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CONSUMPTIVE USE OF IRRIGATION WATER
IN WYOMING

II. PROCEDURE

Consumptive Use Equation
Blaney and Criddle1 found that, disregarding the unmeasured factors, consumptive use (U) varies with the temperature and daytime hours (F) and, with the available moisture (precipitation, irrigation, and/or soil moisture and ground water).

Expressed mathematically, U = KF = sum of kf
where
U = Consumptive use of crop for a season
F = seasonal consumptive use factor; or sum of the monthly consumptive use factors for the season or period
K = seasonal consumptive use coefficient
t = mean monthly temperature in degrees Fahrenheit
p = monthly percent of daytime hours for the latitude of the Weather Bureau station (Table I)
f = (t x p)/100 = monthly consumptive use factor
k = monthly consumptive use coefficient
u = kf = monthly consumptive use in inches
r = mean monthly precipitation or rainfall
re = mean monthly effective precipitation
Consumptive irrigation requirement = u - re

The computer will not print lower case letters, therefore, in Table IV (p. 22) which is the computer printout of the consumptive use calculations, only capital letters represent the lower case letters in the above discussion.

           TABLE I - MONTHLY PERCENTAGE OF DAYTIME HOURS (p) OF 
           THE YEAR FOR LATITUDES 18° TO 65° NORTH OF THE EQUATORa
  ---------------------------------------------------------------------------------------------
   Latitude
    North    Jan.   Feb.   Mar.   Apr.   May   June   July   Aug.   Sept.  Oct.  Nov.  Dec.
  ---------------------------------------------------------------------------------------------  
     65°     3.52   5.13   7.96   9.97  12.72  14.15  13.59  11.18  8.55  6.53  4.08   2.62
     64°     3.81   5.27   8.00   9.92  12.50  13.63  13.26  11.08  8.56  6.63  4.32   3.02
     63°     4.07   5.39   8.04   9.86  12.29  13.24  12.97  10.97  8.56  6.73  4.52   3.36
     62°     4.31   5.49   8.07   9.80  12.11  12.92  12.73  10.87  8.55  6.80  4.70   3.65 
     61°     4.51   5.58   8.09   9.74  11.94  12.66  12.51  10.77  8.55  6.88  4.86   3.91
     60°     4.70   5.67   8.11   9.69  11.78  12.41  12.31  10.68  8.54  6.95  5.02   4.14
     59°     4.86   5.76   8.13   9.64  11.64  12.19  12.13  10.60  8.53  7.00  5.17   4.35
     58°     5.02   5.84   8.14   9.59  11.50  12.00  11.96  10.52  8.53  7.06  5.30   4.54
     57°     5.17   5.91   8.15   9.53  11.38  11.83  11.81  10.44  8.52  7.13  5.42   4.71
     56°     5.31   5.98   8.17   9.48  11.26  11.68  11.67  10.36  8.52  7.18  5.52   4.87
     55°     5.44   6.04   8.18   9.44  11.15  11.53  11.54  10.29  8.51  7.23  5.63   5.02
     54°     5.56   6.10   8.19   9.40  11.04  11.39  11.42  10.22  8.50  7.28  5.74   5.16
     53°     5.68   6.16   8.20   9.36  10.94  11.26  11.30  10.16  8.49  7.32  5.83   5.30
     52°     5.79   6.22   8.21   9.32  10.85  11.14  11.19  10.10  8.48  7.36  5.92   5.42
     51°     5.89   6.27   8.23   9.28  10.76  11.02  11.09  10.05  8.47  7.40  6.00   5.54
