1. Visiting Ph.D. Student, Dept. of Civil and Materials Engineering, Univ. of Illinois, 842 West Taylor St., Chicago, IL 60607; presently, Ph.D. Student, School of Environment, Tsinghua Univ., Beijing 100084, China.
2. Graduate Research Assistant, Dept. of Civil and Materials Engineering, Univ. of Illinois, 842 West Taylor St., Chicago, IL 60607.
3. Professor, Dept. of Civil and Materials Engineering, Univ. of Illinois, 842 West Taylor St., Chicago, IL 60607 (corresponding author).
4. Professor, School of Environment, Tsinghua Univ., Beijing 100084, China.
5. Research Soil Scientist, U.S. Dept. of Agriculture-Agricultural Research Service (USDA-ARS), Soil and Water Management Unit, St. Paul, MN 55108; and Adjunct Professor, Dept. of Soil, Water, and Climate, Univ. of Minnesota, 1991 Upper Buford Circle—439 Borlaug Hall, St. Paul, MN 55108.