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1 THE STATE OF WYOMING Water Development Office 6920 YELLOWTAIL ROAD TELEPHONE: (307) CHEYENNE, WY FAX: (307) TECHNICAL MEMORANDUM TO: Water Development Commission DATE: November 23, 2011 FROM: Dave K. Myer, P.E. REFERENCE: Snake/Salt River Basin Plan Update, 2012 SUBJECT: Tab VII (2012) Contents 1.0 Introduction Irrigation Zones Irrigated Acreage Irrigated Crops Climate Data Crop Irrigation Requirements Consumptive Use Effective Precipitation Crop Coefficients StateCU Model Results Irrigation Days Irrigation Diversions and Depletions Full-Supply Diversions for the Spreadsheet Models Supply-Limited Diversions Predicted by Spreadsheet Models References Appendix A: PRISM Climate Data for Hydrologic Model... i Appendix B: Comparisons to Previous Basin Plan... iv Appendix C: Diversion Data for Spreadsheet Models... ix 1.0 Introduction The purpose of this technical memorandum is to describe the methodology used to determine crop water requirements as part of the 2012 Snake/Salt River Basin Plan Update (2012 Update). Irrigation zones (or climate zones) created for this analysis are discussed, along with associated cropping patterns and climatic data. An overview of irrigated acres is presented, followed by a description of irrigation days. This memorandum concludes with an estimation of diversion data used as input to the spreadsheet models and a summary of the agricultural depletions. Results related to crop water requirement calculations are provided throughout the memorandum. The consumptive use methodology and data developed for the previous Snake/Salt River Basin Plan (previous Basin Plan) were used as a starting point for the 2012 Update (Sunrise, 2003). These methods and data were previously documented in : Basin Water Wyoming Water Development Office Page 1

2 Use Profile Agriculture (Sunrise, 2002a). The reader can refer to this memo for background information. The methodology and data used for the previous Basin Plan were reviewed to determine whether they could be implemented for this analysis. With the exception of additional acreage added to account for actively irrigated lands with the Greys River Sub-Basin, the tallies of irrigated acreages developed for the previous Basin Plan was found to be satisfactory for use in this update. Irrigation days established for the previous Basin Plan were also determined to be satisfactory. However, a departure involved the use of a different methodology to estimate crop irrigation requirements. For this study, StateCU was used. StateCU is a public domain model developed by the State of Colorado as part of Colorado s Decision Support System tools (State of Colorado, 2008). Overall, the objectives of the 2012 Update with regards to crop water requirements and the new study period of 1971 through 2010 involved the following: Gather and review information from the previous Basin Plan related to mapping and quantification of irrigated acreage and association to demand nodes in the spreadsheet models; update if necessary. Establish new irrigation zones that serve as a basis for obtaining representative climatic data. Confirm cropping patterns within each irrigation zone. Gather climatic data required for use in the StateCU model based on the irrigation zones. Prepare the required input files for use in the StateCU model and execute the model to determine crop irrigation requirements. Compile results into full-supply diversion data that can be used as input to the spreadsheet models. 2.0 Irrigation Zones For calculating crop water requirements, the previous Basin Plan utilized the following five irrigation zones that corresponded to sub-basins and climate stations located within or near each sub-basin: Upper Snake Lower Snake Upper Salt Lower Salt Teton This previous delineation of irrigation zones was reexamined with respect to the planned methodology for acquiring updated climatic data. The climate stations used in the previous Basin Plan were found to be somewhat limited in terms of available data and proximity to irrigated lands. Instead of relying on climate station data, a new approach was taken that involved accessing data-sets from the PRISM (Parameter-elevation Regressions on Independent Slopes Model) climate mapping system (Oregon State University, 2010). For information on PRISM and the techniques used to gather climate data for this study, refer to Appendix A. Wyoming Water Development Office Page 2

3 Since PRISM is a gridded data-set, data could be gathered for any point on the ground without regard for where the nearest climate station was. Therefore, two additional irrigation zones were able to be established for this study to represent the irrigated lands within the Hoback Sub-Basin and the Greys Sub-Basin. These new zones were established so that the unique locations and elevations of these lands could be better represented in terms of climatic data. For the 2012 Update, temperature, precipitation, and growing season data were collected using the PRISM data-sets for the following seven irrigation zones established as part of this study: Zone 1: Teton Zone 2: Upper Snake Zone 3: Lower Snake Zone 4: Hoback Zone 5: Lower Salt Zone 6: Upper Salt Zone 7: Greys Figure 1 shows the irrigated lands within the entire Snake/Salt Basin, distinguished by the seven irrigation zones. Wyoming Water Development Office Page 3

