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<br />Procedure <br /> <br />The hydraulic design of bridges with risk analysis will consist of <br />several. steps: <br /> <br />1. Pefine and understand the project. <br /> <br />2. Select analytical procedures for computing water-surface <br />elevations, flow distribution, flood frequency, and discharge <br />and stage hydrographs. Collect the field data necessary <br />to use these procedures. <br /> <br />3. Compute the natural water-surface profile, lateral flow <br />distribution, and peak-discharge-frequency relation. <br /> <br />4. Define the combination of bridge deck lengths and embankment <br />elevations which could conceivably be built. <br /> <br />5. Po a hydraulic analysis for each structural combination to <br />be considered. Compute the expected water-surface profile, <br />the design discharge, the velocity of flow through the <br />bridge, and the distribution of flow over the road. <br /> <br />6. Determine the cost of rerouting traffic in case of an <br />embankment overtopping or washout. Compute the overtopping <br />time and depth of flow and estimate the cost of traffic <br />interruption. <br /> <br />7. Evaluate the flood damage due to backwater by computing the <br />difference between the damage with the bridge in place and <br />the natural condition. <br /> <br />. <br /> <br />8. Evaluate the potential for embankment damage and estimate <br />the cost to repair damage that might occur. <br /> <br />9. Evaluate the capital costs that will vary in the analysis. <br />Include costs for foundations in alluvial beds and protection <br />measures which are particularly dependent upon embankment <br />elevation and bridge length. Exclude costs for right-of-way <br />and design which will not vary appreciably in the analysis. <br />Devices added to prevent risks are added to construction <br />costs. Decide on a service life for the structure and an <br />interest rate. Compute the annual capital costs. <br /> <br />10. Evaluate the cost of any other potential damages which may <br />be unique to the site such as structural damage, embankment <br />costs, debris, ice, and scour. <br /> <br />11. compute the risk. <br /> <br />12. Add the annual construction cost and risk to obtain the. <br />total expected project cost. <br /> <br />13. plot two families of curves as illustrated conceptually in <br />figure 2. In one case, plot total expected cost versus <br />embankment elevation. In the other case, plot design <br />discharge and return interval versus embankment elevation. <br /> <br />10 <br />