How to Use the USGS Flood Inundation Mapper

A Lesson

How to Use the USGS Flood Inundation Mapper

by Grace Fear, Operation Clean Stream intern

A representative of the United States Geological Survey (USGS) Central Midwest Water Science Center (CMWSC) came to the OSC office on Wednesday, June 5th, 2019, to demonstrate how to appropriately read streamflow and water levels from USGS stream gauges. Current streamflow and water level information for USGS gauges in Missouri, Iowa, and Illinois can be found on the CMWSC USGS Water Dashboard. At select stream gauges, the spatial extent of streamflow and water levels during flooding can be found on the USGS Flood Inundation Mapper, or FIM, and we were taught how to access them, read them, and understand them.

USGS provides scientific research on “the natural hazards that threaten lives and livelihoods, the water, energy, minerals, and other natural resources we rely on, the health of our ecosystems and environment, and the impacts of climate and land-use change”(1). As a fact-finding organization, USGS obtains data and shares it with the public.

In order to measure flooding, USGS has gauges throughout rivers that measure the water levels and send information back to a lab, which processes the data. In the graphs below, we can see both the USGS measured information that has been reported back to the lab and the National Weather Service predictions of water levels. These water level measurements and predictions can be used for planning and preparedness.

By utilizing the FIM, we can see many different aspects of flooding. When you select a gauge, you can see both the height of the gauge and how much water is passing through it. There is also a sliding scale where you can see how much the river would flood if the gauge reaches a certain height. For example, in the screenshot below, the gauge was being measured at 18.35 feet. You can also click on a section of the map to see what the estimated water depth is at a certain gauge height.


If you are interested in seeing how high the water would be at a certain gauge height, you can adjust the slider to increase it. If you slide it to 30 feet, you can see the estimated flooding portrayed on the geographic map. Again, you can see the estimated depth at a specific location in order to plan for and prevent damage caused by flooding.

Knowledge of this tool and how to use it is important for organizations who engage volunteers in river cleanups and other events on our region’s waterways in order to be more prepared. If you are interested in learning more about USGS, you can do so at https://www.usgs.gov and you can access the Flood Inundation Mapper at this link.



  1. United States Geological Survey Website