Percolation Ponds at Ysidora Basin

Percolation Ponds at Ysidora Basin

At the present time, as shown in figure 99, the Ysidora Basin Percolation Ponds are heavily vegetated with willow, Salix spp., cottonwood, Populus fremonti, emergent aquatic species, and some exotics including giant reed and salt cedar. These plants became established after the levees were breached in the 1993 flood. The levees are either barren or support grasses and forbs, and often weed species. Dense riparian scrub surrounds the exterior levees. The area is heavily utilized by least Bell's vireos and other riparian habitat-dependent avian species.

The design for the restoration of the Ysidora Basin Percolation Ponds, figure 100, is to allow the Santa Margarita River to flood the pond basins by removing all existing levees. Without periodic flooding the existing vegetation in the Percolation Ponds would succeed into an old, even aged stand of limited species diversity. Habitats with these characteristics are of little value to least BellÕs vireos, the target species for this restoration project. The restoration of the historic flooding pattern would permit periodic scouring of segments of the basins, exposing sites suitable for pioneering riparian plant establishment. A self-sustaining, transient pattern of differentiated age stands of willow, cottonweed, sycamore, Platanus racemosa, mulefat, Roaccharis glutinosa, and herbaceous species should result. The structural diversity and temporal variability of this pattern should meet the criteria described in the least Bell's vireo habitat model and should also be sufficiently diverse to support a variety of other avian species.

This design assumes an aggressive giant reed and salt cedar control program. An ongoing effort is necessary to keep these and other weed species from outcompeting native riparian species on sites exposed by flood events.