Computes Discharge given Diameter, Material, and Head Loss using Swamee Jain (1976)
 
 
  D = Pipe diameter (in feet or meters) 
  g = Gravitational acceleration constant (32.2 ft/s^2 or 9.8 m/s^2) 
 hl = Head loss (in feet or meters) 
  L = Pipe length (feet or meters) 
 ks = Equivalent sand roughness height (a material property; in feet or meters) 
  v = Kinematic viscosity (in feet^2/second or meter^2/second)  
Notes: 
Swamee and Jain, A. K., 1976. Explicit equations for pipe-flow problems.  
ASCE J. of Hyd. Div., 102(HY5) pp. 657-664