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<br />. <br /> <br />39 <br /> <br />3.2 <br /> <br />Veloci ty <br /> <br />. <br /> <br />Velocity is often accepted as the most important factor when designing <br /> <br /> <br />stable alluvial channels. A general rule is that sediment transport increases <br /> <br /> <br />with flow velocity to the fourth power at low discharges and to larger powers <br /> <br />at high-flow discharges. Design velocity, during major flows, for channel <br />improvements shall follow the recommendations as presented in Section 2.3.lA <br /> <br />of "Maj or Drainage" in the Urban Storm Drainage Criteria Manual, Volume 2. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />3.3 Depth <br />In a natural river system, depth is an important indicator of: (l) the <br />size of the channel; (2) the stability of the channel; and (3) the shear <br />stress exerted on the channel boundary by the flow. Also, scouring power <br />of water increases in proportion to a third to fifth power of depth. Design <br />depth, during major flows, for various types of channel improvements are <br /> <br />recommended in "Major Drainage" of the Urban Storm Drainage Criteria Manual, <br /> <br />Volume 2. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />3.4 S lopc_ <br />The slope of the energy gradient plays an extremely important role in the <br /> <br />hydraulics of river channels. Slope is utilized in velocity equations such as <br /> <br />the Manning's equation to estimate velocity; it is also utilized in the tractive <br /> <br />force equation to estimate the tractive force exerted on the bed and banks of <br /> <br />open channels. A long reach of river channel may be subjected to a general <br /> <br />lowering or raising of the bed level over a long period of time due to changing <br /> <br />incoming sediment supply caused by activities such as urbanization, construc- <br /> <br />tion of a reservoir, and etc. An equilibrium channel slope is defined as the <br /> <br />slope at which the channel's sediment transporting capacity is equal to the <br /> <br />incoming sediment supply. Under this condition, the channel neither aggrades <br /> <br />. <br /> <br />. <br /> <br />. <br />