The depression of a culvert is the vertical drop of the inlet control section below the stream bed. An inlet depression is defined by entering a value for each of the following items (see drawing below):
- Depression Slope
- Crest Width
The vertical drop of inlet control section below the stream bed.
Slope between the stream bed and the face invert. The depression slope must be set between 2:1 and 3:1.
Length of weir crest at the top of the depression slope. Designing the crest width becomes an iterative process in HY-8 as the user must select a crest width wide enough so that it does not control the headwater calculations. If the selected crest width is not wide enough the crest section will produce a higher headwater elevation than the culvert throat. The user must continue to increase the crest width and run the analysis until the headwater depth ceases to change with increasing crest width. Once this occurs the crest section no longer controls and may be used in analysis and construction.