To determine contraction scour depth under clear water conditions *y*_{s},
the calculator requires the following information:

Mean flow depth below the bridge, before scour *y*_{o}, in m (or ft).

Discharge in the contracted section *Q*, in m^{3}/s (or cfs).

Bottom width in the contracted section, excluding piers *W*, in m (or ft).

Median diameter of the bed material *D*_{50}, in mm (or ft).

1. The coefficient *K*_{u} is determined according the unit system.

2. Because D_{50} is not the largest particle in the bed material, the scoured section can be slightly armored. Therefore, the D_{m} is assumed to be 1.25 D_{50}.

3. The contraction scour depth can be then calculated using the following equation:

*y*_{s} / *y*_{o} = {[( *K*_{u} *Q*^{ 2} ) /
( *D*_{m}^{0.667}*W*^{ 2})] ^{0.429} (1/y_{o})} - 1
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y_{o} = Given

K_{u} = Determined in step 1

Q = Given

D_{m} = Calculated in step 2

W = Given