Drainage Design Manual - the City of San Luis Obispo

whenever possible, as outlined in Section 5.3. Bank Stabilization shall focus onthe use of biotechnical methods, as described in Section 3.9.2 and Section 6.0.3.5 Floodplain ManagementThis Design Manual recognizes that much of the floodplain in the middle one-third (1/3) of theSLO Creek watershed has been substantially built- out, and that the City has an Urban Reserveboundary to encourage in-fill development and prevent urban sprawl. The City’s policy is toencourage in-fill development, or the building or redevelopment of vacant parcels surrounded byexisting developed parcels within urban areas. The floodplain has already been substantiallymodified within the in-fill urban areas, and significant additional off-site flood impacts are lesslikely to occur in these areas. The primary policy objective for these areas is to minimize flooddamage to existing and new buildings, and minimize additional obstructions to flood waterpassage. Additional floodplain management regulations are provided for the flood prone MidHiguera Specific Plan Area, which extends from the Marsh Street Bridge along San Luis ObispoCreek to below Madonna Road. In-fill floodplain regulations will apply to these areas.Development of large vacant parcels located within the floodplain at the edge of the SLO urbanarea has a much greater likelihood of creating increased off-site flood damage. The policyobjective for these areas is to prevent or minimize downstream impacts from floodplaindevelopment. Accordingly, two sets of standards and design criteria are utilized, one for “urbanin-fill development” within the existing urban area, and one for “non- in-fill development” inlarge vacant parcel areas at the edges of the existing urban area. Special FloodplainManagement Zones regulations apply to these non-in-fill areas.Areas designated as non-in-fill development or Special Floodplain Management Zones areshown in Figure 3.1. The Mid Higuera Specific Plan area is also shown on this figure. The CityCommunity Development Director in consultation with the City Engineer and the CountyPlanning Director in consultation with the County Public Works Director shall designate otherareas as Special Floodplain Management Zones as appropriate, as General Plans are updated, oras needed. The following floodplain standards are in addition to other City, County, state, andfederal rules and regulations governing FEMA defined 100-year floodplains and flood hazardareas. The 10 and 100-year floodplains, as determined from the SLO Waterway ManagementPlan, are shown in Figure 3-2.3.5.1 In-fill Floodplain RegulationsIndividual new development projects on vacant parcels, and redevelopment projects within theFEMA designated 100-year floodplain that are within the in-fill areas shown in Figure 3-2 (notwithin Mid-Higuera or special Floodplain Management Zone) have been determined to have nosignificanteffects on flood elevations, provided these Design Criteria are met. No significantimpacts for floodwater surface elevation rise, means a cumulative increase of less than 64-mm.(2 1/2 inches), or as determined by the City Engineer.• All finished lowest floor elevations for new buildings, and building additions shall be atleast 0.3 m (1 ft) above the defined FEMA 100-year flood elevation at time ofSLO Creek Drainage Design Manual 12 February 2003