Streambed Alteration Agreement concerning a San Diego Creek

Streambed Alteration Agreement concerning a San Diego Creek

The Operator proposes to alter the streambed to widen the existing southbound Interstate 405 bridge as part of operational improvements between MacArthur Boulevard and Culver Drive. The bridge will be widened 12 feet in order to accommodate an additional southbound lane. In order to do this, the existing two bridge pier walls will be extended south ward. This work will include excavation to locate an existing water line, pile driving, construction of additional footing, falsework to construct the bridge deck and relocation of rock rip rap on teh upper slopes of the channel bank. The streambed at this location of rock rip rap on the uppper slopes of the channel bank. The streambed at this location consists of an earthen trapezoidal channel that, except for a City of Irvine restoration site just south of the right of way on the eastern slope, is actively maintained by the Orange County Flood Control District and therfore contains very little vegetation. Temporary impacts consist of 0.11 acre for an access ramp on the west bank of the channel. This bank does not support any vegetation and the access ramp will be removed after the project is completed. Permanent impacts to the streambed include 0.047 acres consisting of the new pier wall footprint and shading from the bridge structure, 0.04 acres for an access path on the east bank, and 0.02 acre of rip rap relocation; the total area of permanent impact is 0.107 acre consisting of early successional southern willow scrub. The mitigation for this impact will occur offsite at Serrano Creek, which is a tributary to San Diego Creek, and will consist of restoration of 0.28 acre of riparian woodland.

Irvine

Orange