Disclaimer: Information about the Whittier Narrows Dam Safety Modification Project is constantly evolving and subject to change based on project updates from the USACE.

Context

The U.S. Army Corps of Engineers (USACE) completed construction of the Whittier Narrows Dam in 1957. The dam is designed to protect from flooding while supporting water conservation efforts. Over the years, the dam has become structurally unsafe and at-risk of failing in the event of a severe storm. Based on the National Dam Safety Study completed after Hurricane Katrina in 2005, the USACE identified the Whittier Narrows Dam as the highest priority of the 13 highest risk dams in the United States.

Dam failure could cause massive flooding of up to 25 cities in the surrounding region, from Pico Rivera to Long Beach, and such flooding could result in disastrous consequences including loss of life, damage to property, and major environmental and economic impacts. 

To repair the dam and prevent catastrophic failures, the USACE will be completing the Whittier Narrows Dam Safety Modification Project (Project). Funded by the federal government, the $385 million, multiyear effort is expected to complete construction in 2026. To date, Congress has approved the allocation of $192.5 million to the Project through the Energy and Water Appropriations Bill. The remaining balance will be allocated in future federal budgets on a year-to-year basis.

Maximum Flood Depth Map

Two (2) Feet of Water Depth Map

Legislative Update

Project Details

The Whittier Narrows Dam is currently at risk of failing in the following ways:

1. Backward Erosion Of the Dam’s Foundation

The Whittier Narrows Dam sits on a previous foundation, meaning that it can be penetrated by water. When water enters the foundation, also known as seepage, a pipe can begin to form between the reservoir and the other side of the dam. As the pipe continues to form, the dam can become increasingly unstable, eventually leading to a breakthrough in which the water seeping through the pipe entirely destroys the foundation of the dam.

2. Overtopping

While the Whittier Narrows Dam has spillways to drain excess water, they are currently not designed to weather the most severe storm. In this event, storm water may exceed the capacity of the reservoir and the spillways, leading to overtopping—the uncontrolled spilling of water over the dam—and catastrophic flooding in the surrounding region.

3. Premature Opening of the Spillway Gates

In the event of a severe storm, spillways are designed to safely drain water that exceeds the capacity of a dam reservoir. Currently, the Whittier Narrows Dam spillways are at risk of opening prematurely. If the spillways were to open prematurely, catastrophic flooding could occur in the surrounding region.

The anticipated repairs include, but are not limited to, addressing the internal erosion of the foundation and building a new compacted concrete filler to prevent overflowing at the top of the dam. As seen in the anticipated project schedule below, the primary project elements include (1.) utility relocation and staging, (2.) dam improvements and (3.) road enhancements.

Environmental Impact Statement Documents

Download the documents below to view studies and reports related to the Whittier Narrows Dam.

Download – Final Environmental Impact Statement
Download – Final EIS Appendices Volume 1
Download – Final EIS Appendices Volume 2