How floods are predicted
How the system works
The flood warning system requires a cooperative effort
A local system for Steuben and Chemung Counties in NY (audio clip)

A TECHNICAL REPORT ABOUT HOW THE SYSTEM PERFORMED DURING THE JANUARY 1996 FLOOD (PDF)

How floods are predicted

Forecasters use past experience, computer models, knowledge of flood-prone areas, weather forecasts, and observed data such as rainfall, river stages, and water flow to make predictions about how high rivers and streams will get at certain locations and when they will recede.

Knowledge of topography, geology, and hydrology is important. The following are two distinct ways that the basin's topography and geology contribute to flooding.

The first situation occurs when a section of river is very wide, but then is suddenly squeezed into a steep, narrow gorge. During heavy rainfall events or when the winter ice begins to break up, the increased flow of water or ice backs up in the narrow gorge, causing the river to overflow its banks. Also, when the ice jam breaks, a sudden surge of water can cause downstream flooding.

The second situation occurs when a river flows through an area with very little slope, and shallow banks. In this topography, which is fairly common in the basin, the river levels out and flows slowly. During heavy rainfall events, the river quickly swells and overflows its banks. When winter ice breaks up, the slow-moving flow causes the ice to jam easily, creating obstacles and backing up the water.

How the system works

The flood warning system requires a cooperative effort

The National Weather Service is in charge of issuing daily river forecasts and flood warnings.

The U.S. Geological Survey provides data to the National Weather Service on precipitation, river stages and water flow from a network of stream gages. The Baltimore District of the U.S. Army Corps of Engineers also provides reservoir and gaging information.

Warning time is increased as a result.
Click here to hear AUDIO CLIP. 42 sec. RealAudio)

"The Environmental Emergency Services in Steuben and Chemung Counties operates an automated rain river gage. And we actually have climate stations also tied into an automated system. That goes into a computer providing alarm capability and greater lead time. To be able to pull this information together over two counties to get a good concise amount of information of what a weather system is actually doing to our area. It allows us to provide much, much more accurate information and in a much more timely basis so that the warning time is increased a great deal for this area." -Mike Sprague, Director, Steuben County Emergency Services

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