Reading the depth of the Mississippi River is high-tech stuff in the 21st century compared to decades ago, when engineers used sticks and pressure lines to measure water levels.

Still, a clear measure of water in the river when levels are low can be confusing even when updated hourly on the Internet. To get the amount, elevation above sea level comes into play.

“You go ask a farmer and tell them Vicksburg is going to about 103.5 (feet) and he would say, ‘No idea what that means.’ No clue,” said Drew Smith, a civil engineer with the U.S. Army Corps of Engineers. “That’s about what the elevation was last year at the bridge. But, if you tell them Vicksburg’s going to 57 feet … he knows what that means.”

The river stage was 1.7 feet in Vicksburg on Saturday, but that doesn’t mean the river is dried out. Most of the Corps’ Vicksburg District’s 170 river gauges use zero as a base to record depths — which current and former hydraulics engineers readily admit aren’t accurate measures of water in the river.

“The gauge has nothing to do with depth of water,” said Wayland Hill, a retired civil engineer who worked in the district’s water control division for 41 years. “What it tells you is the surface elevation.”

At Vicksburg, a “zero” mark measures out to 46.23 feet deep, the depth of the local gauge above mean sea level. Elevations on the river vary from one station to the next. Any depth below zero is recorded as a negative number. The best way to measure water in the river during low times is to add the official stage to the elevation. Today’s amount would be about 47 feet when elevation is added and last spring’s record flood was 103.33 feet when elevation is added to the official 57.1-foot crest.