Modified Blaney-Criddle for Excel This allocation program which calculates a maximum monthly supplemental crop requirement and an average annual supplemental requirement using the Modified Blaney-Criddle method. The District assumes no responsibility to the user for the accuracy of this program. The District advises the user that additional information is available in the Basis of Review Volume III. There may be discrepancies between the result obtained by the user(s) and those results obtained by the District. This program was updated on September, 2000 Worksheet Developed by Jeffery Scott Questions Concerning the Worksheet: Please Contact Jeffery Scott at SFWMD West Palm Beach Office 1-800-432-2045 Ext. 6924 or E-mail [email protected]
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Modified Blaney-Criddle for ExcelModified Blaney-Criddle for Excel This allocation program which calculates a maximum monthly supplemental crop requirement and an average annual supplemental
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Modified Blaney-Criddle for Excel
This allocation program which calculates a maximum monthly supplemental crop requirement and an average annual supplemental requirement using the Modified Blaney-Criddle method.
The District assumes no responsibility to the user for the accuracy of this program. The District advises the user that additional information is available in the Basis of Review Volume III.There may be discrepancies between the result obtained by the user(s) and those results obtained by the District.
This program was updated on September, 2000
Worksheet Developed by Jeffery Scott
Questions Concerning the Worksheet:Please Contact Jeffery Scott at SFWMD West Palm Beach Office 1-800-432-2045 Ext. 6924 or E-mail [email protected]
1-in-10 Maximum Monthly Supplemental Crop Requirement = 5.35 inches
Maximum Monthly Supplemental Crop Water Use:
5.35 inches X MG
Notes:Evapotranspiration was calculated using a modified Blaney-Criddle method.Average effective rainfall is the amount that is useful to crops in an average year.2-in-10 drought rainfall is the rainfall minimum expected with a probability of 2 year in 10.2-in-10 effective rainfall is the amount that is useful to crops in a 2-in-10 drought rainfall.Average irrigation is the net amount that should be required for maximum yields during an average year.2-in-10 irrigation is the net amount that should be required for maximum yields during a 2-in-10 drought year.
1 Acres X 1.33 X 0.02715 MG/AC-IN =
1.45
0.19
1.33 X 0.02715 MG/AC-IN =
Calculations Of Irrigation Requirements (1-in-10)
Sprinkler1.00
Turf Grass0.801.33
1 Acres X
0.75
2-in-101-in-10
Maximum Monthly Supplemental Crop Water Use: 0.00 MG0.00 inches/acre
0.000.000.000.000.000.000.000.000.000.000.000.00
2-in-10Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 2.268 7.594
2-in-10 Rainfall(inches)1-in-10 Rainfall(inches)Evapotranspiration(inches) 2-in-10Evapotranspiration(inches) 1-in-102-in-10 Irrigation(inches)1-in-10 Irrigation(inches)2-in-10 Max MonthAlloc (inches/acre)""1-in-10 Max MonthAlloc (inches/acre)"
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Enter "X" for 1-in-10 calculations >>> 2-in-10 1-in-10Otherwise, 2-in-10 values will be calculated x
Enter Station Number>>> 24 1 Archbold 21 Loxahatchee2 Avon Park 22 Melbourne (No Data)3 Belle Glade 23 Merritt Island (No Data)4 Big Cypress (No Data) 24 Miami5 Clewiston 25 Moore Haven6 Everglades 26 Naples7 Fellsmere (No Data) 27 Okeechobee8 Fort Drum 28 Orlando9 Ft. Lauderdale 29 Pompano Beach
10 Ft. Myers 30 Punta Gorda11 Ft. Pierce 31 Stuart12 Hialeah 32 S-6513 Homestead 33 S 140 W14 Hypoluxo 34 Tamiami 415 Immokalee 35 Titusville (No Data)16 Indiantown (No Data) 36 Vero Beach (No Data)17 Jupiter 37 West Palm Beach18 Kissimmee19 La Belle20 Lake Placid (No Data)
2-in-10 Rainfall(inches)1-in-10 Rainfall(inches)Evapotranspiration(inches) 2-in-10Evapotranspiration(inches) 1-in-102-in-10 Irrigation(inches)1-in-10 Irrigation(inches)2-in-10 Max MonthAlloc (inches/acre)""1-in-10 Max MonthAlloc (inches/acre)"
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PART B
WATER USE MANAGEMENT SYSTEM
