Chapter Hazard Analysis

Chapter 2. Hazard Analysis

2.1.Overbank Flooding

The most common and most damaging floods occur along rivers and streams and this is called overbank flooding. Overbank flooding of rivers and streams can be caused by one or more of three factors:

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  Too much precipitation in the watershed for the channels to convey
  
• 
  Obstructions in a channel, such as an ice jam or beaver dam, and
  
• 
  Large release of water when a dam or other obstruction fails.
  

All three of these factors are reviewed in this section, but most floods are caused by the first, too much precipitation in the watershed.

Flooding can also occur in streets when rainwater can’t flow into a storm sewer. Basements can flood when rainwater can’t flow away from the house or when the sewers back up. These problems are usually caused by heavy local rains and are often not related to overbank flooding or floodplain locations. Data on these sewer backup and local drainage problems are included in the later section on thunderstorms.

Precipitation: Kane County receives an average of 32 – 36 inches of rain each year, including an annual average of 39 inches of snow (generally, 7 inches of snow has the equivalent water content of one inch of rain). However, it is not spread out evenly over the year. The amount of rain that falls varies from storm to storm and varies over an area.