An Interpretation of Reservoir Sedimentation II. Clay Mineralogy

The more that is known of the influence of the nature of the contributing watershed upon sedimentation, the more will it be possible to protect reservoirs from early loss of capacity. The particular purpose of this study was to learn to what extent the mineralogical composition of the watershed soils determines the rate of sedimentation and the mineralogy of the sediments in reservoirs. Even though the soils of the 13 watersheds in Indiana and Illinois were similar in clay composition, significant relationships were found. There were only small differences between the composition of the soil clay of the watershed and that of the resulting sediment clay. The amounts of vermiculite, mica, kaolinite, and amorphous alumina in the sediment clays could be accounted for by the amounts in the soil clays. In most cases montmorillonite occurred in larger proportions in the sediment clays, while in case of quartz this relationship was reversed. The estimation of sedimentation rates from geomorphological data, including soil texture, (Paulet, Kohnke, & Lund, 1972) could not be improved by adding mineralogical parameters. This does not necessarily mean that clay composition had no effect upon sedimentation rates, but rather that the soil clays were too similar to demonstrate a definite trend.