Hahamongna sediment removal project

The County of Los Angeles is planning a massive earth moving project to be implemented in Hahamongna on an emergency basis. Ryan Butler of the Water Resources Division of the Los Angeles County Department of Public Works gave a detailed presentation concerning the Devil's Gate Dam and Reservoir Postfire Sediment Removal Project to the Hahamongna Watershed Park Advisory Committee at its November 30 meeting.

The project is required because of the Station Fire which burned nearly 100% of the undeveloped Arroyo Seco Watershed. Nearly one million cubic yards of sediment were washed into the basin in last winter's rains and the sediment level rose 15 feet in the basin. Should similar rains occur this coming winter, the sediment level could rise an additional 15 feet, putting the operation of the dam at risk, according to Butler. Devil's Gate Dam protects parts of Pasadena, South Pasadena, and the City of Los Angeles.

The County's plan is to remove 1,671,000 cubic yards of sediment from behind the dam. This amount was chosen because it is an estimate of the amount of sediment which could accumulate behind the dam should a 50 year intensity storm occur when the watershed is entirely burned. The excavation area is planned to be about 50 acres. About 15 acres of willow trees will be permanently removed when the basin behind the dam is widened and deepened. The precise number of trees to be removed has not yet been determined.

The huge amount of debris to be removed will require 300 - 400 truckloads of sediment per day to be removed Monday - Friday for at least three years at a cost of $35 million. The haul route will be along Oak Grove Drive and the 210 Freeway and will not impact the Pasadena neighborhoods adjacent to Hahamongna. The plan is to haul all the sediment away to the Manning Sediment Placement Site and Azusa Land Reclamation although the County is open to working with Pasadena to leave some fill onsite to create the proposed new sports fields. The County is also proposing a paved two land road on the west side of Hahamongna near the dam which could be used for future sediment removal projects. The road will cross the existing trail and could necessitate closing the trail and the Flint Wash Bridge during the work week for the three year duration of the project.

The project, scheduled to begin in September 2011, is proposed to be implemented on an emergency basis with an exemption from the California Environmental Quality Act so that no environmental impact report will be required, despite the massive scale of the project and the sensitive nature of the habitats in Hahamongna. The County will, however, be required to obtain all necessary permits from agencies such as the California Department of Fish and Game, the Los Angeles Regional Water Quality Control Board, and the U.S. Army Corps of Engineers. Environmental damage will be mitigated although, as one Committee member pointed out, this mitigation does not have to be done in Hahamongna but could be done elsewhere.

Despite recognizing the necessity of sediment removal, the Advisory Committee and the public at the meeting expressed many concerns. One of the most frequently heard was a concern that other, less draconian, solutions had not been thoroughly explored as would have been required had the normal CEQA process been followed. One audience member referred to the proposal as a "scorched earth" approach which would have a catastrophic impact upon the wildlife in the park. Other issues raised were traffic impacts on an already congested Oak Grove Drive, air pollution and the nearby school children and noise pollution. Committee members questioned the need for a permanent two lane road in the park. The Committee also expressed a strong interest in jobs and contracts being awarded to local residents.

The Committee passed a formal motion which included the following:
Committee notification of when the project comes before the County Board of Supervisors
Posting of the County's project presentation on the Pasadena city website
Strong support for jobs for local residents, especially women and minorities
Request that the County study alternatives which would have less impact upon the natural habitat and which would cause less noise, air pollution and traffic impact
Request that the County study the maintenance road in terms of its surface, permanent nature, and width
Request that the County seek opportunities to reduce the impacts of the project upon park users
Regular quarterly updates to the Committee about the project from city staff and a presentation by County staff after they have their permits from the regulatory agencies