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Arroyo Seco Canyon Project Supporters Hope to Create Local Reliance on Water Supply

Published on Monday, October 26, 2020 | 3:55 am
Artist’s rendering of future plans for the intake structure.

The Pasadena City Council’s Municipal Services Committee will review updates on the Arroyo Seco Canyon Project (ASCP), an investment in infrastructure that will increase reliance on local water supply, during a special virtual meeting at 4 p.m. Tuesday, Oct 27.

Backers of the project also hope to enhance recreation and habitat by better using Pasadena’s longstanding water rights and adding management tools to enhance the groundwater basin.

The ASCP includes the construction of a replacement diversion weir – a low-head dam – and intake in the same location as the current facility, which is over 90 years old, according to a report from Pasadena Water and Power General Manager Gurcharan Bawa.

He will be presenting the updates on the project at Tuesday’s special meeting.

The proposed structure will span the width of the existing channel and feature an operable weir crest gate that can be raised for diversion to the intake structure and lowered to bypass diversions.

An engineered roughened channel will be constructed in the section of the stream directly downstream of the diversion structure for future fish passage. The new intake will be equipped with a trash rack and fish screens.

The proposed project also reconfigures two ponds and two basins with expansion into a previously paved area to accommodate the increased diversions for infiltration into the Raymond Basin.

Asphalt was removed from the nearby Jet Propulsion Laboratory parking area in 2016 in anticipation of work on the basin expansion. PWP has re-imagined the spreading basin design from the original rectangular concept through the use of curvilinear basin features that more closely resemble natural channel and stream functions with shading and vegetation.

Bawa’s report said the project is projected to increase diversions during average streamflow conditions by about 1,000 acre-feet per year (AFY), from current diversions which average about 2,000 AFY. Even with the project, most of the stream flows will remain in the Arroyo Seco on an annual basis.

As far as the status of the project is concerned, the report said the application for the conditional use permit (CUP) modification is currently being completed and will be submitted to the Department of Planning and Community Development with the goal of seeking approval of the permit and the final EIR from the City’s Hearing Officer in December.

Once the EIR has been certified and the design is substantially complete, applications for the Streambed Alteration Agreement from the California Department of Fish and Wildlife (CDFW) and the nationwide permit from the U.S. Army Corps of Engineers can be finalized. The water quality certification which was previously obtained from the Regional Water Quality Control Board will be updated.

When the EIR and permits are approved, the project plans and specifications will be finalized and advertised for bid. Separate bid packages will be prepared for Area 2 (the diversion and intake upgrades) and Area 3 (spreading basin reconfiguration/expansion). Contracts for the construction of the ASCP will be competitively bid. Work on Area 2 could take up to three months, and Area 3 improvements could take up to nine months, PWP said, targeting a late spring to early fall construction window.

To access the public meeting on Tuesday, go to or to

Public comments can be submitted to before Tuesday, or through on the day of the meeting.

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