had anticipated, so we amended the soil and planted the area where poor soil remained. It has taken considerable effort to revegetate it.  

Invasive Spartina Project  

 Since 2003, Friends has been the local sponsor for the Invasive Spartina Project, the multi-agency project led by the Coastal Conservancy, to eradicate invasive cordgrasses from tidal areas of San Francisco Bay. Hal Brown Park was the introduction site for two of the four invasive species: Spartina densiflora and S. anglica. S. densiflora had spread throughout the tidal areas of the watershed and beyond. S. anglica, at the extreme southern edge of its range, did not spread out of the park. An intensive effort using digging, mowing, and treatment with the herbicide imazapyr has eliminated over 99% of both infestations, as well as the S. alterniflora that spread into tidal wetlands of Corte Madra Creek from elsewhere in San Francisco Bay. The final push to document three years with no detections of invasive cordgrasses is underway. For complete descriptions of the many components of the Invasive Spartina Project visit www.spartina.org 

Earlier Habitat Enhancement Projects 

• White Hill School, Fairfax. Habitat enhancement along Fairfax Creek and adjacent to the games field. 
• 300 Olema Road, Fairfax. Culvert replacement, erosion control and planting along Fairfax Creek. 
• Archie Williams High School, San Anselmo. Habitat enhancement along Sleepy Hollow Creek, and adjacent to Sir Francis Drake Boulevard. 
• Hal Brown Park, Larkspur. Habitat enhancement to benefit Ridgway’s rail by planting the transition zone between the Corte Madera Creek Path and the marsh. 
• Larkspur Creekside, Larkspur. Habitat enhancement in an upper tidal area along Corte Madera Creek.