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e. For Deep Foundations (Drilled Shaft And Driven Pilinq) with Footinqs Or Caps, Placing the top of the footing or pile cap below streambed a depth equal to the estimated contraction scour depth will minimize obstruction to flood flows and resulting local scour. Even lower footing elevations may be desirable for pile supported footings when the piles could be damaged by erosion and corrosion from exposure to river currents. f. Stub Abutments on Pilinq Stub abutments positioned in the embankment should be founded on piling driven below the elevation of the thalweg in the bridge waterway to assure structural integrity in the event the thalweg shifts and the piling scour to the thalweg elevation. 8. Repeat the procedure in Steps 2 - 6 above and calculate the scour for a superflood. It is recommended that this superflood or check flood be on the order of a 500-year event or a flood 1.7 times the magnitude of the lOa-year flood if the magnitude of the 500-year flood can not be estimated. However, flows greater or less than these suggested floods may be appropriate depending upon hydrologic considerations and ~he consequences associated with damage to the bridge, An overtopping flood within the range of the lOa-year to 500-year floc~ may produce the worst-case situation for checking the foundation design. The foundation design determined under step 7 should be reevaluated for the superflood condition and design modifications made where required. o Check to make sure that the bottom of spread footings on soil or weathered rock is below the scour depth for the superflood. o All foundations should have a minimum factor of safety of 1.0 (ultimate load) under the superflood conditions. Note that in actual practice, the calculations for step 8 would be performed concurrently with steps 1 through 7 for efficiency of operation. 27