1. EVALUATING SELECTED SCOUR EQUATIONS FOR BRIDGE PIERS IN COARSE STREAMBEDS IN NEW YORK L.J. Welch, Jr. and G.K. Butch In cooperation with New York State Department of Transportation by

2. Field Conditions Turbulent flow Armored streambed

3. Scour is the result of work Sf= stream force (kg  m/s 2 ); D 84 = grain size >84 % of armor layer (mm).

4. Stream Force Sf= stream force (kg  m/s 2 );  = water density (10 3 kg/m 3 ); y 1 = water depth (m); w= flow width (1 m); V 0 = flow velocity (m/s).

5. Database Statistics

6. Model Calibration Calculated 19 scour depths measured in 1996 (10 = 0.0 m) 1996 MEAN ERROR MEAN ERROR (m)

7. New York Equation (1972-96). Sf = stream force (kg  m/s 2 ); D 84 =grain size >84 % of armor layer (mm).

8. Relation of Scour Depth to Stream Force and Bed Material

9. Sensitivity Analysis

10. FHWA Equation y s = scour depth; K 1 = pier-nose shape; a = pier width; K 2 = pier shape & flow alignment; y 1 = water depth; K 3 = streambed condition; Fr 1 = Froude number; K 4 = armoring by bed-material size.,

11. K 4 (modified by Mueller) If D 50 > 2 mm and D 95 > 20 mm and f(V) > 0, otherwise K 4 = 1 D 50 = median grain size; D 95 = grain size >95 percent of armor layer; V 0 = approach flow velocity; V / cD 50 = approach velocity corresponding to critical velocity at pier for D 50 ; V / cD 95 = approach velocity corresponding to critical velocity at pier for D 95 ; V cD 50 = critical velocity for incipient motion for D 50.,

12. Froehlich Equation y s = scour depth;  = pier shape; g= gravity; V 0 = flow velocity; y 0 = water depth; b= pier width; D 50 = median grain size.

13. Estimated Scour vs Measured Scour

14. Summary of Estimated and Measured Scour

15. New Hampshire Study Field measurements

16. New Hampshire Study GPR & fixed instruments

17. SUMMARY New York equation: - scour a function of stream force and bed material - derived from field measurements - alternative for coarse streambeds - estimates associated with specific peak discharges Mueller modified-K 4 and Froehlich equations: - less error than FHWA equation in New York study