We completed the Managed Aquifer Recharge trial on the Broxstead Estate in 2019. The aim was to determine whether we could use spray irrigation to top-up (recharge) natural groundwater stores in the winter, for re-use the following summer.
What did we find? The trial demonstrates that it is possible to ‘recharge’ the Suffolk Crag aquifer with significant volumes of water using surface irrigation. We found that we could apply up to 192mm of water (equivalent to 4 months of rain) within 6 weeks without causing runoff, damage to soils or nutrient leaching.
Following each irrigation pass, a wetting front was observed moving through the surface 1.2m and into the aquifer below although this became increasingly attenuated with depth. Attenuation and retention of water in the unsaturated zone meant that we were unable to detect any change to groundwater levels but we have to assume that nearly all of the water entered the aquifer.
Application by spray irrigation has the advantage of emulating natural rainfall and it minimises the risk of aquifer contamination but it is extremely labour intensive. This means that, taken over a 20 year period, the cost of using spray irrigation to achieve MAR storage is only slightly less than constructing an equivalent farm reservoir.
Water shortages will become more acute as the climate changes. Continued exploration of MAR is needed to help find economically viable and environmentally friendly ways to tackle this problem. The Topsoil trial has already provided valuable insights, helping to design a full scale Interreg funded pilot (felixstowehydrocycle.com) using recharge trenches in place of irrigators at Bucklesham, which will take place in 2020/21.
We would like to thank to Sustainable Water Solutions and the Broxstead Estate for running the trial, Soil Moisture Sense Ltd for providing probes, and our funders; Interreg, Suffolk County Council, Amenity & Accessibility Fund, Sustainable Development Fund and Galloper Wind Farm Fund.
The final report is available here.