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<br />. <br /> <br />W. D. White and S. G. Wells <br /> <br />was measured in each type of burn-intensity area. The amount of runoff per <br />unit area increased as the devegetation increased (fig. 13). Runoff in the <br />intense-burn basin may be 60 times greater than in the light-burn area. Addi- <br />tionally, figure 13 and table 5 indicate that runoff is not directly proportional <br />to drainage basin size. because the moderate-burn watershed is smaller than <br />the light-burn watershed. In undisturbed watersheds} runoff as a dependent <br />variable bears a direct power relation to drainage basin size. Relief and <br />drainage den.5ity are the geomorphic parameters which influence the runoff in <br />devegetated drainage basins. Table 5 compares sey:cted basin parameters to <br />runoff and sediment yield and shows that runoff increases with increasing <br />relief and drainage density. Drainage density is given in qualitative terms <br />because the density changes with time due to head ward growth of drainage <br />lines. <br /> <br />Sediment Yield <br /> <br />Sediment yield from the instrumented watersheds is determined from <br />erosion-pin data. erosion-contour plot data. and sediment-trap data. Calcu- <br />lated sediment yields from the pin- <br />and contour-plot data wer'e compared <br />to the volume of sediment trapped <br />in buried drums. Sediment col- <br />lected in the trap installed in the <br />intense-burn basin of Burnt Mesa <br />gave a sediment yield of 0.7 m3}yr <br />over-. a 92 m2 area. Using the <br />erosion rate of 0.5 cm /yr. deter- <br />mined from'. erosion-pin data, the <br />computed sediment yield is 0.5 m31 <br />yr over a 92 m2 area. The two <br />types of measurements are similar. <br />so the use of erosion-pin data may <br />provide minimum estimates of sedi- <br />men t yields. <br /> <br />In the Burnt Mesa watersheds <br />the intense-burn basin has the <br />highest sediment yield. but the <br />light-burri basin has a higher <br />sediment yield than the moderate- <br />burn watershed due to animal ac- <br />tivity (table 5), Hadley and <br />Schumm (l961) demonstrated that <br />sediment -yield increases with in- <br />creasing relief-ratios in small <br />drainage basins in the western <br />United States. In the devegetated <br />watersheds of the Jemez Moun- <br />tains. sediment yield is not as <br />sensitive to basin slope relation- <br />ships as to types of mechanical <br />weathering. In this area other <br />drainage- basin variables affect <br /> <br />7 <br /> <br />6 <br /> <br />. <br /> <br /><( <br />IJJ <br />Q: <br /><( <br /> <br />. <br /> <br />.....- <br />-E <br />z. <br />::>' <br />...... <br />It'; 3 <br />O~ <br />z- <br />::>- <br />Q: <br /> <br />2 <br /> <br />Figure 13. <br /> <br /> <br />LIGHT MODERAi!; INTENSE <br />BURN INTENSITY <br />(Increoslnq o.v.t-'Otion) <br /> <br />Comparison of runoff per <br />unit area and burn intensi- <br />ty, Burnt Mesa study area. <br />