Laserfiche WebLink
<br />The hydraulic and channel properties that most completely describe an open <br /> <br />channel (fig. 2) include discharge (Q), width (T), area (A), wetted perimeter <br /> <br />(P), water-surface slope (Sw), maximum depth (dm), and maximum velocity (Vm). <br /> <br />From these, hydraulic radius (R), Froude number (F), mean depth (da), and mean <br /> <br />velocity (Va) may be determined, and various combinations of these properties <br /> <br />may be expressed in the form of ratios. The subscript "a" refers to mean <br /> <br />(average) values, and the subscript "m" to maximum values. A summary of <br /> <br />hydraulic properties and channel geometry determined at more than 700 cross <br /> <br />sections of streams is given in tables 1 and 2. The sites were selected to <br /> <br />represent a wide range of channel conditions. All sites are on natural open <br /> <br />channels not affected by control structures such as bridge openings or <br /> <br />jetties. For many sites, statistics such as the median, mean, and standard <br /> <br />deviation of certain hydraulic properties are important, but the minimum and <br /> <br />maximum values are also presented to indicate the range in data. The data for <br /> <br />the different streams are grouped on the basis of slope (table 1) and <br /> <br />curvature (table 2). <br /> <br />As shown in figure 3, hydraulically best channel cross sections are not <br /> <br />commonly found in natural channels. Instead, natural channels usually have a <br /> <br />cross-sectional shape between a trapezoid and a triangle. The relationship of <br /> <br />flow depths for natural channels (fig. 3) indicates that in the design of a <br /> <br />trapezoidal channel bed with bank protection, allowances should be made for an <br /> <br />increase in maximum depth by scour. <br /> <br />14 <br />