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Comments to SWSIJ November 3, 2003t by John Wiener 28 Does this example define the problem? If not, can it be corrected or repafred? If it doest then the approach which seems most usefu' right now is a meeting of the rjght people, to work on how and under what circumstances the kind of Uclose enough II estimations described can be producedt For example, are there geological limitationst such that Plains alJuvial river valleys could use an approach that wouJd not work well enough in montane environments, or vice versa? Are soil conditions critical, or simply a factor that has to be taken into account? And can NACS maps suffice, or shourd there be some program for competent engineers to make measures which wou'd suffice? And so on... I envision this, if it can be done, to be a sort of very transparent expert system applying the necessary terms and information to make useable estimations to begin experiments with new management techniques. Additional features of the problem: What are the variables? FortunatelYt there are a smaU number of changes in technology that may be sufficiently common to warrant consideration~ But~ are there a relatively small number of other important features to make this feasibre? Can the slope, son, depth of horizonst and other factors be treated in simple enough form to make adequate estimations achievable with the needed speed and low cost? Or, are there some conditions in which these estimations can be madet and others in whjch they should not be used? From a different perspective, there are various conditions identified in materials such as those from the Cooperative Extension Service, on how to identify best management practices (BMPs) for irrigation for a given field (e.g~ Waskom 1994). These variables may be important for the problem at hand. They include: Soil and crop properties: 1. Water holding capacity of different soil textures (sometimes called fierd capacity; measure usually by inohes of water per foot of soil); additionally, depth to different soil horizons may be important 2. Maximum rooting depths of different crops4 3. Approximate efficiency of the various irrigation appUcation methods (for BMP considerations, mean percentages of technologies have been described as: · furrow - 40% · surge -. 60% · sprinkler - 75% · drip - 90% These are means for rough guidance] subject to site and particular technology features. 4. The total seasonal crop water use is also important for selection of irrigation technology, and should be relevant to estimation of the consumptive use from a glven combination of choices and place. There are also relatively few changes in irrigation technology that make sense and increase water de'ivery effici~ncy (Smith et al 1996; CP'A, various)~ They include: Structural changes to irrigation technology~ 1 4 ditch to pipe 1. ditch to Uned pipe (significantJy different from pipe?)