Orange County Branch Newsletter

July 2012

Hydrology and Hydraulics Technical Group

Laguna Canyon Flood Mitigation

By William Lawson, P.E.

Early in the morning of December 22, 2010, Laguna Canyon and the City of Laguna Beach were hit by intense rainfall and flooding which required the rescue of 25 people from homes and vehicles, and more than 90 homes and 70 businesses were damaged. In February of 2011 the Laguna Beach City Council voted to establish the Laguna Canyon Flood Mitigation Task Force to review relevant data, review past proposals, and to endorse measures that could be undertaken by the City.  In addition, the City of Laguna Beach can recommend measures to the County of Orange and/or Caltrans in order to be better prepared for the next flood.  An eleven-member Task Force was selected by the City Council from public applicants and other City officials and volunteers.  The Task Force met twice monthly for a period of nearly eight months, and their findings and recommendations were presented to and adopted by the City Council in November 2011. Implementation of the Task Force's recommendations, and those of another City consultant, Dr. Frank Weirich, is currently in progress.

A presentation about the Laguna Canyon Flood Mitigation program and the Task Force's recommendations was given by William E. Lawson, PE, F.ASCE to HHTG at their June 7, 2012 luncheon.  The presentation covered the unusually intense nature of the December 22, 2010 rainfall and resulting flooding.  Video clips of the flood were shown at the beginning of the program, see below.  Mr. Lawson provided an overview of the existing Laguna Canyon flood control facilities, beginning at the outlet to the Pacific Ocean and extending upstream to the San Joaquin Hills Transportation Corridor (SR 73).  The presenation included photographs of the changes in conveyance that have occur over the length of the watercourse. A few of those photos are also included in the Photo Gallery accompanying this article.

A majority of the presentation dealt with the Task Force committee and the recommendations that they developed. The Task Force's Report to the Laguna Beach City Council was assembled from the consolidated efforts of all of the Task Force members and was submitted to the City Council for review and approval. A total of 26 recommendations were made which covered four following categories: 1) Physical Modifications to the Laguna Canyon Creek Channel; 2) Enhancing the City's Capability for Early Warning of Flood Events; 3) Encouraging Advance Preparation by Residents and Businesspeople; and 4) Recommendations for the Use of Flood Gates by Downtown Businesses.

Steve May, PE, Laguna Beach Director of Public Works / City Engineer, and Carl R. Nelson, PE, HHTG and Task Force Member, each assisted Mr. Lawson in answering questions.  City Councilwoman and Task Force Member Verna Rollinger and Task Force Report Editor Barbara Metzger were also in attendance at the luncheon.

It was pointed out during the presentation that the Task Force was officially disbanded once their report was approved by the City Council.  The City is currently moving forward with the design of the Laguna Canyon Flood Warning System, and installation of rain gauges, video cameras and moisture sensors will be completed later this summer.  Some of the Task Force's recommendations were actually given early approval, and funding where needed.  In July and August of 2011 the City authorized a program to complete some of the more critical recommendations before the start of the 2011-2012 rainy season. 

The PowerPoint is provided below.

Click on a photo to open the photo viewer.