Figure 2.37. Stage-discharge relation for a sand channel (Los Gatos Creek at El Dorado
As flow passes through a channel constriction most of the energy losses occur as expansion
losses downstream of the contraction. This loss of energy is reflected by a rise in the water
surface and the energy line upstream from the bridge. The rise in water level is referred to as the
bridge backwater. Hydraulic engineers are concerned about the computation of backwater with
respect to flooding upstream of the bridge. Other concerns discussed in the following chapters
include the stability and scour around embankments, general scour depths due to constriction,
and local scour around piers.