For hundreds of years, the Arroyo Seco was a central life-giving resource for first the Tongva people, and then the successive waves of settlers. A seasonal tributary of the Los Angeles River, the Arroyo provided water, food, transportation and—perhaps most importantly—meaning to the communities along its banks. But a series of changes would sour that long and fruitful relationship. Between the completion of the Owens Valley Aqueduct in 1913 and the Colorado River Aqueduct in 1935, as well as a series of disastrous floods in the 1930s, the Arroyo Seco (and the Los Angeles River in general) turned from essential to the city's growth, to being seen as an obstacle to its expansion.
The efforts of local governments to control floods had long been inadequate, but a unique series of events—namely the Great Depression and the New Deal—opened the door to the first truly systemic attempt to manage the Arroyo Seco. Engineers embarked on a study (the first ever) of the hydraulic properties and the history of flooding in the 1930s, and the result was a flood-control proposal that included plans to segment large portions of the Los Angeles River, diverting and confining it into concrete channels.
The channelization of the Arroyo Seco, which began in 1935, was initially a boon to the local economy. The employment opportunities offered by the massive project were welcomed by workers still frozen out of jobs by the Great Depression. There was plenty of work to do, as the channelization was not the only structural change to the Arroyo Seco. Plans for a parkway through the canyon were well underway by the time construction on the channel commenced. Confinement of the river to a channel allowed the parkway to be realized; the parkway's integrity could no longer be endangered by the river's seasonal flooding. Between 1935 and 1940, the Works Progress Administration spearheaded the channelization of the river as part of the construction of the Arroyo Seco Parkway.
The completion of channelization effectively tamed the river and brought systemic order to the basin. The Edenic features of the Arroyo Seco that had played such an important role in drawing people to the area, however, began to vanish with the structural developments. The environmental impact of the project, including its adverse effect on water quality and damage to the native riparian habitat, proved to be detrimental. Decades would pass before the health of the Arroyo Seco's ecosystem would be cogently addressed.
Above, William Deverell, director of the Huntington-USC Institute on California and the West, discusses the conflicts in building infrastructure in spite on natural limitations; Timothy Brick, Managing Director of the Arroyo Seco Foundation, details the Los Angeles River channelization.