DESIGN AND EVALUATION AIDSI. SUPPLEMENTAL CROP REQUIREMENT
AND
WITHDRAWAL CALCULATION SUPPLEMENTAL CROP REQUIREMENT AND WITHDRAVAL CALCULATION
Introduction
An important aspect of successful crop production or landscape maintenance is ensuring that the vegetation receivessufficient moisture to meet its evapotranspiration demands. When rainfall is less than evapotranspiration, irrigationmust be applied to meet the deficit. As part of its consumptive water use permitting program, the South Florida WateManagement District issues permits for irrigation water use. The goal of the permitting program is to provide anallocation of irrigation water sufficient to meet the deficit between effective rainfall and evapotranspiration through adrought event that has a probability of occurring once in every ten years (1-in-10). That allocation is designed to meeboth the needs of a prolonged drought of up to one year as well as to meet peak monthly demands
The South Florida Water Management District uses a modified Blaney-Criddle equation to determine cropevapotranspiration and the method developed by the United States Department of Agriculture Soil ConservationService to determine supplemental irrigation needs
The Blaney-Criddle Equation
The Blaney-Criddle equation for estimating evapotransiration is
(1)
where:U = crop evapotranspiration for a given period,
k = an annual seasonal, or monthly empirical consumptive use coefficient which varies according to the cr
p = percent of daytime hours of the year which occur during the period,
t = mean temperature for the period, in Farenheit, and
m = month.
The equation has been modified to include:
(2) k = kt x kc
where:
kt = a climatic coefficient which is related to the mean air
� m
1
U = p t /100(1)
temperature, the value of which is expressed as
kt = 0.0173t - 0.314
kc = a coefficient reflecting the growth stage of the crop (Table B-I-1)
Calculation of Monthly Supplemental Crop Requirement and Allocation
The calculations to determine crop evapotraspiration are based on selected crop growth coefficients (Table B-I-1),rainfall, temperature and solar radiation for selected rainfall stations (Figures B-I-1 through B-I-15 and Table B-I-2)and net depth of application (Figures B-I-1 through B-I-15). In order to estimate monthly evapotranspiration, theDistrict approximates equations (1) and (2) as follows:
(3) f (m) = ( t (m) x p (m) ) / 100
(4) kt (m) = (0.0173 x t (m)) - 0.314
(5) kt f (m) = f (m) x kt (m)
(6) U (m) = kt f (m) x kc (m)
where:
m = month of year
f (m) = monthly evapotranspiration factor,
t (m) = average monthly temperature (Table B-I-2),
p (m) = monthly percentage of annual daylight hours (Table B-I-2),
Ul (m) = monthly effective rainfall factor considering monthly evapotranspiration,
F1 = soil factor,
D = net depth of,application (see Figures B-I-1 through B-I-15), and
Re (m) = monthly effmonthly effective rainfall.
Calculation of Water Use Allocations
After the monthly evapotranspiration, U (m), and the monthly 1-in-10 effective rainfall, Re (m), have been determined,the monthly supplemental crop requirement, Sup (m), is calculated as:
(11) Sup (m) = U (m) - Re (m)
for each month of the year for each of the perennial crops specified in the Water Use Application Crop InformationTable (Table D), or each month during which a crop is planted for annual crops, as specified in Table D. The irrigationquantity needed to supply the supplemental crop requirement Sup (m) is determined by:
(12) Q (m) = Sup (m) x k a x A
where:
k a = allocation coefficient multiplier (BOR Section 2, Table 2-1) for the irrigation system specified in Table D
A = irrigated acreage for the crop.
The individual monthly supplemental irrigation requirements for each month for each of the crops specified in theTable D are summed to determine the annual allocation. The supplemental irrigation requirements for each of thecrops specified in Table D are summed by month, and the largest of the monthly sums is the maximum monthlyallocation.
Additional Information:
Additional detail on this method may be found in "Irrigation Water Requirements," Technical Release no. 21, USDA, Soil Conservation Service, Engineering Division, 1970.