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<br />8. Erosion Control (Major Drainageway) <br /> <br />The requirements for erosion control for grass lined channels <br />shall be as defil11ed in the USDCM, Se!ct:ion 2.3.6, "Major <br />Drainage Erosion Control." The design of riprap and erosion <br />control devices shall be in accordance 'with Sections 10.1 and <br />10.2 of these criteria. <br /> <br />9. Water Surface Profi.1es (Major Drainageway) <br /> <br />Computation of the! water surface profile shall be presented <br />for all open channels utilizing standard bacl<:water methods, <br />taking into conside:ration losses due to changes in velocity or <br />channel cross sl.,ction, drops, wate,rway openings, or <br />obstructions. Th.:. energy gradient shall be shown on all <br />design drawings. <br /> <br />5.4.3 <br /> <br />Concrete Line.;! ChannelS (Maior Drai,lUI~ <br /> <br />The criteria for the de!sign and construction of concrete lined <br />channels is presented below: <br /> <br />1. Hydraulics (Major Drainageway) <br /> <br />a. <br /> <br />Freeboard - Adequate channel freeboard above the designed <br />water surface shall be provided and shall not be less <br />than determined by the following: <br />- (d) 1/3 <br />H~ - 2.0 + 0.025 V <br /> <br />(Equation 5.3) <br /> <br />Where: <br /> <br />Hrs <br />V <br />d <br /> <br />= freeboard height (feet) <br />= velocity (fps) <br />= depth of flow (feet) <br /> <br />Freeboard shall be in addition to super-elevation, <br />standing waves, and/or other water surface disturbances. <br />These special :situations should be addreSSE!d in the Final <br />Drainage Report. <br /> <br />Concrete side slopes shall be extended to include the <br />freeboard hei~rht. <br /> <br />b. Super-elevatiem - Super-elevation elf the water surface <br />shall be determined at all horizontal curves, and design <br />of the channel section adjusted acc.ordingly. <br /> <br />c. Velocities - Flow velocities shall be :such that critical <br />or super critical flow conditions arE! not created. In no <br />case shall the, velocity exceed 18 fps. <br /> <br />d. Critical or super critical flow cClnditions are not <br />allowed. Drop structures or other clppropriate energy <br />dissipation f:'lCilities may be required to maintain a <br />subcritical flow regime. <br /> <br />5-8 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />