Geomorphic Assessment of Channel Systems
does provide a guide to the types of information that may be available for a specific
watershed. The following is a list of possible sources of historical information:
! U.S. Army Corps of Engineers
! U.S. Department of Agriculture, National Resource Conservation Service
! Agriculture Research Service
! State Highway Department
! State Archives
! United States Geological Survey
! State Land Office
! County Offices
! City and Municipality Offices
! State and Local Historical Societies
! Newspapers
! Local Drainage and Levee Districts
! Local and County Soil and Water Districts
A wealth of information can be gleaned from topographic and geological maps, aerial
photos, and in the case of larger watersheds, satellite images. In the planning phase, emphasis
is placed on determining means of legal access to the stream, locating areas of possible
erosion, breaks in the plan geometry of the stream, channelized sections of the stream, land
use, and the location of existing structures. Through the use of a stereoscope, aerial
photographs can be utilized to ascertain channel dimensions and gain a more detailed view
of the river than is possible using topographic maps alone.
Geologic reports and, particularly, geologic maps are very beneficial in the
geomorphic analysis of a drainage basin. The geology and stratigraphy of a drainage basin are
the two parameters which have the most effect upon the drainage pattern and long profile of
the streams. The natural tendency of a stream is to adopt a course which coincides with the
most easily erodible materials available within the drainage basin or to follow surface
expressions of structural weaknesses within the earth's surface. Being able to identify the
geological and structural features within the basin that exert an element of control on drainage
pattern, and determining the stream's response to each different unit is the key to
understanding the development of the basin's drainage network.
A historical background of the changes which have taken place within the basin is
necessary to fully evaluate the river's response to changing conditions. Historic maps and
photos may be available from archives maintained by many of the agencies listed above.
The culmination of this preliminary data assembly phase will enable you to employ
field reconnaissance time more judiciously. You will be able to select key reaches of the
drainage network where abnormalities in planform and/or profile occur, to locate areas where
there are changes in the stratigraphy of the basin, and to obtain a preliminary determination
of zones between which the stream may respond differently to the conditions imposed upon
it.
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