CLINTON — Living near the Mississippi River has its ups and downs, just like the river itself has those same highs and lows.
In an attempt to comprehend its ever-changing nature, the U.S. Army Corps of Engineers utilizes lock and dam gauges to navigate those changes and make adjustments accordingly.
“When the locks were built 80 years ago, the Corps surveyed the river and set the gauges,” Lock and Dam 13 Lock Master John Mueller said. “We still use those same gauges today.”
The gauges Mueller referred to are what the U.S. Army Corps of Engineers uses to measure river levels on a regular basis, during flooding and during drought seasons.
Contrary to belief, those gauges are not set from the river floor, but actually are set at a level known as zero datum.
According to the U.S. Army Corps of Engineers’ website, zero datum is a hydrological term that refers to a specific point at which all river measurements are taken.
For instance, when the river level reads 5.4 on the advanced hydrologic prediction scale, it is measuring 5 feet, 4 inches above zero datum, Mueller said.
Chief of Water Control with the U.S. Army Corps of Engineers Jim Stiman said the datum points were set many years ago and it is unknown as to why those specific numbers were chosen.
“It’s kind of arbitrary for why they chose those datums,” Stiman said.
Stiman’s best guess is that the numbers were picked to avoid negative readings when measuring river levels, although that has happened in the past.
“The gauge at St. Louis, Missouri, read minus numbers last year during the drought, but it is a really rare event,” Stiman said.
The datums in the Rock Island District, which covers Lock 11 through Lock 22, range from 588.20 feet in Dubuque down to 446.10 feet in Saverton, Mo.