The work upon which this report is based was supported in part by funds provided by the OFFICE OF WATER RESOURCES RESEARCH, U.S. Department of the Interior, through the WATER RESOURCES RESEARCH INSTITUTE of the State of Oregon as authorized under the Water Resources Research Act of 1964, a research and development grant from the PACIFIC POWER AND LIGHT COMPANY, Portland, Oregon, and matching grant funds from the Oregon State University AGRICULTURAL EXPERIMENT STATION.