An ambitious effort to re-imagine the future of the Los Angeles River’s entire 51-mile length will begin where the waterway gets its start — in Canoga Park, the west San Fernando Valley neighborhood that is home to the river’s headwaters.

The first of a dozen community meetings to gather input on a new, countywide “master plan” for the river is set to take place from 6 to 8 p.m. Wednesday inside the cafeteria of Canoga Park High School, at 6850 Topanga Canyon Blvd.

Los Angeles County Supervisor Sheila Kuehl invited people throughout the county, as well as those who live in and around Canoga Park to share their thoughts and to “dream along with us.”

“What can this place be for them, and what can it be for Los Angeles County?” she asked.

Representatives from Kuehl’s office as well as from state Senator Henry Stern and Los Angeles City Councilman Bob Blumenfield’s office are expected to be at the meeting.

The Los Angeles River runs through 17 cities. A dozen meetings, including the one in Canoga Park, will be held over the next two years to hear what people who leave near and along the river have to say about the river’s future. The input will be used to create the blueprint, which updates an existing master plan adopted in 1996.

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The master plan is expected to layout not only the ways in which the river could be used as a park, but also any engineering, hydrological, ecological and economic potential it might have.

Kuehl said there was no particular reason why the first community input meeting was being held in Canoga Park, but there was a feeling the people there “were kind of prepared as a community to begin to talk about this.”

The Canoga Park community recently saw the opening of a new greenway along the river that provides a walking and bike path. The river is in the backyard of many residential neighborhoods, and in recent years has drawn the down-and-out who have set up homeless encampments under the bridges that span it.

Much of the river’s history in the last century has been linked to engineering, with many parts of the river paved in concrete during the early part of the 20th century to prevent the disastrous flooding that had threatened and destroyed surrounding neighborhoods around that time.

In recent years, the river has gotten renewed interest from river-enthusiasts, as well as public officials, who promote its potential as an ecological habitat, and as a park area where people can not only picnic and ride their bike, but also kayak and fish.

The county’s master planning effort is being led by engineering firm Geosyntec, which is working with Frank Gehry’s architectural firm, Gehry Partners, and OLIN, another architectural firm. The nonprofit RiverLA is also working with Geosyntec to do community engagement.

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Nearly half, or 24 miles of the river’s length, goes through the Southern portion of the Valley from Canoga Park to Glendale. The river then swings through the Elysian Valley to downtown Los Angeles, and then into a string of Southeast Los Angeles cities that include Maywood, Commerce and Bell, before making its way through Compton and Carson, finally letting out into the ocean via Long Beach.

Kuehl said that cities often worked separately to get projects going in their areas, but the master plan process is meant to bring everyone together to work toward a “regional solution.”

The series of community meetings will “let us imagine what the river from end to end could be like in this county,” she said.