4 Figure 1: Snake/Salt Basin Irrigation Zones Wyoming Water Development Office Page 4

5 3.0 Irrigated Acreage The final quantification of irrigated acreage determined during the 2012 Update is presented in Table 1. The table shows the irrigated acreage by sub-basin and also tallies the acreages by the new irrigation zones that were established for this analysis. With the exception of the Teton Sub-Basin, which was not analyzed in the spreadsheet models, these acreages correspond with those used in the analysis of crop water requirements and subsequent input to the spreadsheet models. For further information on the quantification of irrigated lands for this study, refer to, Tab VI: Irrigated Acreage. Table 1: Irrigated Acreages for the 2012 Update 2012 Description Acreages Sub-Basin Irrigation Zone Salt (excluding Greys Sub-Basin) 65,190 Snake (including Hoback Sub-Basin) 28,963 Teton 4,647 Greys 229 Total 99,029 Zone 1: Teton 4,647 Zone 2: Upper Snake 6,967 Zone 3: Lower Snake 18,017 Zone 4: Hoback 3,979 Zone 5: Lower Salt 33,810 Zone 6: Upper Salt 31,380 Zone 7: Greys 229 Total 99, Irrigated Crops The types of crops grown in the Snake/Salt Basin are greatly influenced by climate. Typical farmland in the basin is located in the high mountain valleys with low to moderate precipitation. These valleys have short growing seasons and long winters with significant accumulations of snow. Hard frosts have been observed in every month of the year. Because of these conditions, typical crops consist of alfalfa, small grains (mainly barley with some oats), native hay and grass. Cropping patterns for the Snake/Salt River Basin were compiled in the previous Basin Plan as previously described in : Cropping Patterns in the Basin (Sunrise, 2002b). Additional information was also presented in : Basin Water Use Profile Agriculture (Sunrise, 2002a). As part of the 2012 Update, cropping patterns were reexamined to ascertain any changes from the previous Basin Plan. Information was solicited from various state hydrographers within the Snake/Salt Basin to confirm the distribution of crops grown in each of the irrigation zones. The estimates obtained were based on their knowledge of the area and of the crops grown by various producers. Given the hydrographers responses, cropping mixes assumed for this study were similar to those used in the previous Basin Plan and consisted of alfalfa, small grains, pasture grass, and mountain meadow hay. The distinction between grass pasture and mountain meadow hay is based on the method of irrigation, with grass pasture being sprinkler irrigated and mountain meadow hay being flood irrigated. It is important to note that in some locations, crops Wyoming Water Development Office Page 5

6 are rotated between alfalfa and small grains, and that the acreage of each crop will vary somewhat each season. The resulting distribution of crops by irrigation zone is presented in Table 2. Visual depictions of the cropping patterns are shown on Figures 2 and 3 with Figure 3 showing the cropping distribution as related to acreages. Note that for the purpose of relating these crops to cropping coefficients, mountain meadow hay was simulated as Grass Pasture TR-21 in the StateCU model, and grain was simulated as Spring Grain TR-21. Table 2: Crop Distribution by Irrigation Zone Irrigation Zone Alfalfa Grain 1 Grass Mtn. Meadow Pasture 2 Hay 3 Zone 1: Teton 40% 30% 30% -- Zone 2: Upper Snake % Zone 3: Lower Snake % 98% Zone 4: Hoback % Zone 5: Lower Salt 58% 25% 12% 5% Zone 6: Upper Salt 50% 18% 24% 8% Zone 7: Greys % 1. Grain simulated as Spring Grain TR-21 in StateCU model. 2. Grass pasture is sprinkler irrigated. 3. Mountain meadow hay is flood irrigated; simulated as Grass Pasture TR-21 in StateCU model. Wyoming Water Development Office Page 6

7 100% 90% 80% 30% 5% 12% 8% 24% 70% 25% 60% 50% 30% 100% 98% 100% 18% 100% 40% 30% 20% 40% 58% 50% 10% 0% Zone 1 Teton Zone 2 Upper Snake Zone 3 Lower Snake Zone 4 Hoback Figure 2: Crop Distribution by Irrigation Zone 2% Zone 5 Lower Salt Zone 6 Upper Salt Alfalfa Grain Grass Pasture Mountain Meadow Hay Zone 7 Greys Wyoming Water Development Office Page 7

8 35,000 1,691 30,000 4,057 2,510 25,000 8,453 7,531 20,000 5,648 15,000 10,000 17,657 19,610 15,690 5, ,394 1,394 1,859 Zone 1 Teton 6,967 Zone 2 Upper Snake Zone 3 Lower Snake Zone 4 Hoback Figure 3: Crop Distribution as Related to Acreage 360 3,979 Zone 5 Lower Salt Zone 6 Upper Salt Alfalfa Grain Grass Pasture Mountain Meadow Hay 229 Zone 7 Greys 5.0 Climate Data This section presents a summary of the climate data collected for the 2012 Update in terms of the requirements of StateCU. Climate data were obtained for each irrigation zone from the PRISM data-sets as described in, Tab XVI: Climate. Within the study period of 1971 through 2010, climate requirements for the StateCU model consist of monthly average temperature and precipitation data for each irrigation zone. The following frost conditions were also required for each irrigation zone. These frost dates specify the beginning and end of each growing season. Within the model, each individual crop can be assigned one of these conditions. For instance, the growing season for alfalfa ends on the first fall 28 degree F. day, while spring grain ends its growing season on the first fall 32 degree F. day. Last spring 28 degree F. day Last spring 32 degree F. day First fall 32 degree F. day First fall 28 degree F. day Within the expressed terms of the modified Blaney-Criddle formula, which was chosen for use in the consumptive use analysis, percent daylight is also required. Data for percent daylight is hard-coded within the StateCU program. The values used in the model s calculations are based Wyoming Water Development Office Page 8

