Fundamentals of Engineering Design
Table 5.1 Suggested Sources of Historical Information (USACE, 1994)
Previous studies and reports: Corps of Engineers, U.S. Bureau of Reclamation, consultants
U.S. Geological Survey Quadrangle Sheets: old and new series
Aerial photographs
Topographic maps by the Army Map Service and others
FEMA Flood Insurance Studies
County maps and city plots
Offices of county, state, highway, and railroad engineers
Local newspapers
Older inhabitants, especially farmers
U.S. Geological Survey: gage histories and descriptions, gaging notes, rating curves through period of
record; water supply papers; provisional discharge records
National Weather Service: storm and flood records
Municipal water and power plants: gage records
Irrigation and drainage districts: gage records
5.1.1
GEOLOGY
Geological considerations include valley slope, description of the predominant material in which the
channel is formed, tectonic activity, and the effects of large-scale man-made projects. Valley slope affects
several characteristics. The slope of the valley can be determined from field surveys and from topographic
maps. Soil erosion in the basin depends, to a certain extent, on the valley slope. Steep valley slopes
increase the erosion capacity of the overland flow which can lead to increased sediment yields.
Discontinuities in the slope can also affect stream pattern and stream sediment carrying capacity.
Classification of the material of which the channel is formed directly affects the erosion resistance.
Material properties will influence the susceptibility of the basin to geomorphic and sedimentary processes.
A channel incised in bedrock can be considered to be a stable reach that will not migrate significantly and
requires little control to keep it from shifting location or pattern. Alluvial streams, in contrast, are those in
which the bed and banks are composed of material that has been deposited by the flow. Because the bed
and banks of alluvial streams are generally composed of erodible material, the channels are dynamic
features that are free to shift position or patterns. One consequence of this characteristic is that alluvial
streams readily respond to changes in the basin. Rock outcrop in alluvial streams act as a control and can
restrict horizontal and lateral migrations as well as affect the depth of flow. The positions and any obvious
effects of outcrop on the flow should be noted.
Although tectonic activity usually occurs at very slow rates and is difficult to quantify, the effects
on fluvial processes and evolution can be significant. Tectonic forces such as faulting, folding, or tilting
primarily affect river systems through differential changes in gradient. Uplift or subsidence may disrupt the
environment or produce a change in hillslopes in the basin and alter the delivery of sediment (Leopold et
al., 1964, p. 475). Channel pattern is a sensitive indicator of valley slope change. To maintain a constant
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