Flood Information

According to the National Oceanic and Atmospheric Administration (NOAA), “Storm surge is the abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide. The surge is caused primarily by a storm’s winds pushing water onshore. “

The exact height of the storm surge and which coastal areas will be flooded depends on many factors:

• the strength, intensity and speed of the hurricane or storm,
• the direction the storm is moving relative to the shoreline,
• the slope of the sea floor is along the shore.

Storm surge causes sea levels to rise for a relatively short period of time, typically four to eight hours often resulting in extensive coastal flooding that can weaken or destroy coastal structures. Some areas may take much longer to recede to their pre-storm levels. Storm surge permits “dangerous and battering waves” and floating debris to come in contact with coastal areas and structures not built to withstand the punishing effects of ocean waves.

Battering waves cause beach erosion and extensive damage to coastal structures such as buildings, roadways, bridges, marinas, piers, boardwalks, and sea walls. Breaking waves at the shoreline become very destructive, causing damages to natural and manmade structures by hydrodynamic pressure, battering solid objects and scouring sand from around foundations.<>

While hurricanes are the most violent type of storm and receive the most attention, serious flooding and erosion problems are also caused by other coastal storms. In the Atlantic, extratropical storms also known as Nor’Easters, develop in the fall, winter and spring occurring much more frequently than tropical hurricanes. They may be more than 1,000 miles in diameter, much larger than a tropical hurricane. Maximum winds speeds of Nor’easters are usually of lower than those of tropical hurricane winds, some wind gusts with hurricane velocity of 75 miles/hr. or greater. These storms may stall off the coast of the North Atlantic states and produce high tides that persist for several days.

Overbank flooding of rivers and streams is the increase in volume of water within a river channel and the overflow of water from the channel onto an adjacent area of low-lying ground. This represents the classic flooding event that most people associate with the term “flood.” Overbank flooding is the most common type of flood event. Hundreds of riverine floods, great and small, occur annually in the United States.

The City of Newport News is situated at the junction of the James River and the Chesapeake Bay. Due to this location, many of the effects of riverine flooding along the James River are lessened in the Chesapeake Bay resulting in flooding more like tidal flooding. Along rivers such as the James, the timing and elevations of flood peaks can be predicted relatively far in advance and with considerable accuracy.