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<br />.-::-: <br /> <br />rJ1 <br />~ <br />"'4 <br /> <br />c, <br /> <br />Summa,ry of increased runoff due to man's action in the forest areas: <br /> <br />State <br /> <br />Increase in Runoff- <br />acre feet <br /> <br />Colorado <br />Wyoming <br />Utah <br />New Mexico <br />Total <br /> <br />457,000 <br />32, 900 <br />91, 000 <br />1,200 <br />582,100 <br /> <br />MAN'S EFFECT ON GR AztNG LAND RUNOFFS <br /> <br />In a miscellaneous publication of the Department of Agriculture dated <br />July. 1940. the following statement is made: In a reCent survey of the <br />no. OOO~ 000 acres of grazing lands in the western one-half of the United <br />States. of which 216, 000, 000 acres are classed as forest lands-- <br /> <br />34"/0 was found to be 25 to 50"/0 depleted <br />37"/0 was found to be 51 to 75% depleted <br />16% was found to be 76 to 1000/0 depleted II <br /> <br />Note: There is no reason to believe the Colorado River Basin is in any <br />better shape. It is probably worse. <br /> <br />The S. W. Forest and Range Experiment Station of the Department of <br />Agriculture found: <br /> <br />1. With range cover approximately 25"/0 depleted, 22"/0 of annual <br />precipitation was surface runoff. <br /> <br />2. With cover 50 to 75% depleted, surface r1.1lloff was 28 to 32%. <br />of precipitation. . <br /> <br />3. With allowance for vegetation, on a watershed designated A, <br />to increase from 16"/0 in 1920 to 40% in 1924, the summer runoff <br />was reduced 64%. (This experiment would probably worlt in <br />reverse. ) <br /> <br />On the Boise River watershed in Idaho, studies have been made that <br />demonstrate the value of vegetation in preventing erosi()n and conser- <br />ving water. The bunch grass type. which has the greatest forage value <br />of any local range type, and to which most of the grazing land in the area <br />will ultimjl.tely revert if unabused, yielded only 0.4% runoff. The downy <br />chess and needle grass, lupine types, which have succeeded the bunch <br />grass on (wer-grazed ranges at lower and higher elevations, respectively. <br />are distinctly less effective watershed covers. On the average 25.5% of <br />the precipitation on the downy ohess oover and 47.60/0 on the needle grass. <br /> <br />-9- <br />