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ATTY/RESO.0035/CC RESO CERTIFYING FINAL EIR – 1548 MAPLE REV: 04-30-18 PR Page 19 of 49 • The potential for improvements within 100-year flood zones, coastal flooding hazard areas, and drainage courses to result in changes to the extent and depth of flooding, The detailed hydraulic evaluations should also identify receptors and properties that could be affected by the potential changes to flooding conditions. If project improvements could cause erosion, alter existing flooding conditions, or contribute to exceeding the capacity of stormwater drainage systems, project designs shall be modified to reduce the potential flooding and erosion impacts. Modifications to project designs may include the following measures. • Altering the location and design of the retaining wall and embankments that would be constructed to raise the elevation of the project site. • Installing erosion controls systems such as rock protection or erosion resistant vegetation. • Increasing the size of proposed culverts. • Installing cross-flow culverts for improvements through flood zones. • Improving existing off-site stormwater drainage systems that would receive runoff from the project site. • Installing on-site stormwater detention systems in accordance with the City's drainage guidelines for residential development. • Including additional storage by replacing the existing storm drain line within Maple Street with a new 48-inch storm drain line or larger from US 101 up to and including the tide gate at Redwood Creek to account for tide gate operation of the existing outfall, as determined by the Engineering and Transportation Division. The detailed hydraulic evaluations and proposed changes to the project designs, if necessary, shall be submitted to the City and any other regulatory agencies that have jurisdiction over the improvements prior to the issuance of a grading permit. Finding: Implementation of Mitigation Measure HYD-2 would reduce project-related impacts to the depth and velocity of flood flows along the existing banks of Redwood Creek, potentially resulting in erosion and siltation, to a less-than-significant level. Facts in Support of Finding: This mitigation measure appropriately identifies the need for hydraulic evaluations for improvements within 100-year flood zones, as well as modifications consistent with best management practices to reduce potential flooding and erosion impacts. Impact HYD-3: Placement of engineered fill to raise the elevation of the project site and placement of surcharge materials would alter existing drainage patterns which could result in flooding of off-site areas during construction of the proposed project and the project variant. Mitigation HYD-3: The project applicant shall prepare a Construction Period Stormwater Drainage Control Plan which shall be submitted to the City for review and approved prior to the issuance of a grading permit. The Construction Period Stormwater 7.A. - Page 56