Consequences for high tide flooding

For the last 27 years the sea levels have risen by almost 4 inches (100mm) - with an average of ⅛ inch (3.3mm) per year. It is partly attributed to the increase in ocean temperature, which causes sea water to expand. Another contributing factor is the added water from melting glaciers.

Sea level rise is, however, only a part of why flooding has become more frequent. More intense storm surges, caused by global warming, is another important reason. The combination of these factors makes coastal areas more exposed to being flooded than ever before and the problem is likely to increase in the future.

The amount of stormwater is also increasing in many geographical areas and the amount of storm water is less evenly spread. Rain and water melting from snow and ice is appearing in larger quantities.

High tide flooding is increasing in the US

High tide flooding has increased with 50% in the last 20 years and with 100% the last 30 years in the U.S. By 2035, nearly 170 coastal communities in the United States are projected to experience flooding more than 26 times per year.

An example of an area that has been impacted by flooding is Wilmington North Carolina and Mount Pleasant in South Carolina to just mention a few. Both these locations have been able limit the impact of high tide flooding by using check valves.

The consequences of flooding cause long term problems

Flooding from high tides causes long term effects for inhabitants and will also affect the environment in a negative way. It also generates major costs for cities, its businesses, and residents. The financial impact will also lead to higher taxes or that other important infrastructure projects will be delayed. Society needs to be one step ahead of the flood.

We have divided the consequences into the following three categories:

Problems for the environment

  • Untreated water from water treatment plants and pump stations can flow into the sea and other water bodies
  • When flooding occurs stormwater can be polluted and more easily transport environmental toxins to the sea and other water bodies

Problems for inhabitants

  • Costs for decontamination and insurance of houses and wastewater sewers
  • Bad smell in buildings
  • Private property that cannot be relocated will be affected

Problems for cities and communities

  • The society will be affected and stop functioning as usual
  • Saltwater can damage roads and buildings so that it needs to be rebuilt or repaired
  • Saltwater can damage cars and public transportation equipment
  • Flooding can have a major impact on cultural objects and buildings
  • Long term costs will arise for rebuilding infrastructure and buildings
  • Short term costs will arise for decontamination, rescue, and insurances

Consequences of high tide flooding for sewer and stormwater systems

When the water level is rising in seas and rivers, water can start to flow backwards in the sewer and stormwater system. This might lead to that water level reaching the pump stations emergency overflow. The pump station might be damaged if they will be flooded. The pump stations might also start to pump cleaned water to the water treatment plants. The backwards flow of water can also lead to flooding on streets, basements and in wastewater systems.

When the wastewater treatment plant is flooded it needs to treat already clean water on top of the normal wastewater flow. A wastewater treatment plant constructed for a specified daily flow cannot handle increased water flows effectively. This will increase costs for wastewater treatment.

The treatment itself will also become less effective. Seawater can affect the bacteria that is used for treating wastewater. Water that is not treated according to specifications will reach the sea. This leads to an increased environmental impact and fines can be raised for not treating wastewater in line with environmental rules and regulations.



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