1Hydrologist, Agric. Res. Serv., USDA, Beltsville, MD
2Research Associate, Agric. Eng. Dep., Washington State Univ., Pullman
3Research Hydrologist, Agric. Res. Serv., USDA, Pullman, WA 99164
4Soil Scientist, Agric. Res. Serv., USDA, Pullman, WA 99164, respectively.