Hydraulic Design of Highway Culverts - DOT On-Line Publications

Routine design and maintenance precautions may be taken if the debris accumulation potential
is minimal. Provision for a smooth, well-designed inlet and avoidance of multiple barrels and
skewed inlets will help to align and pass most floating debris. Periodic maintenance at culvert
entrances will reduce the chances of severe problems and identify culverts which may require
structural solutions.
Three debris control methods are available for culvert sites with more serious risks: interception
at or above the culvert inlet protecting culvert performance; deflection of debris away from the
entrance to a holding area for eventual removal; and passage of the debris through the culvert.
The latter may be accomplished by oversizing the culvert or utilizing a bridge as a replacement
structure. The costs of this solution should be closely compared with other solution methods.
Regardless of the solution method employed, it may be desirable to provide a relief opening
either in the form of a vertical riser or a relief culvert placed higher in the embankment.
Debris control structures often provide a cost effective solution. Debris interceptors functioning
upstream of the culvert entrance include debris racks, floating drift booms, and debris basins.
Debris interceptors functioning at the culvert inlet include debris risers and debris cribs. Debris
deflectors vary from a simple inclined steel bar or rail placed in front of the inlet to more complex
V-shaped debris deflectors (Figure VI-16). Debris fins are built to help align floating debris with
the axis of the culvert to assist in passage of the debris. Design information for commonly
employed debris control structures can be found in HEC No. 9, "Debris Control Structures" (45).
D. Site Related Modifications
Figure VI-16--Debris Deflector
A good culvert design is one that limits the hydraulic and environmental stress placed on the
existing natural water course. This stress can be minimized by utilizing a culvert which closely
conforms to the natural stream in alignment, grade, and width. Often the culvert barrel must be
skewed with respect to the roadway centerline to accomplish these goals. Alterations to the
normal inlet alignment are also quite common. Multiple barrels are used in wide, shallow
streams to accommodate the natural width of the stream.
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