With much of the UK still underwater and flooding set to continue, knee jerk reactions abound. Politicians bicker, flooded communities and farmers lobby their causes and calls are made to dredge rivers and raise embankments. All efforts should be made to protect lives and infrastructure during the flood, but the real question is not how to stop the flooding now – that is disaster management. The real question is what happens after the floods have gone.
The legacy of decisions made after flooding have long term implications and costs that are borne by future generations. A little look at history shows the types of flood prevention we should avoid and those we need to implement. One thing is clear, areas upstream and downstream of rivers are connected and must work together to tackle future flood risks.
History lessons
The great floods of 1947 – still the worst in some rivers – led to wholesale dredging, the widening and embanking of watercourses, including the removal of bankside trees, and the construction of sluices. In short, the kind of response being suggested by some as an appropriate management for our rivers after this winter’s floods.
But the 40 years of river and land management policy adopted after the 1947 floods and the flash floods in Lynton and Lynmouth in 1952 caused major environmental decline in our watercourses. The litany of loss includes swathes of wetland habitats, decline in species and the wholesale change in our rural landscape, as a result of intense agriculture production.
Rivers became characterised by higher temperatures (no shade), greater levels of silt deposits (more sources and routes for soil from intensive farming), more nitrate and phosphates (from fertiliser) and increased efficiency of flood water movement from field to flood channel. Consequently, channels were choked with vegetation and sediment, and river banks failed because they were undermined by dredging. The cost of maintaining these new watercourses was colossal to environment, exchequer and on future generations.
We’re all connected
Geomorphology and hydrology, the sciences of sediment and water respectively, show us a different view of flooding to that portrayed by the scenes of flooded individuals and communities. They show that flooding is characterised by connections between atmosphere and land (rain), land and rivers (drainage), upstream management activity and downstream flooding, upstream communities and those living downstream. The water and silt in the kitchens of flooded houses passed over the fields, through the land drains and streams, and along the rivers of those people living in the upstream catchment. Flooding reminds us that people are connected to one another by water and sediment.
In this respect, debates about town vs country are unhelpful – everyone in a catchment is involved in flood risk management now and in the future. A connected view shows us how floods are generated and how interventions we make in one place can be transmitted to other communities in the catchment. The fact is that flood peaks are a result of the intensity and amount of rainfall (climate), how quickly this water is transferred from upstream to a given downstream point (land surface characteristics and efficiency of drainage) and local factors such as the gradient of the river and the size of the channel.
Decades of government funded drainage and dredging has increased that rate of delivery of water and sediments to downstream communities. This brings with it the soils and fertilisers that build up in flood channels and require expensive dredging and weed clearance, reducing aquatic biodiversity. Similarly, urbanisation and development produces very rapid rates of water transfer into rivers, locally increasing flood levels.
Understanding connectivity also points us away from site-based solutions such as dredging, and instead opens up a much wider range of solutions that may well be cheaper to implement, more effective in the long term and under a changing climate, and less damaging to the environment. As we learned after the millennium floods and the much more damaging floods of 2007, we need a significant change in our approach to flood risk management. Crucially, we need to make it happen rather more quickly.
Strategies to slow the flow
The Slowing the Flow project is one example of what a new approach to flood risk management might look like. Developed following the 2007 floods, it is about working with nature to try and store more water in the landscape and slow its passage downstream. Here the community has been able to use a SimCity-style computer model that enabled them to see what solutions worked best and where. Local people were invited to simulate felling trees into rivers in the headwaters and then see how these affected the flood peak downstream.
So what to do after the flood? First and foremost there needs to be a full review to learn lessons both nationally and locally. This must have clear objectives to identify how better to deliver help to flooded communities under such events, what flood defences to repair and which to improve.
The entire range of options available for increasing the resilience of our catchments to future extreme events must also be reviewed. These should include zero tolerance of new floodplain development, identifying measures to trap and store more water and sediment in headwaters and on upstream floodplains.
It might include removing some old flood embankments or raising the bed levels in watercourses that were dredged in the past, where it can be demonstrated that it will reduce flood risk to communities downstream. A current example is being demonstrated by the efforts made to reduce flooding in Winchester by raising the bed of the River Itchen upstream in order to temporarily store water in meadows and wetlands.
We must also look carefully at the strategic planting of woodlands and using low berms (raised barriers) to slow the flow and store sediments upstream. We must also look at ways of offsetting the impacts of increased flooding on land upstream, ensuring that food and flood risk can operate together as part of a farm economy. For those in homes on the floodplain greater support is needed to improve flood proofing of properties, including the redesign of urban landscapes. Water storage must be increased in low risk areas and surfaces retrofitted to absorb more water.
Rising groundwater is a more difficult challenge to cope with. As these long duration floods are demonstrating, this is also a major cause of flooding. Groundwater flooding is pervasive and long lasting. New sustainable solutions for this are urgently needed.