Rising to the occasion: how nature can fight flooding

You won’t be surprised to hear that heavy rainfall can cause flooding. It can saturate the land, leading to surface water flooding, and cause rivers to burst their banks. One of the most dangerous forms of flooding is flash flooding, which occurs within three hours of extremely heavy rainfall.

Storm surges are a phenomenon that occurs on our coasts; high tides combine with strong winds and low pressure to whip up sea levels and cause water to surge over coastal defences. In the UK, our east coast is particularly susceptible to storm surges due to its proximity to the southern North Sea which narrows greatly between Kent and France.

When north-northeasterly winds force more water into this narrow region, it causes higher sea levels between East Anglia, the Netherlands and Belgium. When these conditions combine with low pressure and high tides, storm surges can occur.

Flooding caused by the melting of snow and ice is relatively rare in the UK. However, if a thick blanket of snow melts rapidly, it can quickly overwhelm urban drainage systems and raise water levels in rivers and streams. If snow and ice melt on already saturated or frozen ground, surface water flooding can occur too.

The urbanisation of wetlands and floodplains essentially removes those environments (and natural flood barriers) from the water cycle. By removing vegetation, compacting the soil and concreting over these areas, we reduce the land’s ability to absorb water almost entirely. Instead, water can flow over the landscape with ease, leading to flooding.

Mismanagement and the intensification of farming can also lead to an increased risk of flooding. Excessive ploughing, the planting of monoculture crops and compacting of the land lead to degradation of the soil. This reduces the earth’s ability to absorb and hold water, encouraging greater surface run off.

Many farmers are now turning to natural water management practices, including the restoration and creation of wetlands, to combat the effects of extreme rainfall.

Perhaps the most obvious human consequence of flooding is the physical damage it can cause to homes and communities. This includes damage from the water itself and the debris and silt that it transports. However, such events also incur a financial burden and can take an emotional toll on the people and communities affected.

When a flood hits, birds, especially wetland species, are generally well adapted to survive. However, flooding can lead to habitat loss for these birds. For example, storm surges can erode valuable habitats such as saltmarshes and reedbeds, which are vital for rare species like the Bittern.

Land-dwelling species of invertebrates and mammals, such as snakes and Harvest Mice, can also find themselves caught up in extreme flooding events and, ultimately, perish. It’s worth remembering, though, that where flooding isn’t worsened by human factors like climate and land use changes, it’s a natural process and even helps to maintain wetland habitats.

In the context of conservation, hydrological engineering is a term that covers a wide variety of practices used to manage, restore, and future-proof wetland habitats. Methods include the beneficial use of dredged sediment (BUDS) and the controlled removal of sea defences.

LIFE on the Edge was a five-year collaboration between the RSPB and the National Trust and saw the restoration of a wide variety of Special Protected Areas (SPAs) across England. The project used a variety of techniques, such as BUDS, to restore these coastal wetland habitats for wildlife. In turn, the sites also became more resilient against climate change and flooding.

Traditional flood defences, like seawalls and river embankments, can be a useful tool to combat flooding. However, as climate change causes sea levels to rise and weather to become more extreme, many of our existing flood defences are proving inadequate.

With that in mind, it doesn’t make sense, financially, to build ever-larger sea defences. Instead, the combination of conservation-led hydrological engineering and natural flood management techniques can be an effective alternative.

From coastal habitats like brackish lagoons to inland peat bogs, wetlands are a brilliant natural defence against flooding. They store water during wet weather and release it gradually over time. Therefore, the restoration and conservation of our floodplains and wetlands could be an incredibly effective alternative flood defence, while also providing vital habitats for a variety of species.

Conservation techniques like the planting of native trees and plant species can also minimise the risk of flooding. Trees, for example, intercept rainfall and reduce surface run off. Meanwhile, Sphagnum moss, a key species in the formation of peatbogs, can store up to 20 times its weight in water.

Another example of conservation aiding flood management is the reintroduction of Beavers. As the rodents build their dams, they create new wetlands which store and slow the flow of water. This process can be replicated on a smaller scale when we mimic natural treefalls and create a ‘natural dam’ across rivers and streams.