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Show SECTION 3-- SNOWFALL AND PRECIPITATION Net snowfall is the depth of snow accumulated on the ground for any given interval. Precipitation is the amount of water reaching the earth's surface in a given interval, either in the solid form as snow or in the liquid form as rain. There are no satisfactory and reliable instruments to measure snowfall automatically. Manual measurement and recording are required. A plate or board is placed on a level snow ( ground) surface, the depth of snow accumulated on it measured with a ruler ( A8a or A8b) inserted vertically, and the board is then reset at the surface. The board location must be marked by an adjacent stake. A painted piece of 1/ 4- inch plywood 2k inches square makes a satisfactory plate. For convenience, the ruler or tape is usually replaced by a stake anchored to the middle of the plate. The snow surface level can then be conveniently read at any time. The stake must be stout and firmly anchored to the plate, for the assembly will suffer abuse when dug out of the snow, especially where snowfalls are deep and dense. Figure 7 gives construction details for a snow stake of proven sturdiness and durability. Lighter construction is not recommended; ordinary yardsticks or metersticks, for instance, are not strong enough. On the other hand, a stake which is too bulky will locally modify snow deposition and make accurate reading of the surface level difficult. A 2- by 2- inch stake is too large. The total snow depth stake, however, may conveniently be a length of 2 x 2 lumber, for greater strength and stiffness are required. The total length should exceed the maximum expected snow depth. Every effort should be made to place this stake in the middle of a level area, otherwise the force of snow creep on even a very gentle slope will tend to tilt it. The stake should be straight- grain, clear fir, free of knots. Preferably it should be free- standing and supported only by the ground anchor. The accumulating snow cover will firmly support it during mid- winter, but in a windy location ( to be avoided if at all possible), it may be necessary to guy the stake top when the snow cover is shallow. Guy wires should run horizontally to nearby trees, posts or poles. Do not guy the total snow stake with wires running diagonally from the stake top to anchors at ground level; snow settlement pressure will stretch or bend the guys, or pull and buckle the stake. Bottom of the stake should be clamped or bolted to a metal anchor firmly fixed in the ground, the nature of which must be chosen according to the character of the ground. A heavy angle- iron driven in 3 to k feet is satisfactory in soil. 19 |