     50°     5.99   6.32   8.24   9.24  10.68  10.92  10.99   9.99  8.46  7.44  6.08   5.65  
     49°     6.08   6.36   8.25   9.20  10.60  10.82  10.90   9.94  8.46  7.48  6.16   5.75
     48°     6.17   6.41   8.26   9.17  10.52  10.72  10.81   9.89  8.45  7.51  6.24   5.85
     47°     6.25   6.45   8.27   9.14  10.45  10.63  10.73   9.84  8.44  7.54  6.31   5.95
     46°     6.33   6.50   8.28   9.11  10.38  10.53  10.65   9.79  8.43  7.58  6.37   6.05
     45°     6.40   6.54   8.29   9.08  10.31  10.46  10.57   9.75  8.42  7.61  6.43   6.14
     44°     6.48   6.57   8.29   9.05  10.25  10.39  10.49   9.71  8.41  7.64  6.50   6.22
     43°     6.55   6.61   8.30   9.02  10.19  10.31  10.42   9.66  8.40  7.67  6.56   6.31
     42°     6.61   6.65   8.30   8.99  10.13  10.24  10.35   9.62  8.40  7.70  6.62   6.39
     41°     6.68   6.68   8.31   8.96  10.07  10.16  10.29   9.59  8.39  7.72  6.68   6.47
     40°     6.75   6.72   8.32   8.93  10.01  10.09  10.22   9.55  8.39  7.75  6.73   6.54
     39°     6.81   6.75   8.33   8.91   9.95  10.03  10.16   9.51  8.38  7.78  6.78   6.61
     38°     6.87   6.79   8.33   8.89   9.90   9.96  10.11   9.47  8.37  7.80  6.83   6.68
     37°     6.92   6.82   8.34   8.87   9.85   9.89  10.05   9.44  8.37  7.83  6.88   6.74
     36°     6.98   6.85   8.35   8.85   9.80   9.82   9.99   9.41  8.36  7.85  6.93   6.81 
     35°     7.04   6.88   8.35   8.82   9.76   9.76   9.93   9.37  8.36  7.88  6.98   6.87
     34°     7.10   6.91   8.35   8.80   9.71   9.71   9.88   9.34  8.35  7.90  7.02   6.93
     33°     7.15   6.94   8.36   8.77   9.67   9.65   9.83   9.31  8.35  7.92  7.06   6.99
     32°     7.20   6.97   8.36   8.75   9.62   9.60   9.77   9.28  8.34  7.95  7.11   7.05
     31°     7.25   6.99   8.36   8.73   9.58   9.55   9.72   9.24  8.34  7.97  7.16   7.11
     30°     7.31   7.02   8.37   8.71   9.54   9.49   9.67   9.21  8.33  7.99  7.20   7.16
     29°     7.35   7.05   8.37   8.69   9.50   9.44   9.62   9.19  8.33  8.00  7.24   7.22
     28°     7.40   7.07   8.37   8.67   9.46   9.39   9.58   9.17  8.32  8.02  7.28   7.27
     27°     7.44   7.10   8.38   8.66   9.41   9.34   9.53   9.14  8.32  8.04  7.32   7.32
     26°     7.49   7.12   8.38   8.64   9.37   9.29   9.49   9.11  8.32  8.06  7.36   7.37
     25°     7.54   7.14   8.39   8.62   9.33   9.24   9.45   9.08  8.31  8.08  7.40   7.42
     24°     7.58   7.16   8.39   8.60   9.30   9.19   9.40   9.06  8.31  8.10  7.44   7.47
     23°     7.62   7.19   8.40   8.58   9.26   9.15   9.36   9.04  8.30  8.12  7.47   7.51
     22°     7.67   7.21   8.40   8.56   9.22   9.11   9.32   9.01  8.30  8.13  7.51   7.56
     21°     7.71   7.24   8.41   8.55   9.18   9.06   9.28   8.98  8.29  8.15  7.55   7.60
     20°     7.75   7.26   8.41   8.53   9.15   9.02   9.24   8.95  8.29  8.17  7.58   7.65
     19°     7.79   7.28   8.41   8.51   9.12   8.97   9.20   8.93  8.29  8.19  7.61   7.70 
     18°     7.83   7.31   8.41   8.50   9.08   8.93   9.16   8.90  8.29  8.20  7.65   7.74

