Average depth after scour in the contracted section. This is taken as the section inside the bridge at the upstream end in HEC-RAS (section BU)
feet (meters)
y_1
Average depth in the main channel or floodplain at the approach section
feet (meters)
y_0
Average depth in the main channel or floodplain at the contracted section before scour
feet (meters)
Q_1
Flow in the main channel or floodplain at the approach section, which is transporting sediment
cfs (m3/s)
Q_2
Flow in the main channel or floodplain at the contracted section, which is transporting sediment
cfs (m3/s)
W_1
Bottom width in the main channel or floodplain at the approach section. This is approximated as the top width of the active flow area in HEC-RAS.
feet (meters)
W_2
Bottom width of the main channel or floodplain at the contracted section less pier widths. This is approximated as the top width of the active flow area.
feet (meters)
k_1
Exponent for mode of bed material transport.
V /ω*
k1
Mode of Bed Material Transport
< 0.50
0.59
Mostly contact bed material discharge
0.50 to 2.0
0.64
Some suspended bed material discharge
> 2.0
0.69
Mostly suspended bed material discharge
V^* = (g y1 S1)1/2 , shear velocity in the main channel or floodplain at the approach section, ft/s (m/s). \omega = Fall velocity of bed material based on D50, ft/s (m/s). g = Acceleration of gravity, ft/s2 (m/s2). S_1= Slope of the energy grade line at the approach section, ft/ft (m/m).