Missouri River Expected to Surge Past Agriculture Levee

The city of Chesterfield is mobilizing its flood watch/warning system in response to the likely prediction that the Missouri River will have overtopped the agriculture levee in Chesterfield Valley by Sunday morning. 

According to the predictions from the National Weather Service late Saturday night, the river will crest at around 33.4 feet at its St. Charles gauge a half-day downstream from the Valley. The river is considered to have reached "major" flood stage at 36 feet.  

By comparison, the great flood of 1993 saw the same gauge hit 40.4 feet. For more information, read the alert below from the city's public works department sent out Saturday afternoon. 

In accordance with the City of Chesterfield's operations plans, we have initiated the Valley Watch phase.

Given the news related to the storms, flooding and river levels, amount of news regarding flooding, levees, and severe weather; I Just wanted to share the current and near term predicted levels for the Missouri River.

Public Works Staff monitors river conditions continuously and as conditions warrant, we will initiate reports and advisories in accordance with the City's adopted flood watchwarning system.

As you can see from the chart below, the St. Charles gauge (which is approximately one-half Day downstream from Chesterfield Valley) was read at 29.78 feet at 8:30 am this morning. It is expected to rise significantly in the next 24 - 36 hours, with an expected crest of 35.7 feet. These projections Included expectedpredicted precipitation for the next 24 hours.

The Hermann gauge, which is approximately one day upstream of the City, is used as a predecessor indicator of what is heading our way. The Hermann gauge had a reading of 31.6 this morning, and is expected to crest at 32.7 early Sunday morning. 

We expect that the agricultural levee, located on the north side of the main Monarch-Chesterfield levee, north of Highway 40/64 will overtop in the next 24 hours. While overtopping of the agricultural levee in itself does not constitute any threat to the main levee, it is an event that is visible and often mis-interpreted. The agricultural levee is at a level that is expected overtop at ten year intervals on average.

That area between the Monarch-Chesterfield levee and the agricultural levee, will likely become inundated in the next 24 hours. A significant portion of the Monarch-Chesterfield Levee Trail is already closed due to the construction of the new Missouri River Bridge. However, as river levels increase, it may be necessary to close other sections in order to provide for the best river monitoring and response scenarios.

By way of comparison, the Great Flood of 1993 crested at an elevation of 40.4 feet at St. Charles. Since that time, the Monarch-Chesterfield levee has been raised and improved dramatically. I would also point out that the agricultural levee has not been overtopped since 1995. The agricultural levee is generally described as a ten year levee. Under normal, average conditions, we would expect the agricultural levee to overtop on a ten year average frequency.

For a more recent comparison, Herman crested on September 17th of 2008 at 28.9 feet, and St. Charles crested at 31.74. The Agricultural levee was not overtopped and water barely reached the toe of the levee on the west end. Every event is unique and has its own set of conditions, but this should provide a reasonable perspective.

That being said, it is also important to understand the difference between riverine flooding and flash flooding. Given the saturated ground conditions and seemingly continuous rainfalls, small waterways, creeks, and tributaries are subject to flash flooding. Localized intense rainfalls can cause such waterways to quickly rise, flood, and inflict dramatic damage.

Please be aware of the dangers of flash flooding. If you encounter flooded roads or standing water, do not attempt to drive through the water. Find another route. As little as 6 to 8 inches of water can lift and float a vehicle. If the water is flowing, it is even more dangerous. Avoid creeks and waterways when possible.