Irrigation Demands, Water Supplies and Shortages
The preprocessor module ET/Recharge calculates the net demands for the Lower East Coast Developed Area using the Agricultural Field Scale Irrigation Requirements Simulation Model (AFSIRS) Model to calculate irrigation demand for a particular land use (UT)and crop type on a Basic Element Area (BEA). SFWMM then computes gross irrigation demands, GIRRDMD, for each land use:
GIRRDMD(UT) = NIRRDMD(UT) / IRREFF(UT),
where NIRRDMD(UT) is net irrigation demand for usae type UT and IRREFF(UT) is the irrigation efficiency for use type UT The efficiency is quantified by:
IRREFF(UT) = GIRRSUP(UT) / NIRRSUP(UT),
where GIRRSUP(UT) is the gross irrigation supply for use type UT and NIRRSUP(UT), is the net irrigation supply for use type UT.
GIRRSUP(UT) = min{monGIRRDMD(UT), GIRRMAX(UT,P)} *
{GIRRDMD(UT) / monGIRRDMD(UT)}
where GIRRDMD(UT) is the gross irrigation demand volume for use type UT, GIRRMAX(UT,P) is the maximum monthly gross irrigation withdrawal for use type UT during phase P cutback
GIRRMAX(UT,P) = MAXIRRAPL(UT,P) * IRRAREA(UT)},
where MAXIRRAPL(UT,P) is the maximum monthly irrigation application rate for use type UT during a phase P water restriction [inches/month/acre], and IRRAREA is teh area of the SFWMM grid cell that is irrigated for use type UT [acres].
Shortage volume for irrigation use type UT is calculated by
SHRTG (UT) = GIRRDMD(UT) - GIRRSUP(UT)
Shortages for public water supply is calculated by:
SHRTGPWS = CBFRAC(P) * PWSDMD
PWSSUP = min(PWSDMD, PWSDMD - SHRTGPWS),
where PWSSUP is the public water supply withdrawal at the well, SHRTGPWS is the shortage volume for public water supply, and CBFRAC(P) is the fraction of cutback during phase P restrictions.
Gross, net and total irrigation supplies are quantified by.
NIRRSUP(UT) = GIRRSUP(UT) * IRREFF(UT),
NIRRSUPTOT = UT NIRRSUP(UT)
GIRRSUPTOT = UT GIRRSUP(UT)
where NIRRSUP(UT) is the net irrigation supply for the use type UT, GIRRSUP(UT) is the gross irrigation supply for use type UT, and IRREFF(UT) is the irrigation efficiency for use type UT, NIRRSUPTOT is the total net irrigation supply and GIRRSUPTOT is the total gross irrigation supply.
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