While working on yesterday’s Weather Watch post, I decided that it was important to know what the normal river levels were this time of year. After all, knowing the river stage is pretty useless without context. Flood stage is pretty easy to find for most sites, but that doesn’t necessarily provide context for low-water situations. For example, the Ohio River at Louisville, KY (McAlpine Lock and Dam, lower) has a flood stage of 55 feet, so being 15 feet below flood stage is normal. In contrast, 15 feet below flood stage for the Wabash River at Lafayette, IN is four feet below ground. The concept of pool stage exists, but it’s not widely used. So how can river depth be put in the proper context for low-water situations?
Like most other data meteorological, a comparison to the average value over some period of time is apt. The question then becomes “where do I find the average river height for a particular site?” Of course, the average height can vary greatly over the course of a year based on local and upstream precipitation patterns, so month-by-month data is preferable. Unlike temperature and precipitation, though, the National Weather Service does not issue daily climate summaries for rivers (at least not that I’ve seen).
Fortunately for the numerically-minded, the United States Geological Survey (USGS) has a wealth of data available for free on the Internet. It’s a little tricky to navigate, but with patience, the National Water Information System (NWIS) will surrender the desired information. With data for approximately 1.5 sites available in a variety of readable and parseable formats, there’s enough to keep even the most efficient data nerd busy for a long time. For easier-to-navigate real-time hydrologic data and forecasts, see http://water.weather.gov/ahps/.