Hydraulic Design of Highway Culverts - DOT On-Line Publications

elevation in the stream The reduction is also limited by the outlet control performance curve. If
the water surface elevations in the natural stream had fallen below curve D, curve D gives the
maximum reduction in headwater elevation at the design flow. Flow depths calculated by
assuming normal depth in the stream channel may be used to estimate natural water surface
elevations in the stream at the culvert inlet.
Curve A has been previously established for the inlet control section. To define any other inlet
control performance curve such as curve B, C, or D for the inlet control section:
1. Select the point of interest on the outlet control performance curve.
2. Measure the vertical distance from that point to curve A. This is the difference in FALL
between curve A and the curve to be established. For example, the FALL on the control section
for curve A plus the distance between curves A and B is the FALL on the control section for
curve B.
Figure C-5--Possible Face Design Selections Tapered Inlet
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