FLOOD01360

• County: Statewide
• Title: Hydraulic Design of Highway Culverts
• Date: 9/1/1998
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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ting a large capacity culvert to
accommodate all of these events with no
detrimental flooding effects are normally
outweighed by the initial construction
costs. Thus, an economic analysis of
the trade-offs is performed with varying
degrees of effort and thoroughness.

1, Benefits and Costs. The purpose
of a highway culvert is to convey water
through a roadway embankment. The major
benefits of the culvert are decreased
traffic interruption time due to roadway
flooding and increased driving safety,
The major costs are associated with the
construction of the roadway embankment
and the culvert itself. Maintenance of
the facility and flood damage potential
must also be factored into the cost an-
alysis.

2. Analysis. Traditional economic
evaluations for minor stream crossings
have been somewhat simplistic. Culvert
design flows are based on the importance
of the roadway being served with little
attention given to other economic and
site factors. A more rigorous
investigation, termed a risk analysis,
is sometimes performed for large culvert
installations. The objective of the
risk analysis is to find the optimum
culvert capacity based on a comparison
of benefits and costs. (figure 1-16)
The designer should be aware of the risk
analysis process and consider using it to
analyze alternatives where flood damage
is large or culvert cost is significant.

II

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COST ______
RIS K ________
COST a RISK _

CULVERT

AREA

Figure I-16--Risk analysis
benefit versus cost curve.