9 on the average latitude of each irrigation zone that is input by the user. For each irrigation zone, the average latitude is presented in Table 3. The table also shows the average elevation of each zone, which is also required input to the StateCU model. These average latitudes and elevations were extracted from GIS mapping of the irrigated lands. Table 3: Average Latitude and Elevation of Irrigation Zones Average Latitude Average Elevation Irrigation Zone (decimal degrees) (ft) Zone 1: Teton Zone 2: Upper Snake Zone 3: Lower Snake Zone 4: Hoback Zone 5: Lower Salt Zone 6: Upper Salt Zone 7: Greys Figures 4 and 5 illustrate the average monthly temperature and precipitation data, respectively, that were obtained from the PRISM data-sets for each irrigation zone within the study period ( ). Figure 6 illustrates the average historic frost dates by irrigation zone, including the last spring 28- and 32- F. degree dates and the first fall 32- and 28 F. degree dates Temperature ( F) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Zone 1: Teton Zone 2: Upper Snake Zone 3: Lower Snake Zone 4: Hoback Zone 5: Lower Salt Zone 6: Upper Salt Zone 7: Greys Figure 4: Average Monthly Temperatures by Irrigation Zone Wyoming Water Development Office Page 9

10 Precipitation Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Zone 1: Teton Zone 2: Upper Snake Zone 3: Lower Snake Zone 4: Hoback Zone 5: Lower Salt Zone 6: Upper Salt Zone 7: Greys Figure 5: Average Monthly Precipitation by Irrigation Zone Wyoming Water Development Office Page 10

11 Figure 6: Average Historic 28 and 32 Degree F. Frost Dates by Irrigation Zone 6.0 Crop Irrigation Requirements Crop irrigation requirement (CIR) (also called irrigation water requirement (IWR)) is the amount of water required from surface or ground water diversions to meet crop consumptive needs. It is calculated as crop consumptive use (CU) minus the amount of water contributed by precipitation during the growing season (effective precipitation) as follows: CIR = CU Re Equation 1 where, CIR = crop irrigation requirement CU = crop consumptive use (or crop evapotranspiration) Re = effective precipitation In the previous Basin Plan, CIR data were obtained from the publication, Consumptive Use and Consumptive Irrigation Requirements in Wyoming (Pochop, 1992). CIR values in this publication were based on climatic data within a study period that ended in However, the study period for the 2012 Update extended through the year Therefore, in order to derive CIR estimates based on climatic data that represented the entire study period, this analysis departed from the use of the Pochop data. Wyoming Water Development Office Page 11

12 For the 2012 Snake/Salt River Basin Plan Update, StateCU was used for estimating crop irrigation requirements. StateCU is a public domain model developed by the State of Colorado as part of Colorado s Decision Support System (CDDS) tools. The StateCU program can use diversion data, irrigated acreage, and crop types to estimate the amount of water that is consumptively used by the crop for its representative diversion and time period (State of Colorado, 2008). StateCU allows several levels of analysis, including the following: Crop Irrigation Water Requirement by CU Location (a Climate Station Scenario) Water Supply Limited Crop Consumptive Use by Structure (a Structure Scenario) A Climate Station Scenario calculates crop consumptive use and irrigation water requirements based on user inputs primarily consisting of climatic and crop type data. A Structure Scenario offers a more complex level of analysis, requiring historic diversion data as input. Since comprehensive diversion data are not available within the Snake/Salt Basin, a Climate Station Scenario was used for this study. The lack of diversion records was documented in the previous Basin Plan, : Basin Water Use Profile Agriculture (Sunrise, 2002a). For the Climate Station Scenario, a total of seven CU Locations were defined, each corresponding to one of the seven irrigation zones. For each CU Location, StateCU output consisted of monthly values for consumptive use, effective precipitation, and crop irrigation requirement through every year within the study period of 1971 through Input to the StateCU model is stored in a number of properly formatted, text-based files. The majority of these required files were custom-created for this study, although two of the files pertaining to standard Blaney-Criddle crop coefficients and characteristics were obtained from modeling data-sets available on Colorado s Decision Support System website (State of Colorado, 2011). A summary of the StateCU input files created for this analysis is presented in Table 4. Wyoming Water Development Office Page 12

13 Table 4: StateCU Required Input Files File Type File Name Description 1 Contains the names of input data files StateCU Response SnakeSalt_Response.rcu required to run the model. Contains information to control the model Model Control SnakeSalt_Control.ccu simulation. Provides climate station location Climate Station Information 2 SnakeSalt_ClimateStation.cli information. Provides information on StateCU Scenario Structure Location SnakeSalt_Structure.str type selected. Contains monthly average temperatures for Monthly Temperature SnakeSalt_Temp.tem each climate station for study period years. Contains total monthly precipitation for each Monthly Precipitation SnakeSalt_Precip.prc climate station for study period years. Contains required information on frost dates Frost Date SnakeSalt_Frost.fd for each climate station. Provides info on planting, harvesting, and Crop Characteristics 3 SnakeSalt_CropChar.cch root depth for each crop type. Provides the crop coefficient curves for the Blaney-Criddle Crop Coefficients 3 SnakeSalt_Coeffients.kbc SCS modified Blaney-Criddle method. Contains the total acreage (or percentage) of Crop Distribution SnakeSalt_CropDistribution.cds crops for each climate station. 1. Descriptions as provided by StateCU Documentation (State of Colorado, 2008). 2. Climate stations are synonymous with irrigation zones in this study. 3. File sourced from CDSS website (State of Colorado, 2011). It should be noted that the previous Basin Plan determined CIR values for three hydrologic conditions: dry, average, and wet years. For this study, however, only a single set of values was determined, corresponding to monthly CIR values averaged across the entire study period. This set of CIR values was used to derive the full-supply diversion data for input to all three of the spreadsheet models. The elimination of the dry, average, and wet year CIR classifications for this study was based on rational that was developed during the Wind/Bighorn River Basin Plan Update of 2010 which stated the following: As with the previous Basin Plan, because climatic dry, average and wet periods in summer months during irrigation are often different than the dry, average and wet periods in the winter that produce runoff, the average CIR was used in the hydrologic model for years in all three hydrologic conditions. This assumption should be reasonable as the hydrologic year designations used for the hydrologic components of the model are based on streamflow, which typically depends on winter moisture, whereas crop irrigation requirements are dependent upon summer temperature and moisture, which may not correlate directly with winter precipitation. (MWH, 2010) Crop irrigation requirements determined in this analysis are provided in Section 6.4. Wyoming Water Development Office Page 13

