FLOOD04031 - Laserfiche WebLink

Home Browse Search

Figure 4-5. Recommended Management Tools for Development Scenarios in Alluvial Fans, San Diego County, California Projected Development Density Sparse Moderate Density No construction No construction Zoned open space Zoned open space Elevation on piles Local dikes or armored fill Elevation on piles or armored fill Hydraulic Zones Channelized Flow Braided Flow , ~ , > B " Sheet Flow High Density Debris basin- or channel Local dikes Elevation on piles or armored fill Local dikes , o ~ ~ J ~ .~ .~ , ~ > ~ o ~ Projected Development Density Sparse Moderate Density Debris basin' or channel Local dikes Hydraulic Zones Channelized Flow Braided Flow Sheet Flow ~ ~ " ~ ~ , ~ , , "- ~ g c Local dikes High Density Debris basin' or channel Debris basin' or channel Local dikes Hydraulic Zones Channelized Flow Projected Development Density Sparse Moderate Density o ~ o ~ E , ~ ~ , if Braided Flow Sheet Flow " \'\,'ithflood storage convey the flmv of "vater and debris away from and around buildings, but consideration must be given to additional maintenance if roads are damaged and destroyed. Individual homes can be configured to deflect debris to either side of the building. NFIP regulations contain standards for construction in AO zones (areas with shallow water depths or unpredictable flow paths; see the mapping section in Chapter 1), which include alluvial fans. These standards include elevating structures and utilities above certain levels and providing adequate drainage paths around structures. VValls, \vindmvs, and doors on the uphill side of homes should be reinforced to 'iNithstand \vater and debris impact. Building foundations should be made of reinforced concrete \vith no \vindmvs. The appropriate mechanisms used by a locality \vill depend on several factors, most importantly the nature and extent of the flood hazards, the amount of existing development on the alluvial fans, and future development projections on the fan. The local government's ability to pay for expensive structural protection, or its authority to require developers to pay 36 High Density Debris basin' or channel Debris basin' or channel Debris basin' or channel for such structures, will also have bearing on the methods selected. The projected or existing density of development may also determine \vhich measures are appropriate. For example, it may be more cost-effective to construct channels to divert \vater and debris around or a\vay from high-density developments than to require elevation or flood proofing of individual structures. lAThen developers are required to pay for expensive public improvements as a condition of subdivision approval, those costs are typically passed on to home buyers in the form of higher housing prices. The unique, high-level hazards that occur in alluvial fans necessitate special consideration in the design of subdivisions in these areas. As a general rule of thumb, development should be avoided in v,That can best be determined as the most active or hazardous portions of the fan. Riverside County, California, has adopted controls for subdivisions in alluvial fans that base allmvable development densities in the fan areas on the anticipated level of flood flows at various points. In some areas of the county, the regulations require existing lots to be combined (to reduce future density)