Spatial targeting of diffuse pollution mitigation features: from landscapes to sub-catchments within the SCIMAP approach.
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The design of diffuse pollution mitigation schemes at the landscape scale is difficult since the spatial structure of the landscape means that not all land contributes equally. The variation in sources, related to land management, soils and geology, and the pattern of hydrological connectivity mean that critical source areas are distributed across the landscape. If diffuse pollution mitigation measures can be targeted to intercept these critical source areas, they can be more effective and hence the same water quality improvement can be achieved at lower cost and with a lower impact on agricultural activities.
The SCIMAP risk mapping framework provides an approach to predicting the location of diffuse pollution sources within the landscape based on GIS data layers. Through the analysis of the land cover information and digital terrain model, the source and mobilisation risk can be determined. The relative strength of the hydrological connectivity is calculated with the Network Index by tracing flow pathways across the digital terrain model. The sources and connectivity datasets are then integrated and accumulated through the network to produce a map of the likely source areas for diffuse pollution.
The SCIMAP risk mapping approach is normally applied with the 5m NextMap DEM dataset which gives results at the landscape extent with sub-field details. This scale of application is useful to determining which sub-catchment and which fields would be most effective for mitigation features to be targeted in those locations. Once the target areas have been identified, it is possible to use detailed Lidar or drone based topographic datasets at sub-metre resolutions. These highly detailed datasets accurately show the effects of land management, such as tracks and tramlines in fields, and the topographic drivers of the erosion risk and hydrological connectivity. Therefore, these datasets are highly useful in developing spatially targeting mitigation plans. This is an approach used by government agencies, river trusts and catchment partnership in the UK to spatially target works within the catchment.
This presentation will describe the SCIMAP framework and show how it has been applied within the Defra funded River Eden Demonstration Test Catchment project, Cumbria, England. The full River Eden catchment (2300 km2) has been mapped using the 5m dataset for both diffuse pollution and flood risk issues. The presentation will also show how drone mapping has been used to develop a 0.4m dataset for the Newby Beck sub-catchment of the River Eden to generate a spatially targeted mitigation plan. These examples will show how SCIMAP can be used to develop and refine spatially targeted mitigation plans at a range of scales.