Sediment–landform assemblages and digital elevation data: Testing an improved methodology for the assessment of sand and gravel aggregate resources in north-western Britain

This paper uses the results of a series of sand and gravel resource assessment surveys to refine and improve the methods used for identifying aggregate resources in north-western Britain. Geomorphological surveys of the Cors Geirch and Rhosesmor areas of north Wales and the lower Ribble valley in Lancashire, carried out by 1:10,000 scale field mapping, are compared to resource assessments made using high resolution Digital Elevation Models (DEMs) of the same ground. The DEMs proved useful tools for remote geomorphological survey, but precision was significantly better for the Intermap NEXTMAP and, particularly, the Environment Agency LiDAR dataset. Only the LiDAR data revealed with any clarity small-scale and low relief features, for example scroll-bar palaeochannels on river terraces. The identification of sediment–landform assemblage zones from geomorphological survey permits the identification of the primary sedimentary process responsible for each assemblage and the attachment of an ideal sedimentary facies model to it. Each model can then be used to predict sedimentary composition, the optimal location of boreholes and the location of resource blocks. Combining the use of DEM data and the Spatial Analyst toolset within ArcGIS™ (ESRI) allows rapid accurate delineation of landforms and the use of cut and fill functions allows more accurate estimation of the volume of resources than the traditional calculations based on area and average thickness. These new methods improve the accuracy and cost-effectiveness of geomorphology-based aggregate assessments, notably where the mineral-bodies are concealed beneath minimal overburden and produce characteristic landforms.