U.S. Geological Survey field crews in Maine are working December 20-23 and December 26-30 looking for evidence that will tell scientists and communities how high the flood waters reached from the recent heavy rains that hit New England and most of the East Coast. Crews are also measuring flood waters in some areas and repairing USGS streamgages damaged during the storm.

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Preliminary USGS data suggests the ongoing flooding in many places across The Pine Tree State is likely the second worst in the state’s recorded history. The data collected from these field efforts are crucial for scientists to accurately determine flood levels and verify any flood records that may have been set. 

USGS crews will work throughout the state with a focus on rivers in or near Augusta including the Kennebec, Saco, Piscataquis and Androscoggin rivers. These specialists will scout the areas looking for high-water marks – telltale signs of how high waters reached. During a flood event, rising waters are laden with floating debris that can stick to trees, buildings or other structures. Once flood waters recede, the line of debris left behind is a high-water mark and these delicate lines will indicate to scientists the highest point the flood reached. In total, crews across the state are aiming to collect around 500 water marks.

The physical evidence of flood levels that high-water marks provide is valuable information that can be combined with other flood data USGS experts can use to reconstruct precisely where, at what depth, to what height, and to what extent floodwaters inundated a region. Right after a storm, the USGS’s early information from high-water marks can help emergency managers make informed flood management decisions, which can help protect lives and property.

As with most major flood events, the USGS is partnering with the Federal Emergency Management Agency and other state and federal agencies to flag and survey high-water marks elevations in areas that were flooded to determine the extent and severity of the flooding.

The data associated with high-water marks has other uses long after flood waters recede. For instance, those marks connected to inland river flooding can be used for future flood forecasting, predicting the severity of future floods and also for delineating the FEMA floodplain maps. High water mark data collected across Maine from this flood will allow FEMA to revise its current maps for the affected areas and be used for their flood frequency calculations, which identifies areas that are likely to experience high water in the event of a flood that has a 1 percent chance of happening in any given year. These floods, known as 100-year floods, serve as the foundation for flood management planning.

Another significant use for these high-water marks is the USGS Flood Inundation Mapping effort. A flood inundation map shows the extent and depth of flooding that occurred in various communities as a result of a major storm or flood event.

Inundation maps are one factor used to determine where changes should take place in building codes to help communities be more resilient; where evacuation routes should be; where (and how high) a bridge or road should be; and other community planning efforts. Once these flood inundation maps are complete, they will be documented in a USGS-series report and the associated data will be publicly available online.

For more than 125 years, the USGS has monitored flow in selected streams and rivers across the United States. The information is routinely used for water supply and management, monitoring floods and droughts, bridge and road design, determination of flood risk and for many recreational activities.