Flooding, Floodproofing, & The Water Cycle

Flooding & Flood Zones

Building in a flood zone is considered a special construction circumstance as it presents special problems and issues to think about. If possible, it should always be avoided. Whether or not a site gets flooded, heavily influences a site's value. Building in a flood zone is typically done near or in urban areas that are already established with cultural value and the need outweighs the risks. Flood zones are typically around rivers and low lying elevation areas. If you have a marsh, stream, river, lake, or other water feature on/near the site, you should do more investigation into whether water will affect your building site.

• Because through the natural cycle of water, the floodplain will eventually be flooded at some point in time. That type of land should ideally be reserved for open space uses, such as recreation and agriculture. This land can provide a natural, park-like easily maintained setting.

# Year Flood

100 year flood zone is an area which has a 1% chance of having a flood.

• This process is done by taking “one” divided by the year (100/1 = 1%)
• This means there is a 1% chance of having a flood within ANY given year.
• A 100 year flood has a much larger magnitude than a 10 year flood, and inundation a lot more land than the 10 year flood. Therefore, when designing, its best to use the 100 year floodplain as a base, and build up from there.

1,000 year flood zone is an area that has a 0.1% chance of having a flood.

• (1000/1 = .1%), or a 100% chance of happening once every 1,000 years.
• Another way to think of it is that it has a theoretical 100% chance of happening sometime in 1,000 years.

While a 100 year flood technically has a 1% chance of happening any year, it's not uncommon for it to happen twice within a couple years. The fact that weather patterns are changing has made weather patterns less predictive and more violent. It is likely that flooding will continue to get worse than previously expected.