advantages are their ability to trap snow and 

 to hold the snowmelt water. Under normal con- 

 ditions, snowstorms in the Northern Great 

 Plains are accompanied by high winds and a 

 considerable amount of drifting. Characteris- 

 tically, a field that is plowed or fallowed will 

 be blown clear of snow in the wintertime. 

 A stubble field will trap some snow, to a depth 

 of slightly less than the height of the stubble. 

 The snow cover on pasture is usually slight, 

 depending somewhat on how much and how 

 uniformly it was grazed during the fall. The 

 level bench systems at Mandan, however, 

 trapped large quantities of snow, particularly 

 from storms in which the wind blew at right 

 angles to the benches (fig. 2). This points up 

 a distinct advantage of the level bench system. 

 Frozen soil can absorb very little water. 

 If the soil on sloping ground is frozen when 

 the snow melts, the water runs off and is lost. 

 On level benches, however, snowmelt water is 

 held in place by the dikes even if the soil is 

 frozen when the snow melts (fig. 3). As soon 

 as the ground begins to thaw out, the water 

 begins to soak into the soil. 



Alternative means of trapping drifting 

 snow have been tried. "Shelterbelt" plantings, 



consisting of one or more rows of trees, will 

 trap large quantities of snow, and one or more 

 rows of tall-growing annual crops, such as corn 

 or sorghum, have sometimes been used effec- 

 tively. Even though each tree row will catch 

 a large amount of snow, the rows are not 

 usually spaced to give a uniform depth of 

 snowcover for an entire field. In general, 

 snowdrift control is effective for distances 

 from the tree row of some 12 to 14 times the 

 height of the trees inordinary windbreaks (22). 

 Snowdrifts are deep on the leeward side of the 

 tree row, but there is little snow cover on the 

 rest of the field (8). During spring thaw; the 

 snow may melt rather rapidly; drainage chan- 

 nels will be formed along the snowdrift to 

 carry the water away, and small gullies may 

 result. The damage might be reduced if the 

 tree rows were planted across the slope in- 

 stead of up and down, but such plantings are 

 not always practical. 



Crop Yields 



Yield data for both the cropland study 

 and the grassland study for a period of 4 

 years show a decided variation between crops 



I 



J*- 



Figure 2.— Snow deposit on a level bench. 



