Hydraulic Design of Highway Culverts - DOT On-Line Publications

Figure VI-15--Sediment Deposition in Culvert
Certain culvert installations may encounter sedimentation problems. The most common of
these are multibarrel installations and culverts built with depressions at the entrance. Culverts
with more than one barrel may be necessary for wide shallow streams and for low fills. It is well
documented that one or more of the barrels will accumulate sediment, particularly the inner
barrel in a curved stream alignment. It is desirable for these installations to be straight and
aligned with the upstream channel. Culverts built with an upstream depression possess a barrel
slope which is less than that of the natural channel. Sedimentation is the likely result, especially
during times of low flow. However, self-cleansing usually occurs during periods of high
discharge. Both design situations should be approached cautiously with an increased effort in
the field investigation stage to obtain a thorough knowledge of stream characteristics and bedbank
materials.
4. Debris Control. Debris is defined as any material moved by a flowing stream. This
normally includes some combination of floating material, suspended sediment, and bed load. A
stream's propensity for carrying debris is based upon watershed land uses and certain stream
and floodplain characteristics. A field investigation of the following conditions is warranted.
• Stream velocity, slope, and alignment.
• Presence of shrubs and trees on eroding banks.
• Watershed land uses, particularly logging, cultivation, and construction.
• Stream susceptibility to flash flooding.
• Storage of debris and materials within the flood plain (logs, lumber, solid waste, etc.).
Debris can accumulate at a culvert inlet or become lodged in the inlet or barrel. When this
happens, the culvert will fail to perform as designed. Flooding may occur, causing damage to
upstream property. Roadway overtopping will create a hazard and an inconvenience to traffic
and may lead to roadway and culvert washouts. Maintenance costs will accrue as a result of
these circumstances.
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