FLOOD03064

• County: Statewide
• Basin: Statewide
• Title: Evaluating Scour at Bridges
• Date: 11/1/1990
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Floodplain Report/Masterplan

f. Scour data on other bridges in the area.

g. Slope of energy grade line upstream and downstream of the
bridge.

h. Estimation of the bed material sediment discharge for
flood discharges (flood discharges are mean annual, and
5, 10, 25, 50, 100 and 500 year frequencies). Use
Colby's method for sand-bed streams and Meyer-Peter,
Muller for coarse bed streams (7).

i. History of flooding.

j. Location of bridge site with respect to other bridges in
the area, confluence with tributaries close to the site,
bed rock controls, man-made controls (dams, old check
structures, river training works, etc.), and downstream
confluences with another stream.

k. Character of the stream (perennial, flashy, intermittent,
gradual peaks, etc.),

1. Geomorphology of the site (flood plain stream; crossing
of a delta, youthful, mature or old age strean; crossing
of an alluvial fan; meandering, straight or braided
stream; etc.).

m. Erosion history of the stream.

n. Development history (past, present and future) of the
stream and watershed. Collect maps, ground photographs,
aerial photographs; interview local residents; check for
water research projects planned or contemplated.

o. Sand and gravel mining from streambed up and downstream
from site,

p. other factors that could affect the bridge.

q. Make a qualitative evaluation of the site witn an
estimate of the potential for stream movement and its
effect on the bridge.

B. STEP 2. ANALYSIS OF LONG-TERM BED ELEVATION CHANGE

1. Using the information collected in step 1 above, determine
qualitatively the long-term trend in the stream elevation.
Where conditions indicate that significant aggradation or
degradation is likely, estimate the change in bed elevation
over the next 100 years using one or more of the following:

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