Wednesday, 9 November 2005 - 1:45 PM
266-3

Nine Years of Mulistep Outflow Experiments at the George E. Brown Jr. Salinity Lab.

Peter Shouse, Jack A. Jobes, Walter B. Russell, and JoAn Fargerlund. George E. Brown Jr. Salinity Lab, 450 W. Big Springs Rd., Riverside, CA 92507

Most soil physicists agree that soil hydraulic properties are essential for predicting water and solute transport through soils. They also agree that measuring these properties is time consuming and expensive. What a dilemma! By automating Tempe cell transient outflow experiments and using inverse modeling to estimate soil hydraulic parameters we have reduced the effort and cost of characterizing these properties. We measure a retention curve by brining the sample to equilibrium (zero outflow) between pressure steps. We also measure selected static retention points on the curve, including those outside the Tempe cell range of measurement (>1000 cm), with pressure plates. Using a standard method we measure Ksat under steady flow conditions. By combining these static and dynamic measurements we estimate the van Genuchten hydraulic parameters using HYDRUS 1-D. We measure bulk density, and an exhaustive particle size distribution, including 9 hydrometer readings and 5-13 wet sieve sizes. All characterization measurements are done on the same soil sample. At present we have characterization data for over 500 samples, the vast majority of which are undisturbed (less than 3% are repacked).

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