14 6.1 Consumptive Use Consumptive use (also called evapotranspiration (ET)) is defined as the total amount of water that would be used for crop growth if provided with an ample water supply. Monthly evapotranspiration was estimated within the StateCU model using the SCS TR-21 modified Blaney-Criddle method described by the following equation (SCS, 1970): ET P = Kc Kt t Equation 2 where, ET = evapotranspiration (or monthly consumptive use) (inches) Kc = monthly crop growth stage coefficient Kt = climatic coefficient: t t = mean monthly temperature ( F) P = monthly percentage of annual daylight hours The Blaney-Criddle approach to determine crop evapotranspiration is widely used due to its limited climate data requirements. Blaney-Criddle only requires average monthly temperature, whereas other methods may require daily parameters such as temperature, precipitation, wind speed, vapor pressure, and solar radiation. Mean monthly temperature data were obtained from the PRISM data-sets as described in Section 5.0. Crop coefficients (Kc) used in this analysis are described in Section 6.3. Values for the monthly percentage of annual daylight hours are calculated within the StateCU model based on the average latitude of each CU Location, or in this case, irrigation zone. (Refer to Table 2.) Consumptive use values determined in this analysis are provided in Section Effective Precipitation Effective precipitation is that portion of the total precipitation that satisfies or reduces crop consumptive use requirements. The remainder of the rainfall is lost either by deep percolation below the root zone, surface runoff, or direct evaporation of water intercepted by the plant foliage. This lost rainfall is not considered effective in reducing the CU requirements. Therefore, the rainfall that can be effectively used by the crops is dependent upon the amount, timing, and intensities of the rainfall, soil permeability, the soil s water-holding capacity, runoff characteristics, and the rate of crop evapotranspiration. In order to determine the amount of irrigation water that the crop actually needs, it is important to estimate the portion of monthly precipitation that the plants can directly use. For this study, effective precipitation was estimated within the StateCU model by employing the widely used USDA-SCS technique described by the following equation: Wyoming Water Development Office Page 14

15 Re = ( ) ( Rt ) ( 10 CU ) F where, Re = monthly effective precipitation (inches) Rt = monthly total precipitation (inches) CU = monthly crop consumptive use (inches) F = D D D 3 where, D = normal depth of application, assumed to be 3.0 inches Equation 3 Monthly total precipitation data were obtained from the PRISM data-sets as described in Section 5.0. Effective precipitation values determined in this analysis are provided in Section Crop Coefficients Ideally, locally developed crop coefficients are used in the Blaney-Criddle method. Since these were not available for the Snake/Salt River Basin, the standard Soil Conservation Service (SCS) TR-21 crop coefficients were used (SCS, 1970). (The Soil Conservation Service is now known as the Natural Resources Conservation Service (NRCS).) Within the StateCU model, the Blaney-Criddle crop coefficient input file (*.kbc) contains the crop coefficient curves for the modified Blaney-Criddle method. Section 4.0 defined the crop mix for this analysis. For the purpose of relating these crops to an SCS TR-21 coefficient, mountain meadow hay was simulated as Grass Pasture TR-21, and grain was simulated as Spring Grain TR-21. Within the model, both grass pasture and mountain meadow hay are defined as perennial crops, while spring grain is defined as an annual crop. Temporal variations in crop coefficients for perennial crops are defined by the day of the year; crop coefficients for the annual crop is defined by the percent of growing season. The crop coefficients used in this analysis are presented in Table 5. Wyoming Water Development Office Page 15

16 Table 5: TR-21 Crop Coefficients used in the StateCU Model Perennial Crops Annual Crop Day of Grass Percent of Alfalfa Year Pasture Growing Season Spring Grain Jan Jan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec Dec StateCU Model Results Results from the StateCU model are presented in this section as monthly averages over the study period. Figure 7 displays the monthly crop irrigation requirements for each irrigation zone. Table 6 summarizes the monthly consumptive use, effective precipitation, and crop irrigation requirement by irrigation zone. Refer to Appendix B for a comparison of these results to those reported in the previous Basin Plan. Wyoming Water Development Office Page 16

17 6 5 4 CIR Apr May Jun Jul Aug Sep Oct Zone 1: Teton Zone 2: Upper Snake Zone 3: Lower Snake Zone 4: Hoback Zone 5: Lower Salt Zone 6: Upper Salt Zone 7: Greys Figure 7: Monthly Crop Irrigation Requirement by Irrigation Zone Wyoming Water Development Office Page 17

18 Table 6: Consumptive Use (CU), Effective Precipitation (Re), and Crop Irrigation Requirement (CIR) by Irrigation Zone Month CU Zone 1: Teton Zone 2: Upper Snake Zone 3: Lower Snake Zone 4: Hoback Re CIR CU Re CIR Apr May Jun Jul Aug Sep Oct Annual (cont d) Month CU Zone 5: Lower Salt Zone 6: Upper Salt Zone 7: Greys Monthly Total Re CIR CU Re CIR Apr May Jun Jul Aug Sep Oct Annual CU CU Re Re CIR CIR CU CU Re Re CIR CIR Wyoming Water Development Office Page 18

