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Posted 10/3/2013

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By David A. Salazar
Los Angeles District Public Affairs

LOS ANGELES—The Los Angeles River is regarded as an icon of LA’s sprawling hyperurbanization.  To some, it’s nothing more than a part of the landscape that splits the concrete jungle in two.  To others, it’s an eyesore; a resplendent piece of nature stunted in a tomb of steel and cement.

But the 51-mile-long river wasn’t always a flood control channel. 

In fact, it’s believed the river—in some form or fashion—has been in existence for thousands of years, having supplied water to indigenous people and early explorers.

Historical references indicate that the river changed courses on numerous occasions, due to heavy floods, across the large alluvial plain, which makes up present-day Los Angeles and Orange counties.  Although Los Angeles is typically a dry area, receiving an average of rainfall of 15 inches per year, the surrounding mountain ranges receive upwards of 40 inches of rain per year.  Gravity then takes over and the millions of gallons of water fall from headwater elevations of nearly 1,000 feet to zero feet above sea level in just 50 miles.  This creates the perfect recipe for flash floods during the winter months when precipitation in the area is most common.

The nature of these dramatic inflows led to damage to property and infrastructure and loss of life very early in the history of Los Angeles.  Historical records indicate that a total of 17 floods occurred between 1815 and 1938, calling for the river to be tamed, especially in light of an influx of population to the area.

James G. Jobes, a senior engineer for the Los Angeles District, led initial studies on the impact of the floods in the area in 1939 and noted “the Los Angeles area—from the standpoint of value of damage experienced or potential, per square mile of flooded area—is the most outstanding of any area in the United States and possibly the world.”

The Los Angeles County Flood Control District requested federal aid from the Works Progress Administration, which, during the Great Depression, served as a funding source for many infrastructure projects during that time.  Funding for dam and channel construction was approved, with the stipulation that 90 percent of laborers be hired from the agency’s relief rolls and that the Corps of Engineers lead the efforts.  In one year’s time, the District grew in size from 15 people to 17,000—95 percent of which were hired from federal unemployment rolls.

Construction on various flood control projects for the Los Angeles, Rio Hondo, and San Gabriel Rivers began after the projects were funded under the Flood Control Act of 1936.  The district hired 14 contractors in 31 separate contracts and moved more than 20,000,000 cubic yards of earth, poured more than 2,000,000 cubic yards of concrete, placed nearly 150,000,000 pounds of reinforced steel, and set 460,000 tons of grouted stone slope protection.  This feat of ingenuity was remarkable for a number of reasons, most notably the fact that technology was limited and almost all work was done by hand in the initial stages of the project.  Contractors completed an average of 200 linear feet of slope paving per day.

During construction of these projects in 1938, a heavy flood caused $795 million (in 1990 dollars) in damages and killed 49 people.  The Los Angeles County Flood Control District immediately appealed to Congress to secure support services from the Los Angeles District.  Congress passed the Flood Control Act of 1938, appropriating additional funding for what would eventually become known as the Los Angeles County Drainage Area.

By 1939, the district and various partners and contractors had completed 14 dams.  As the Great Depression continued to make funding more difficult to obtain, especially with World War II underway in Europe and the Far East, it became apparent that a new funding strategy was necessary.  The commander of the South Pacific Division, Col. Warren T. Hannum, impressed upon the National Resources Committee on March 1, 1941, that completion of the project would not just protect life and property, but would ensure that progress continued for national defense as well.

“The necessity of solving these problems in addition to protecting lives and property increases very appreciably the justification of flood control in the areas where national defense industries are located,” Hannum said.  The Southern California area had seen a boom in defense industry contractors—primarily aircraft manufacturers--that called the area home, including the Lockheed Corporation, Douglas Aircraft Company, the Glen L. Martin Company, and many others.  This led to Congressional approval of the LACDA plan, authorizing $240 million for continued construction. 

The LACDA project included the construction of Hansen, Sepulveda, Santa Fe, Whittier Narrows, and Lopez flood control basins, debris basins in 31 tributary canyons, construction of 93 miles of main channel and 147 miles of tributary channels, including 316 bridges on the Los Angeles, Rio Hondo, and San Gabriel rivers.  Construction of the project took 20 years to complete as the population in Los Angeles rose to more than six million residents.

After a flood in 1980 tested the capacity of the lower Los Angeles River channel, Los Angeles County officials requested support from the district to study the channel’s capacity to protect against larger floods.  In 1987, the district completed the study and found that the lower Los Angeles and Rio Hondo rivers provided no more than a 40-year level of protection, which was far less than the standard level of protection against 100-year floods.  This finding affected 82 square miles of densely populated areas, including half a million people and more than 175,000 structures.  As a result of the findings, the Federal Emergency Management Agency required that residents and business owners purchase flood insurance, since the likelihood of flooding in the area was greater than previously believed.

Funding for improvements to the LA and Rio Hondo rivers was approved in 1995 and additional funding was granted in 1999.  The project, which consisted of raising the height of 21 miles of existing levees by building up earthen embankments or constructing walls on top of the levees and completing required modifications to railroad, traffic, and pedestrian bridges, was expected to cost $364 million and take 10 years to complete and would prevent $2.3 billion in flood damages in the event of a 100-year flood.  These improvements also resulted in the revocation of the flood insurance mandate imposed by FEMA.

The district completed its most recent report on the river Sept. 13.  The Los Angeles River Ecosystem Restoration Feasibility Study details viable alternatives for restoring an 11-mile segment of the river.  Each of these alternatives requires that channel walls remain intact or be modified, but not removed, while eliminating the channel’s concrete bottom to allow for healthy vegetation growth.  If Congress decides to approve and then fund a restoration project for the Los Angeles River, the Corps hopes to see restored habitat connections and ecological functions in the 11-mile stretch, while preserving the flood protection that is provided by the existing channel system.

construction Corps of Engineers flood control channel Great Depression LA River Los Angeles restoration study