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<br />In addition to locations and elevations, property values need to be established. <br />Rlgm=-ot='way sect10ns 1n highway-agenc-maf'e-g-ooa--sou~rce,oflnfannahan- 011 <br />praperty and building values. State Departments of Agriculture and the <br />State offices of the u.S. Sail Conservatian Service are excellent saurces for <br />crop val ue infannation. <br /> <br />e <br /> <br />Residences are assumed to have contents worth one-half the value of the <br />building. Crops are valued at market-value less harvesting and hauling <br />costs. In ather words, the value to be used in risk analysis is the value <br />of a mature crop in the field. <br /> <br />Land-use data should be summarized in a systematic fonnat. Two techniques of <br />tabulating land use data may be used: (1) assume property lies halfway between <br />cross-sections or (2) assume property lies an the closest cross-section. The <br />latter technique is probably preferable unless all the property of interest <br />happens to fall between two cross sections. Far a given cross section, all <br />similar buildings at a predetennined elevation are grouped into one unit. <br /> <br />. <br /> <br />, <br /> <br />The upstream and lateral extent af land use data needed can be approximated <br />by a preliminary hydraulic analysis considering the smallest bridge, highest <br />embankment and largest flood. <br /> <br />6.1.2 Flood Plain Geametry <br /> <br />Flood plain geometry can be described by several cross sections upstream and <br />downstream of the crossing and by 1-2 foot interval contour maps. Typically <br />there should be six or seven cross sections that cover a reach of the flood <br />plain approximately 1 valley width downstream to 2 or 3 valley widths upstream ~ <br />of the crossing. Cantour maps can be developed from aerial and/or ground ,..., <br />surveys. <br /> <br />6.1.3 Hydrologic and Hydraulic Data <br />6.1.3.1 Flow Magnitudes <br /> <br />Data from gaging stations upstream and downstream of the crossing and associated <br />drainage areas should be assembled. <br /> <br />6.1.3.2 Hydrographs <br /> <br />A family of stage hydrographs is needed to estimate embankment overtopping <br />times. Usually a complete family of measured hydrographs will not be <br />available, but measured hydrographs for one or two floods can be used <br />as patterns for other floods. If no measured hydrographs are available, <br />synthetic hydrographs can be used. <br /> <br />e <br /> <br />20 <br />