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Uniform Flow

Uniform Flow. Introduction. Flow depth does not change with distance is called uniform flow and corresponding depth is called the normal depth. (Chaudhry, 2008). Uniform Flow Features. The depth, water area, velocity and discharge at every section of the channel reach are constant.

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Uniform Flow

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  1. Uniform Flow

  2. Introduction • Flow depth does not change with distance is called uniform flow and corresponding depth is called the normal depth (Chaudhry, 2008)

  3. Uniform Flow Features • The depth, water area, velocity and discharge at every section of the channel reach are constant. • The energy line, water surface, and channel bottom are all parallel, their slopes are all equal, () • Uniform flow is considered to be steady only! (In natural streams, even steady uniform flow is rare, for rivers and streams in natural states scarcely ever experience a strict uniform-flow condition) • Uniform flow concepts offer a relatively simple and satisfactory solution to many practical problems. (In general, uniform flow can occur in very long, straight, prismatic channels)

  4. Flow Resistance • “The water of straight rivers is the swifter the farther away it is from the walls, because of resistance. Water has higher speed on the surface than at the bottom. This happens because water on the surface borders on air which is of little resistance, because lighter than water, and the water at the bottom is touching the earth which is of higher resistance, because heavier than water and not moving. From this follows that the part which is more distant from the bottom has less resistance than that below.” Leonardo da Vinci

  5. Flow Resistance Equations • Chezy Equation (French engineer, 1768, water supply system of Paris) • ; • Chezyconstant (depends upon channel roughness) • Hydraulic Radius • slope of the energy grade line (nonuniformflow) • slope of the channel bottom (uniform flow)

  6. Manning Equation • It is difficult to estimate Chezy constant so several attempts have been made. • (Widely used in English speaking countries!), SI-units • In English units • is manning coefficient and depends upon surface roughness, amount of vegetation, channel irregularity

  7. (Chaudhry, 2008)

  8. Normal Depth Computation • The Manning equation for uniform flow can be expressed as: , • [left hand is called section factor] • Specific values of , ,and we solve this equation to determine the normal depth in a given channel

  9. Design Curves • A trapezoidal channel with b= 20 ft, z=2, =0.0016, and = 0.025, carries a discharge of 400 cfs. Compute the normal depth and velocity. (Chaudhry, 2008)

  10. Trial and Error Procedure

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