double subcatch_getRunoff(int j, double tStep)
//
// Input: j = subcatchment index
// tStep = time step (sec)
// Output: returns total runoff produced by subcatchment (ft/sec)
// Purpose: Computes runoff & new storage depth for subcatchment.
//
// The 'runoff' value returned by this function is the total runoff
// generated (in ft/sec) by the subcatchment before any internal
// re-routing is applied. It is used to compute pollutant washoff.
//
// The 'outflow' value computed here (in cfs) is the surface runoff
// that actually leaves the subcatchment after any LID controls are
// applied and is saved to Subcatch[j].newRunoff.
//
{
int i; // subarea index
double nonLidArea; // non-LID portion of subcatch area (ft2)
double area; // sub-area or subcatchment area (ft2)
double netPrecip[3]; // subarea net precipitation (ft/sec)
double vRain; // rainfall (+ snowfall) volume (ft3)
double vRunon = 0.0; // runon volume from other areas (ft3)
double vOutflow = 0.0; // runoff volume leaving subcatch (ft3)
double runoff = 0.0; // total runoff flow on subcatch (cfs)
double evapRate = 0.0; // potential evaporation rate (ft/sec)
// --- initialize shared water balance variables
Vevap = 0.0;
Vpevap = 0.0;
Vinfil = 0.0;
Voutflow = 0.0;
VlidIn = 0.0;
VlidInfil = 0.0;
VlidOut = 0.0;
VlidDrain = 0.0;
VlidReturn = 0.0;
// --- find volume of inflow to non-LID portion of subcatchment as existing
// ponded water + any runon volume from upstream areas;
// rainfall and snowmelt will be added as each sub-area is analyzed
nonLidArea = Subcatch[j].area - Subcatch[j].lidArea;
vRunon = Subcatch[j].runon * tStep * nonLidArea;
Vinflow = vRunon + subcatch_getDepth(j) * nonLidArea;
//// Added to release 5.1.009. //// //(5.1.009)
// --- find LID runon only if LID occupies full subcatchment
if ( nonLidArea == 0.0 )
vRunon = Subcatch[j].runon * tStep * Subcatch[j].area;
////
// --- get net precip. (rainfall + snowfall + snowmelt) on the 3 types
// of subcatchment sub-areas and update Vinflow with it
getNetPrecip(j, netPrecip, tStep);
// --- find potential evaporation rate
if ( Evap.dryOnly && Subcatch[j].rainfall > 0.0 ) evapRate = 0.0;
else evapRate = Evap.rate;
// --- examine each type of sub-area (impervious w/o depression storage,
// impervious w/ depression storage, and pervious)
if ( nonLidArea > 0.0 ) for (i = IMPERV0; i <= PERV; i++)
{
// --- get runoff from sub-area updating Vevap, Vpevap,
// Vinfil & Voutflow)
area = nonLidArea * Subcatch[j].subArea[i].fArea;
Subcatch[j].subArea[i].runoff =
getSubareaRunoff(j, i, area, netPrecip[i], evapRate, tStep);
runoff += Subcatch[j].subArea[i].runoff * area;
}
// --- evaluate any LID treatment provided (updating Vevap,
// Vpevap, VlidInfil, VlidIn, VlidOut, & VlidDrain)
if ( Subcatch[j].lidArea > 0.0 )
{
lid_getRunoff(j, tStep);
}
// --- update groundwater levels & flows if applicable
if ( !IgnoreGwater && Subcatch[j].groundwater )
{
gwater_getGroundwater(j, Vpevap, Vinfil, tStep);
}
// --- save subcatchment's total loss rates (ft/s)
area = Subcatch[j].area;
Subcatch[j].evapLoss = Vevap / tStep / area;
Subcatch[j].infilLoss = (Vinfil + VlidInfil) / tStep / area;
// --- find net surface runoff volume
// (VlidDrain accounts for LID drain flows)
vOutflow = Voutflow // runoff from all non-LID areas
- VlidIn // runoff treated by LID units
+ VlidOut; // runoff from LID units
Subcatch[j].newRunoff = vOutflow / tStep;
// --- obtain external precip. volume (without any snowmelt)
vRain = Subcatch[j].rainfall * tStep * area;
// --- update the cumulative stats for this subcatchment
stats_updateSubcatchStats(j, vRain, vRunon, Vevap, Vinfil + VlidInfil,
vOutflow + VlidDrain,
Subcatch[j].newRunoff + VlidDrain/tStep);
// --- include this subcatchment's contribution to overall flow balance
// only if its outlet is a drainage system node
if ( Subcatch[j].outNode == -1 && Subcatch[j].outSubcatch != j )
{
vOutflow = 0.0;
}
// --- update mass balances
massbal_updateRunoffTotals(RUNOFF_RAINFALL, vRain);
massbal_updateRunoffTotals(RUNOFF_EVAP, Vevap);
massbal_updateRunoffTotals(RUNOFF_INFIL, Vinfil+VlidInfil);
massbal_updateRunoffTotals(RUNOFF_RUNOFF, vOutflow);
// --- return area-averaged runoff (ft/s)
return runoff / area;
}
double subcatch_getRunoff(int j, double tStep)
//
// Input: j = subcatchment index
// tStep = time step (sec)
// Output: returns total runoff produced by subcatchment (ft/sec)
// Purpose: Computes runoff & new storage depth for subcatchment.
