Excavation Configurations







Configuration A — The Project

Sediment Removal Phase

The sediment removal phase constitutes the construction phase of the Proposed Project. Approximately 2.9 million cy of sediment is the current excess amount of sediment in the reservoir; however, additional sediment accumulation is anticipated during the upcoming storm seasons due to the denuded surfaces of the watershed created by the 2009 Station Fire. Proposed Project excavation activities will take place within the project’s excavation limit boundaries. The proposed excavation will remove approximately 2.9 million cy of current excess sediment in the reservoir in addition to any additional sediment received from storm flows during the Proposed Project sediment removal phase.

Excavation/Reservoir Configuration

At the time the NOP was released, an area of 178 acres was considered for the Proposed Project; this was refined to an area of 120.42 acres for the EIR. Specific excavation limits and reservoir configuration for the Proposed Project are shown in Figure 2.5-1: Proposed Project, Configuration A Excavaton Area and Configuration A Management Area, Option 1. As shown in Figure 2.5-1, the basin will be excavated to a 985-foot elevation at the face of the dam, sloping up to a 1,070-foot elevation at approximately 4,977 feet north of the dam. In addition to the sediment excavated as part of the Proposed Project, sediment stockpiled at Johnson Field as part of the IMP will also be removed. Proposed Project excavation will not involve the Oak Grove area of Hahamongna Watershed Park, the area of the reservoir above the northern end of excavation limits, or the City of Pasadena’s spreading grounds on the east side of the basin.


Removal Method  Project Site and Easement  Removal Goal







Alternatives


Excavation activities will remove approximately 2.8 million cubic yards (cy) of current excess sediment in the reservoir in addition to any additional sediment received during the project.

Excavation/Reservoir Configuration

The basin will be excavated from the face of the dam to approximately the middle of the reservoir. The basin will be excavated to a 985-foot elevation at the face of the dam, sloping up to a 1,055-foot elevation at approximately 4,977 feet north of the dam. This configuration will involve approximately 83 acres of the reservoir. As part of this Alternative, sediment stockpiled at Johnson Field as part of the IMP will also be removed. Excavation will not involve the Oak Grove area of Hahamongna Park, the area of the reservoir outside the western and northern excavation limits, or the City of Pasadena’s spreading grounds on the east side of the basin.

Sediment Removal and Reservoir Management Areas will involve two excavation areas. As shown, the lower excavation area will be excavated to a 985-foot elevation at the face of the dam, sloping up to a 1,045-foot elevation at approximately 2,901 feet north of the dam. The upper excavation area will be excavated to a 1,050-foot elevation at approximately 3,580 feet north of the dam, sloping up to a 1,065-foot elevation at approximately 4,727 feet north of the dam. This configuration in total will involve approximately 84 acres of the reservoir. As part of this Alternative, sediment stockpiled at Johnson Field as part of the IMP will also be removed. Excavation will not involve the Oak Grove area of Hahamongna Watershed Park, the area of the reservoir outside the excavation limits of the two excavation areas, or the City of Pasadena’s spreading grounds on the east side of the basin.

The basin will be excavated to an elevation of approximately 985 feet at the face of the dam, sloping up to a 995-foot elevation where the basin splits and narrows into two excavation branches. Both branches slope up to a 1,040-foot elevation, at which point the western branch ends and the eastern branch widens and continues to slope up to a 1,060-foot elevation at approximately 4,700 feet north of the dam. The final configuration will involve approximately 76 acres of the reservoir. Additionally, this alternative will include removal of sediment stockpiled as part of the IMP at Johnson Field. Excavation will not involve the Oak Grove area of Hahamongna Park, the area of the reservoir outside the excavation limits shown, or the City of Pasadena’s spreading grounds on the east side of the basin.