Hahamongna Committee to Hear About Arroyo Seco Spreading Basin Expansion

The Hahamongna Watershed Park Advisory Committee is scheduled to receive a Pasadena Water and Power briefing on Area 3 of the Arroyo Seco Canyon Project — an expansion of the spreading basins in Hahamongna Watershed Park — at its Sept. 22 meeting.

The presentation is an information item, so the committee, which has no independent authority and advises the Pasadena City Council, is scheduled to receive it rather than act. The project would rework the basins and ponds that capture Arroyo Seco stream water to recharge the local groundwater basin — work bearing on Pasadena’s long-term water supply and on public access to park trails and parking.

Pasadena Water and Power has diverted Arroyo Seco stream water, up to 25 cubic feet per second, since 1912 to recharge the groundwater basin and reduce dependence on imported water. Area 3 plans call for regrading the site, reconfiguring the existing basins and ponds to create nine stepped basins, and adding a new sedimentation basin and a flume to measure diversion flow. The changes would increase spreading capacity by three acres, convert a previously paved JPL parking lot to basin use, realign Explorer Road, and add a recreational parking lot, native plants and educational signs.

During construction, vehicle access would be closed during the Explorer Road realignment, and Horse Trail sections may face restricted access, with detours provided when possible. Final design and bidding are scheduled for fall; Area 3 construction, about nine months, is tentatively planned from spring through winter 2027, pending approvals. Roumiana Voutchkova, a principal engineer, is scheduled to present.

Need to know: The Hahamongna Watershed Park Advisory Committee meets Tuesday, Sept. 22, at 6 p.m. at City Yards, Public Works Building, Second Floor, 233 West Mountain Street, in Pasadena. Admission is free and open to the public; the meeting is in person, and public comment may be given in person or emailed in advance to kkiefer@cityofpasadena.net. For more, call (626) 744-7311 or visit https://www.cityofpasadena.net/commissions/agendas/. Project details: https://pwp.cityofpasadena.net/arroyosecoproject/.