19 7.0 Irrigation Days By estimating the number of days irrigation takes place in the basin, the effects of being short of water in a particular sub-basin are taken into account. Also, the period of time when irrigation is stopped to harvest crops is counted. For example, fields under flood irrigation must have the water shut off for a number of days in order to let the ground dry for harvest. However, areas under sprinkler irrigation experience very little down time as many will have the sprinklers back on one side of the field before the harvest is completed on the other. In the previous Basin Plan, the number of days in which crops were irrigated was determined for each sub-basin. The main source of data for irrigation days was conversations with various state hydrographers. (Refer to documentation in the previous Basin Plan, : Basin Water Use Profile Agriculture (Sunrise, 2002a.)) For the 2012 Update, information presented for irrigation days from the previous Basin Plan was reviewed and determined to be satisfactory for use again in this analysis. Irrigation days used in this study for the seven irrigation zones are shown in Table 7. Wyoming Water Development Office Page 19

20 Table 7: Irrigation Days by Irrigation Zone Irrigation Days in Month Zone Month Zone 2: Upper Snake Zone 3: Lower Snake Zone 1: Teton Zone 5: Lower Salt Zone 6: Upper Salt Zone 4: Hoback Zone 7: Greys Irrigation Days Fraction 1 Apr May Jun Jul Aug Sep Oct Apr May Jun Jul Aug Sep Oct Apr May Jun Jul Aug Sep Oct Apr May Jun Jul Aug Sep Oct Fraction of Month Irrigated = Irrigation Days / Days in Month In the previous Basin Plan, the number of irrigation days was estimated for three hydrologic conditions: dry, average, and wet years. However, for the purpose of this analysis within the spreadsheet models, the number of irrigation days for average hydrologic condition was used in the dry and wet year models as well as the average year. The rationale for this approach was that the number of irrigation days in historically dry years does not represent demand. In other words, irrigators may have been shorted and would have taken more water if it had been available, and it was important for the spreadsheet models to simulate this. Essentially, within Wyoming Water Development Office Page 20

21 the spreadsheet models, irrigation is cut off when streams go dry so shortages can be estimated. This same approach was taken for the 2012 Update. In other words, the number of irrigation days established for an average hydrologic condition in the previous Basin Plan was used again in this analysis to derive the full-supply diversion data for the dry, average, and wet year spreadsheet models. The number of irrigation days within the Hoback and Greys irrigation zones was assumed to be equal to those determined in the previous Basin Plan for the Upper Snake Sub-Basin. This assumption was deemed appropriate given the similarities in elevation and cropping patterns within these sub-basins. 8.0 Irrigation Diversions and Depletions Because actual diversion records were unavailable within the Snake/Salt River Basin, the spreadsheet models simulate the depletions, that is, the consumptive portion of the diversion being taken from the stream. Since the model treats this quantity as if it was the diverted amount, and for consistency with other basin spreadsheets, this document refers to this information as diversion data or full-supply diversions although it is a depletion quantity. On the other hand, supply-limited consumptive use or supply-limited diversions, which can also be considered a depletion quantity, is ultimately determined in the spreadsheet models. Subject to available water supply, the supply-limited consumptive use may be less than the fullsupply diversion amounts requested in the spreadsheet models. (Refer to Section 8.2.) Agricultural irrigation depletions, synonymous with diversion quantities input to the Snake/Salt Basin spreadsheet models, consist of the water supplied by artificial means that is consumed by irrigated crops. This is water required by the plants beyond natural precipitation. As depicted in Equation 4, the determination of irrigation depletions consisted of taking the monthly CIR for each irrigation zone (weighted by crop type) and multiplying that value by the number of irrigated acres. This monthly result was then adjusted based on the number of days irrigated for each month, resulting in the irrigation depletion, or in the case for input to the Snake/Salt Basin spreadsheet models, full-supply diversions. Diversion = CIR Acres Fraction Equation 4 where, Diversion = irrigation depletion quantity (acre-feet per month) CIR = crop irrigation requirement (feet per month) Areas = number of irrigated acres Fraction = fraction of month irrigated Resulting irrigation depletions (or full-supply diversions within the spreadsheet models) for each irrigation zone are summarized in Table 8. As indicated in the table, the total annual irrigation depletion equates to 84,671 acre-feet. This constitutes a reduction of approximately 18,000 acrefeet from the previous Basin Plan. A discussion and comparison of the results of this study to those reported in the previous Basin Plan is presented in Appendix B. Wyoming Water Development Office Page 21

22 Table 8: Irrigation Depletions, or Full-Supply Diversions 1 (Acre-Feet) Irrigation 2012 April May June July August September October Zone Acres Zone 1: Teton 2 4, ,006 1, ,908 Zone 2: Upper Snake 6, ,333 1,917 1, ,531 Zone 3: Lower Snake 18, ,367 4,211 5,703 4,560 1, ,694 Zone 4: Hoback 3, , ,060 Zone 5: Lower Salt 33, ,548 12,025 5, ,860 Zone 6: Upper Salt 31, ,358 7,890 10,576 5,330 1, ,434 Zone 7: Greys Total Total 99, ,888 23,801 33,274 19,035 4, , Irrigation depletions represented in this table are synonymous with the full-supply diversion quantities input to the spreadsheet models. The values in the table, however, do not represent supply-limited depletions, which are ultimately determined by the spreadsheet models for dry, average, and wet hydrologic conditions. (Refer to Section 8.2.) 2. Note that the Teton Sub-Basin is not represented in the spreadsheet models. Wyoming Water Development Office Page 22

