20C - AA - STORM DRAIN MASTER PLAN

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Plan- modeling program CivilStorm. The hydraulic model developed as part of this task will provide the baseline model to identify system deficiencies and to test the modification alternatives of the recommended storm drain improvements. The storm drain water surface profile models will only be generated for the main "collector" or "trunk" storm drain lines (storm drain lines of 36" and larger, estimated to be 42 miles from current County data), and the private or local facilities outside of public right-of-way intercepting the lot/building surface drainage will not be analyzed. The water surface data and hydraulic information will be summarized in tabular format for each reach or element of the facility to allow easy use and review. Deliverables: 1. Hydraulic Network in CivilStorm Task 3.2 Existing Municipal Storm Drain - Capacity Analysis, Hydraulic Deficiency Identification, Flooded Width Calculation The hydraulic models generated for the "existing" mainline storm drain systems will be analyzed in a sensitivity analysis to determine the maximum hydraulic "capacity" of the system. The maximum allowable hydraulic capacity will be defined as the highest elevation of the hydraulic grade line below the street that allows the surface inlets to function. A sensitivity analysis will be performed by factoring the "design" discharges to a lower amount until the storm drain operates without causing flooding of surface inlets. The hydraulic model will also more accurately quantify with a numerical amount the amount of hydraulic conveyance that the existing system is deficient. The hydraulic capacity will be converted to "level of flood protection" numerical value through a ratio of the capacity flowrate to the estimated 100-year ultimate flowrate. As part of the CivilStorm modeling results, RBF will evaluate where street flooded width calculations, based on gutter flow, at critical street locations. The calculations will be conducted to ensure conformance with City drainage design criteria. The street flooded width analysis will be based on normal depth calculations and using City of Santa Ana standard street sections. The street flooded width calculations will be used to identify locations that do not meet City critical and may require additional underground storm drain improvements. Deliverables (Tables summarizing): 1. Capacity Analysis 2. Flooded Width Analysis Task 3.3 Deficiency Removal and Alternatives Formulation / Feasibility Analysis /CIP RBF will develop preliminary alternatives formulation for removal of hydraulic deficiencies within the existing "mainline" storm drain improvements. The conceptual assessment will focus on either utilizing (1) increasing the hydraulic capacity through enlarged drainage facilities or new parallel system adjacent to existing facilities, (2) diversion system, or (3) detention storage for flow reduction and water quality benefits. The overall watershed system will be divided into study reaches for refined analysis on a reach-by-reach basis (within the predefined Drainage Areas). A list of potential design options will be identified which meet the primary flood protection objectives and major constraints associated with the alternatives will be discussed. A feasibility analysis will be performed to screen the alternatives and develop the recommended alternative based on selection criteria, including least costs and minimize public impacts. Deliverables: 1. A technical memorandum will be prepared that summarizes the results of the alternatives analysis. The memorandum will serve to reference the methodology, design assumptions, guidelines, and criteria developed for the identification and evaluations of the drainage alternatives. The text of the document will be prepared on MS Word. I Task 3.4 Drainage Improvement Facility Sizing and Alignment Utilizing the results of Task 3.3, RBF will determine the proposed increased pipe sizing based upon the hydrodynamic hydraulic analysis. Preliminary horizontal and vertical alignments will be developed for the `8u4';F` 24 20C-25