Much of the Los Angeles watershed was buried under concrete in the 1950s, when the freeways opened orange groves to development and the Los Angeles River and its major tributaries were turned into flood control channels engineered to rush water to the ocean at maximum speed. Water that used to feed the aquifers was lost in transit, but back then, few people worried: more could always be imported from the north.

Now, however, in the face of climate change, water quality concerns, and expectations of drought, a movement is afoot to capture as much as possible of the streamflow and rainwater in the county for use in projects that would mitigate pollution while also replenishing depleted groundwater supplies.

A unique new park and greenway, with a natural-looking stream, was opened on November 7, 2007, in the Valley Glen neighborhood of Los Angeles. It runs a mile along both sides of the Tujunga Wash Flood Control Channel, between Vanowen Street and Oxnard Avenue. Each side of the greenway is 65 feet wide; the rectangular channel in the middle is about the same. The Tujunga Greenway and Stream Restoration Project, created by Los Angeles County and the Mountains Recreation and Conservation Authority (MRCA) and funded by $7 million from bond acts and other public sources, could well become a model for others.

On an overcast winter day, Anne Canright and I parked on Vanowen, entered through a handsome wrought-iron gate (by Brett Gladstone, who designed most of the gateworks on the Los Angeles River), and strolled along a gravel path, with the fenced vertical bank of the channel to our left, and to our right a friendly little stream. The shallow stream meandered over small stones and gravel, flanked by young alders, cottonwoods, ferns, salvias, and other greenery. Interpretive signs at the trail explained that the stream is fed by water diverted from the channel through a half-mile-long pipe. As the water flows through the greenway, it is filtered and cleaned by sand, gravel, and tree roots. Some percolates into the ground, the rest is returned to the flood control channel via another pipe.