2.2 Site Requirements
Finding the best possible site for the gauge is important and careful consideration
should be given to the quality of precipitation catch prior to the final installation. The
most accurate rainfall measurements are made in sheltered areas that block wind and
eddy currents in the vicinity of the gauge. The best exposures are often found in
orchards or openings within a grove of trees, bushes, or shrubbery. Fences or other
objects can act together to serve as an effective windbreak. As a general rule in such
areas, the heights of the objects and the distance from the gauge should be uniform.
The height of nearby objects above the gauge should not exceed about twice their
distance from the gauge. Individual or small groups of isolated objects near a gauge
may set up serious eddy currents. Since it is not always possible to select sites that
provide adequate protection from adverse wind effects, an open site away from isolated
objects may be the only location available. Wind shields help minimize loss of
precipitation catch by breaking up the air flow immediately over the gauge funnel. Wind
effects on catch losses are much greater during snowfall than rainfall. Windshields are
not generally installed at gauge site locations where snowfall constitutes less than 20%
of the mean annual precipitation.
Good exposures are not always permanent. The growth of vegetation, trees, and
shrubs can change an excellent exposure into an unsatisfactory one within a relatively
short time. Sites should be inspected and groomed regularly.
In areas where heavy snowfall occurs, rain and snow gauges are mounted onto
supports (tower) at a height well above the average snow level. A location with this type
of exposure would be improved if the tower can be located within an area of trees of
comparable height.
2.3 Installation
The 260-2501-A rain gauge is shipped from the factory with the three mounting legs
attached upside down on the 1/4-20 bolts. Be sure the leg mounting bolts are tightly
fastened. Carefully remove all packing material and any tape, foam pieces, cable ties,
or rubber bands used to keep the tipping bucket from moving during shipment. Operate
the tipping bucket to verify that the bucket can now move freely.
Insert the inner funnel into the top of the tipping bucket assembly, then place the outer
funnel into the top of the gauge. The gauge housing must be mounted as level as
possible on its platform. The holes in the mounting legs are sized for 1/4" diameter
mounting bolts. For correct measurement of precipitation, the open end edge of the rain
gauge funnel must lie in a horizontal plane. This can be tested by laying a carpenter’s
level across the top edge of the gauge funnel using two 90Edirections, one direction
crossing the other at right angles. If the top is not level in both directions the condition
should be corrected. Each of the three mounting legs can be adjusted, or washers can
be used as leveling shims between the mounting legs on the gauge and the platform or
tower mounting plate.
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