Laserfiche WebLink
<br />As outlined in these manuals, each installation shall be <br />checked for the limiting capacity, inlet control or outlet control. <br />Nomographs for this purpose from Circular No. 5 are attached as <br />"Appendix B." General criteria for design shall be: <br /> <br />1. The culvert, including inlet and outlet structures, shall <br />properly take care of water, bed-load and debris at all <br />stages of flow. <br /> <br />2. Inlets shall be designed to minimize entrance and <br />friction losses. For large structures, provisions <br />shall be made to resist possible structural failure <br />due to hydrostatic uplift forces. <br /> <br />3. Outlets shall be designed to avoid sedimentation and <br />erosion of the downstream channel. Additional outlet <br />control may be required where excessively high discharge <br />velocities occur. <br /> <br />4. Freeboard above the headwater and tailwater equal to <br />the amounts specified for open channels shall be provided. <br /> <br />5. The minimum size of culverts shall be 18 inches or the <br />hydraulic equivalent. <br /> <br />6. All culverts shall be designed to withstand an HS-20 <br />loading for the appropriate embankment conditions. <br /> <br />D. Storm Sewers <br /> <br />At the point which the allowable street capacities are <br />reached, collection and transmission of the flows in a storm <br />sewer becomes necessary. This section will discuss the trans- <br />mission or main line system. Collection systems (storm inlets) <br />will be included as Section IV-E. <br /> <br />The procedure used for the sizing of the main line system <br />shall be to calculate the energy grade line (EGL) for the system. <br />The hydraulic grade line (HGL) or pieziometric surface can then <br />be determined by subtracting the velocity head, V2j2g. In order <br />to fully utilize pipe capacities, the HGL should be at or above <br />the soffit of the pipe (full pipe flow), yet low enough to allow <br />inflow from catch basins. <br /> <br />The first step is to determine the points of control for <br />the system. These will be the discharge conditions (i.e. free <br />discharge, submerged discharge) and any changes from subcritical <br />to supercritical flow (hydraulic jumps). If flow is supercritical <br />the calculations follow the direction of flow; if the flow is <br />subcritical the calculations are against the flow or upstream. <br />The EGL and HGL are calculated at all manholes and junctions, <br />taking into account friction slope and point energy losses. At <br />each manhole, the invert elevations should be established so the <br /> <br />42 <br /> <br />I\! <br />,,'J' <br /> <br />, <br />, <br />! <br />I <br />to.. <br /> <br />! <br />~! <br />, <br /> <br />... <br /> <br />I; <br />ill <br /> <br />, <br />I, <br />L <br />I <br />II <br />I <br />L <br />I <br />ll.. <br />Ii <br />L <br />, <br />I <br />L <br />I <br />~ <br />, <br />