23 8.1 Full-Supply Diversions for the Spreadsheet Models To generate the full-supply diversion data for entry into the spreadsheet models, Equation 4 was applied to each model node. As presented in, Tab VI: Irrigated Acreage, every model node was associated with an acreage it is meant to represent. Each node was also associated to an irrigation zone for the purpose of relating it to a cropping pattern, crop irrigation requirements, and irrigation days. Calculations to obtain diversion quantities for each model node were performed in the hydrologic database as described in, Tab IX: Spreadsheet Models and Hydrologic Database. As within the previous Basin Plan, the Teton Sub-Basin was not analyzed within a spreadsheet model. Therefore, no model nodes exist. Flows within the Teton Sub-Basin are not hydraulically connected to flows in the mainstem of the Snake or Salt Rivers. Also, its basin area is relatively small when compared to the Snake and Salt River Basins. Water resources planning and management are less complex, and therefore, the development of a spreadsheet model for the Teton Sub-Basin was not warranted. However, crop water requirements and depletions for the Teton Sub-Basin are as reported within this memorandum. Appendix C presents the diversion data that were used as input to the Snake and Salt Basin spreadsheet models. To reiterate, unlike the previous Basin Plan, this study did not separate the crop water requirement calculations into dry, average, and wet year hydrologic conditions. Consequently, the same diversion data were used in dry, average, and wet year spreadsheet models. 8.2 Supply-Limited Diversions Predicted by Spreadsheet Models For comparisons between the full-supply diversions and the supply-limited diversions determined in the 2012 Update, the supply-limited diversions (or supply-limited consumptive use) as determined by the spreadsheet models are summarized in Table 9. For the Snake River Basin, the spreadsheet models predicted that the full-supply diversions were met for each hydrologic condition. In other words, the supply-limited diversions were equal to the requested full-supply diversions for the dry, average, and wet year simulations. In the Salt River Basin spreadsheet models, however, the requested full-supply diversions were only met during a wet year. Results of the dry year spreadsheet model indicated shortages in the Dry Creek and Toms Creek tributary reaches. In the dry year simulation, irrigation diversions on Dry Creek requested 2,865 AFY but were only supplied 2,627, resulting in an annual shortage of 238 AFY. In Toms Creek, irrigation diversions requested 1,005 AFY but were only supplied 884 AFY, resulting in an annual shortage of 120 AFY. Results of the average year spreadsheet model for the Salt River Basin indicated a shortage in Toms Creek where irrigation diversions requested 1,005 but were only supplied 989 AFY, yielding an annual shortage of 16 AFY. Wyoming Water Development Office Page 23

24 Table 9: Supply-Limited Diversions as Predicted by the Spreadsheet Models Spreadsheet Model 1 Dry Year Average Year Wet Year (AFY) (AFY) (AFY) Snake River Basin 26,284 26,284 26,284 Salt River Basin 54,120 54,463 54,479 Total 80,404 80,747 80, Note that the Teton Sub-Basin is not represented in the spreadsheet models. Wyoming Water Development Office Page 24

25 References MWH. Wind/Bighorn River Basin Plan. : Task 3A Agricultural Water Use ( May 16, Oregon State University. PRISM Climate Group ( Pochop, Larry. Teegarden, Travis. Kerr, Greg. Delaney, Ronald. Hasfurther, Victor. Consumptive Use and Consumptive Irrigation Requirements in Wyoming. University of Wyoming Cooperative Extension Service and Wyoming Water Research Center. WWRC Publication # Soil Conservation Service (SCS). Irrigation Water Requirements Technical Release No. 21. April, 1967, revised September, State of Colorado. Colorado s Decision Support System (CDSS), StateCU Documentation. StateCU Interface Version 7.0, StateCU Fortran Version September, State of Colorado. Colorado s Decision Support System website ( Sunrise Engineering, Inc. Snake/Salt River Basin Plan. : Basin Water Use Profile Agriculture ( August 23, 2002(a). Sunrise Engineering, Inc. Snake/Salt River Basin Plan. : Cropping Patterns in the Basin ( July 29, 2002(b). Sunrise Engineering, Inc. Snake/Salt River Basin Plan, Final Report. ( June, Wyoming Water Development Office Page 25

