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The bank full stage is often used as a trigger point for mobilizing flood fight operations. Notes As water levels increase, the river begins to overtop its' banks and expand out onto the floodplain. The next benchmark that may be reached is flood stage. Flood stage is an artificial level established by the National Weather Service (NWS) in cooperation with local officials. It is designed to indicate an elevation where appreciable damage begins to occur to urban or agricultural properties. Note that a river may be out of its banks and still not be at flood stage. Also, flood stages may be adjusted from time to time as changing conditions warrant. Flood Stage Bank Full Stage Increasing water levels can be measured at United States Geological Service (USGS) monitoring stations or private river gages. A good system of river gages is a vital tool for river forecasters and can increase the accuracy of flood warnings. Ideally, gages are placed where they can be easily read, even at high water levels. Assured access routes to gage sites are important. In areas where the gage may be isolated by high water ------~---levels,consideration should be given to automating the reporting functions of the site. ) All river gages should be "zeroed." River gages should not be arbitrarily installed along a river system. Survey crews or engineers are normally called to survey gage sites and determine surface elevations. The readings on the river gage should correlate to local surface elevations based on the National Geodetic Vertical Datum (NGVD) or elevation above mean sea level (MSL). This allows the gage reading to be correlated to surface elevations on topographic and other survey maps. The "zero" of a gage is the elevation added to a gage to obtain the true height of the gage above MSL. In addition, gages should be installed so that they do not obtain negative readings, even at very low water levels. Negative gage readings increase the chance for reporting errors. Page 1 - 5