//
{
int i; // subarea index
double area; // portion of subcatchment area (ft2)
double netPrecip[3]; // subarea net precipitation (ft/sec)
double rainVol = 0.0; // rain volume (ft3)
double evapVol = 0.0; // evaporation volume (ft3)
double infilVol = 0.0; // infiltration volume (ft3)
double outflowVol = 0.0; // runoff volume leaving subcatch (ft3)
double outflow = 0.0; // runoff rate leaving subcatch (cfs)
double runoff = 0.0; // total runoff rate on subcatch (ft/sec)
double pervEvapVol = 0.0; // evaporation over pervious area (ft3)
double evapRate = 0.0; // max. evaporation rate (ft/sec)
// NOTE: The 'runoff' value returned by this function is the total runoff
// generated (in ft/sec) by the subcatchment before any internal
// re-routing is applied. It is used in the Exponential Washoff
// function to compute pollutant washoff. The 'outflow' value
// computed here (in cfs) is the runoff that actually leaves the
// subcatchment (which can be reduced by internal re-routing and
// LID controls) and is saved to Subcatch[j].newRunoff.
// --- save current depth of ponded water over entire subcatchment
Vponded = subcatch_getDepth(j) * Subcatch[j].area;
// --- get net precipitation (rainfall + snowmelt) on subcatchment
getNetPrecip(j, netPrecip, tStep);
if ( Evap.dryOnly && Subcatch[j].rainfall > 0.0 ) evapRate = 0.0;
else evapRate = Evap.rate;
// --- initialize runoff rates
outflow = 0.0;
runoff = 0.0;
// --- examine each type of sub-area
for (i = IMPERV0; i <= PERV; i++)
{
// --- check that sub-area type exists
area = (Subcatch[j].area - Subcatch[j].lidArea) *
Subcatch[j].subArea[i].fArea;
if ( area > 0.0 )
{
// --- get runoff rate from sub-area
getSubareaRunoff(j, i, netPrecip[i], evapRate, tStep);
runoff += Subcatch[j].subArea[i].runoff * area;
// --- update components of volumetric water balance (in ft3)
//Subcatch[j].losses += Losses * area;
rainVol += netPrecip[i] * tStep * area;
outflow += Outflow * area;
evapVol += Vevap * area;
infilVol += Vinfil * area;
// --- save evap losses from pervious area
// (needed for groundwater modeling)
if ( i == PERV ) pervEvapVol += Vevap * area;
}
}
// --- evaluate LID treatment as if it were another type of sub-area
// while updating outflow, evap volumes, & infil volumes
if ( Subcatch[j].lidArea > 0.0 )
runoff += lid_getRunoff(j, &outflow, &evapVol, &pervEvapVol,
&infilVol, tStep);
// --- update groundwater levels & flows if applicable
if (!IgnoreGwater && Subcatch[j].groundwater )
gwater_getGroundwater(j, pervEvapVol, infilVol, tStep);
// --- save subcatchment's outflow (cfs) & total loss rates (ft/s)
area = Subcatch[j].area;
Subcatch[j].newRunoff = outflow;
Subcatch[j].evapLoss = evapVol / tStep / area;
Subcatch[j].infilLoss = infilVol / tStep / area;
// --- save volumes (ft3) for use in pollutant washoff calculation
Vrain = rainVol;
Vevap = evapVol;
Vinfil = infilVol;
Voutflow = outflow * tStep;
Vrunon = Subcatch[j].runon * tStep * area;
// --- compute water flux volumes over the time step
rainVol = Subcatch[j].rainfall * tStep * area;
stats_updateSubcatchStats(j, rainVol, Vrunon, Vevap, Vinfil,
Voutflow, outflow);
// --- update system flow balance
// (system outflow is 0 if outlet is another subcatch)
outflowVol = Voutflow;
if ( Subcatch[j].outNode == -1 && Subcatch[j].outSubcatch != j )
{
outflowVol = 0.0;
}
massbal_updateRunoffTotals(rainVol, evapVol, infilVol, outflowVol);
// --- return area-averaged runoff (ft/s)
return runoff / area;
}