Fundamentals of Engineering Design
1.
For channels with substantial inflows of bed materials, a minimum velocity or shear stress to
avoid deposition may be as important as a maximum to avoid erosion. Such as value cannot
be determined using allowable data for minimal erosion.
2.
In bends and meandering channels, bank erosion and migration may occur even if average
velocities and boundary shear stresses are well below allowable values.
3.
An allowable velocity or shear stress will not in itself define a complete channel design,
because it can be satisfied by a wide range of width, depth, and slope combinations.
4.
The shear stress computations apply to a uniform flow over a flat bed. In sand channels the
bed is normally covered with bed forms such as ripples or dunes, therefore shear stresses
required for significant erosion may be much greater than that indicated in the computations.
5.3.5
REGIME THEORY CHANNEL DESIGN
Regime theory is not a theory in the strict sense of the term, for it does not incorporate physical
explanations for findings. The essence of the system lies in the development of convenient and simple
empirical equations from field data collected from rivers and from successfully operating artificial canals
(Henderson, 1966). In 1895, Kennedy (Lacey, 1931) developed the first well known regime equation in
India on the Upper Bari Doab Canal. He used the silt of the Upper Bari Doab Canal as a standard of
reference to quantify sedimentation on canal systems. Many relationships have been developed from the
Indian canals.
In the United States, Simons and Albertson (1963) continued regime development by combining
data from canal studies in India (Punjab and Sind) and the United States (Imperial Valley, San Luis Valley,
and canals in Wyoming, Colorado, and Nebraska). Their motive for additional development of regime
analysis is the inadequacy of previous regime methods. The three primary inadequacies are (Simons and
Albertson, 1963):
1.
the regime equations have not been developed based on the wide variety of conditions
encountered in practice;
2.
the regime equations fail to recognize the important influence of sediment transport on design;
and
3.
the regime equations involve factors that require a knowledge of the conditions upon which
the formulas are based if to be applied successfully.
Their data are separated into three groups based on the composition of streambed and
streambanks. This eliminates the need for computing bed, bank or silt factors needed for previous types
of equations (Watson and Abt, 1991). Simons and Albertson (1963) equations are referred to as the
Modified Regime Equations and are presented in Table 5.9.
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