Quote of the Day
If physics was about proofs, von Neumann would be a pretty good physicist.
— Wolfgang Pauli, after reading a rigorous mathematical proof about some aspect of quantum mechanics by John von Neumann.
Figure 1: Chart of Eagle Lake Level Relative to Sea Level. The Ordinary High-Water Mark (OHWM) is the level used by the State of Minnesota for determining how far away buildings must be placed from the water.
My wife and I are building a vacation home on the shores of Eagle Lake in Itasca County, Minnesota. We also are active members of the local lake association, which is a group of homeowners who work on projects to keep our lake healthy. One task I perform on a yearly basis for the lake association is to draw a graph of how our lake level is varying over time (Figure 1). The lake level is important to homeowners because it affects the amount of beach that is exposed and the length of their docks.
Figure 1 shows how our lake level has varied since 2001. The peaks correspond to recent heavy rains. The low points tend to corresponds to times when a beaver dam at the lake outflow fails, releasing water, and causing a quick reduction in lake level. In general, the beavers perform excellent maintenance on their dams, but trappers occasionally remove the beavers, and then the beaver dams fall into disrepair until a new beaver pair arrives. No lake level measurements are taken during the winter because the lake is frozen and covered in snow. I indicate winter in Figure 1 with a snowflake symbol.
I attach my spreadsheet here for those who are interested in how this chart is obtain the lake level information. Power Query is used to grab the data from the State of Minnesota and clean the data up for graphing. I use standard Excel commands for plotting the data.