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. Ie I . I I I I I .e I I I I I I I ,e I 2. orifice Flow The equation governing the orifice opening and plate is the orifice flow equation: Q = CdA (2gh) 1/2 Where Q = flow (cfs) Cd= orifice coefficient A = area (fe) g = gravitational constant = 32.2 ft/sec2 h = head on orifice measured from centerline (ft) (Equation 11. 6) An orifice coefficient (Cd) value of 0.65 shall be used for sizing of all square edged orifice openings and plates (see Figure 11-4). 11.5 Design standards for Open space Detention 11.5.1 state Engineer's Office Any dam constructed for the purpose of storing water, with a surface area, volume, or dam height as specified in Colorado Revised statues 37-87-105 as amended, shall require the approval of the plans by the state Engineer's Office. Those detention storage facilities subject to state statutes shall be designed and constructed in accordance with the criteria of the state. 11.5.2 Grading Re~irements Slopes on earthen embankments less than 5 feet in height shall not be steeper than 4H: 1V. For embankment heights between 5 and 10 feet, the slopes shall not be steeper that 3H:IV, but horizontal slope distance shall not be less than 20 feet. For embankments greater than 10 feet in height, the slopes shall be such to maintain slope stability, but horizontal slope distance shall not be less than 30 feet. . All earthen slopes shall be covered with topsoil and re-vegetated with grass. Slopes on riprapped earthen embankments shall not be steeper than 3H:IV. For grassed detention facilities, the minimum bottom slope shall be 0.5 percent, measured perpendicular to the trickle channel. 11.5.3 Freeboard Re~irements The minimum required freeboard for open space detention facilities is 1 foot above the computed 100-year water surface elevation. The invert of the emergency spillway shall be placed at or above the computed 100-year water surface elevation. 11 - 5