a After SCS USDA, 19679

U. S. Weather Bureau records were used to define the growing season. Perennial forage crops, such as alfalfa and grass, consume water for the entire season as long as moisture is available for plant growth. A common definition for growing season for forage crops is the number of days between the last spring killing frost (28F) and the first killing frost in the fall4. Observations have indicated that forage crops begin to grow and consume water as soon as the maximum daily temperatures stay well above the freezing point for an extended period of days3. The season continues despite later freezes. The end of the season occurs when the daily minimum temperature repeatedly falls below freezing and mean dally temperatures recede. The growing season for alfalfa and grass was assumed for this report to be the period when mean daily temperatures are above 40°F. Table II gives the forage crop growing season at the Wyoming weather stations.

            TABLE II - GROWING SEASON FOR ALFALFA AND
            GRASS AT WYOMING WEATHER BUREAU STATIONS
  ---------------------------------------------------------------------------
				     Normal Date of 40°F     Length of
				    Mean Daily Temperature  Growing Season
   Station	   	County		Spring	  Fall	       (Days)
  ---------------------------------------------------------------------------
   Afton		Lincoln		 4-21	  10-23		185
   Alta 1 NNW		Teton		 4-22	  10-22		183
   Arvada 3N		Sheridan	 4-3	  10-31		211
   Basin		Big Horn	 3-27	  11-3		221
   Bedford 2SE		Lincoln		 4-21	  10-24		186
   Big Piney		Sublette	 4-25	  10-10		168
   Border 3N		Lincoln 	 4-17	  10-23		189
   Buffalo		Johnson		 4-6	  11-1		209
   Casper AP		Natrona		 4-8	  11-2		208
   Cheyenne AP		Laramie	  	 4-11	  11-1		204
   Chugwater		Platte		 4-3	  11-1		212
   Cody			Park		 4-4	  11-5		215
   Colony		Crook		 4-5	  11-3		212	
   Diversion Dam	Fremont		 4-7	  10-30		206
   Dixon		Carbon		 4-9	  10-26		200
   Douglas		Converse	 4-4	  10-30		209
   Dubois		Fremont	 	 4-21	  10-24		186
   Dull Center 1SE	Converse	 4-3	  11-2		213
   Encampment 10ESE	Carbon		 4-16	  10-28		195
   Evanston 1E		Uinta		 4-19	  10-23		189
   Farson		Sweetwater	 4-16	  10-19		186
   Ft. Washakie 2S	Fremont		 4-5	  10-29		207
   Gillette 2E		Campbell	 4-8  	  10-31		206
   Green River		Sweetwater	 4-5	  10-29		207
   Jackson		Teton		 4-19	  10-22		186
   Kaycee		Johnson		 4-9	  10-31		205
   Kemmerer		Lincoln		 4-18	  10-22		187
   Kendall		Sublette	 5-5	  10-12		160
   LaGrange		Goshen		 3-30	  11-7		222
   Lake Yellowstone	Yellowstone NP	 5-18	  10-7		142
   Lamar RS		Yellowstone NP	 4-29 	  10-14		168
   Lander AP		Fremont		 4-7	  10-30		206
   Laramie		Albany		 4-18	  10-27		192
   Lovell		Big Horn	 4-4	  10-31		210	
   Lusk			Niobrara	 4-6	  11-2		210
   Midwest		Natrona		 4-2	  11-4		216
   Moran 5WNW		Teton		 5-2	  10-14		165
   Newcastle		Weston		 4-4	  11-2		212
   Pathfinder Dam	Natrona		 4-6	  11-2		210
   Pine Bluffs		Laramie		 3-30	  11-3		218
   Pinedale		Sublette	 5-2	  10-13		164
   Powell		Park		 4-3	  11-1		212
   Rawlins AP		Carbon		 4-12	  10-28		199
   Riverton		Fremont		 4-3	  10-28		208
   Sage 4NNW		Lincoln		 4-18	  10-20		185
   Saratoga		Carbon		 4-15	  10-26		194
   Sheridan AP		Sheridan	 4-7	  11-2		209
   South Pass City	Fremont		 5-8	  10-8		153
   Spencer 10NE		Niobrara	 3-16	  10-31		229
   Sundance		Crook		 4-10	  10-30		203
   Sunshine 2ENE	Park		 4-19	  10-23		187
   Thermopolis		Hot Springs	 3-31	  10-31		214
   Torrington Exp. Farm	Goshen 		 3-28	  11-3		220
   Wamsutter		Sweetwater	 4-11	  10-25		197
   Wheatland 4N		Platte		 3-26	  11-8		227
   Worland		Washakie	 3-31	  10-27		210
  ------------------------------------------------------------------------
The growing season for other crops was estimated with the assistance of specialists in the College of Agriculture, University of Wyoming. The season for these crops is regarded as between the planting date and harvest. Planting dates were determined to be ten days earlier than the 40°F date (Table II) for small grains, fifteen days later than the 40°F date for sugar beets, thirty days later for corn, forty days later for beans, and fifty days later for potatoes. The harvest dates were estimated to be August 1 for small grain, October 10 for sugar beets, October 1 for corn, September 1 for beans, and September 15 for potatoes.

Consumptive Use Coefficients
The monthly consumptive use coefficients used for this report are shown on Figures 1 through 7 (pp. These values were assumed to be applicable to Wyoming after considering all available sources of data.

Effective Precipitation
Not all of the precipitation that falls on an area is effective for meeting consumptive use needs of plants. This is because of many factors. Showers of small intensity and duration are commonly evaporated. The rainfall intercepted by plants before reaching the ground is likewise evaporated directly from leaves. Runoff and groundwater accretion remove portions of the rainfall from large storms, reducing the amount of water retained in the soil for plant use from these storms.

A method suggested in the U. S. Bureau of Reclamation Manual and in the U. S. Department of Agriculture Technical Bulletin No. 12751 to estimate effective rainfall was used in this study. Mean monthly precipitation is divided into one inch increments, and the effective rainfall is calculated from the following percentages:

       TABLE III - METHOD FOR ESTIMATING MONTHLY EFFECTIVE PRECIPITATION
   ------------------------------------------------------------------------
    Total Amount            Monthly Precipitation Considered Effective
   of Precipitation         ------------------------------------------  
    in Any Month		Part of each	    Accumulated Total
			       inch increment
   ------------------------------------------------------------------------
        Inches                     Percent                Inches
          1 			      95		   0.95
          2			      90		   1.85
          3 			      82		   2.67
          4			      65		   3.32
          5			      45		   3.77
          6 			      25		   4.02
        Over 6			       5		   ----
   -----------------------------------------------------------------------

For an example, with an average monthly precipitation value of an inch and one-half at a weather station, the effective rainfall for the month would be 1.40 inches.

During some of the early months of the growing season, the effective rainfall may exceed the consumptive use yielding a negative value for irrigation requirement. In these cases, the consumptive irrigation requirement was assumed equal to zero.

At the start of the growing season, regardless of the beginning date, the amount of effective rainfall for the entire first month was subtracted from the consumptive use to determine consumptive irrigation requirement. This assumes that the precipitation prior to the start of the growing season is stored in the soil and is available to satisfy the requirements, At the end of the growing season, the fractional portion of the month within the growing season was multiplied by the effective rainfall and this value was subtracted from the estimated consumptive use.

Calculation of Consumptive Use
A computer program in Fortran IV for the Blaney-Criddle Method was written for the computer at the University of Wyoming. The program is included herein as Appendix 1.


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