Laserfiche WebLink
<br />Determine if there are existing or potential future factors that will <br />produce a combination. of high discharge and low tail water control. Are <br />there bedrock or other controls (old diversion structures, erosion control <br />checks, other bridges, etc.) that might be lowered or removed? Are there <br />dams or locks downstre~ that wo~ld control the tail water elevation <br />seasonally? Are there dams upstream or downstre.. that could control the <br />elevation of the water surface at the bridge? Select the lowest reasonable <br />downstream water surface elevation and the largest discharge to estimate <br />the greatest scour potential. Assess the distribution of the velocity and <br />discharge per foot of width for the design flow and other flows through the <br />bridge opening. Consider also the approach flow and the flow distribution <br />downstream (the contraction and expansion of the flow). This should take <br />into consideration present conditions and anticipated future changes in the <br />river. <br /> <br />C. From the output of the above computer programs and from other hydraulic <br />studies determine the discharge and velocity input variables or par...ters <br />needed for the scour calculations (See Appendix B) <br /> <br />D. Collect and summarize the following information as appropriate. <br /> <br />1. Boring logs. <br /> <br />2. Bed material size distribution in the bridge reach. <br /> <br />3. Existing stream and flood plain cross-section. <br /> <br />4. Stream geomorphic plan form. <br /> <br />5. Watershed characteristics. <br /> <br />6. Scour data on other bridges in the area. <br /> <br />7. Slope of energy grade line upstream and downstream of the bridge. <br /> <br />8. Estimation of the bed material sediment discharge for flood discharges <br />(flood discharges are mean annual, and 5, 10, 20, 50, 100 and 500 year <br />frequencies). Use Colby's method for sand bed streams and Meyer-Peter <br />Muller for coarse bed material streams (6). <br /> <br />9. History of flooding. <br /> <br />10. Location of bridge site with respect to other bridges in the area, <br />tributaries to the stream close to the site, bed rock controls, man- <br />made controls (dams, old check structures, river training works, <br />etc.), and downstream confluences with another stream. <br /> <br />11. Character of the stream (perennial, flashy, intermittent, gradual <br />peaks, etc.). <br /> <br />12.. Geomorphology of the site (flood plain stream; crossing of a delta, <br />youthful, mature or old age stream; crossing of an alluvial fan, etc.). <br /> <br />18 <br /> <br />~ <br /> <br />I <br />I <br />~;~-, <br />.' <br />, I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />