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14. Select a bridge length and embankment elevation combination. Determine the corresponding design discharge and return interval. The optimum combination defines the lowest point on the lowest curve of total expected cost versus embankment elevation. The curves are often relatively flat and the selected combination may provide considerable safety factor against traffic interruption without much additional cost. 15. Evaluate the cost of the safety factor, if any. 16. Document the results in a report. The entire analysis could be computerized. Tseng and others (1975) have published a program for the purpose. However, once a computer program is constructed, it locks in some analytical techniques which may vary among analysts. This report approaches the analysis in blocks. The hydrology, hydraulics, construction costs, traffic costs, and flood damage could and, in fact, did come from separate sources. There are no known verified techniques for estimating damage to the embankment due to flow over the road. Therefore, one was devised using a couple of experience points and engineering judgment for the purposes of this report. While much of the report can be easily developed by hand with the assistance of a calculator, other parts may be expedited with a computer. These include the computation of water-surface profiles when step backwater or more sophisticated techniques are used. The bookkeeping involved in conducting a depth-damage analysis can be simplified with the use of a computer program. In this report, a computer program was available for the urban site which computed the damage and risk due to flood-plain inundation. For traffic and embankment erosion, the damages for each component flood were computed. The techniques used and the computer model selected are not important so long as they are sufficiently accurate. THE REPORT Report Outline A suggested outline for a report to document the results is shown in table 2. The two sample reports are included in appendices A and B and are written in a narrative form. In this chapter of this manual, each topic outlined in table 2 is annotated describing techniques and sources of information. In this way, the reader may refer to corresponding sections in the two example problems. Although the sample reports are written in narrative form, it seems possible that tables, graphs, computer printouts, check sheets, or drawings might be substituted for parts of the analysis in order to minimize the time involved in preparing a report. 12