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®Storm Drain Master Plan <br />Phase 2 RFP No. 16-02_"� .. _._ <br />As Michael Baker identifies potential drainage alternatives to reduce City flooding hazards, efforts to <br />coordinate with all impacted agencies and stakeholders will be made. It is the goal to find solutions that <br />consider all stakeholders' objectives including synergistic solutions which enhance water quality and <br />provide environmental benefits. <br />The goals of the study include: <br />• Reduce flow discharge using the expected value hydrology method <br />• Identify locations for storm drain improvements (based on revised hydrology and/or LID projects) <br />• Identify locations for LID improvements <br />• Research funding opportunities <br />• Prepare list of Priority Projects <br />• Cost Analysis <br />Approach <br />As part of the effort to identify potential feasible and creative strategies to reduce flooding within the City, <br />hydrology will be re-evaluated using an expected value method. Expected value hydrology method will <br />be performed for each drainage basin within the project Master Planned area in accordance with Orange <br />County Hydrology Manual in providing protection levels for existing facilities. <br />Identification of potential locations to implement underground storage facilities and other LID strategies <br />will begin with a high level approach identifying all of the City owned open space and recreational areas. <br />According to the general plan land use, the City has approximately 806 acres designated as open space. <br />These areas will be prioritized based on their ability to implement relatively larger detention systems that <br />will have the most capacity to store and attenuate runoff, and where the most cost effective LID systems <br />can be implemented. Where these open space areas are limited other creative LID solutions will be <br />considered in order to mitigate flooding. These locations will be ranked based on potential storage <br />capacity and location within the City. Locations within the City which are prone to flooding will have a <br />higher priority than those which currently experience little to no flooding. Once we have identified potential <br />locations for the proposed strategies, a feasibility analysis will be conducted to evaluate soil conditions, <br />site constructability constraints, costs, as well as water quality and environmental benefits. After the <br />feasibility analysis is complete, a hydrologic and hydraulic analysis will be completed for the priority sites <br />in order to determine the potential reductions in flooding each of the proposed facilities are capable of <br />providing. <br />Rational method and small area hydrograph hydrology for the expected value method will be calculated <br />for the 5-, 10-, 25-, and 100-year storm return periods, using the AES software program. <br />Recommended facility improvements will be evaluated for the most feasible ultimate facilities based on <br />revised hydrology and alternative infrastructure improvements. Michael Baker will review the available <br />capacities (or constraints) associated with the existing downstream County regional drainage systems to <br />identify opportunities to better utilize these systems or determine project impacts. Alternatives shall also <br />consider the use of stormwater detention basins to reduce peak flows to the available capacity of the <br />existing systems. Stage -storage -discharge rating curves will be developed for priority project detention <br />basin locations. These storage areas could be underground storage chambers, multi -use recreation <br />facilities etc. Basin routing for discharge mitigation will be performed to understand the impacts of such <br />facilities. <br />Page 1 7 <br />INTERNATIONAL <br />