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Description
The main focus of this investigation was to assess spatial variation of hydraulic conductivity in riverbed material and characterize sediment and hydraulic parameters at the sites sampled. Nine grids and one transect at six different waterways in San Diego County were core sampled, and hydraulic conductivity was assessed through the permeameter laboratory method and the Hazen grain-size analysis method. With the exception of organic material, all of the average sediment collected falls within the medium sand USCS classification, and samples range from poor to well sorted. Trend in grain-size sediment distribution is dependant on stream geometry and area encompassed by the sampling grid. There is a continuous trend throughout this project of poor correlation between the Hazen method and the permeameter method results, as the Hazen method does not account for sediment microstructure, which was shown to be a dominating factor in controlling hydraulic conductivity in riverbed material. Therefore, the permeameter method is considered a more accurate representation of natural hydraulic conductivity and is utilized for statistical evaluation throughout the project. The most appropriate mean K values from the varying sampling locations range from 7.15 ft/d at Las Flores Creek Tank Road Site to 161.2 ft/d at Santa Margarita River Site 3. Average values of K are not similar enough among the sites to designate a mean K value for riverbed lining in San Diego County as a whole. Correlation length and sampling scale evaluations of the data indicate that in most cases, a more intensive sampling scheme will result in more accurate mean hydraulic conductivity, but reasonable accurate results can still be gained using larger sampling interval. Ultimately, the appropriateness of varying sampling schemes can be based on the need for a certain level of accuracy in the resulting data. The electronic appendix, which includes all calculations, is available for viewing in the Media Center of Love Library.
