Flood Prevention:

Flooded Road in Illinois, July 2010

Although floods are a natural occurrence, nearly all of the most severe damage caused by flooding is preventable if intelligent land-use practices are followed.

In recent history, efforts to prevent damage from floods have focused on engineering-based approaches to flood control. I prefer to talk about a more holistic type of flood prevention which combines some engineering-based solutions with land-use patterns that minimize the negative effects of floods.

Floods: Human causes vs Natural causes:

There is nothing inherently bad or problematic with flooding. Floods are natural, and have occurred long before humans existed; healthy ecosystems are able to deal just fine with flooding, and many of them actually rely on floods to deposit nutrient-rich soil. Floods only become a problem when they occur in areas where humans have built permanent structures, or if they occur rapidly in areas where people are out in nature, and the people do not have enough time to safely evacuate.

Preventing Destructive Floods:

Floods always have a random element to them, and there is no absolutely foolproof way to prevent all flood damage. However, much of the damage caused by floods is fully preventable, by following three simple rules of land use:

• Do not build in flood-prone areas. This seems common sense, yet it is the #1 cause of damage from flooding. Most rivers naturaly have a floodplain, a flat area that naturally floods at least every several years or so. Building in a floodplain is the #1 reason that humans are negatively affected by floods.
• 
  Brick sidewalks that allow drainage create much less runoff than concrete or asphault surfaces.
  Minimize the runoff from all land. Yes, this means all land, including both agricultural, wild, urban, and suburban. Wild ecosystems, such as forests, grasslands, and wetlands, tend to absorb water slowly and hold it for a very long period of time. The few exceptions, among wild ecosystems, are deserts and exposed rocky areas, where water can run off quickly. When land is converted from wild land to urban or suburban use, or to agriculture, the runoff from the land is typically drastically increased, but this does not need to be the case. When building or paving areas, a sufficient drainage system can allow the land to drain all its water directly into the groundwater without generating any additional runoff. Or, holding ponds or artificial wetlands can be created, which can have the same effect.
• 
  Vegetation both slows runoff and speeds evaporation through transpiration
  Maximize vegetation cover. Vegetation both slows or delays runoff and speeds the transfer of water from water table to air. The more vegetation, the stronger both of these effects. Trees and other vegetation catches rainwater as it falls; some of it never reaches the ground, and that that does reach the ground reaches it slower. The root system of trees and other plants also makes soil more permeable so that water sinks into the soil rather than runs off. Plants in wetlands slow the flow of water downstream. Also, plants are constantly drawing water up from the ground and releasing it into the air in a process called evapotranspiration.

Why are we experiencing so many floods nowadays?

If you examine the history of land use practices in most of the U.S., you will find that we have violated all three of these guidelines, carrying out what is, in many respects, the worst possible land-use practices for preventing flooding:

• We have repeatedly built permanent structures in floodplains.
• Up until recently, we have engineered buildings, highways, cities, and other human edifices to run water off the land as quickly as possible.
• We have engaged in numerous practices that destroy or minimize vegetation cover, including the use of bare, treeless lawns in both residential, commercial, and public areas, the clearing of forests for timber, and the draining of wetlands to use for building on.

Use Google maps to look at aerial photographs of different parts of the U.S. How much of the land do you see left as intact ecosystems? What portion of areas in cities and suburbs are effectively maximizing vegetative cover? Unfortunately, it is a very small portion.

Most flood damage is not an "act of God"; it is a direct result of human error:

Holding ponds reduce runoff and also have other ecological benefits.

If we addressed all three of these issues, building in flood-prone areas, runoff engineering, and vegetative cover, it would not prevent all catastrophic flooding, but it would prevent many floods, and it would greatly reduce the severity of all floods.

You can use your knowledge of this subject to prevent flooding, saving lives as well as preventing the massive financial losses associated with flood damage. Maintain your own property so as to minimize runoff and maximize cover with vegetation, and make your voice heard so that you can influence policy. Zoning that prevents building in floodplains and prohibits property modifications that increase runoff can go a long way towards preventing flood damage.

Comments are moderated. Follow Cazort.net's comment policy for your comment to be approved.