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UK Drainflow modelling

drainflow modelling, Probabilistic modelling, Spatial assessments, Geographical Information Systems, Aged sorption

New CRD tool for UK higher-tier drainflow modelling

A new tool will soon be released by CRD to assist in UK-specific higher-tier drainflow modelling. The tool exists as a spreadsheet that allows the calculation of Predicted Environmental Concentrations (PEC) in surface water following drainage in UK conditions. The spreadsheet automates the creation of input files for the 12 main UK scenarios (a combination of 4 soil scenarios and 3 weather scenarios), then running the simulations in the MACRO model for 20 years and processing the output files to calculate the annual maximum PECs.

This tool could prove to be a significant step forward with regard to harmonising the modelling submitted by different applicants, however, there are some issues that have been identified at this early stage. Firstly, users will need access to a 32-bit PC or virtual machine, as the tool uses MACRO 4.3, which historically runs on 32-bit computers. CRD is planning to develop a future update that uses one of the later MACRO 5 versions, though this may take some time. Secondly, some risk assessments can require a fourth weather scenario to be modelled (e.g. when assessing applications to maize and grassland) and this is not currently covered by the tool being developed by CRD.

Currently, the assessment requires spatial statistics for calculating the overall percentage of exceedances: Geographical data in SEISMIC (NSRI) or alternative GIS software is used to calculate the crop distribution across the drained soil types in the UK. It is expected that the new guidance that will be published with the release of the new tool will no longer require the need for spatial statistics. Then the assessment can be passed successfully by passing the criteria for each soil-weather scenario (failing no more than 60% of years in any one scenario).

Enviresearch automated approach for standard drainflow assessments

Enviresearch has been providing higher-tier drainflow assessments ever since the start of the company 15 years ago. Over time we have developed systems for automating our processes. Our in-house drainflow modelling tool is optimised for maximum efficiency:

  • Fully automated drainflow assessment from input of basic substance properties to creating the reporting tables
  • Dedicated 32-bit server to speed up model simulations
  • Cropping statistics are included for all crops listed in SEISMIC
  • Covers 20 UK scenarios (CRD approved), including the very wet weather locations

The automated process allows fast standard assessments and reporting. Quick explorative simulations can be performed for new substances or for optimising the GAP. When required, the standard higher-tier assessments are further refined, specific for the product’s need.




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