Laserfiche WebLink
<br />Standard hydraul ic theory and analyses indicate that when the water <br /> <br />slope exceeds critical slope, that is when the Froude number exceeds <br /> <br />unity, higher velocities and supercritical flow result. The data col- <br /> <br />lected for this and other studies indicate that the Froude numbers for <br /> <br />flow in steep, natural mountain streams are less than unity. There is <br /> <br />no tendency for Froude numbers to increase with slope. Subcritical flow <br /> <br />is due to the combined effects of channel and cross-section variations, <br /> <br />bank roughness, spill resistance, and to an increase in the effect of <br /> <br />these factors with increasing discharge, which creates extreme turbulence <br /> <br />and energy losses that result in increased flow resistance. During <br /> <br />floods large amounts of channel erosion occur, energy is required to <br /> <br />transport the material, and energy is lost because of bed-form rough- <br /> <br />ness. During large floods, flow conditions may approach, but do not <br /> <br /> <br />exceed, critical flow, except in very localized areas in the channel. <br /> <br /> <br />Further 'efforts should be made to document flow conditions during large <br /> <br /> <br />floods. <br /> <br />I <br /> <br /> <br />~1 <br /> <br />