Why flood gauges vary locally

As we head into flood season in the next week, you may be confused by some of the river levels you hear on area rivers. You're not alone.

Here's an example.

On the Minnesota River at Granite Falls "flood stage" is 888 feet.

Just up the river in Montevideo, flood stage is 14 feet.

Why the difference?

At Granite Falls the gauge is based on elevation above sea level. In Montevideo, it's based on what's called a "zero point" somewhere on the river locally. I know, I don't get it either.

The best way I've heard this explained is that through the years, gauges have been added at different locations using different local measurements to set the flood gauge. Historically gauges have been different, and local control has been the deciding factor in how a gauge reads at any location.

My partner in weather crime (and former Twin Cities NWS Chief) Craig Edwards tells me that many years ago there was an effort to standardize river gauges nationwide. That effort fell to the usual politics and red tape surrounding the cost of replacing many of the river gauges, and with local officials wanting to keep things as they were because they felt their local residents understood that current system.

I'll be posting more info in the coming days to help with interpreting river levels and forecasts. In the mean time, here's a guide to hydrologic information on the web from NOAA.

You can access the latest river hydrographs and flood forecasts for southern Minnesota rivers here.

Red River forecasts info is here.

PH