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,. -. e, 8l .\ River Valley; it gives them the ability to predict whether deple- tions are likely over a 1 O-year period; and, if there are, they can take actions to replace those depletions, such as putting more water into storage in an offset account in John Maliin Reser- voir. Finally, I want to address a recommendation that I think is of intere~t to water users in the South Platte River Basin. The Special Master accepted a new method to determine potential evapotranspiration in the model that is being used to determine Compact compliance, In previous versions of the model, the modified Blaney-Criddle method developed by the Soil Conservation Service 'was used to determine the potential evapotranspiration of crops in the Arkansas River Valley. It is a widely used method, and it has been used to. determine historical consumptive use for water rights transfers in Colorado and has been widely accepted as giving reasonable results. producing areas in the field resulted in slightly lower yields than in the lysimeter. He also noted that the alfalfa yields from the Iysimeter were 40 percent higher than the Twin Falls courity average, but noted that the county crop averages included several large ar- eas that were water-short in most years. So; some of that yield reduction was due to the fact that there was a limited water sup. ply, but he also noted that these were areas where alfalfa was not considered a high priority crop. Those comments concern me in applying those crop coefficients in the Arkansas River or in the South Platte River Basin to deter- mine the' potential consumptive use of crops like alfalfa, which is the largest crop in the Arkansas Valley and a large crop in the South Platte Basin. In my opinion, there needs to be additional research of the type that Dr. Wright conducted at the Agricultural Research Station in Kimberly, Idaho, to determine whether the Penman-Monteith equation is, in fact, reasonable for use in Colorado and whether the crop coefficients developed by Dr. Wright need to be adjusted for conditions in Colorado, in particular, for salinity...I believe that additional research is im- portant for water users through- out the state, including the South Platte River Basin, and urge your support for such research. However, the scientific and engineer- ing communities are committed to using more physical1y~based equations . to determine potential evapotranspir.a- tion, using what are called "reference crop ET" methods. which use crop coefficients that are multiplied times a reference crop ET to determine the potential evapotranspiration of crops. Such methods are now widely used for irrigation scheduling. The Special Master accepted the Kansas position that the Penman-Monteith equation is the most accu- rate method to determine reference crop ET. He also accepted the Kansas position that crop coefficients developed by Dr. James Wright of the Agricultural Research Service in Kimber- ly, Idaho, were appropriate to determine the potential evapo- transpiration of crops in the Arkansas River Valley. After hearing the experts testify, I remain somewhat skeptical about the use of the Penman-Monteith equation and, in particular, the crop coefficients that Dr. Wright developed to determine potential evapotranspiration. Those crop coefficients were developed under what I would describe as ideal conditions. Dr. Wright has published ~ nqmber of papers that describe the research he conducted to determine those crop coefficients. He placed a lysimeter in an. alfalfa field near the Agricqltural Re- search Station in Kimberly, Idaho, to determine the consump- tive use of alfalfa. Howev.er, he noted that the alfalfa y~eld in the lysimeter was slightly greater than in the surrounding field. The alfalfa in the Iysimeter was hand-harvested. The alfalfa in the surrounding field was mechanically harvested, and he thought that the m.echanical harvesting equipment Zl!ld lower .22~' In my opinion, there needs to be additional research ofthe type that Dr. Wright conducted at the Agricultural Research Station in Kimberly. Idaho, to determine whether the Penman-Monteith equation is, in fact, reasonable for use in Colorado an'd 'whether the crop coefficients developed by Dr. Wright need to be adjusted for conditions in Colorado, in particular. for salinity. We have higher salinity levels in the Ar- kansas River Basin than in the Snake River near Twin Falls, Idaho, which can reduce the amount of .crop consumptive use. So. I am here to make a pitch to those of you attending the South Platte River Forum today to support research on the use of the Penman~Monteith equation in Colorado. The scientific and engineering communities are clearly mov- ing in the direction of using reference crop ET methods to determine crop consumptive lise. and continued use of the modified Blaney-Criddle method will be challenged. A U.S. Supreme Court Special Master has accepted Penman-Monte- ith equation and he has accepted crop coefficients developed by Dr. Wright. The Penman-Monteith eqqation with the crop coefficients developed by Dr. Wright will calwlate higher potential evapotranspiration for some crops, which in many cases will result in higher transferable consumptive use and a reduction in the amount of return flows that applicants are obligated to rePlace in water rights transfers. For that reason I believe that additional research is impOliant for water users' throughout the state, including the South Platte River Basin and urge your suppOli for such research. .