RBF CONSULTING 1 - 2007 - Laserfiche WebLink

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City of Santa Ana Proposal for 601 North Parkcenter Drive Initial Study and Mitigated Negative Declaration discussion with City or County staff regarding the specific drainage requirements for the project and specific criteria for this area. Watershed Boundary Delineation. Analysis of the existing watershed and drainage patterns associated with the proposed project boundary will be prepared. RBF will determine the local watershed subboundaries for the tributary drainage area in order to evaluate (1) the storm drain watershed area and (2) existing facility requirements. This task includes measurement of the drainage areas and the watershed parameters associated with the subareas for the different analysis. Critical concentration points will be identified to develop a "link -node" rational hydrology model. RBF will provide watershed delineation forthe proposed development, which includes only a single landuse plan. It is assumed that the client will provide a conceptual grading plan to identify the drainage patterns. Existing Hydrologic Conditions Analysis. RBF will prepare preliminary estimate peak runoff rates associated with the existing surface hydrology for the onsite watershed drainage area. The tributary offsite areas will be determined utilizing the City's Master Plan of Drainage. In addition, the onsite drainage boundaries and subareas will be delineated, and results of the hydrology analysis will be summarized on a hydrology map. RBF will prepare the 25-year and 100-year frequency storms rational hydrology analysis for the onsite watershed. The analysis will utilize Orange County Hydrology procedures and criteria to develop peak discharges, which are consistent with the procedures outlined in the Orange County Hydrology Manual. Proposed Development Hydrology. RBF will prepare preliminary developed condition surface hydrology analysis for the project site based upon Orange County hydrology criteria and methodology to quantify the design runoff rates. A single rational hydrology analysis for a single proposed landuse plan will be prepared for the property. The analysis will develop peak discharges for the 25- and 100-year rainfall event to satisfy the jurisdictional design requirements. Drainage subareas and patterns will be identified based upon the proposed local storm drain system and grading indicated on the plans or approved landuse concept provided by the Client. Proposed Drainage Facilities/Hydraulic Impacts. RBF will prepare an evaluation of the preliminary underground storm drain system requirements to provide the necessary level of flood protection and hydraulic conveyance. Preliminary horizontal alignments of facilities and an estimate of the size requirements for hydraulic conveyance assuming uniform depth will be identified. Unique structures and conceptual locations of stormwater quality features will be identified. RBF will perform conceptual sizing of the detention basins to determine the necessary stormwater storage volume onsite, if mitigation is required, to attenuate the peak development flowrates to the existing conditions. Surface Water Quality Facilities Sizing. RBF will prepare a preliminary assessment and sizing of the required stormwater detention facilities based upon Regional Water Quality Control Board criteria. A list of a variety of acceptable facilities will be identified which can provide mitigation of water quality concerns as part of a conceptual water quality program for the development and an adopted solution can be selected from the recommended list. JN 10-105908 • 4 • August 8, 2007