After a few years of endless conversations about it being too wet, we have now had a spring and summer that was too dry. Met Office data shows that we are receiving (on average) more rainfall each year, with the UK now receiving about 100mm more rain per year than in 1980. We have all experienced this, plus the additional disruption to normal annual patterns of rainfall, with a greater proportion falling in winter and less in summer.
A year like this reminds us that the most has to be made out of rain when it falls, yet as this comes after consecutive winters of flooded fields there is also a need for solutions which prevent the build-up of too much water. This blog explores methods to manage water across a landscape, so that it can be stored in times of excess for use in times of scarcity. Large infrastructure projects can be invested in, such as reservoirs, however there are also much smaller actions that can be taken to improve overall resilience to flooding and drought.
Building strong foundations - Improving soil health
One of the simplest, low-cost actions to prevent waterlogging, excess runoff and drought is improving soil health. This can be done in a variety of ways depending on the soil type and land use, but increasing organic matter, encouraging biological activity and keeping the soil covered will often begin to improve its water holding capacity and water retention.
Increasing organic matter through adding compost, animal manures or plant residues improves a soil’s structure meaning that water can infiltrate much easier and deeper, allowing it to then be held in the soil for longer. Having deep rooting plants in the crop rotation, or in cover crops, can also improve this structure, and help to prevent the formation of pans which cause quicker horizontal throughflow deeper in the soil profile.
Having living roots and increased organic matter can also encourage higher levels of microorganisms and fauna to live in the soil. Some microorganisms excrete glue-like compounds which stick the soil together, increasing its structural resilience to large volumes of rainfall. Having large numbers of worms and insects in the soil can improve soil structure further as they create deep burrows and channels which rainfall can quickly flow through. In lighter soils, where drainage isn’t a problem, organic matter will still improve the soil structure, holding it together and slowing down the drainage, meaning that it will be much more resilient to drought.
Keeping the soil covered with cover crops, living mulches or undersowing will slow down the rate at which rain hits the soil. The leaves provide a surface from which water can evaporate, and also create a microclimate underneath, which keeps the soil moist and reduces the intensity at which raindrops hit the soil, helping to prevent erosion.
Managing the flow – landscape design
Whilst improving soil health is a vital first step, there is a limit to how much impact it can have. Building semi-natural features into the landscape can store greater amounts of water and hold onto it until a time of need. Swales are ditch-like features dug across a field in parallel with the contour lines at a given point. These act as a water and sediment trap in times of high rainfall, preventing runoff and holding nutrients and soil which would otherwise wash off the field. As the land dries out down the slope, this water is slowly absorbed into the soil meaning that the field has a much more gradual supply of water over a longer period. On a much smaller scale this action can be mimicked by carrying out any cultivations perpendicular to the slope. This means that at frequent intervals any water running over the field surface will be intercepted by a miniscule dam, and so its speed will be greatly reduced and it will be more likely to infiltrate before the end of the field.
Agroforestry can increase the water holding capacity of a field through the deep roots of the trees and increased biomass above ground. To amplify its impact, keyline design can be applied, meaning that the trees are planted curved along contour lines rather than in straight lines. This means that the tree rows bring some of the benefits of a swale, intercepting water as it travels down the slope, and holding the soil together. Using swales and keyline agroforestry together could bring the benefits of both systems, storing water, creating shading and microclimates, preventing erosion and improving soil structure (among many more).
Holding onto what’s there – Managing waterbodies
Rivers, ponds and the land around them are understandably key to water management on farm. Depending on the size, type and requirements of a waterbody there is a range of measures which can be added to improve its water holding capacity.
Water bodies are often connected and reliant upon other rivers, streams, stores and flows in the surrounding landscape, therefore the most effective management of these often come from collaboration with neighbours or other stakeholders so that issues aren’t tackled in isolation.
Measures such as leaky dams, pond and reed bed creation, adding riparian buffer strips (trees along river banks) or re-wiggling rivers can all have a large effect on the storage and flow of larger bodies. Smaller actions can also begin to have a positive impact on both water and biodiversity. Working with actors such as a local rivers trust can be a good place to start to get advice on which measures are most likely to work in the farm’s context and importantly to see what funding is available.
A years’ worth of rain
With sporadic rainfall patterns appearing to become the norm, it is essential that systems are in place to manage excess water in a constructive way. Forward planning enables resilience on farm to buffer unpredictable weather patterns. Considering the volume of rainfall we have had over the last few years, it has been concerning to see how quickly everything has dried out this spring and summer, especially as the UK largely isn’t set up for irrigating crops. Unlike some of the typically dry areas of the world we have seen that the UK still receives plenty rainfall. Measures such as the ones discussed here can be implemented to store water in selected locations to reduce the risk or intensity of flooding, whilst creating an opportunity to harvest water to be used later when needed. Thinking about water over a larger spatial area (such as across the whole farm or river catchment) and across a longer timescale of at least an entire year is becoming of increasing importance in the design of a resilient farm business.
By Megan Dunn, soils and natural resources assistant at Innovation for Agriculture
