Fluvial flooding can be referred to as flooding from the river during persistent and high rainfall events. The Environment Agency tends to refer to flood risk is terms of probability of occurrence:
- Less than 1 in 1000 (0.1%) chance in any given year very Low
- Less than 1 in 100 (1%) but greater than or equal to 1 in 1000 (0.1%) chance in any given year Low
- Less than 1 in 30 (3.3%) but greater than or equal to 1 in 100 (1%) chance in any given year Medium
- Greater than or equal to 1 in 30 (3.3%) chance in any given year High
Over the last few years, Yorkshire has been subjected to numerous high flow and flood events which has had serious implications, putting people lives, businesses and properties at risk.
Below are some reasons why we might be seeing increase frequency of flood events;
Climate Change: A warmer atmosphere has the ability to hold more moisture, therefore we have evidence of increase extreme events, resulting in heavier rainfall.
Over population: As we become more populated, we need more houses to support growing populations. This ultimately puts more people at risk of flooding, especially when more houses are being built on natural flood plains.
Increasing impermeable surface: Urbanisation has led to more impermeable surfaces. Increasing run off rates which means more water is entering rivers and stream quicker.
Changes to the natural environment: Throughout history, humans have made changes to to the natural environment which could increase our risk of flooding.
- Trees: The UK has relatively little tree cover, especially compared to a few centuries ago. Trees play an important role of retaining water in the environment as well as slowing the flow of water.
- Channel modifications: Straightening, channelisation, dredging and reinforcing of river banks have all led to increase rates of water moving downstream. Many of our rivers are heavily incised, which means water has less chance of using its natural floodplain.
- Compaction: Intensification of agriculture has led to increased compaction of the land from increased stocking rates and heavier machinery. Compacted land has less ability to absorb water increasing the rate of surface water run off.
- Loss of in-stream habitat: With the loss of trees, we have also experienced the loss of in stream habitat, such as Large Woody Material falling into river. This types of in stream structure increases channel roughness which ultimately slows the flow of water.
- Loss of wetland habitat: Like our tree cover the Uk has significantly lost its amount of wetlands. Wetlands play an important role of storing water in the environment.
For more information visit the National Flood Forum website.