RIVER FORECAST CENTRE

What Is An Automatic Snow Pillow (ASP) Station?

Our snow pillows consist of 3m diameter bladders containing antifreeze solution. As snow accumulates on the pillow, the weight of the snow pushes an equal weight of the antifreeze solution from the pillow up a standpipe in the instrument house. This weight of the water content of the snow is termed Snow Water Equivalent (SWE). The distance the antifreeze is pushed up the standpipe is recorded by a float connected to a shaft encoder.

As well as the vertical standpipe from the pillow, the instrument shelter contains the electronics, consisting of a Data Collection Platform (DCP), a shaft encoder which tracks the movement of the float in the standpipe from the pillow, 12 volt wet cell batteries for powering the electronic equipment, and regulators for the externally mounted solar panels for recharging the batteries. The DCP contains a transmitter to send the recorded data by satellite to us. On the outside of the instrument shelter are the solar panels for the charging system, and an air temperature sensor.

At some of the snow pillow sites, precipitation gauges and snow depth sensors are also installed. The precipitation gauges consist of a 380 mm diameter PVC standpipe varying from 1.2 to 1.8 m in length, depending on the amount of precipitation expected in the area. A pressure transducer is mounted externally to the bottom of the standpipe, its output giving a reading of the total amount of fluid in the raingauge. To inhibit freezing as the antifreeze becomes diluted with increasing precipitation, a 12-volt pump is used to circulate the fluid inside the precipitation gauge. The gauges are mounted on top of a 3 m high tower to keep them above the snow pack.

The snow depth sensor is mounted on an arm extending from a 6 m high tower, and points toward the ground above the pillow. The sensor works similarily to an autofocus sensor in a camera in that it measures the distance from the sensor to the surface below it and, as the snow depth increases the distance measured decreases. All of the B. C. Provincial ASPs are installed and maintained by staff of the River Forecast Centre. Our data base and graphs also include ASPs operated by B.C. Hydro and Alcan.

The photographs below show a typical ASP station, this one at Spuzzum Creek (1D19P). They also show the magnitude of the non-typical snowpack of the 1998-99 season in the South Coast Range. Both pictures were taken by Jim Whyte of the Ministry's River Forecast Centre at Spuzzum Creek snow pillow site. This site is located at an elevation of 1180 metres above the village of Spuzzum about 40 km north of Hope in the Fraser Canyon.

The first picture shows the snow pillow site just after installation was completed in the summer of 1998. The top of the solar panels are approximately 7.5 metres (25 feet) above the ground. The second picture shows the site on March 5, 1999 with the Snow Surveyor (Don Child of MELP's Surrey office.) His feet are on the roof of the instrument hut!

While the remote stations are made as robustly as possible, the stresses caused by severe winter conditions can cause failure. The following photograph shows the installation at the Tumeka ASP station (4D10P) as photographed on February 13, 2001. The cap of snow has partially covered the solar panel and the temperature sensor. However, the reason we were getting no readings was that the antenna with which the data are transmitted to the GOES satellite had snapped under the weight of the snow. The photograph shows it pointing to the ground instead of at the satellite!