WSP10386 - Laserfiche WebLink

Home Browse Search

"2. Take offset samples for the affected points snow and in a line parallel to the snow course. ate comments on the snow notes. in undisturbed Make appropri- Ofn258 -33.- Courses and aerial markers usually are placed at relatively high alti- tudes, at sites which catch a substantial amount of snow inmost years, but at which drifting is minimum. ' As has been stated, commonly their objective is a consistent index ,to each year's net accumulation of snow on the adjacent region as of the date of measurement., Usually they are not intended to measure total snowfall because some of the snow wastes continually, as by runoff or by sublimation (passage of solid-state snow immediately into water vapor); also because under certain conditions a snowpack may gain in water equivalent owing to condensation of moisture from the atmosphere. In forested areas, small sheltered clearings offer advantageous sites for both courses and aerial markers. Obviously, a clearing will minimize interception of snow by the forest canopy; such interception can be sub- stantial and can vary greatly from one storm to another. A small clearing will minimize transport of snow by wind, and so will promote uniform dis- tribution of snow along the course. Isolated trees close to a course are undesirable; snow which they intercept may subsequently fall or be blown onto the course in non-representative amount. Other desirable features of a site are: (1) A land surface relatively free of large rocks, logs, or other such "roughness." Otherwise, samples may not represent mean thick- ness and water equivalent of the snowpack. (2) An altitude at which winter melt is small. (3) A relatively level but well-drained area that does not intercept drainage from adjacent slopes and, in particular, does not pond melt water in the spring. Thus, many mountain meadows are unsatisfacto:ry. (4) A site that is reasonably accessible but at the same time sufficiently remote to be free from winter-sport visitors and unaffected by snow removal along highways and roads. To be avoided are the crests of exposed ridges and areas immediately downwind from them, because there the snow may drift excessively. Also to be avoided are the steeper slopes on which snowslides may be common. These criteria notwithstanding, all too frequently poor sites must be used for snow courses. In respect to proximity of roads, an instruction bulletin of the California Department of Water Res,ources states: "Unfortunately for the snow survey program there is an increasing number of instances each winter where snow courses near roads are either affected by plowing operations or by those I Little People' who build snow men or forts in snow, thereby adding or subtracting snow at the sample points. When faced with obtaining snow samples on a course where the snow cover has been altered by these activi- ties, snow surveyors should do two.things: "1. Measure all sample points on the regular snow course, noting the extent that any points have been affected by human activities.