26 APPENDIX A PRISM CLIMATE DATA FOR HYDROLOGIC MODEL

27 Appendix A: PRISM Climate Data for Hydrologic Model Introduction Online, map-based applications have experienced an explosion in popularity over the past decade. The success of these systems is largely due to their ability to provide a spatial framework for data exploration and for the visual context (e.g., satellite images) they offer. Detailed here is the ongoing development of new online mapping tools that will assist hydrologic modelers retrieve climate data used for the StateMod and StateCU type Decision Support Models for surface water modeling. Known as the Wyoming PRISM Climate Data Server, this web-mapping application uses modeled GIS climate data in a Google Map platform to provide "one-stop-shopping" for key climate datasets. While capitalizing on the success of previous online mapping efforts (i.e. the Wyoming Water and Climate Map Server), WRDS has developed a new suite of climate data retrieval tools that highlight the potential for additional applications and functionality. Moving beyond the simple viewing of maps and data, improvements to this system now allow users to download point-specific gridded PRISM climate data for use in an array of applications. This Technical memorandum focuses on the use of PRISM Climate Data ( in the StateCU Consumptive Use Model. PRISM Climatological Data PRISM climate data, provided by Oregon State University ( uses point measurements of precipitation, temperature, and other climatic variables to produce continuous, digital 4km x 4km grid estimates of monthly, yearly, and event-based climatic parameters from 1895 through Using a routine to query a specific PRISM raster cell, this application retrieves monthly and annual climate data for mean, maximum, minimum, and dewpoint temperature and precipitation data for any point in the continental U.S. from 1895 to These data are returned to a user in a separate browser window in a delimited format that can be copied to a user-preferred database or spreadsheet (Figure A1). Climate Data Tools for Streamflow Modeling As part of the River Basin Planning process sponsored by the Wyoming Water Development Commission (WWDC), streamflow models for each of Wyoming s seven river basins (Bear, Green, Platte, Snake/Salt, Powder/Tongue, Northeast, and Wind/Bighorn) have been developed over the past decade ( These spreadsheet models were used to estimate water usage, and thus the remaining available water for development, throughout a river basin during dry, average, and wet years. The manner in which these spreadsheets modeled available water was limited and newer modeling software based on StateMod type simulation models are now being used during the updates to the river basin plans (for more information visit As Wyoming updates the available streamflow for each river basin using the StateCU program (software developed by the State of Colorado used to estimate historical consumptive use based on user input data such as Wyoming Water Development Office Appendix A Page i

28 water supply, cropping, and climate data), consumptive use becomes an important input variable that, itself, must be calculated. Crop consumptive use and return flows must be calculated as part of the modeling effort. Crop consumptive use calculated by StateCU is that portion of the diverted water the crop uses. Return flows are waters that are diverted but not used by the crop and returned to the source. The StateCU model is now being used as the method for determining both crop and non-crop consumptive use in the Snake/Salt River Basin in northwest Wyoming. The StateCU model requires basic weather station information such as latitude and elevation in addition to climatic inputs such as average monthly precipitation, monthly mean temperature, and the dates of first and last frost/freeze (defined in the model as the dates of the first Fall temperatures less than 32F and 28F and last Spring temperatures below 28F and 32F). Unfortunately, modelers are limited to using weather station data that may not be representative of the area or which may be incomplete or inadequate records in the area of interest. Modelers must extrapolate weather station data using precipitation and temperature correction factors for use at specific points. The development of gridded PRISM data and the new data tools created by WRDS allows a user to select a specific, relevant point on a map (away from any weather stations) and retrieve all of the necessary climate data, in the necessary format, for the StateCU model. In the Snake/Salt River Basin, seven groups of irrigated lands were identified as being in similar geographic locations, therefore the center points of these seven groups were selected to view the climate parameters required for the model. Climate data from each of the seven groups were extracted and inputted to the StateCU model. Future Use Now that this climate data retrieval tool is available online and as the WWDO continues to update hydrological models in the state s river basins, this application can serve as a short-cut for modelers to obtain climate data. References Oregon State University. PRISM Climate Group ( Wyoming Water Development Office Appendix A Page ii

29 Wyoming Water Development Office Appendix A Page iii

30 APPENDIX B COMPARISONS TO PREVIOUS BASIN PLAN

31 Appendix B: Comparisons to Previous Basin Plan Appendix B presents a comparison of the crop irrigation requirements and agricultural depletions (or full-supply diversions) results of this study to those reported in the previous Basin Plan, : Basin Water Use Profile Agriculture (Table 3, page 4) (Sunrise, 2003). For each irrigation zone, a series of charts (Figure B1) illustrate the comparison of crop irrigation requirements. Annual CIR values are presented on each chart. For the Teton, Lower Salt, and Upper Salt irrigation zones, CIR values compare reasonably well, despite the occurrence of some lagging. However, an overall decrease in CIR values is evident in the Upper Snake, Lower Snake, Hoback, and Greys irrigation zones. This reduction can most likely be attributed to the different methodologies used to estimate CIR, updated climatic data, and the changes made to the delineation of irrigation zones for the 2012 Update. It should be noted that that the Hoback and Greys irrigation zones were compared against the Lower Snake and Lower Salt CIR values, respectively, that were presented in the previous Basin Plan. In the previous Basin Plan, irrigated lands within the Hoback Sub-Basin were assumed to have the same climatic data that were gathered for the Lower Snake Sub-Basin, and irrigated lands within the Greys Sub-Basin were not analyzed. For the 2012 Update, the Hoback and Greys Sub-Basins were treated as individual irrigation (climate) zones. Separate climatic data were gathered for each of these which resulted in a more realistic CIR estimation, better representing the increased precipitation and shorter growing seasons that occur in the higher elevations of these zones. The reduction in CIR values is also reflected in the decrease in agricultural depletions as summarized in Table B1 and illustrated on Figure B2. Excluding the Greys River Sub-Basin, the total annual depletions determined in this study amount to 84,487 acre-feet, a decrease of approximately 18,000 acre-feet from the previous Basin Plan. The majority of this difference is evident in the Lower Snake Sub-Basin. It should be noted that for direct comparison to the depletion data that were presented in the previous Basin Plan, the 2012 depletion values for the Hoback and Lower Snake irrigation zones are combined in the tabulations presented for the Lower Snake Sub-Basin. Since irrigation in the Greys Sub-Basin was not analyzed in the previous Basin Plan, no comparisons are offered in terms of depletions. Figure B1: Crop Irrigation Requirements by Irrigation Zone, Comparisons to Previous Basin Plan Table B1: Irrigation Depletions, or Full-Supply Diversions, by Sub-Basin, Comparison to Previous Basin Plan (Acre-Feet) Figure B2: Irrigation Depletions, or Full-Supply Diversions, by Sub-Basin, Comparison to Previous Basin Plan Wyoming Water Development Office Appendix B Page iv

