AREAL AND SEASONAL VARIATIONS IN BEACH AND NEARSHORE SEDIMENTS AT LA JOLLA, CALIFORNIA

Abstract
The study showed that the areal distribution of certain physical properties of beach and near shore sediments tend to be continuous, and that these attributes vary in a systematic manner within the environment. Seasonal factors such as wave energy and direction of approach result in marked seasonal variations of some sediment properties, but in general seasonal changes in the sediments are not of sufficient magnitude to overshadow properties that can be attributed to the location or environment of deposition of the sediment. The importance of environmental factors in determining sediment properties enabled the samples from Scripps Beach and the inter canyon shelf to be grouped into 3 general types (beach, surf and shelf, and slope) depending upon their location. Sediments within these types all have particle-size distribution that can be correlated with environment. Samples from the rocky shelf around Point La Jolla, where sediment occurs in isolated patches, were frequently bimodal and showed no such correlation with environment. The areal distribution patterns showed that there is a pronounced alignment of sediment properties, which in general is parallel to the beach and surf zone. Comparison of size distributions of the sediments by sieving and by hydraulic methods showed that the latter technique gives more meaningful results in a study of the areal distribution of sediment attributes.

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