Progress report on use of water by riparian vegetation, Cottonwood Wash, Arizona

Measurements of streamflow, ground-water levels, and meterological data obtained in a 4.1-mile reach of the flood plain of Cottonwood Wash, Mohave County, Ariz., define the use of water by riparian vegetation in that part of the stream valley. The computed evapotranspiration loss during the growing season of 1959 was 175 acre-feet, which represented about 33 percent of the water that entered the reach. The maximum rate of loss during the season was slightly more than 8 acre-feet per week, or about 60 percent of the inflow.

The project reach is divided into two parts: An upstream subreach of 2.6 miles and a downstream subreach of 1.5 miles. Seasonal losses in the upstream and downstream subreaches were 75 and 100 acre-feet respectively. Losses in the shorter downstream subreach were larger because of the greater plant population.

During the summer of 1960 the vegetation in the lower subreach will be chemically defoliated as a part of the experiment to determine the savings in water losses that can be effected by modifying riparian vegetation. Tests on chemical defoliants indicate that a single spraying eliminates the leaves on cottonwood trees for 7 or 8 days and that no permanent damage results.