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MEMORANDUM December 13, 2013 Issues with Selecting an Appropriate Crop Growth Stage Coefficient for the SCS Mod. Blaney Page 21 of 34 Figure 19 – Comparison of calculated irrigation requirement Apart from overestimating consumptive use in Kersey, the Task Memo 59.1 curve has changed shape when compared to the SCS TR-21. shape and only be shifted upwards to match the Task Memo 59.1 curve may suggest that more than the coefficients have changed in the calibration process. DWR32 Calibrated Blaney-Criddle Crop Coefficient Using the procedures and data specified i an attempt to duplicate the results ASCE and Blaney-Criddle ET estimates. Climate Data. Climate data from Ft Lupton (FTL01), Ft automatically imported from the web Unfilled Greeley data were used to fill both the Ft Collins and Ft Lupton data. Ft Lupton data were used to fill Greeley data as specified in the task memo ( ASCE Crop Coefficients. Task Memo 59.1 indicates that mean crop coefficients were taken from Manual 7033. In Chapter 8, Allen34 equations” when selecting appropriate crop coefficients. In other words, contrary to Task Memo 59.1, the coefficients from Manual 70 cannot be used adjustment.” Table 8.7 in Chapter 8 provi application with the ASCE ET Equation in Manual 70. The updated mean crop coefficients for ryegrass to note that ryegrass is specified as a perennial crop 8 reflect common pasture grasses in Colorado. Fescue grows 3 to 4 feet tall and Orchar parameters in IDSCU were changed 32 In the context of this analysis, “DWR” represents D. Santistevan, Assistant Division Engineer in Division 1 33 Jensen, et al. (1990), p.6 34 Allen, et al. (2005), p.46 0 5 10 15 20 25 30 35 40 45 1992 1994 1996 An n u a l C r o p W a t e r R e q u i r e m e n t SCS TR-21 Task Memo 59.1 (Upper Plains) ASCE, ETrs Issues with Selecting an Appropriate Crop Growth Stage Coefficient for the SCS Mod. Blaney-Criddle Eqn. Comparison of calculated irrigation requirement Apart from overestimating consumptive use in Kersey, the Task Memo 59.1 curve has changed shape 21. In theory, the Task Memo 59.1 curve should mimic the SCS TR be shifted upwards to match the magnitude of The ASCE. The change in shape o suggest that more than the coefficients have changed in the calibration Criddle Crop Coefficients (pasture grasses): Using the procedures and data specified in Task Memo 59.1, an independent analysis was performed an attempt to duplicate the results published in the task memo. IDSCU was used for the calculation of Criddle ET estimates. Climate data from Ft Lupton (FTL01), Ft Collins (FTC01), and Greeley (GLY03) were automatically imported from the web into IDSCU and were weighted by 33%, 33%, and 34% respectfully. Unfilled Greeley data were used to fill both the Ft Collins and Ft Lupton data. Ft Lupton data were used s specified in the task memo (TM59.1, p.9). Task Memo 59.1 indicates that mean crop coefficients were taken from indicated that “it is important to establish the differences ” when selecting appropriate crop coefficients. In other words, contrary to Task Memo 59.1, the coefficients from Manual 70 cannot be used directly “in the ASCE Standardized method without any Chapter 8 provides mean crop coefficients that have been “ application with the ASCE ET Equation,” which were derived from the same data set as those published mean crop coefficients for ryegrass from Chapter 8 were used to note that ryegrass is specified as a perennial crop 8 to 15cm (3 to 6”) in height and may not accurately reflect common pasture grasses in Colorado. For example, Smooth Brome grows 2 to 4 feet tall. Tall Fescue grows 3 to 4 feet tall and Orchardgrass can grow 2 to 5 feet tall. The crop characteristics parameters in IDSCU were changed so that pasture grass reflects a perennial crop. , “DWR” represents D. Santistevan, Assistant Division Engineer in Division 1 1998 2000 2002 2004 2006 2008 Year Task Memo 59.1 (Upper Plains) Criddle Eqn. Apart from overestimating consumptive use in Kersey, the Task Memo 59.1 curve has changed shape Task Memo 59.1 curve should mimic the SCS TR-21 in ASCE. The change in shape of the suggest that more than the coefficients have changed in the calibration an independent analysis was performed in IDSCU was used for the calculation of Collins (FTC01), and Greeley (GLY03) were were weighted by 33%, 33%, and 34% respectfully. Unfilled Greeley data were used to fill both the Ft Collins and Ft Lupton data. Ft Lupton data were used Task Memo 59.1 indicates that mean crop coefficients were taken from it is important to establish the differences between ET ” when selecting appropriate crop coefficients. In other words, contrary to Task Memo 59.1, the in the ASCE Standardized method without any des mean crop coefficients that have been “converted for ,” which were derived from the same data set as those published were used. It is important 6”) in height and may not accurately grows 2 to 4 feet tall. Tall he crop characteristics a perennial crop. It is important to 2008 2010