Fundamentals of Engineering Design
gradient, a stream that is steepened by uplift will increase sinuosity while a reduction in valley gradient will
lead to a reduction in sinuosity. A secondary effect of the changing gradient is the change that may occur
to the sediment load. Active tectonics can result in a unstable stream, which can be reflected by incision,
deposition, bank erosion, meander cutoffs, or change in stream patterns (Gregory et al., 1987, p. 65). A
more complete description of the effects of tetonic activity on alluvial rivers can be found in Schumm et al.
(1982).
The effects of man are the next variable to be examined. Many man-made structures affect the
stream in the same manner as geographic and geologic controls. Water diverted through diversion
structures can significantly alter discharge in the main channel. Dams and reservoirs affect the sediment
budget, depth of flow, total discharge, as well as the hydrograph shape. Bridge abutments, check dams,
and other man-made structures can act like constrictions and seriously affect the flow characteristics. The
presence of these structures should always be noted in the study reach as well as any obvious effects on
the flow regime.
5.1.2
GEOGRAPHY
The geography of the region should be examined. This includes a description of the general
location of the site, the basin size and terrain, primary land use, basin habitat and vegetation, and large-scale
disturbances or instabilities. The general location and description of the site can be referenced by stream
name, township, range and section location, the nearest town or distinguishing landmark, and the county
and state in which the reach occurs. If a global positioning system unit is available, a latitude and longitude
can be added to location description. It is important to be able to identify the site for future reference. A
topographic map can also be used to determine the size and terrain of the drainage basin.
The primary land use should be documented as this variable directly affects the degree of runoff
potential, hydrograph shape, sediment yield, and to some extent the amount of human interaction that can
be expected with the stream. Land use (Table 5.2) is categorized as urban, rural, agricultural, or
conservation. Urban is defined as intensive residential, recreational, commercial, or industrial use. Urban
land use is considered significant if greater than 25 percent of the basin contributing to the study reach is
urban and is characterized by possible large quantities and high variability of the sediment load. Rural land
use is defined as containing small farms and low density residential areas and contribute smaller sediment
loads, on average, and experience less variability in the sediment load. Rural land use is considered
significant when more than 45 percent of the drainage basin is rural. Agricultural land use refers to areas
where crops, orchards, pastures, and forests are being used for production and can contribute large
amounts of sediment, depending on the cropping practices employed. Agricultural classification is
appropriate for basins in which more than 35 percent of the basin is utilized for production. Conservation
land use is defined as no development and can include swamps, grasslands, forests, and lakes and the
quantities and variability of sediment are generally both very small. Conservation land use is considered
significant if more than 65 percent of basin is undeveloped. In all of the land use classifications,
knowledge of the
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