AN EVALUATION OF FRACTAL DIMENSIONS TO QUANTIFY CHANGES IN THE MORPHOLOGY OF FLUVIAL SUSPENDED SEDIMENT PARTICLES DURING BASEFLOW CONDITIONS
✍ Scribed by DIRK H. DE BOER
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 213 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0885-6087
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✦ Synopsis
The morphology of suspended sediment particles re¯ects the origin of the suspended load and any modifying processes that may have occurred during transport and storage in the aquatic system. The objective of this study was to evaluate the use of four fractal dimensions to quantify visually observed changes in the morphology of ¯uvial suspended sediment particles during base¯ow conditions. Samples were collected during summer low ¯ow in a small stream on the Canadian Prairies. Particle morphology data were obtained with a transmitted light microscope, a CCD camera and an image analysis system. The morphology of the particle population was characterized using four fractal dimensions (D, D K , D 1 and D 2 ). D was derived from the area±perimeter relationship and showed an increase from 1Á26+ 0Á02 on 30 June, to 1Á34+ 0Á02 on 4 July, to 1Á42 +0Á01 on 7 July. Visually, the increase in D represented the formation of large particles with intricate shapes and increased perimeters. D K was determined from the area±rank relationship and varied from 1Á86 + 0Á01 on 30 June, to 1Á90+0Á00 on 4 July, to 1Á74+0Á00 on 7 July. The decrease in D K between 4 July and 7 July would indicate a greater concentration of the particle area over a small number of large particles. Although the decrease in D K is consistent with observed changes in the particle size distributions, D K should be used with the considerable caution because D K varied more than one standard error between replicates. D 1 and D 2 were determined from the length±perimeter and length±area relationships, respectively. D 1 proved to be of little value for quantifying changes in particle morphology as it showed little change with time, despite considerable visual changes. D 2 however, was useful, despite some variation between replicates. Over the sampling period, D 2 for the composite data sets showed a steady decrease from 1Á74 + 0Á02 on 30 June, to 1Á68+0Á02 on 4 July, to 1Á60 +0Á01 on 7 July. This change in D 2 indicates that, through time, the larger particles became longer and thinner relative to the smaller ones. This study shows that temporal changes in D, D K and D 2 were consistent with, and allow quanti®cation of, observed changes in particle morphology. D 1 did not re¯ect observed morphological changes, and is therefore of little value for this type of study. The changes in particle morphology coincided with an increase in primary production in the form of algae.