peak discharges can also be used. In using this method, the conveyance of the channel is
calculated using the Manning equation in which the roughness coefficient, n, needs to be
estimated from the discussion presented in Chapters 2 and 3. By referring to a catalog of
(color) photographs, similar channel situations to the specific site can be identified and a
relatively inexperienced engineer may make a reliable estimate for n.
Whatever approach is used, the reader is cautioned not to blindly accept computer printout as
the final answer in estimating a flood frequency relationship. The data should be plotted on
probability paper as analyzed by several commonly used methods. Sometimes paleo (ancient)
hydrology techniques need to be employed to resolve historic outliers at very sensitive sites.
8.1.10 Environmental Data
In making environmental impact analyses of highway projects on streams and rivers, it is
necessary to obtain water quality and biological data for the streams. Such data are not readily
available for many rivers. Municipal water and sewage treatment facilities and industrial plants
utilizing river water should have recent records regarding river water quality which will be
helpful in making comprehensive environmental analyses. Water quality data for certain rivers
can be obtained from the U.S. Geological Survey. Wildlife information such as migration
patterns of deer and elk should be determined and local game refuges should be located.
Information regarding fishes and their river habitat should be obtainable from the state fish and
game agencies. Species of trees and other vegetation should be determined, and some
information regarding sensitivity of the flora to auto emissions should be obtained. Data should
also be obtained in order to enable assessment of stream turbidity during and after highway
construction. Information on soil type to be used in construction of embankments would be
helpful in this regard.
8.2 CHECKLIST OF DATA NEEDS
As an aid in collecting data preparatory to analysis of rivers and highway encroachment of
rivers, the relevant types of data have been listed in Table 8.1. There may be more data items
included in this table than are needed for a given project site, and some judgment is required.
For data which are not available, the checklist should be helpful for planning a field
investigation or other data acquisition program.
8.3 DATA SOURCES
The best data sources are national data centers where the principal function is to disseminate
data. But it might be necessary to collect data from a variety of other sources such as from a
field investigation, interviews with local residents, and a search through library material.
Detailed information on the location of these federal agencies across the U.S. is available in
Appendix A of the manual HEC-19, (FHWA 1984). The list of sources in Table 8.2 is provided
to serve as a guide to the data collection task.
8.5
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