Limitations to the bottomless culvert scour analysis.

In order to use this method of analysis for a culvert, there must be a downstream control that will maintain flow depths inside the culvert so that velocity decreases as scour increases. If there is no control downstream, then it is likely that channel degradation will occur downstream, through and upstream of the culvert. If the user encounters this flow condition in the culvert, the ABSCOUR bottomless culvert module should not be used to design the culvert since it does not account for the effect of anticipated increases in the velocity of flow in the culvert.

Hydraulic flow conditions should be checked for several discharges to verify that the downstream controls are effective for low and intermediate flows as well as the design flow.

For the flow conditions described above, including supercritical flow, the user is encouraged to consider one of the following options: