2.4.5 Evaluation procedure: Step 1— Delineate 

 affected area. 



The area affected by a proposed plan consists of 

 the floodplain plus all other nearby areas likely to 

 serve as alternative sites for any major type of ac- 

 tivity that nnight use the floodplain if it were protect- 

 ed; one example of a major activity-type is commer- 

 cial. If the potential use of the floodplain includes 

 industrial use within a standard metropolitan statisti- 

 cal area (SMSA), the entire SMSA is the affected 

 area; for residential use, even within an SMSA, a 

 much smaller area may be designated the affected 

 area. 



2.4.6 Evaluation procedure: Step 2— Determine 

 floodplain characteristics. 



The existing characteristics of the floodplain must 

 be determined before its actual use can be estimat- 

 ed; therefore, undertake an inventory of the flood- 

 plain to determine those characteristics that make it 

 attractive or unattractive for the land use demands 

 established in steps 3 and 4, with emphasis on 

 those characteristics that distinguish the floodplain 

 from other portions of the affected area. Use the 

 following categorizations as a guide: 



(a) Inherent characteristics of a floodplain. Flood- 

 plain characteristics may include: 



(1) Flooding. Describe the flood situation, includ- 

 ing a designation of high hazard areas. The de- 

 scription should include characteristics of the flood- 

 ing, such as depths, velocity, duration, and debris 

 content; area flooded by floods of selected fre- 

 quencies, including 100-year frequency; historical 

 floods, and, where applicable, larger floods. 



(2) Floodway, natural storage. Describe and de- 

 lineate those areas which, if urbanized or structural- 

 ly protected, would affect natural storage, velocity, 

 or stage, or would affect flood flows elsewhere. 



(3) Natural and beneficial values, including open 

 space, recreation, wildlife, and wetlands. Many 

 floodplains, particularly those near urban areas, are 

 potential recreation, open space, wetland, or wild- 

 life preserves. The potential of the floodplain for 

 these purposes should be recognized and present- 

 ed. 



(4) Transportation. Floodplains near navigable 

 streams have inherent attractiveness for industries 

 that demand water-oriented transportation. Flood- 

 plains also serve as sites for railroads, highways, 

 pipelines, and related facilities that are not suscep- 

 tible to senous flood damage but have a tendency 

 to attract industry to the area. 



(5) Other attributes. Other inherent attributes of 

 floodplains may include soil fertility, reliability of 



water supply, waste disposal, and sand, mineral, 

 and gravel deposits. 



(b) Physical characteristics. Describe pertinent 

 physical characteristics, including slope, soil types, 

 and water table. 



(c) Available services. Most activities require 

 some or all of the following services: transportation 

 (highway and rail), power, sewerage, water, labor, 

 and access to markets. Indicate the availability of 

 such services in or near the floodplain, including 

 comparisons with similar services available in other 

 portions of the affected area. 



(d) Existing activities. Include in the inventory of 

 the floodplain a list of existing activity types, the 

 number of acres, and the density, age, and value of 

 structure for each activity-type by flood hazard 

 zone. 



2.4.7 Evaluation procedure: Step 3— Project 

 activities in affected area. 



Base economic and demographic projections on 

 the most recent available studies and include the 

 following: population, personal income, recreation 

 demand, and manufacturing, employment, and 

 output. Additional projections may be necessary for 

 any given area, depending on the potential uses of 

 the floodplain and the sensitivity of the plan to 

 these projections. Base projections on assessment 

 of trends in larger areas and appropriate data (e.g., 

 OBERS); the relationship of historical data for the 

 affected area to trends projected for larger areas; 

 and consultation with knowledgeable local officials, 

 planners, and others. The basis for the projections 

 should be clearly specified in the report. 



2.4.8 Evaluation procedure: Step 4— Estimate 

 potential land use. 



Estimate potential land use within the affected 

 area by converting demographic projections to 

 acres. The conversion factors can normally be de- 

 rived from published secondary sources, from 

 agency studies of similar areas, or from empirical 

 and secondary data available in the affected area. 

 The categories of potential land use need be only 

 as detailed as necessary to reflect the incidence of 

 the flood hazard and to establish the benefits de- 

 rived from a plan. 



2.4.9 Evaluation procedure: Step 5— Project 

 land use. 



Allocate land use demand to floodplain and non- 

 floodplain lands for the without-project condition 



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