Wawona Meadow Ecological Restoration

Section of Wawona Meadow post restoration.

 

History

Looking out onto Wawona Meadow in 1936, Yosemite National Park visitors could have seen Civilian Conservation Corps men hard at work digging two mile-long ditches to divert water to the edges of Wawona Meadow. A walk in Wawona Meadow 70 years later would reveal how these historic ditches, then deepened to 10 feet in some places, had altered meadow hydrology by diverting surface flow, draining groundwater, drying out the landscape, and altering plant communities.

 

Left image
CCC workers digging a ditch in Wawona Meadow, circa 1936

Right image
Finished ditch in Wawona Meadow in 1936

 

Wawona Meadow, one of the first areas explored by Euro-Americans, felt the effects of early settlers decades before the CCC built these ditches. Cattle and horses heavily grazed the meadow, an airstrip occupied the southern portion, and in 1918, the lower third of the meadow was developed into a golf course. The airstrip was decommissioned in the late 1930s, grazing ceased in 1970, and although the golf course is still there, the upper 165 acres of the meadow provides valuable lower montane meadow habitat. With the Wawona Meadow Ecological Restoration Project, park ecologists were able to restore the meadow to its original lush state with ample water—full of willows, sedges, buttercups, and lupine.

 

Cattle grazing in the Wawona Meadow in the 1930s.

 

Project Overview

The primary goal of this project was to ecologically restore the hydrology, native plant communities, and wildlife habitat to the Wawona Meadow.

Ditches that were constructed in the Wawona Meadow in 1936 had altered its hydrology by disrupting both surface and subsurface flow, lowering groundwater levels, drying out adjacent areas, and altering plant communities. The ditch on the south side of the meadow extended for one mile and was reinforced with 22 buried concrete weirs. Fourteen of those weirs were more than 50% exposed. Most of them were located in the 982-feet length of the ditch that had eroded to 10 feet deep. Water flowed through the ditch for most of the year, draining the groundwater from the meadow. This was evidenced by the dominance of upland (rather than wetland) and non-native plants adjacent to the gullied sections of the ditch. The rest of the ditch varied: Some parts had slow moving water (1 to 3 feet deep) and other parts were heavily vegetated with no water flow. The ditch on the north side of the meadow was mostly shallow and had less impact on hydrology. Monitoring of hydrology, plant communities, and wildlife helped to direct restoration actions.

The Wawona Meadow Ecological Restoration Project consisted of two phases. Phase 1 involved gathering data related to meadow hydrology, wildlife habitat, invasive plant species, rare plant species, cultural landscape, historic features, archeological sites, American Indian use, visitor use, helicopter operations, stock use, fire, PG&E access, trailhead parking, and road and trail maintenance. Phase 2 of the project was to restore the meadow itself.

This project implemented the following actions:

• Removal of concrete weirs above ground level and recycle out of the park.

• Filling sections of the ditch with 4,000 cubic yards of native fill.

• Placing "plugs" or grade-control structures to re-contour the area and discourage concentrated water flow.

• In shallower sections of the ditch, pulling back the remaining soil berm.

• Salvaging plants and topsoil prior to restoration disturbance.

• Collecting native seeds from adjacent areas.

• Re-vegetating newly restored areas by replacing topsoil and salvaged plants, seeding, and planting willow.

• Placing five wayside exhibits around the meadow loop describing meadow ecology, historic events, and the restoration process.

 

Before, during, and after photos of a section of the Wawona Meadow.

 

Restoration ecologist spreads a seed mix.

Wawona Meadow provides wetland, riparian and upland habitat for a variety of rare and sensitive plant species and wildlife, including two state endangered birds—the willow flycatcher and great gray owl. Most Sierra Nevada meadows are sustained by sheet flow (water slowly flowing over the surface) and high groundwater levels rather than a channel through the meadow. The ditches built by the CCC in Wawona Meadow interrupted sheet flow by diverting and concentrating surface flow, draining groundwater from the sides, drying out the adjacent areas and changing plant communities. Upland and non-native plants, such annual grasses and wooly mullein, dominated in areas without access to sufficient groundwater altering habitat for wildlife and insects.

The Wawona Meadow Ecological Restoration Project took place September through early November 2010, with additional restoration work in 2011. Despite heavy rains in October 2010, work progressed smoothly with heavy equipment, including an excavator, dozer, skid steerer, loader and dump trucks. Restoration crews successfully filled 1,000 feet of the deepest section of the ditch, planted hundreds of salvaged plants and willows, placed erosion control blankets in vulnerable areas, and seeded the newly restored landscape. Nearly 5,000 cubic yards of soil was transported to the meadow, compacted and spread to restore natural meadow topography. Restoration crews revegetated the area by replanting salvaged vegetation, seeding areas with locally gathered seeds (more than 30 species were collected) and planted plugs of sod taken from nearby sedges.

 

Restoration crews place erosion control blankets to discourage channelization. Once the blankets are in place, woody debris is placed on top to keep it anchored, to capture sediment, and to slow water flow.

Erosion control blankets were anchored in areas experiencing high levels of surface flow to discourage any channelization. The restoration area was then covered with woody debris to slow water flow, capture sediment and discourage any channels from forming.

Groundwater elevations immediately responded to the filling of the ditch and are nearly at the surface with water sheeting across areas in the meadow that have been dry for decades. Direct restoration work occurred on 0.7 acres, and it is anticipated that the raised groundwater elevations will restore 4 acres of wetlands that had converted to upland habitats. Additional filling of shallower sections of the ditch will continue in 2011, further restoring hydrology across the entire meadow.

Because invasive plants, such as velvet grass, can easily establish and dominate newly disturbed areas, close attention to the establishment of any non-native plants in the newly restored area ensured early detection and treatment.

Ongoing monitoring of hydrology, plant communities and wildlife will continue to help determine the success of the project. Park staff has taken every precaution to maximize the protection of the meadow with the ultimate goal of a healthier and more naturally functioning meadow. Work at Wawona Meadow is part of a larger effort to keep the park's meadows healthy.