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The agricultural risk map is based on activity classed as arable horticulture or improved grassland by the CEH land cover map 2007, which is carried out on land parcels scored against a matrix of risk factors and the 2015 status of WFD enrichment indicators. These risk factors have the potential to contribute to in-stream biological, chemical and physiochemical impact. The land cover classes arable horticulture and improved grassland together delineate the boundary areas of intensive agriculture and constrain the area for relative risk assessment. They also contribute to the risk factor scores with a distinction made between their relative risks.
A modelling application SciMAP was applied with a 5m DTM to produce sediment source and deposition areas as well as identifying significant hydrological links to the river network.
Each risk factor has been assigned a relative weighting from 0 – 1 dependant on its contribution to the overall risk (expert judgement/advice and literature review). These weightings have been used as multipliers for a three category risk index, 1 - 3 relating to banding of risk factor variables into increasing risk. The scores are then totaled to provide an overall risk for each land parcel. These can also be filtered on hydrological significance.
Risk categories boundaries are determined by selecting +/- 1 standard deviation of the distribution of the scores. This provides a statistical basis for the low, medium and high risk category limits. Further categories can be created by increasing or relaxing the standard deviation applied. The extent of the area included in each category is dependent on the stringency of the standard deviation applied.