January 23, 2012
And when it snows, my neurons fire around the theme of water: How wet is this snow? Namely, can I make a snowball? Will it slake my thirst if I eat some? If I imagined all this snow melting down and trickling deep down to the water table, how much water is that?
That is, how much water (in inches) would this snow provide for the very dry days of July, August and September?
Clearly I had to make some assumptions based on the landscape. It turns out that the well from which we drink draws water from a rocky basalt section that rests on and in between bedrock. This water makes its way from Mount Adams, but more specifically from the slope north of us, which faces south and allows water to flow our direction.
Here's how I went about that estimation:
1. I measured the height of the snow once it stopped snowing for a little while. I did this by first digging a snow wall with a shovel and using a measuring tape. Like this:
2. Next I found the average density of the snow by taking three samples, one from the top of the snowpack, one from the middle, and one from the bottom. I did this by using a small cylindrical cup and a spatula, carefully inserting the cup horizontally into the layer of snow, using the spatula to seal off the mouth of the cup, and then weighing the snow on a kitchen scale. I then did a little math to figure out the volume of the cup and eventually the density of the snow.
3. More math time! By knowing the density of the snow and the thickness of the snow layer, I found how much water this snow would turn into once it melted. Hooray!
Snowy afternoons are awesome times for geometry and arithmetic. What's even better is that I can sit here sipping something hot and think about how nice it is to have another 8 inches of water with which to hydrate the garden come summertime, when the sky is bright blue for months on end.
[Wait a second: 8 inches? How does that make sense? Water comes in gallons, right?
Well, yes, that too. Turns out that meteorologists and other such people like to describe precipitation in terms of inches or centimenters, which is a linear measurement. What this means is that if it were to rain on the land, and the water did not flow anywhere nor absorb into the ground (which is nigh to impossible), the land would be covered by a layer of water 8 inches in depth. That's a lot of water, considering the annual precipitation average around here is about 30 inches, which isn't much!]