The clay till are interspersed with layers and lenses of sand and gravels of varying extent. Both the predominance of clay tills and the changing depths and thickness of the sand/gravel were confirmed in the Holderness Till. The uniformity coefficients, the ratio of sand to silt, and the percentages of gravel, sand, silt, and clay were calculated for all the catchment samples. Firstly, to determine precisely the extent of the sand/gravel areas within the glacial till and secondly, to establish whether the sand/gravel and the clay areas of the catchment behaved in hydrologically distinctive ways. The results confirmed that the higher the ratios and uniformity coefficients are for the sand areas which contributes to the higher permeability and hydraulic conductivity and that the lower ratios and uniformity coefficients are associated with the areas of clay which contributes to the lower permeability and hydraulic conductivity. The effective size is an indicator commonly used in the application of particle-size distribution to hydrological and hydraulic study.
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