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DEVELOPMENT PLAN 1 2 basins, throughout the City. Portions of the City drain to the Santa Ana River watershed and others drain to the San Diego Creek watershed. The Specific Plan area is tributary to Santiago Creek (County drain E08), which lies south of the south leg of Main Place Drive along the Project frontage. Santiago Creek discharges to the Santa Ana River (County drain E01) about one mile west of the Specific Plan area. The Santa Ana River drains south to the Pacific Ocean. Flood Plain. The Specific Plan area lies within Zone X, which is outside the 100-year floodplain. Zone X is achieved in this area through the presence of levees alongside Santiago Creek. A small portion of the south edge of the south leg of Main Place Drive lies within Zone AE, but the Zone AE designation does not extend to the Mall site or any of the Specific Plan development areas. Existing Facilities. The City has a 36-inch diameter reinforced concrete pipe (RCP) storm drain in Main Street that increases in size to a 42-inch diameter RCP before it discharges to Santiago Creek. Approximately 15.3 acres of the north and east portions of the site, including surface parking, a portion of the existing Macy's building, and the existing easterly parking structure, drains to a series of on - site inlets and drainage pipes. This portion of the private drainage system discharges to the Main Street Storm Drain. Approximately 30.4 acres of the site, including the mall building and the two exiting parking structures in the northwest quadrant of the site, drains into the existing on -site loop road storm drain and into two existing City reinforced concrete pipes that run northwest under Main Place Drive. The City pipes discharges into the adjacent Caltrans drainage system that drains north toward the existing freeway interchange. The remainder of the site, approximately 8.4 acres, consisting primarily of surface parking and drive aisles within the southwest quadrant of the property, drains to a separate City drain. This RCP runs west under Main Place Drive, accommodating drainage from the Main Place Drive right-of-way, and discharges to a separate Caltrans drainage system that drains south and connects directly to Santiago Creek. On -site drains ranging in size from 12-inch diameter to 30-inch diameter exist on -site. Generally, the on -site main drains are found in the private ring road. The aforementioned acreages include on - site area and area within the Main Place Drive right-of-way. The City has confirmed that any connections to the City system will require City review only. Caltrans and County review of site drainage will not be required as long as site drainage connects directly to City infrastructure. Proposed Drainage System. The City's Master Plan of Drainage includes the drainage facilities within the Specific Plan area and no deficiencies are present in the system. As the Specific Plan land use program does not increase the amount of impervious area, the drainage characteristics are anticipated to remain the same as in the existing condition. Thus, no retention is required for stormwater runoff from the Specific Plan area. The proposed improvements to the storm drain system are limited to the following: Re-routing of several existing storm drain lines into the private drives within the Specific Plan area from their present locations within future development sites. Re-routing an existing storm drain around a future development site into Main Place Drive on the Specific Plan area's western edge. Figure 2-14, Drainage Plan, shows the existing and proposed drainage system, as well as the drainage areas of the site and the water quality features to which they drain. The proposed drainage MAINPLACE SPECIFIC PLAN 1 2-23