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<br />OO0b5~ <br /> <br />. <br /> <br />. <br /> <br />~ <br /> <br />\ <br /> <br />(3) Effects of wind <br /> <br />Ivind plays an important role in transportation and distribution of <br />snow. l11e effect of winds on snow distribution are reported by some authors <br />(I, 3, 20, 31). Winds also scour the snow in clearcut areas and effect subli- <br />mation losses. l1\lls, the increase in .water yield due to timber cutting is <br />influenced by the winds in a given location. <br /> <br />(4) Orientation of slopes (north vs. south) <br /> <br />Slope orientation is an important consideration in timber cutting for <br />increased water yield. Generally, on south slopes there is an increased solar <br />radiat ion which results in higher evaporation loss from the snow. The orien- <br />tation effects were studied by Cline, et a1. (4) .on a small (ZOO ft. x 650 <br />ft.) experimental forest in northern Idaho. The results from this study indi- <br />cate that clearcutting on south slopes created less favorable conditions than <br />the north slopes. It is important to note that most north slopes have a dense <br />forest and south slopes a comparatively thin forest. It appears reasonable <br />that north slopes are more favorable than south slopes for increased yields of <br />water. <br /> <br />(5) Soil moisture and evapotranspiration <br /> <br />, <br />,. <br /> <br />Soil moisture and evapotranspiration from forests play a very important <br />role in timber cutting for increased water yield. Soil moisture depends upon <br />density and type of trees, orientation of slope (north or south), winds, etc. <br />In a forested area, evaporation takes place from snow cover and soil, and <br />transpiration from trees. Trees provide protective cover for soil and snow, <br />thus reducing evaporation. . Removal of tree cover increases evaporation and <br />reduces transpiration which results in a decrease in the soil moisture deficit <br />(8, 15, 16, 22, 27, 28, 30); thus, increasing streamflows. With the regrowth <br />of vegetation or reforestation, the soil moisture deficit increases (1, 2, 3, <br />4, 30, 34), which results in reduction in water yield over time. <br /> <br />(6) Sno"melt and runoff <br /> <br />:,j <br /> <br />Timber harvesting effects the hydrologic system of the watershed. Some <br />of the factors influencing water yield are discussed previously. In this <br />subsect ion, snowmelt and rWloff are discussed. Most of the invest igators <br />claim an increase in water yield due to clearcutting or patchcutting 0, 2, 3, <br />4, 11, 27, 30, 34). Leaf 0) reports that most of the rWlOff frolll the <br />increased snow acculllulation due to patchcutting comes in the spring and the <br />recession part of the hydrograph did not. change much. However, studies by <br />Cline (4) indica te that for bare land on ;) north slope, 17% of the increa sed <br />annual \;ater yield occurred during the period of /Iugust 27 to October 31. No <br />increased water yield occurred for forested areas on north slopes and bare <br />land on south slopes during the same period. This indicates that on north <br />slopes it is possible to have increased water yield, due to clearcutting, <br />during late slmuner months. One should note here that the size of the experi- <br />mental watershed lIsed by Cline (4) is very small (200 ft. x 650 ft.). <br /> <br />-3- <br /> <br />.._~" <br /> <br />... <br />