City of Frisco Engineering Standards

Engineering Standards
• Column 21: Street capacity based on Manning’s equation. For sag inlets calculate the street
capacity for both the lower and higher station sides of the inlet and use the greater of the two.
(cfs)
• Column 22: Total right-of-way capacity as a function of the cross-sectional area of the rightof-way
at the inlet. For sag inlets, the total right of way capacity on the lower station side of
the inlet. (cfs)
• Column 23: Not used for on-grade inlets. For sag inlets, the total right of way capacity on the
higher station side of the inlet. (cfs)
• Column 24: Depth of gutter flow "yo" in approach gutter from spread of water or from direct
solution of Manning's equation for gutter capacity. For sag inlets, the depth of gutter flow on
the lower station side of the inlet. (ft)
• Column 25: Not used for on-grade inlets. Depth of gutter flow "yo" in approach gutter from
spread of water or from direct solution of Manning's equation for gutter capacity. For sag
inlets, the depth of gutter flow on the higher station side of the inlet. (ft)
• Column 26: Spread of water (T) or width of ponding in the gutter measured from the face of
curb. Column 19 times column 24, or the distance from the gutter to the crown, if the crown
height is exceeded. For sag inlets, the spread of flow on the lower station side of the inlet. (ft)
• Column 27: Not used for on-grade inlets. Spread of water (T) or width of ponding in the
gutter measured from the face of curb. Column 19 times column 25, or the distance from the
gutter to the crown, if the crown height is exceeded. For sag inlets, the spread of flow on the
higher station side of the inlet. (ft)
• Column 28: Gutter cross slope (Sw) (%)
• Column 29: Width of depressed gutter section (ft)
• Column 30: 100-year ratio of flow in the depressed gutter to the total flow (E 0 )
• Column 31: Gutter depression depth (a) (ft)
• Column 32: Equivalent cross slope (Se) (%)
• Column 33: 100-year inlet length required to capture 100% of the gutter flow (L T ) (ft)
• Column 34: Actual length (L) in feet of inlet which is to be provided (10’, 15’ or 20’). For
wye inlets the length provided is equal to the perimeter of the opening intercepting flow. The
length for wye inlets may be less than the total perimeter if the wye is not located in a sag
location.
• Column 35: Efficiency of a curb inlet where the length provided is shorter than the length
required. (E)
• Column 36: Discharge (Q) in cubic feet per second which the inlet in question actually
intercepts.
Section 4 – Drainage Design Requirements May 2012 Page 4-17