Environmental permitting for TRRP rehabilitation sites, and for earlier bridge modifications, generally requires 1:1 replacement of riparian vegetation types as classified by the California’s Wildlife Habitat Relationships (WHR) over a 10 year period. Vegetation replacement is expected to come from both plantings and natural regeneration in roughly equal amounts. TRRP monitors vegetation recovery and at a 5-year mark, assesses the likelihood of achieving the 10 year goal.
Given the competing rehabilitation needs for removing vegetation from low-water banks, TRRP’s site designs attempt to encourage vegetation regrowth on floodplains, essentially moving the riparian vegetation a little back from the river’s low-water edge.
TRRP actions fall under the ‘no net loss’ requirements for wetlands as delineated by the U.S. Army Corps of Engineers. Wetland restoration and enhancement is a frequent component of TRRP rehabilitation actions. Therefore, restoration is likely to actually increase the extent of wetlands along the river.
Bullfrogs are an invasive species from the eastern side of North America, and are aggressive predators that can wipe out native amphibian populations. Therefore, wetlands constructed or enhanced by TRRP are generally designed either to dry up over the summer (which kills bullfrog tadpoles while native frogs metamorphose and move elsewhere), or to connect with the river during high flows (which allows fish into the wetlands that can consume bullfrog tadpoles).