Quantifying the effects of return flows from spray irrigation in a regional model

Regional groundwater models are the standard method in England for assessing impacts of abstractions on environmental receptors. Whilst these models account for numerous natural and anthropogenic processes, the application of spray irrigation to crop-growing areas has been omitted. Using the North East Anglian Chalk (NEAC) groundwater model, the effects of including spray irrigation as additional rainfall to arable areas is investigated. Under a fully licensed scenario, increased evapotranspiration accounts for approximately 60% of the assigned spray irrigation volume, with increased recharge equivalent to 28% of the total and smaller increases in interflow (9%) and runoff (3%). The majority of this additional recharge occurs between October and December, after the main April to September period for spray irrigation, highlighting the effects of wetter soils that encourage greater infiltration of winter rainfall. Overall, modelled compliance to environmental flow metrics is improved under both Q50 and Q97 conditions, indicating greater availability of water and highlighting the importance of modelling all elements of the water balance.