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included, and the requirement that the Response Plan be reviewed and approved by the Regional Water Board. Impact HYD -2: The retaining wall, placement of fill material, reconstruction of Maple Street, or other improvements occurring within the current 100 -year flood zone along Redwood Creek could increase the depth and velocity of flood flows along the existing banks, which could result in erosion and siltation during operation of the proposed project and the project variant. Mitigation HYD -2: Proposed improvements within 100 -year flood zones and coastal flooding hazard areas, and proposed improvements affecting stormwater drainage systems (e.g., the proposed retaining wall and placement of fill and/or other potential improvements) shall be analyzed using detailed hydraulic evaluations to ensure that the improvements would not impede or redirect flood flows, contribute to exceeding the capacity of existing stormwater drainage systems, or alter the hydrodynamics of stormwater flows such that erosion could occur. The detailed hydraulic evaluations shall be performed and certified by a professional engineer, and shall quantify the following information. The potential for improvements within 100 -year flood zones, coastal flooding hazard areas, and drainage courses to impede or redirect flood flows including storm -related flooding and coastal flooding hazards including tsunamis, sea level rise, and extreme high tides. The potential for improvements to stormwater drainage systems to exceed the capacity of existing off-site stormwater drainage systems. • 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. ATTY/RESO.0035/CC RESO CERTIFYING FINAL EIR — 1548 MAPLE RESO. NO. 15661 REV: 04-30-18 PR MUFF NO. 601 Page 19 of 49