Height of Afflux

• At high flows, afflux is a rise in water level that can occur upstream of a structure (see right).
• Aflux is defined as the greatest difference in water level for a given period of time.
• If the structure were to be demolished, the flow would be disrupted. It is a result of energy.
• It is made at high flows through bridges and culverts, and it is made at high flows through bridges and culverts. Blockage makes things worse.
• Afflux can have a major bodily impact. Increased losses are possible as a result of rising flood levels due to a blockage As a result, it must be depicted in a river.

The maximum increase in water surface elevation above that of an undisturbed stream caused by the presence of a structure in the stream, such as a bridge or culvert, is known as afflux.

Figure 1-1 depicts affluent for a bridge structure in a stream with a uniform slope. The undisturbed stream's usual water surface is represented by the dashed line. When the structure is present, the solid line symbolises the water surface. Afflux is defined as the highest increase in water level over the undisturbed stream's normal depth (Y1). The afflux differs from the head loss over a structure in that the latter is a variable that depends on the measurement locations upstream and downstream.

There is a local loss of stream energy when a structure such as a bridge or culvert is placed in a stream. The fluid friction in contact with the structure, as well as the stagnation zones that border the contracting (Sections 4–3) and expanding (Sections 2–1) flow reaches upstream and downstream of the structure, cause this. This local loss of energy is balanced by an increase in stream potential energy immediately upstream of the structure to maintain a steady flow. As a result, a backwater is formed, which begins at the afflux point.

Because afflux can increase flood risk, structures are typically built to keep it to a minimum. When extreme floods occur or structures become obstructed, however, the design conditions may no longer apply. Under these situations, afflux increases. Under extreme conditions, affluent can elevate water levels by up to a metre.