Discharge increases steadily downstream as more tributaries add water to the river. The map on the left shows the locations of four gaging stations and the graph above illustrates how discharge increases on the river between its source and St. Louis. The large increase near St. Louis is caused by the addition of the flow of the Missouri River. Click here to go to a satellite view of flooding on the Mississippi and Missouri Rivers near St. Louis. The character of the floodplain has changed to accommodate agriculture and urbanization.
Wetlands act as natural storage reservoirs for floodwaters.
They absorb water during heavy precipitation and release it slowly thus reducing run-off to streams and decreasing flood volumes. The river channel itself has been artificially constrained by levees and floodwalls. These structures serve to increase the volume of water that can be held in the channel and thus increase the size of the flooded area if the levee breaks. Build reservoirs on tributary streams to store floodwaters for later release. Levees may fail because the flood water rises over the top of the structure or the levee collapses under the weight of the water.