Hydraulic Design of Highway Culverts - DOT On-Line Publications

Figure II-4--Flood hydrograph shape modification
Storage routing is the numerical translocation of a flood wave (hydrograph). This process is
applicable to reservoirs, channels, and watersheds. The effects of the routing are threefold:
volume conservation, peak reduction, and time lag. Reservoir routing is dependent only upon
storage in modifying a flood wave. Channel routing is dependent upon inflow and outflow as well
as storage in a stream reach. Watershed routing incorporates the runoff attenuating effects of
the watershed and is of importance in some hydrograph generation methods. Reservoir routing
is of special interest in culvert design, and it will be discussed further in Chapter 5.
B. Site Data
1. General. The hydraulic design of a culvert installation requires the evaluation of a large
amount of data including culvert location, waterway data, roadway data, and the design
headwater. Each of these items and its importance is discussed in the following paragraphs.
2. Culvert Location. A culvert should ideally be located in the existing channel bed to
minimize costs associated with structural excavation and channel work. However, this is not
always possible. Some streambeds are sinuous and cannot accommodate a straight culvert. In
other situations, a stream channel may have to be relocated to avoid the installation of an
inordinately long culvert. When relocating a stream channel, it is best to avoid abrupt stream
transitions at either end of the culvert. Figure II-5 displays two examples of culvert location
procedures (14). In one case, the culvert follows the natural channel alignment. In the second
case, the channel has been relocated to reduce the culvert length. Brice concluded that minor
channel relocations for culvert alignments have been successful unless the natural channel was
already unstable (15).
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