Determine the location of trench drain to intercept the runoff.

If on a slope, calculate the runoff to be captured by the trench drain in terms of cfs per foot of slope width. The maximum intercept rate, calculated from the weir equation, is 1.4 cfs per foot of length per side of trench drain for the Department specified grate. Flows exceeding 1.4 cfs per foot of length per side will require a different method of interception or multiple rows of trench drain inlets.

Select the outfall location for the trench drain. The maximum length of the trench drain is measured from the outfall location because the depth of the outfall, whether natural ground or a storm drain pipe, will determine the maximum depth of the trench drain. Trench drain is normally available with either a fixed invert slope or neutral invert without slope.

Look at the manufacturer's data to select the segments needed by part number.

Select the trench drain outlet, horizontal or vertical, and size.

Calculate the allowable flow in the drain outlet using the orifice equation.

Select the method of connection to the storm drain pipe.