Slot Inlet in Sag
Weir Flow
Slotted inlets located in sag operate as weirs to water depths, d (measured at the curb from the normal cross slope), of about 0.06 m (0.2ft).
The intercepted flow Qiw is expressed as:
Qiw = CwLd1.5
| Cw | = | Weir coefficient—varies with flow depth and slot length (typically 1.4 SI, 2.48 U.S. customary) | |
| d | = | Water depth at curb, measured from normal cross slope (m, ft) | |
| L | = | Slot length (m, ft) |
Orifice Flow
At water depths (measured at the curb) greater than about 0.12 m (0.4 ft), slotted inlets perform as orifices.
The intercepted flow Qio is expressed as:
Qio = 0.8LW(2gd)0.5
Transitional Flow
At depths between 0.06 m (measured at the slot from the normal cross slope) and 0.12 m, the flow is in a transition stage.
The intercepted flow Qi is conservatively calculated in this depth range as:
Qi = min(Qiw, Qio)