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<br />~ <br />w <br />en <br />~ <br /> <br />Results <br /> <br />Final constant infiltration rates were very low on both the gray crusted shale <br />pediment soil and the dissected badland formation, averaging 0.3 cm/hr (0.12 <br />in/hr) and 0.13 cm/hr (0.05 in/hr), respectively. No runoff was generated on <br />the light brown, cracked aeolian soil. <br /> <br />Suspended sediment concentrations for the gray, crusted pediment soil averag~d <br />2,000 mg/l (CV=0.25) except for a peak in concentration of approximately 5,900 <br />mg/1 (s=134 mg/1) which occurred immediately after runoff was initiated on the <br />first run on each plot _(Fig. 3). This compares to peak suspended sediment <br />concentrations of 647,000 mg/1 and 500,000 mg/1 for the first and second run <br />respectively on the dissected shale badland unit (Fig. 4). On that unit, <br />sediment concentration generally corresponded to discharge. Roughly 80% of <br />the sediment generated on the shale badland unit was due to rilling, 9% to <br />cutting of tributary channels, 8% to cutting of the main channel, and 3% <br />resulted from creep of the upper 15 cm (6 in) of the weathered shale surface. <br /> <br />EC in runoff (which served as an index to TDS concentration) increased an <br />average of 35 umhos/cm (CV=0.05) on the gray, crusted, pediment soil over EC <br />measured in the rainfall. This contrasts to an increase in EC of roughly <br />2,400 umhos/cm over that in the rainfall on the dissected shale badland (Figs. <br />5 and 6). <br /> <br />Conclusion <br /> <br />Simulated rainfall study results serve only as relative indexes of runoff, <br />erosion and salt-producing characteristics of a site. This study suggested, <br />however, that a similar rainfall-runoff event would produce considerably more <br />salt and sediment from raw shale badlands than from lower-relief gray shale <br />bottom1ands. We believe that the high sediment and salt concentrations in <br />runoff from the dissected badland unit are due to the dominance of ril1ing as <br />an erosion mechanism, and the continued downcutting to salt-rich shales. The <br />surprisingly low concentrations of sediment and salt in runoff from the gray, <br />crusted pediment unit appears to be due to: <br /> <br />1) the erosi.on protection provided by the surface soil crust and <br />mild slopes, and <br />2) less saline surface soils. <br /> <br />Erosion rates were apparently insufficient to expose deeper, more saline <br />soils, and capillary processes were apparently insufficient to replenish <br />surface salt concentrations on the gray pediment soil. <br /> <br />Management and control of diffuse sources of salinity in Mancos shale regions <br />will require careful analysis of salinity sources as a function of soi1- <br />landform characteristics because of the highly variable runoff and erosion- <br />producing attributes of different soil units. <br /> <br />19 <br /> <br />~~~ <br /> <br />