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<br />uptake found from soil samples <br />the empirical nature of KSAT. <br />reflect both the limitation of <br />soil-water properties of field <br /> <br />taken before and after simulator runs confirms <br />Best-fit vaiues are plot-average values that <br />the equation and the inherent variability of <br />soils. <br /> <br />Results of fitting KSAT to reproduce runoff from rainfall-simulator runs, <br />and results from fitting KSAT to reproduce runoff from observed rainfall events <br />on the plots, are inconsistent. Fitted values of KSAT for rainfall-simulator <br />runs conducted on plots 1 and 2 during the summers of 1981-82 show little <br />resemblance to values for observed summer rainstorms of 1982. In contrast, <br />results for plots 3 and 4 are in reasonable agreement with results from <br />observed rainstorms. Fall runs on plots 1 and 2 indicate that cooler soil <br />temperatures may influence the infiltration process. In contrast, fall runs <br />on plots 3 and 4 show no consistent effect of cooler soil temperatures; the <br />October 29, 1982 run on plot 3 is a very extreme case; frost occurred the <br />previous night. Reasons for these anomalous results are unknown; however, <br />the implication of a site-specific effect is apparent. Some speculation on <br />reasons for these differences might provide the basis for future study. <br /> <br />The effect of the dissimilarity between artificial and natural raindrops <br />is not known. Natural rainstorms have varying rates, accompanied by varying <br />size of drops. The rainfall simulator is designed to operate at a rate of <br />2 in/h. Any change in rates is achieved by adding or subtracting sprinklers. <br />Output from each sprinkler remains the same, and drop size is unchanged. <br />Neff (1979) determined that the rainfall simulator, at a rate of 2 in/h, <br />produced maximum size drops considerably smaller than those occurring in <br />natural rainfall at the same rate. Total kinetic energy at 2 in/h is about <br />40 percent of that from natural storms. The effect of these differences on <br />the infiltration process (the crusting phenomenon) is poorly understood. <br />Studies aimed at identifying the conditions under which a surface crust tends <br />to develop and influence the infiltration process would give valuable insight. <br />into where, when, and if the rainfall-simulator could be used to quantify <br />natural infiltration characteristics. <br /> <br />Atmospheric conditions during simulator runs often are considerably <br />different than atmospheric conditions in rainstorms. Regional temperature <br />during rainstorms usually drops sharply; regional temperature during simu- <br />lator runs remains fairly constant. Rainstorms occur at different times of <br />day; in eastern Colorado, summer storms most often occur in late afternoon <br />or evening hours. Because of wind conditions, simulator runs were conducted <br />in the morning or at midday. The effect of different ambient soil temperatures <br />and the difference between natural and artificial rain temperatures on the <br />dynamics of heat and water flux in the soil profile may have an important <br />influence on water uptake. Several simulator runs made in the fall indicate <br />a site-selective temperature effect. Studies aimed at resolving this apparent <br />anomaly and its relationship to a crusting phenomenon are needed. <br /> <br />57 <br />