Graduate Thesis Or Dissertation
 

Hydrologic significance of the granitic parent material of the San Gabriel Mountains, California

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/p8418r19f

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  • The study was conducted on the San Dimas Experimenta1 Forest in southern California. It deals with a field and laboratory evaluation of several physical and hydraulic properties of the weathered parent material and suggests how these properties may relate to flood runoff problems. A simple correlation analysis shows that only one variable, non-capillary porosity had a significant relationship with saturated hydraulic conductivity. A factor analysis indicated that information from 19 descriptive variables could be attributed to 5 common factors. The 5 common factors show the types of variables that would be most useful in describing parent material. Darcy's equation was used to compute saturated hydraulic conductivity. The resulting computations, utilizing Reynolds number criterion, yielded values which were well within the laminar flow range. However, differing Reynolds numbers were obtained by using average grain size as compared to average pore diameters. A comparison between field hydraulic conductivity and laboratory hydraulic conductivity showed no significant correlation between the two measurements. Moisture-retention curves of the surface and parent material show little difference between the two materials. Retention and detention storage values for the soil and parent material were calculated and used to assess the occurrence of overland flow. The importance of the parent material, as it influences overland flow, was evaluated utilizing existing rainfall records, streamflow hydrographs, moisture storage values and the permeability results of this study. Total storm and 24-hour rainfall data were not very useful for evaluating the presence or absence of overland flow. Rainfall was budgeted into the soil and parent material according to the respective permeabilities and storage capacities of those two strata. Overland flow was computed by subtracting the amount of water in-filtered from the amount of rain falling during a six minute time period. Rainfall hyetographs and streamflow hydrographs indicated that overland flow is of limited occurrence even during flood runoff periods. Flood peaks were thought to be the result of storm seepage flow from the side slopes rather than from direct channel interception or overland flow. Any overland flow coming from recently burned watersheds probably results from a change in the soils permeability characteristics. The soil resists wetting because of a water repellency created by wildfire temperatures.
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