Background Information

Background Information

OCPW has taken measures to address the most critical risk areas of San Juan and Trabuco Creeks to protect the surrounding community from the risk of levee failure through sheet pile improvements. The eight phased sheet pile improvements are located along 8,200 linear feet of San Juan Creek between Stonehill Drive and the I-5 freeway, as well as 8,400 linear feet of Trabuco Creek from its confluence with San Juan Creek to upstream of Del Obispo Street. The sheet pile will be installed through 14 to 17 feet of levee and extend 31 to 34 feet below the channel bottom for a total depth of approximately 48 feet from the top of the levee, providing immediate and long-term bank stability in the segments. Phases I through III for have been completed.

Eight Sheetpile Phases

History

The creeks (San Juan, Oso, and Trabuco) were channelized by Orange County without Corps involvement during the 1960’s with slope protection consisting of 4-inch thick unreinforced concrete panels. Storm flows have scoured the sandy channel invert below the bottom of the embedded unreinforced concrete channel lining leading to uplift and loss of the concrete panels during storm events in 1998, 2005 and December 2010. During the 1997-98 storms a pedestrian bridge on Trabuco Creek upstream of Del Obispo Street Bridge was severely damaged by flooding to the point that it needed to be rebuilt. In addition, the embankment adjacent to the San Juan Capistrano City Hall was breached due to loss of the concrete channel lining and significant erosion of the embankment fill. The Corps provided emergency reconstruction and rehabilitation of the channel levees under PL 84-99 following the significant damage and near failure. During the 2005 storms, approximately 1,250 feet of channel lining was lost on San Juan Creek and the exposed earthen levee was nearly lost due to scour. Emergency placement of large rip rap was required to contain storm flows. During the emergency, five surrounding neighborhoods were evacuated. OCPW again received PL 84-99 assistance in the flood fight and immediately after the storms portions of the damaged levee were patched with grouted stone. Since the 2005 storm event, the unstable levees have continued to deteriorate, most recently in December 2010, when a storm event caused significant damage and near failure of levees protecting surrounding residential areas.

Stakeholders/Study Participants

This effort is being conducted and coordinated by the U.S. Army Corps of Engineers, Los Angeles District and Orange County Public Works (OCPW). In addition, Federal, state and local government agencies; environmental resource agencies; interest groups; and other stakeholders provide valuable contributions to the evaluation process.