The Physical Impact & Effects of Floods on Drinking Water & Sewage Systems

The most dangerous effect of flooding is the large scale contamination of water for human consumption and the biggest threat of contamination lies in damaged sewage systems. When this occurs certain illnesses can affect large numbers of people. Theses illnesses include cholera, dysentry, gastroenteritis and typhoid. Due to the proliferation of water-borne illnesses during floods, boiling or chemically sterilizing water for human consumption is paramount.

Drinking Water

• Flooding can cause fuels to mix with flood waters which makes the sterilization of drinking water more difficult as it becomes harder to boil.

  If flood levels become greater than the height of well walls then contamination occurs as the flood water mixes with drinking water. Also water flowing directly over wells or intakes poses a threat of contamination.

  Flood waters can move animal carcasses closer to intakes which increases the chance of bacteria contaminating the drinking water supply. The spread of bacteria also occurs when rising levels of water cause sewage to back up into lower lying areas such as home interiors and public throughways through toilets and manholes.

  The turbidity (cloudiness) of water can increase during flooding as can pollution from other contaminants. Both can make water unfit for human consumption.

Sewerage Systems

• Breaks in sewerage pipes can occur where erosion has left areas of pipe exposed to the elements. Particularly vulnerable areas include where pipe has been exposed across rivers or ravines.

  When the level of ground water rises, pipes can float thus causing stress on joints which can lead to damage. Also if the force is strong enough floods can simply wash sections of pipe away.

Damage to Systems, Tanks

• Where septic tanks are made of masonry rather than reinforced concrete the erosion of foundations can occur. This leads to cracks and the caving-in of tanks walls, releasing waste water which causes contamination

  Like pipes, when the ground water level rises sufficiently tanks can float. This exerts large amounts of stress on connecting joints which can cause ruptures to the septic tank which leads to contamination.

Electrical Damage

• If flood levels rise sufficiently water can damage switchboards,starters, pumps and general electrical engines causing malfunction of sewerage systems.

Sewage Treatment Plants

• As water levels rise waste water can spill out over the tops of levees. If the force of the flood is strong enough erosion can occur around treatment plant intakes, releasing waste water from the system and leading to contamination.