First harvestless farming year?

Originally written for GWCT Gamewise Magazine

18 This Beetle Bank Stopped The Soil Reaching The River

John Szczur reports on unprecedented rain which has damaged habitats and put harvest in doubt. John Szczur is the ecologist at our Allerton Project farm. He is passionate about wildlife and how to help farmers combat climate change.

It is fair to say that the previous winter’s weather brought home the impact that our changing climate can have on farmland and rural communities. A shift towards wetter winters has ramped up the challenges that clay soil farmers face in farming sustainably. These were evident at the Allerton Project farm and nearby research sites as late autumn and winter rains were locally unprecedented, with up to twice as much as for other comparable periods.

It all began with a particularly wet October courtesy of storm ‘Babet’. An intense affair with 45 of the 60mm day’s total in nine hours, following almost 20mm less than a day earlier. This situation did not match the forecast for the Midlands, frustratingly catching out our research monitoring. Fortunately, the ground was not completely saturated when ‘Babet’ hit, otherwise it would have been a different story. Storm ‘Ciarán’ followed onto wetter ground with 27mm (an inch) spread over two days having a similar surface run-off impact to ‘Babet’.

Into November and saturated soils struggled to shed their moisture as soil temperatures dropped below 10°C. Any subsequent heavy rain will form surface run-off and that’s what happened. Storm ‘Gerrit’ was quickly followed by ‘Henk’ leading to the highest local stream levels in the 12 years of monitoring of our ‘Water Friendly Farming Project’. Inevitably, this resulted in damage to our research infrastructure and farmland habitats.

No single measure can alleviate the effect of this amount of rain and a suite of mitigation measures are required. They begin ‘in field’ with the need for a healthy soil. A non-saturated clay soil in good condition will infiltrate 2-5mm/hr of rainfall. Delaying the point of soil saturation will also help and a cover of vegetation can reduce rain erosion and maintain soil water pathways. Once a surface flow begins this vegetation can help slow water/soil movement. Last winter many of our steeper arable fields were modified by surface water run-off creating erosion channels and deposition flats.

18 Leaky Dam Flood

Over 30 leaky log dams were constructed in the upper Eye Brook catchment and these have been shown to be effective in reducing flood peaks.

A local stream, the Stonton Brook, overtops its channel during major rainfall events. This winter saw the stream trying to break into the adjacent arable field, opposite a wood and grassland bank. All remained resilient, but many field drain systems were unable to cope. Over engineering of these systems and culverts may be an action for the future as once in the ditch or stream there are further opportunities to reduce the flow impact. Large well-vegetated ditches slow flow and trap sediment, and diverting flow from these smaller watercourses into areas of temporary storage with no long-term consequences has become a necessity.

The contribution that farmland can make to flood control is paramount. As part of our Water Friendly Farming Project natural flood management techniques are being explored and researched. Over 30 leaky log dams were constructed in the upper Eye Brook catchment and these have been shown to be effective in reducing flood peaks. However, such structures are vulnerable to severe stream flows with seven destroyed and others, along with a temporary storage pond, damaged during last winter’s flows. Newer design leaky dams were largely undamaged. Whether these measures are cost effective is questionable, so in tandem we are exploring more natural methods such as laying trees into the stream (tree-hinging) and creating planted willow barriers. From our research into water sampling of major flows, we can assess just how much soil is being lost from catchments and validate any future mitigation measures. As I write, March and April have continued the wet theme and we are edging ever closer to Allerton’s first harvestless farming year.


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