US Army Corps of Engineers
Arroyo Seco Watershed Feasibility Study

The Arroyo Seco Watershed Feasibility Study is a partnership between the County of Los Angeles Department of Public Works and the U.S. Army Corps of Engineers with the assistance of governmental agencies and environmental organizations within the watershed.

This study was originally intended to be a three year study to investigate long-term solutions for water resources and environmental restoration issues within the Arroyo Seco Watershed.

In 2001 the US Army Corps of Engineers (USACE) initiated a watershed study of the Arroyo Seco. The Reconnaissance Study Section 905(b) (WRDA) Analysis, completed in November, 2002, determined:

“The future or without project condition of the Arroyo Seco Watershed is a serious concern to the public and the LACPW (Los Angeles County Public Works). The limited and fragmented open space and habitat along the Arroyo Seco corridor, especially in the lower watershed, will result in the continual decline of the environmental and aesthetic quality in the Los Angeles Region. In addition, natural groundwater recharge in the watershed is an important component to water conservation in the Raymond Basin. It is the goal of the watershed study to develop the necessary baseline data and analytical tools, and a realistic set of objectives that will encourage management decisions that help reverse negative trends or enhance positive trends to maintain or improve the health of the watershed. Without environmental restoration in the Arroyo Seco Watershed, the problems identified by the public and local sponsor will continue unabated, these problems include:
  1. Water supply and water quality, both for surface and groundwater
  2. Loss of water conservation in the Raymond Basin
  3. Fragmented and degraded habitat along the Arroyo Seco corridor
  4. Localized flooding
  5. Erosion and sedimentation issues
  6. Limited and fragmented open space and recreational opportunities in the lower portions of the watershed.”

The Reconnaissance Study identified a strong federal interest in the Arroyo Seco watershed.

“In accordance with current administration policy, there is a federal interest in watershed based studies that provide a holistic approach to evaluating water resource problems and opportunities leading to the development of a watershed management plan that effectively balances the need for sustainable economic development with the need for protection of watershed natural resources. Since environmental restoration is a likely output of the watershed study with a high budget priority and environmental restoration, water quality, flood control, and other related issues are integral to any comprehensive watershed plans that would be evaluated in the feasibility phase, there is a strong Federal interest in developing a feasibility study for the Arroyo Seco Watershed. There is also incidental Federal interest in other benefits resulting from the study such as recreation and water conservation/supply that could be developed within existing policy. Based on the preliminary screening of alternatives, there appears to be potential watershed plan alternatives that would be consistent with the U.S. Army Corps of Engineers policies, benefits, and environmental impacts.”

A Blueprint for Watershed Management

In May 2005 the USACE released the Project Management Plan for the study with a revised, trimmed budget of $2.7 million dollars and a scope of work that would develop a comprehensive watershed management plan including implementation projects for the entire watershed from the San Gabriel Mountains to downtown Los Angeles. The plan will include water resources, ecosystem restoration, flood management and recreational elements. Key watershed functions and purposes to be studied include:

  1. Ecosystem Restoration
  2. Flood Peak/ Damage Reduction
  3. Water Supply and Re-Use
  4. Passive Recreation
  5. Surface & Ground Water Quality
  6. Public Education

Corps Issues Key Planning Study

In August 2011 the Corps released the Feasibility Scoping Study, which details environmental conditions in the Arroyo Seco and identifies sites for potential projects. This document is a key step toward completion of the Arroyo Seco study.

County Urges Corps to Accelerate and Complete the Study

The Los Angeles County Flood Control District in May, 2013 urged the US Army Corps of Engineers to accelerate and complete the Arroyo Seco Watershed Feasibility Study. On May 8th Gary Hildebrand, Assistant Deputy Director of the County Department of Public Works wrote to Colonel R. Mark Toy, Commander and District Engineer of the Corps, "The LACFCD is willing to accelerate funding to facilitate completion of the Study" and goes on to state, "It is critical that we finalize this effort and move forward with the feasibility portion of the Study, which will allow us to identify potential projects that will benefit the environment and improve the quality of life for the community."

You can view the Flood Control District's letter here: Accelerate Arroyo Seco Study