Central Arroyo Seco Stream Restoration Project
From barren concrete channel to a park teeming with native plants and animals—that’s the trajectory for the Central Arroyo Seco. Even the Arroyo Chubb fish is thriving in the stream’s waters after an 80-year absence. Twenty acres of riparian woodland are now restored thanks to the efforts of the Arroyo Seco Foundation, the City of Pasadena, and a $1.9 million grant from the state’s Proposition 40 Integrated Watershed Management Program.
Prior to its restoration, the Central Arroyo Seco was highly eroded due to a periodic high flows and a lack of riparian vegetation. The nearby trails were unattended during rainy weather and sent soil and pollutants straight into the stream. The place was also overrun with invasive plant species. To add insult to injury, a city parking lot contributed oil and gasoline to the stream during rain.
The park’s transformation has involved constructing weirs and deflectors to create a more sinuous low-flow channel with varying velocities and scour holes, as well as rearing and resting areas for fish. The project included suppressing the non-native species and planting natives, removing debris, restoring a spring and wetland along the west side of the arroyo, and naturally treating stormwater with duckweed, a small flowering aquatic plant that effectively removes phosphates, ammonia and nitrogen. The city’s adjacent parking lot now has vegetative islands to capture stormwater and its pollutants, and was re-graded so that excess water would flow to a drainage system. And, a redesigned pedestrian and equestrian trail now includes educational/interpretive signage for visitors, to raise awareness about watersheds and water quality issues.
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