20C - AA - STORM DRAIN MASTER PLAN

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Storm Drain Master Plan 109, TASK 2 - HYDROLOGY Task 2.1 Hydrology Model Evaluation CivilStorm does not inlcude Orange County Hydrology Methods, therefore, in order to utilize the full hydrodynamic CivilStorm hydraulic model and conform with the County of Orange Hydrology Manual, this will task evaluate hydrology models for inclusion into the CivilStorm hydrodynamic model. RBF, in coordination with the City, will evaluate the following hydrology models for possible inclusion in the master plan: CivilStorm, HEC-WMS, and AES. The models will be evaluated for the following criteria: capability to calculate Orange County Hydrology based on the Orange County Hydrology Manual, ease of use for the City, and integration with the CivilStorm hydrodynamic model. Deliverables: 1. Hydrology Model Evaluation Memo Task 2.2 Delineate Existing Watershed Characteristics Using the established Drainage Basins within the existing City of Santa Ana Updated Master Plan of Drainage by Boyle Engineering Corporation, RBF will update boundaries based on field investigations (Task 1.1) and identify modifications for facilities constructed after 1994 (Task 1.4). Boundaries for the drainage areas have been provided by the City and will be used to determine the minimum critical hydrologic concentration points. The points will be used to assist in the development of the watershed model and analysis requirements for the hydraulic design. Watershed maps, depicting the 7 regional drainage area watersheds, will be developed to document the mapping for the proposed hydrologic modeling. The watershed maps will determine the average characteristic parameters associated with the modified or updated watershed subareas that are necessary for the application of hydrologic analysis. We will obtain and review available data for parameter estimation in the precipitation-runoff model including infiltration, vegetation cover, impervious cover (from City provided GIS landuse files), hydrologic soils data, and watershed hydraulic efficiency. Deliverables: 1. Seven Watershed Maps 1"=500' scale Task 2.3 Hydrology Analysis RBF will prepare a hydrology analysis for the watershed to quantitatively estimate the "ultimate" land use watershed condition surface runoff flowrates and volumes for the 2-,5-, 10-, 25-, and 100-year storm return periods based upon full conveyance of the drainage systems for all storm events. The analysis will include both rational method (used for time of concentration calculations) and hydrograph methods (used for peak flow and volume calculations). The hydrology models will be used to develop a link-node model for critical concentration points previously identified in Task 2.2. Flowrates and volumes developed will be limited in minimum tributary drainage area size to the masterplan or primary backbone facility systems only (i.e. flowrates will not be calculated for each individual surface inlet). Hydrology calculations will be completed in accordance with the City hydrologic criteria and the Orange County Hydrology Manual. Deliverables: 1. Hydrology Flowrates, Volumes, and Tc in tables for the 2-, 5-, 10-, 25-, and 100-year storms for use in CivilStorm hydraulics analysis. TASK 3 - HYDRAULIC ANALYSIS Task 3.1 Existing Municipal Storm Drain - Hydraulic Model Preparation RBF will develop a hydraulic model of the existing City backbone storm drain system. The hydraulic analysis will be based upon evaluation of the hydraulic grade line, rather than "normal depth" calculations (used in the 1994 Master Master Plan). Hydraulic grade line (HGL) calculations will be performed utilizing the dynamic hydraulic 23 20C-24