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<br />are typically layered in the vertical, and are either bare or vegetated on <br />the surface, all complicating factors controlling the entry of water into <br />the soil profile. Best-fit parameter values of this simple characterization <br />of the infiltration-surface-runoff process are plot-average values; they <br />reflect the limitations of the model as well as the natural variability <br />inherent in field soils, roughness elements, and surface-retention <br />characteristics. <br /> <br />Results of the best-fit approach to reproduce individual simulator <br />runs made in 1981 for plots 3-5 (representative of the lowland prairie area) <br />are shown in figures 13 through 15. Plot 5 is located in an area of high <br />clay content where the soil typically shrinks and produces a maze of surface <br />cracks when it is dry. The cracking phenomenon negates a meaningful appli- <br />cation of the Green-Ampt infiltration equation, except possibly under high <br />antecedent moisture conditions when the cracks have healed, and the expanding <br />nature of clay lattices has more or less stabilized. Results for plot 5 (fig. <br />15) are,presented primarily to show the dramatic effect of surface cracking <br />on observed runoff. Both the conductivity term and surface roughness take <br />on high values to simulate the effect of cracking on runoff. <br /> <br />As in the case for the upland plots, results shown in figures 13 and <br />14 indicate a consistent hierarchy of parameter significance. Hydraulic <br />conductivity is the most significant; wet-front pressure, surface-retention <br />capacity, and surface roughness are secondary. In addition, the relative <br />magnitude of fitted parameters is similar for the summer runs. Values of <br />KSAT in the range of 1.0 to 1.3 in/h fit all summer runs on plots 1-4. How- <br />ever, the apparent effect of cooler soil temperatures in the fall, and the <br />associated large reductions in hydraulic conductivity required to fit runoff <br />from plots 1 and 2, were not confirmed by the fall runs on plots 3 and 4. <br />Values of KSAT in the range of 1.0 to 1.3 in/h adequately reproduce the fall <br />runs on plots 3 and 4. The best-fit values of KSAT for the various runs are <br />summarized in table 4. <br /> <br />Table 4.--SummaJ1.Y on n.ute.d value<. on hydtc.a.u.Uc c.onduc.:UvUy <br />nM lILWtnaU.--4.imu1.a::tOlt lUI.Y!./) on 1981 <br /> <br />23 <br />