Building on floodplains
Lessons to be learnt for the Western Growth Corridor
As we approach winter, we have already seen examples locally and nationally of extreme weather events and their impacts on people and wildlife with rivers spilling out into historic floodplains. We had a month’s worth of rain fall on Wainfleet earlier in the year over a 24-hour period. A similar amount of rain caused the devastating flooding in Doncaster, Fish Lake and closer to home on the Barlings and Timberland Delph, flooding houses and farmland. Drone footage, taken over the Western Growth Corridor recently, shows large areas of standing water across the landscape that, once built on, will be people’s houses and gardens.
Lincolnshire is quite a modified landscape with land reclaimed from the sea. Marsh and rivers, that have historically been over-deepened to drain land, are now disconnected from their floodplains. Floodplains serve as a vital storage area for water and fine sediment, which contains valuable nutrients. This is why the River Nile supported the great Egyptian civilisation and was critical to their farming, bringing valuable nutrients when the river spilled out into its floodplain. The situation we have now in Lincoln and Lincolnshire as a whole is that due to dredging and embanking our rivers, the silt is trapped within the channel rather than spreading itself across the land. This silt creates a costly maintenance burden for the river authorities as the river attempts to reverse historic management and shallow up enabling it to reconnect and spill back out onto the old floodplain. This build-up of silt exacerbates flood risk and also leads to an increase in nutrients in the river causing unsightly toxic algal blooms in summer that kill fish and encourage excess wetland plant growth. This further chokes the channel and increases maintenance and flood risk.
These historic changes to the river prevent the river from dispersing its energy by flooding into its floodplain and instead increase the river’s energy and power. This means that flood defences like those in the local area are at more risk of failure and breach. Floodplains are typically wide. In a natural system, the river rises and then, when it spills out into the floodplain, the river’s energy reduces and the river is less prone to eroding or getting to a point where it spills out, and endangers people and property. Compounding the problem of drainage is the run-off from roads, houses and concrete driveways which prevent the water from being absorbed into the ground and instead channels it into the drains and rivers faster than it can drain into the sea. This means increased flood risk but also increased drought risk – as without the water travelling through the soil to underground aquifers we don’t have water supplies for crop irrigation or drinking water.
Rising sea levels from climate change further impact on our rivers’ ability to drain. All our rivers have tidal gates that prevent the sea from flooding the land. When the tide is high, the river can’t discharge and levels build up and flood risk increases. The flood map for 2050 shows half of Lincoln impacted by potential flooding due to sea level rise – never mind extreme weather – with the Witham at Lincoln becoming tidal once again.
With the increase in extreme weather events and 7,000 homes already at flood risk in Lincoln, the Green Party asks, is it sensible to add another 3,200 homes into the floodplain surrounded by the Catchwater drain and the Foss Dyke? Building here will only lead to future heartbreak and devastation in the longer term when floods become more prevalent.
Not to mention the other problems which building more infrastructure into an already overwhelmed city will cause: increased traffic congestion on Skellingthorpe Road; with more air pollution leading to more asthma attacks, heart disease and strokes.
We in Lincoln and Lincolnshire will not be able to build ourselves out of this problem with higher defences, more maintenance (such as dredging) or flood storage schemes to mitigate this risk. These schemes are extremely expensive and are calculated against the risk to population and houses. This is a predominantly rural area and any available funding will need to be spread nationally against other more populated areas that may have more properties and people at risk.
- Do not increase the number of people at risk from flooding by building on unsuitable land
- Look at the benefits of working with nature to allow water to reconnect with historic flood plains
- Provide compensation for farmers who use their land to soak up water and allow our aquifers to recharge.
- Plant trees on flood-prone land or recreate flood meadows or bogs. These measures all help to absorb carbon dioxide, slow the water downstream, take the nutrients out of the river and provide more green spaces for recreation.
These measures need to be carried out alongside the traditional approaches of better flood defences and preventing soil loss into watercourses.