Free Software / Free Documents - As In No Cost

(that is correct - no money to pay)

If it is on this site, then there is a 99%+ probability that it is free... adware, no spyware, just free

IF you can't find something OR need assistance THEN email me AND I'll try to help

Click "HHWQ" above for full listing of 150+ completely free software applications available for download from web site main page (if you are not on the main page already)

Please spread the word by posting links to this site!


EPA SWMM v5.0.016 - Hargreaves Method

The Hargreaves method to compute daily evaporation has been included in the latest release of SWMM. I am unsure of whether this is the original or a modified version of the Hargreaves equation/method. The document with this release did not include detailed information on how the method was implemented, though you can check the source code (available on the EPA SWMM site).

1 comment:

Robert said...

Just for the record this is the code for the new Hargreaves method in SWMM 5.0.016

double getTempEvap(int day)
// Input: day = day of year
// Output: returns evaporation rate in in/day
// Purpose: uses Hargreaves method to compute daily evaporation rate
// from daily min/max temperatures and Julian day.
double a = 2.0*PI/365.0;
double ta = (Tave - 32.0)*5.0/9.0; //average temperature (deg C)
double tr = (Tmax - Tmin)*5.0/9.0; //temperature range (deg C)
double lamda = 2.50 - 0.002361 * ta; //latent heat of vaporization
double dr = 1.0 + 0.033*cos(a*day); //relative earth-sun distance
double phi = Temp.anglat*2.0*PI/360.0; //latitude angle (rad)
double del = 0.4093*sin(a*(284+day)); //solar declination angle (rad)
double omega = acos(-tan(phi)*tan(del)); //sunset hour angle (rad)
double ra = 37.6*dr* //extraterrestrial radiation
(omega*sin(phi)*sin(del) +
double e = 0.0023*ra/lamda*sqrt(tr)*(ta+17.8); //evap. rate (mm/day)
if ( UnitSystem == US ) e /= MMperINCH;
return e;