Abstract

The purpose of this study was to determine if data on the recent sediments of Alameda Creek, Alameda County, California, supported the general observation that the size of stream sediments decreases with increasing distance from the stream's headwaters. Beginning at the stream's headwaters on Valpe Ridge and continuing 18 mi. to the town of Niles, consecutively numbered observation stations were set up at mile intervals. At each station the size, rock type, roundness, and sphericity of the maximum-sized boulder were determined. Also at observation stations 2, 5, 7, and alternate stations thereafter, 200 rocks were measured to determine the size distribution of the gravel. Volume frequency and cumulative percentages were computed from the numerical data. It was found that the maximum boulder size fluctuates throughout the entire length of the stream studied, but generally decreases as distance from the headwaters increases. The fluctuations seem to be due to constrictions in the width of the stream channel and changes in the stream gradient. The median diameter graph is very similar to the maximum-boulder-size graph. The sediments appear to be well sorted. Sphericity of the maximum-sized boulder fluctuates, whereas the roundness increases as the distance from the headwater increases. In general, the data on recent sediments of Alameda Creek support the observations made on other streams and have no major anomalies.

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