Hahamongna Is a Spectacular Environmental Treasure . . .
But It's Not Going to Be When the County's Trucks Start Rolling

Devil’s Gate Sediment Issue Fact Sheet

  • Devil’s Gate Dam in Hahamongna Water Shed Park was the first dam built by the LA County Flood Control District in 1920
  • Over the years sediment has built up behind the dam, but the level of sediment stabilized in the 1930s and has ranged from 2.5 to 4 million cubic yards since then.
  • Pasadena established Hahamongna Watershed Park in 1993 to recognize the unique environmental values and resources found in that rare alluvial canyon at the base of the San Gabriel Mountains. Pasadena has consistently urged the County to conduct an ongoing sediment management program rather than waiting for massive removal programs.
  • The County has not removed any significant quantity of sediment from the basin since 1994, twenty three years ago, when it removed 190,000 cubic yards, 8% of the amount the County now wants to remove.
  • The Station Fire in 2009 and subsequent floods that year and in 2010 added more than a million additional cubic yards to the 2.7 million cubic yards that had previously accumulated over the years.
  • The Flood Control District proposed removing 1.67 million cubic yards from the dam basin in 2010 on an emergency basis, but the plan was rejected by the Regional Water Quality Control Board as too large and disruptive. In April 2011 the County Board of Supervisors instructed the Flood Control District to conduct a full environmental impact report on their sediment removal program for Devil’s Gate Dam.
  • There was a series of public meetings with overwhelming community support for a slow and sustainable sediment management program that would reduce impacts on the surrounding neighborhoods and protect the precious habitat in Hahamongna.
  • In October 2014 the Flood Control District released their Big Dig program, which was approved by the County Board of Supervisors in November 2014 by a 4-1 vote.
  • The cost of the sediment removal program is now estimated to be $100 million dollars.
  • There has been tremendous opposition to the County’ Big Dig program from local communities, the City of Pasadena and environmental advocates
  • The City of Pasadena established a Sediment Working Group in 2014 that developed a sustainable sediment management program for Hahamongna with only a quarter the impacts of the County’s Big Dig.
  • The County Flood Control District has had a very difficult time securing the permits needed for their project because of the inadequacy of their environmental document and mitigation plan. This has delayed the Big Dig implementation which was originally set to begin in the Fall of 2015.
  • In December 2014 the Arroyo Seco Foundation and the Pasadena Audubon Society filed a lawsuit challenging the Big Dig Program on environmental grounds. The case is now scheduled for trial on January 31, 2017.
  • LA County's postion is vulnerable on this issue because of: 1. the County’s failure to develop an ongoing sediment management program, failing to remove any significant sediment from the dam for more than 20 years 2. The County’s refusal to consider a more sustainable sediment management program that takes into account community concerns about traffic, noise, habitat destruction, etc.
  • No Big Dig Resources:




    No Big Dig Video

    For more information, please contact the Arroyo Seco Foundation at savehahamongna@arroyoseco.org or (323) 405-7326;

    Hahamongna is the most special environmental treasure in our region. We can't let LA County Flood Control District destroy it and degrade our neighborhoods. The Arroyo Seco Foundation and the Pasadena Audubon Society have filed a lawsuit to protect Hahamongna and our neighborhoods. Our goal is to secure a more moderate and sustainable program that will reduce impacts on Hahamongna Watershed Park and on our neighborhoods.

    Please give generously. The fate of Hahamongna and our neighborhoods depends on your generosity.

    We are looking for 250 people who can give $100 each to protect Hahamongna for future generations.

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    www.savehahamongna.org  savehahamongna@arroyoseco.org