Breakdown: Why river levels can be negative
MEMPHIS, Tenn. (WMC) - Our ongoing dry weather and drought conditions have taken a toll on the Mississippi River here in the Mid-South.
You’ve likely heard several reports about the “river stage” recently.
But what does “river stage” even mean?
River Stage is an important concept when analyzing how much water is moving in a stream at any given moment.
Stage is the water level above some arbitrary point -- usually with the zero height being near the river bed -- in the river and is commonly measured in feet.
A river’s stage at a point (a gauge reading) is not an absolute measure of the depth of the water in the channel, so when a river gauge reads zero or in the negative numbers, it doesn’t mean that the river has gone totally dry. It means that the gauge is reading at or below the agreed-upon zero level.
- That gauge zero level is chosen considering many factors, like the USGS references (or benchmarks) that are near to the gauge site, or an historical level that may have been used for a hundred years or more. These gauge zero levels aren’t changed very often.
In addition to the local economy being impacted by low river levels, such as river traffic (barges) being halted, or river cruises being delayed, it can also have health impacts.
Reduced stream and river flows can increase the concentration of pollutants in water and cause stagnation, which can affect fish and other aquatic life and water quality.
Also, runoff from drought-related wildfires can carry extra sediment, ash, charcoal, and woody debris to surface waters, killing fish and other aquatic life by decreasing oxygen levels in the water.
Finally, many parts of the United States depend on groundwater as a primary source of water, including the Mid-South. Over time, reduced precipitation and increased evaporation of surface water mean that groundwater supplies are not replenished at a typical rate.
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