The River hasnt been that high since...

If you looked at the Roanoke River during the major flood event last month, you probably realized that the river hadnt been that high in quite some time.  In downtown Roanoke, where the Walnut Avenue river gage is located, the water rose to a depth of 17.82 feet; the highest it had been since April 22, 1992, when it reached a depth of 18.10 feet. 

The United States Geological Survey (USGS) has recorded water levels and flows at the Walnut Avenue gage since February, 1899.  Over the years, the 395 square mile area which encompasses the gages drainage area has undergone many changes.  Significant  in terms of increasing the threat of flooding, has been the amount of urbanization which has occurred within the basin.  Looking back through the 105 years of record available for the Walnut Avenue Gage, major flooding has occurred in Roanoke a total of seven times. 1928, 1940, 1972, 1978, 1985, 1992, and 2004.  The causes for six of the seven major floods were hurricanes.  The 1992 event is the exception, as it was caused by a late Spring low pressure center. Note that five of the seven major floods have occurred in the last 32 years. This might be a consequence of urbanization...or simply that we have experienced an overall greater frequency of heavy rains and hurricane activity during this period.    

The National Weather Service (NWS) in Blacksburg is responsible for forecasting floods on the Roanoke River. At the Walnut Avenue location, the NWS has defined Flood Stage to be 10 feet. We define flood stage as the minimum depth of water at which damage occurs. For example, although Wiley drive and various sections of Wasena Park are flooded when the water reaches 8 feet at the Walnut Avenue gage, no damage is caused. At 10 feet however, cleared land along the river is flooded and several businesses and industries risk loss to equipment or materials. Major flooding in Roanoke begins at 16 feet at the Walnut Avenue gage. The NWS defines major flooding as:  Flooding which results in extensive inundation and property damage. It is usually characterized by the evacuation of people and livestock and the closure of both primary and secondary roads. As many can attest, the September 2004 flood certainly met the criteria for major flooding.