32 Figure B1: Crop Irrigation Requirements by Irrigation Zone, Comparisons to Previous Basin Plan Zone 1: Teton 2012 Annual CIR = in 2003 Annual CIR = 13.4 in Zone 3: Lower Snake 2012 Annual CIR = in 2003 Annual CIR = in CIR 3.00 CIR Apr May Jun Jul Aug Sep Oct 0.00 Apr May Jun Jul Aug Sep Oct 2012 CIR 2003 CIR (Avg. Year) 2012 CIR 2003 CIR (Avg. Year) Zone 2: Upper Snake 2012 Annual CIR = in 2003 Annual CIR = in Zone 4: Hoback 2012 Annual CIR = in 2003 Annual CIR = in CIR CIR Apr May Jun Jul Aug Sep Oct 0.00 Apr May Jun Jul Aug Sep Oct 2012 CIR 2003 CIR (Avg. Year) 2012 CIR 2003 CIR (Avg. Year) (Lower Snake) Wyoming Water Development Office Appendix B Page v

33 Zone 5: Lower Salt 2012 Annual CIR = in 2003 Annual CIR = in Zone 7: Greys 2012 Annual CIR = in 2003 Annual CIR = in CIR 3.00 CIR Apr May Jun Jul Aug Sep Oct 0.00 Apr May Jun Jul Aug Sep Oct 2012 CIR 2003 CIR (Avg. Year) 2012 CIR 2003 CIR (Avg. Year, Lower Salt) Zone 6: Upper Salt 2012 Annual CIR = in 2003 Annual CIR = in CIR Apr May Jun Jul Aug Sep Oct 2012 CIR 2003 CIR (Avg. Year) Wyoming Water Development Office Appendix B Page vi

34 Table B1: Irrigation Depletions, or Full-Supply Diversions, by Sub-Basin, Comparison to Previous Basin Plan (Acre-Feet) Sub-Basin April May June July Teton ,006 1,441 1,951 1,699 Upper Snake ,333 2,605 1,917 2,744 Lower Snake (includes Hoback) 0 0 1,539 3,619 4,982 9,307 6,739 9,764 Lower Salt (excluding Greys) ,812 8,548 11,213 12,025 12,244 Upper Salt (excluding Greys) 9 0 1,358 3,990 7,890 10,916 10,576 10,660 Total 9 0 3,880 9,979 23,759 35,482 33,209 37,111 Sub-Basin (cont d) August September October Total Teton ,908 4,036 Upper Snake 1,556 1, ,531 8,029 Lower Snake (includes Hoback) 5,393 6,586 1, ,754 29,577 Lower Salt (excluding Greys) 5,863 4, ,860 29,785 Upper Salt 5,330 5,127 1, ,434 30,987 Total 18,983 18,861 4, , ,414 Sub-Basin (cont d) 2012 Difference from 2003 Teton -128 Upper Snake -2,498 Lower Snake (includes Hoback) -8,823 Lower Salt (excluding Greys) -1,925 Upper Salt -4,553 Total -17,927 Wyoming Water Development Office Appendix B Page vii

35 14,000 12,000 11,213 10,916 12,025 10,576 12,244 10,660 Agricultural Depletions (Acre-Feet) 10,000 8,000 6,000 4,000 2, ,539 1,358 1, ,619 3,990 8,548 7,890 1,006 1,333 4,982 1,441 2,605 9,307 6,739 9,764 6,586 1,951 1,917 1,699 2, ,556 April May June July August September October Teton Upper Snake Lower Snake (includes Hoback) Lower Salt (excluding Greys) Upper Salt (excluding Greys) Figure B2: Irrigation Depletions, or Full-Supply Diversions, by Sub-Basin, Comparison to Previous Basin Plan 5,393 5,863 5, ,947 4,427 5, , , Wyoming Water Development Office Appendix B Page viii

36 APPENDIX C DIVERSION DATA FOR SPREADSHEET MODELS

37 Appendix C: Diversion Data for Spreadsheet Models Based on the methodology described in this memorandum, Appendix C presents the full-supply diversion data that were used as input to the Snake and Salt River Basin spreadsheet models. Only those model nodes that were assigned a diversion are represented in the tables. Because actual diversion records were unavailable within the Snake/Salt River Basin, the spreadsheet models simulate the depletions, that is, the consumptive portion of the diversion being taken from the stream. Since the model treats this quantity as if it was the diverted amount, and for consistency with other basin spreadsheets, this document refers to this information as diversion data or full-supply diversions although it is a depletion quantity. Note that unlike the previous Basin Plan, the 2012 Update did not separate the crop water requirement calculations into dry, average, and wet year hydrologic conditions. Consequently, the same diversion data were used for the dry, average, and wet year spreadsheet models. Table C1: Model Node Full-Supply Diversions for the Snake River Basin Spreadsheet Models (Acre-Feet) Table C2: Model Node Full-Supply Diversions for the Salt River Basin Spreadsheet Models (Acre-Feet) Wyoming Water Development Office Appendix C Page ix