Hydraulic Design of Highway Culverts - DOT On-Line Publications

Figure II-5—Culvert location methods
3. Waterway Data. The installation of a culvert to convey surface water through a highway
embankment significantly constricts the flood plain. To predict the consequences of this
alteration, accurate preconstruction waterway data must be collected. These data include crosssectional
information, stream slope, the hydraulic resistance of the stream channel and
floodplain, any condition affecting the downstream water surface elevation, and the storage
capacity upstream of the culvert. Photographs of site conditions are often beneficial.
a. Cross Sections. Stream cross sectional data acquired from a field survey at the site are
highly desirable. At least three cross sections should be taken to establish the stream slope, the
culvert inlet, the culvert outlet, and the configuration of the natural channel (Figure II-6).
Sections should be taken: (1) about 30 m (100 ft) upstream from the crossing, (2) at the
centerline of the roadway, and (3) about 30 m (100 ft) downstream from the crossing. The
natural streambed width and side slopes, and the floodplain width may be obtained from these
cross sections. The cross-sectional data will also help to verify the accuracy of existing
topographic maps. If significant ponding is likely, additional sections may be necessary to
determine the storage capacity upstream of the culvert. Likewise, additional downstream
sections may be necessary to establish downstream water level (tailwater) conditions.
If only one cross section of the natural channel is available, it will be used as the typical cross
section. This assumption should be checked using topographic maps and aerial photos.
Additional information on stream slope and upstream storage volume should also be obtained
from the topographic maps.
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