The Meaning of Hahamongna

The original settlers of the region were sometimes called the Hahamongna Indians. The word means "Flowing Waters, Fruitful Valley" in the native Tongva language.

Hahamongna News


How to Haul Sediment from Devil’s Gate Dam





Don Bremner



L.A. County Department of Public Works officials outlined a new plan for temporary storage of sediment to be removed this summer at Devil’s Gate Dam that would sharply reduce the number of trucks hauling material along Windsor Avenue. But from the many sharp questions and comments at the meeting May 26 at La Canada High School, it was not clear that everybody in the audience appreciated the significance of the change from an earlier, widely publicized plan.

JPL buildings and foothills of the San Gabriels form a backdrop for Johnson Field in Hahamongna Watershed Park in northwest Pasadena.

The new plan, described by presenter Steve Sheridan as the county’s preferred alternative, would haul the 25,000 cubic yards of sediment to Johnson Field about half a mile north of the dam on the east side of Devil’s Gate Reservoir. Only the organic materials – mainly tree limbs and brush— removed from the sediment would be trucked out of the reservoir and along Windsor Avenue on the way to disposal sites.

No figure was given at the meeting for how much of the total is organic matter. But Steve Sheridan and another county official later estimated it at 10% to 15%. Using the higher figure would mean about 3,750 cubic yards of organic matter. At 10 cubic yards per truck, it would take 375 truckloads to remove it. The work is expected to last three or four weeks, five days a week, meaning roughly 20 truckloads a day on Windsor, or an average of one each direction every half hour from 7:30 am to 5 pm.

(The original plan was to have all of the material hauled along Windsor Ave., 2,500 truckloads, 125 trucks a day, an average of one each way every five minutes).

Johnson Field, constructed by Pasadena Department of Water and Power volunteers, was once used for informal softball games. It now is a large, oval bowl like the water spreading basins to the north, with a dry dirt bottom, at least 100 yards in diameter rimmed by a dike several feet high, capable of holding 25,000 cubic yards of material. The County would use it in cooperation with the City of Pasadena, which owns it and the rest of Hahamongna Watershed Park.

The 25,000 cubic yards of sediment would be stored at Johnson Field for a year or two until the County conducts a large cleanout of about 1.67 million cubic yards of sediment from Devil’s Gate Reservoir in northwest Pasadena. The Johnson Field sediment then will be hauled away along with the 1.67 million cubic yards. That large, full-scale project is awaiting an Environmental Impact Report that will analyze various alternatives for handling sediment in the basin, their environmental impacts and feasibility.

While the haul route for the full-scale sediment removal will be determined after the EIR is completed, it may be the one favored by the County when the big project was announced last fall. It would go up the west side of the Arroyo Seco near the dam, to Oak Grove Drive, Berkshire Place and the 210 Freeway, passing near La Canada High School and a church.

Many in the audience of about 100 at the May 26 meeting urged the County to use that westside route for the work this summer and spare Windsor Ave. residents the truck traffic. Doing that would require filling in a deep trench carved into the muck just north of the dam by the stream, and maintaining a channel for the stream to continue flowing through the dam’s sluice gate. Sheridan said designing and constructing these structures would delay the 25,000-cubic-yard project beyond Oct. 15, the date when the County wants to finish the sediment removal, as well as alterations to the dam to make its openings less subject to clogging by debris, before the rainy season. The purpose of the project is to keep the dam operating normally and avoid possible flooding downstream during the year or two before the big main cleanout of 1.67 million cubic yards can be started.

Two other alternative haul routes were described, both going up the southeast side of the reservoir near the dam. One would have trucks traveling narrow residential streets on which cars would not be allowed to park, the other would require building a truck ramp and a street intersection. Sheridan said both were unfeasible.

Using Johnson Field for temporary storage, with only the organic matter traveling along Windsor Ave., is the County’s preferred alternative, Sheridan told the meeting. Next would be sending all of the sediment along Windsor. The others—westside and southeast corner—are not feasible in the time available, he said.

Water trucks would be used to minimize dust, metal shaker plates would vibrate dirt off truck tires, and tarps on trucks and street sweepers would help control material.

Assuming that Pasadena City officials approve the use of Johnson Field, the County hopes to start the sediment removal in June or July.