| A | = | Cross sectional area, or drainage area |
| B | = | Bottom width of a channel |
| C | = | Runoff coefficient in Rational Method |
| D | = | Culvert diameter or sediment size |
| D50 | = | Sediment size for which 50 percent by weight of the particles are smaller;
similarly D65, D84, D90 represent sizes for which 65, 84, and 90 percent of the
particles are smaller |
| Fr | = | Froude Number |
| f | = | Darcy Weisbach friction factor |
| g | = | Acceleration due to gravity, 9.81 m/s2 (32.2 ft/s2) |
| H | = | Specific energy |
| Hf | = | Friction loss of head |
| hL | = | Headloss |
| i | = | Rainfall intensity, mm/h (in/hr) |
| K | = | Conveyance |
| ks | = | Height of roughness channels |
| Ku | = | Correction factor for units: SI (English) |
| n | = | Manning's resistance coefficient |
| P | = | Wetted perimeter of the flow |
| Q | = | Discharge (flow rate) |
| q | = | Unit discharge |
| R | = | Hydraulic radius |
| Re | = | Reynolds Number |
| rc | = | Radius of curvature at the center of the stream |
| ri, ro | = | Radius of curvature for inner and outer banks in a bend |
| S | = | Channel slope |
| Sf | = | Friction slope (also called the energy slope) |
| So | = | Bed slope |
| Sw | = | Slope of water surface |
| T | = | Top width |
| V | = | Velocity |
| V* | = |
|
| X | = | Coordinate axis |
| y | = | Coordinate axis, depth of flow |
| yc | = | Critical depth of flow |
| ys | = | Scour depth |
| Z | = | Elevation above arbitrary reference level (and Side slope of channel bank) |
![y sub 2 equals 0.33 divided by 2 times [ the square root of (1 plus 8 times 8.34 squared) minus 1] equals 3.73 m](images/eq95.gif){kind=small}
![y sub 2 equals 0.33 divided by 2 times [ the square root of (1 plus 8 times 8.34 squared) minus 1] equals 3.73 m](images/eq102.gif){kind=small}